THE EFFECT OF ADDITION AGENTS ON

CATaODIC OVERPOTENTIAL AND

CATHODE QU- IN COPPER ELECTROREFINING

ROBERT M. DENI

B. A., B. Eng . , Laurentian University, 1994

A THESIS SUBMITTED IN PARTIAL FULFILMENT

OF THE REQUIREMENTS FOR THE DEG REE OF

MASTER OF APPLIED SCIENCE

MINERAL RESOURCES ENGINEERING

School of Graduate Studies

LAURENTIANUNIVERSITY

April 1997

Copfight by Robert M. Deni, April 1997

uisitions and "9 Acquisiions et Bib ~ographic Services seNices biûliographiques

The author has granted a non- L'auteur a accordé une licence non exclusive licence ailowing the exclusive permettant à la National Library of Canada to Bibliothèque nationale du Canada de reproduce, loan, distriiute or seU reproduire, prêter, distri'buer ou copies of this thesis in rnicroform, vendre des copies de cette thèse sous paper or electronic formais. la forme de microfiche/fiIm, de

reproduction sur papier ou sra format électronique.

The author retains ownership of the L'auteur conserve la propriété du copyright in this thesis. Neither the droit Bauteur qui protège cette thèse. thesis nor substantid exaacts fiom it Ni la thése ni des extraits substantiels may be printed or otherwise de celle-ci ne doivent être miprimés reproduced without the author's ou autrement reproduits sans son permission. autorisation.

This thesis research project was entirely funded by Inco Limited and was jointly

proposed by Pmess Technology personnel at the Copper Cliff Copper Refinery (CCCR)

and Laurentian University.

Though it produces some of the highest quality cathode copper in the world, the

eiectrorefining (ER) tankhouse at the CCCR employs one of the lowest cumnt densities

(183 ~ / m 3 compared to other major copper refineries in the world. Meanwhile,

increasing production demands are pushing for greater productivity. The obvious and

most efficient method of increasing production would be to increase the current density.

since it would involve minimal capital costs. However, ali attempts to increase the

current density by as little as 6 percent and still maintain cathode quality have faiIed.

The electrolyte addition agents presently king used at the CCCR tankhouse

include glue, Tembind and chloride. Thiourea, an addition agent common to ali but two

of the major copper producers worldwide, has proven cathode quality enhmcing

properties. However, thioutea is not used at the tankhouse b u s e its chernical nature

makes it a potential source for sulphur contamination in the cathode deposits, and

because it is suspected of king a risic to human health.

The overall objective of this thesis was to study glue, Tembind, thîourea, chlonde

and reciaimed acid, and determine how their presence (in typical industrial

concentrations), alone and in combination, in synthetic elecû01yte affects the cathodic

overpotential and copper cathode deposit morphology . It was hoped that a solution could

ii

be found to pemit an increase in copper cathode production at the tankhouse by

ernploying higher current density. The first part of the thesis gives an overview of

copper electrorefining, its theoretical fwidamentals as well as its practical use in industry.

The experimental part of the thesis consists of three major sections: laboratory

electrorefining tests, cathodic polarization tests and reclaimed acid characterization.

The laboratory electrorefining tests were done using laboratory sale

electrorefining cells that could simulate the CCCR electrorefuiing operation. The lab

d e cathode deposits were judged by naked eye obsewation, by microscopy of polished

cathode sections, and by hardness meamernenu. Microscopie evaluation of deposits

clarified the macroscopic interpretation and highlighted differences, between the deposits,

that were not evident to the naked eye.

Thiourea was observed to be an excellent addition agent when use- in the proper

combination/concentration. By far, the smoothest, nodule-free deposits were produced

in electrolyte containhg 150 ppm Tembind, 0.2 ppm thiourea and 20 ppm chloride, and

in electrolyte using this identical combination in addition to 5 ppm glue. Given the

similar appearance of these two deposits, it appcand as though the presence of glue did

little to improve the deposit quality. Thiourea, used at low concentrations, could pmve

to be the key addition agent that wiU d o w the tankhouse to Opefate at a higher current

density . As a single addition agent, only Ternbind was found to improve deposit quality

comparecl to additive-fne solution. Glue, thiourea and chloride, alone in electrolyte, al1

iii

gave poor deposits. A dialysed Tembind product from the dialysis experiments was also

used in plating tests. Overall, its deposit enhancing characteristic was unchanged

compared to regular Tembind. This observation indicates that the heavy molecular

weight fraction of Tembind phys an important rde in deposit enhancement, though the

effect of the smaiier weight fraction cannot be discounted. As for the efféct of reclaimed

acid in plating experiments, its presence resulted in deposits that were comparable or

better than deposits produced in the absence of reclaimed acid. Reclaimed acid was most

beneficial when Tembind was not present in electrolyte, and had an effect similar to that

of Tembind. Additionally, deposits produced using synthetic reclaimed acid in the place

of plant reclaimed acid rrsulted in si& deponts, supporting the assurned ielationship

be tween reclaimed acid and Tembind.

Cathodic polaruation tests studied the effect of addition agents (including

reclaimed acid) in various combinations/concennations on cathodic polarization using a

galvanostatic procedure. The experiments gave interesthg and previously umecognized

results. Glue was found to be the oniy addition agent that, when present alone in

elecwlyte, increased cathodic polaruation compared to additive-& electrolyte.

Individuaiiy , Tembind, thiourea and chloride had a dephking effect. Reclaimed acid,

alone in electrolyte, had a depolarizing e f f ' similar to that of Tembind.

Polarization tests using different addition agent combiaations/concentrations in the

presence of reclaxnied acid gave overpotential measurements that were Smilar to those

conducted using pure reclaimed acid-hx electrolyte. Of the four addition agents,

chloride demonstrated the most notable behaviour since in combination with other

additives, it produced a polarization effect opponte to that when present alone in

electrolyte. Chloride, in combination with due, Tembind and thiourea, had a polarking

effect. This was especially evident in electrolyte containhg the 5 pprn glue and 20 ppm

chloride combination, where the increase in potential shift was double compared to

electrolyte containing only 5 pprn glue. The fluctuation of chloride may also have a

previously unrecognized effet on the accuracy of glue determination for tankhouse

electrolyte samples done by the present rnethod that utilizes potential shift measurements.

Two correlations were evident from the experimental results. The first

correlation, one between deposit crystal size and hardness, showed that the hardness

decreased with increased crystal ske. The second correlation showed that as the

overpotential decreased so did the quality of the deposit. However, there were numerous

exceptions that could make prediction of deposit quality based on overpotential

measurements unreliable.

The dialysis and spectrometric (GCIMS, UV, IR and NMR) analyses attempted

to determine the organic compounds present in the nchimed acid (produced at the

CCCR acid plant) which is recycled to the tankhouse. The attempts to liok reclaimed

acid with Tembind, based on phenolic content, were unsuccesshil. This was most likely

due to the high acid a n d h complex organic content (ie. decomposition products of glue

and Tembind) of reclaimed acid. While it was possible to obtain a dialysed Tembind

product, the dialysis of reclaimed acid Wed. As for the various spectrometric

techniques, the spectra were poorly defhed and did not provide any useful information.

Thus, these dialysis and spectromeûic techniques were found to be unsuitable for ihis

P w =

The author would iike to sincerely thank Paula TyroIer (thesis supervisor), a major contributor to this thesis. As weli, the author would like to thank co-supe~sors Stewart Sanmiya of Inco Lirnited and Artin Tombdakian, professor emeritus, of Laurentian University.

Other people whose contributions and efforts were a h appreciated:

Inco Limited

Vladimir Blechta (retired) George Courtney Dale Knieger Paul Rybiak Bill Whittaker

burentian University

Helen Joly Mary Roche Marie-Josée and Maria

Ray Bdet Mike Desormeaux Brian Rogers Casper Vanderpool

Thanlcs also extend to Inco Limited for providing the financial resources necessary for completion of this thesis. Final thanks go to Nancy and the author's family who provided much needed support and encouragement.

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Absîract ii

Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vii

List of Figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xi

List of Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xii

Chapter 1 . INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Chapter 2 . INDUSTRIAL COPPER ELECTROREFINING . . . . . . . . . . . . . 4 2.1. WORLDWIDE COPPER CATHODE PRODUCTION . . . . . . . . . . . . . 4 2.2. TRENDS AND IMPROVEMENTS IN COPPER ELECTROREFINING . . . . 5 2.3. COPPER ELECTROREFINING: ~ ~ D u S C R ~ A L LAYOUT AND

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . OPERATION 7 2.3.1 Plant Practice at CCCR . . . . . . . . . . . . . . . . . . . . . . 8 2.3.2 Production of Rectaimed Acid at CCCR . . . . . . . . . . . . 9 2.3.3. Unique Aspects of the Tankhouse Operation at CCCR . . . 10

Chapter 3 . THEORETICAL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 3.1. ELE~OCRYSTALLEATION . . . . . . . . . . . . . . . . . . . . . . . . 14

. . . . . . . . . . . . . . . . . . . 3.1.1. Electrodeposition of Copper 14 . . . . . . . . . . . . . 3.1.2. Overpotential in Electrocrys~tion 18

. . . . . 3.1.3. Effect of Overpotential on Nucleation and Growth 20 . . . . . . . . . . . . . . . . . . 3.1.4. Electrodeposit Growth Types 21

3.2. FACTORS A F F E ~ G ELECTROCRYSTALLIZED DEPOSITS . . . . . . 24 3.2.1. Current Density . . . . . . . . . . . . . . . . . . . . . . . . . . 24 3.2.2. Hydrdynamics - Mass Transfer . . . . . . . . . . . . . . . . 29 3.2.3. Electrolyte Composition . . . . . . . . . . . . . . . . . . . . . 31 3.2.4. Addition Agents . . . . . . . . . . . . . . . . . . . . . . . . . . 33

3.2.4.1.Glue . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 . . . . . . 3.2 .4. 2. Tembind (Ammonium Lignosulphonate) 38

3.2.4.3. Thiourea . . . . . . . . . . . . . . . . . . . . . . . . . 40 3.2.4.4. Chloride . . . . . . . . . . . . . . . . . . . . . . . . . 43

. . . . . . . . 3.2 .4.5. Combined Effect of Addition Agents 45

Chapter 4 - EXPERlMENTAL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . OBJECTIVES 48

. . . . . . . . . . LAB~RATORY C O P P ~ ELECTROREFINING TESTS 49 4.2.1. Apparatus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2.2. Procedures 50 . . . . . 4.2.2.1. Electrolyte and Addition Agent Make Up 50

. . . . . . . . . . . . . . . . . 4.2.2.2. Electrode Preparation 51 . . . . . . . . . 4.2.2.3. Laboratory Copper Uectrorefining 53

. . . . . 4.2.2.4. Cornparison of Lab and Plant Parameters 56 4.2.2.5. Scope of Work . . . . . . . . . . . . . . . . . . . . . 58

. . . . . . . . . . . . . . . . . . . . 4.2.2.6. Deposit Analyses 61 . . . . . . . CATHODIC POLAREATION ( P O T E ~ L S m ) TEms 61

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.3.1. Apparatus 63

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.3.2. Procdure 64 DIALYSE AND SPECTROMETRIC ANALYSES OF RECLA~MED ACID

ANDTEMBIND . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65 4.4.1. Procedures for Dialysis and S ynthetic Reclaimed Acid

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . Production 66 . . . . . . . . . . . . 4.4.2. Procedures for Spectrometric Analyses 67

Chapter 5 . RESULTS AND DISCUSSION . . . . . . . . . . . . . . . . . . . . . . 70 5.1. LAB~RATORY COPPER ELECTROREFINING TESTS . . . . . . . . . . . 70

5.1.1. Evaluation and Discussion of Elecaodeposit Morphology . 70 5.1.1.1. Macroscopic Characterization . . . . . . . . . . . . 70 5.1.1.2. Mimscopic Characterization . . . . . . . . . . . . . 75

5.1.2. Evaluation and Discussion of Electrodeposit . . . . . . . . . . . . . . . . . . . . . . . . . . . Microhardness 81

5.2. CATHODIC POLAR~ZATION (POTENTIAL S m ) TEsrs . . . . . . . . 82 5.2.1. Cornparison of Cathodic Polarization and Macrodeposit

QuaÜty . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90 5.2.2. Polarization and Electrodeposit Evaluation Summary .... 93

. . . . . . . . . . . . Chapter 6 . CONCLUSIONS AND RECOMMENDATIONS 97 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.1. CONCLUSIONS 97

6.1.1. Laboratory Copper Electrorefining Tests . . . . . . . . . . . 97 . . . . . . . . . . . . . . . . . . . 6.1.2. Cathodic Poîarization Tests 101

6.1.3. Dial ysis and Spectromeiric Analyses of Reclaimed Acid . . . . . . . . . . . . . . . . . . . . . . . . . . . . and Ternbind 103 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.2. RECOMMENDATIONS 104

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Appendices 106 . . . . . . . . . . . . . . . A . Laboratory Electrorefining Data and Results 107

. . . . . . . . . . . . . . . . . . . B . Cathodic Polarization Data and Results 110 C . Photographs of Lab Scale Copper Elecuodeposiu . . . . . . . . . . . . 112

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References 128

Flow sheet of a typical copper electrorefining operation . . . . . . . . . . . . 7 . . . . . . . . . . . . EIectroIyte layen ai the electrode/e1ectrolyte intedace 16

Simplifiecl schematic showing various steps associatexi with the . . . . . . electrocrystallization of a solva?ed copper cation ont0 a cathode 17

. . . . Diagram showing different types of polycrystalline elecnodeposits 23 . . . Graph of 7 versus i showing deposition regions as related to ikCu2' 26

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Graph of 7 versus i, 28 . . . . . . . . . Deposit morphologies observed dong the 7 versus i c w e 28

Natural convection and concentration profila in copper electrorefining . 30 . . . . . . . . . . . . . . . . . . . . . . . . . . . . Chernical formula for glue 36

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Structure of lignin 38 . . . . . . . . . Chernical formulae for (a) thiourea (b) dithioformamidine 41

Expenmental set-up for the lab scale electrorefining cells . . . . . . . . . . 50 . . . . . . . . Drawings of the lab anode and cathode showing dimensions 52

Cross-sectional drawing of a lab piating ceil showing dimensions . . . . . 54 Drawing of the laboratory electrorefining cell banlr and hot water bath showing dimensions (plan view) . . . . . . . . . . . . . . . . . . . . . . . . . 55 Set up of the galvanostatic equipment used for cathodic polarization

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . measurements 63 Photomicrographs of poushed electrodeposit cross~sections . . . . . . . . . 79 Graphs showing the change in PS (mV) as a function of concentration . . 83

Number of Refineries and Copper Cathode Capacity by Country . . . . . . 4 Annual Copper Cathode Capacities for CaMdian Refineries . . . . . . . . . 5 Comparison of Capacity. Current Density and Addition Agents

. . . . . . . . . . . . . . . . . . . . . . Between Major Producers Worldwide 1 1 Comparison of LME Specifications for High Grade Copper Cathodes

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . to ORC Cathodes 12 Assay Analysis of the Laboratory Anodes . . . . . . . . . . . . . . . . . . . 53 Lab and Electrorefining (ER) Tankhouse Operating Parameters . . . . . . 56 Polarization Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87 Macrodeposit Quality Rating and Cathode Polarization . . . . . . . . . . . 91 Cathode Polarization and Electrodeposit Evaluation Summary . . . . . . . 93

xii

Copper Electrorefining was fhst implemented on an indusaial d e more than 100

years ago in 1840 111. Since that time, electrorefining fundarnentals such as current

density and addition agents have, for the most part, remallied the same. The role of

addition agents in industriai copper eleetrorefining is vital since without them it would

not be possible to efficiently produce copper cathodes of acceptable quality. The use of

addition agents is closely linked with cunent density. By virtue of their levelling abilities

in electrolyte, addition agents allow higher current density operation that would not

normally be possible in their absence. Higher current density translates into increased

production and profits for refineries.

Researchers and refinery operators aiike have laboured to detennine the conditions

for producing the best possible cathode deposit. Historically, the use of addition agents

in copper elecnorefining has been more of an art than a science. Trial and error was,

and still is, the primary method in determining which addition agents, and in what

proportions are ideal for producing high quality, smooth copper cathodes. In the last two

to thne decades researchers have taken a more scientific approach to studying addition

agents and the mechanisms by which they work [2]. This includes studying the effects

of addition agents on cathode polarization and morphology, and theh importance in the

electrocry stalhtion process [3,4,5,6 ,n. Continuhg research in electrorefining is

aitical since more than 95% of the world's copper is elecîrorefined [8].

At Inco's Copper Cliff Copper Refinery (CCCR) Elecwrefining (ER) tankhouse,

pilot plant tests in copper electrorefining are king conducted to study the efiect of

various combinations and concentrations of addition agents on cathode deposit quality.

The goal of the testing is to detennine the proper combination of addition agents, as well

as concentrations, that will allow the tankhouse to plate high quality copper at a higher

c m n t density . Al1 pst attempts to raise the current density by as little as 6 96, without

jeopardizing copper quality, have failed [9]. Operating at a higher current density will

allow the tankhouse to handle increased production demands.

Higher cunent density operation represents the most feasible way to increase the

production levels at the tankhouse. The cost of increased energy consumption would be

minimal in cornparison to the capital costs that would be involved in a physical expansion

of the tankhouse. However, increasing current density would not be as simple as tming

the dial on the rectifier. Extensive planning and testing would be required to modify

operating conditions such as electrode pull scheduling and addition agent rates.

Two aspects of the tankhouse operation that gamer attention are the absence of

thiourea as an addition agent and the recycling of reclaimed sulphuric acid to the

tankhouse elecüo1yte. Thiourea has proven deposit enhancing properties and, as such,

is used extensively at other refinenes all around the world. The recycling of reclaimed

acid to the tankhouse has been practised for deades. This acid contains organic

degradation products whose compositions are not known and whose actions are not hilly

understood. Earlier plant and iab observations indicate that the organic component in

reclaimed acid is essentiai for producing good cathodes [9].

Based on the above information, the inteation of the thesis was to use modem

-ch ideas and practices in copper electrorefining to plan and perform lab scaie

experiments, and formulate recommendations that could find practical uses in the CCCR

tankhouse. Lab sale copper elecmfining, polarization testing and reclaimed acid

analyses were canied out in an attempt to advance the present knowledge. Experimental

procedures were conceived and refined throughout the research process. The thesis also

provided a synopsis of the latest information regarding both industrial practice and

research in copper electrorefining.

Electrorefined copper accounts for 95 96 of ali copper refined in the world. The

top five producers in the world in descending order are the U.S.A., Japan, Chile, Canada

and Germany (Table 2-1). Collectively they produce 50% of the total world output of

1 1 million tonnes of electrorefined copper per year [8].

Tabh 2-1. Number of Refinenes and Copper Cathode Capacity by Country [8]

Country

1. United States

2. Japan

3. Chile

4. Canada

5. Gemmy

6. Chino

Totais (top 6)

World Totals

Estimateci Nmber of

R e f ' i i e s

Estimated Total Cathode

Capacity (000 tonneslyr)

hco's Copper Cliff Copper Refinery presently bas a maximum capacity of

170,000 tomes of cathode copper per year. Of the top 92 refiaeries in the world, the

Copper Refinery ranks 18th in size, producing approximately 1.6% of the world's total

copper cathode output [8]. While this may appear to be a small percentage, the Copper

Refinery produces 28% of Canada's total copper cathode output (Table 2-2). Assuming

maximum output and a nominal seîling price of $1.20 per pound of cathode copper, the

Copper Refinery wouid generate $450 million in revenue in a single year.

Table 2-2. Annual Copper Cathode Capacities for Canadian Refineries [8]

Copper Refinery

1. Noraada Cu Smelting and Relïning, CCR

Refinery , Montreai, Que&

2. inco Ltd. Copper CTiff Copper Rehery,

CCCR, Copper Cliff, Ontario

3. Filconbridge Ltd.. Ki& Creek Division,

Timmins, Ontario

CANADIAN TOTALS

WORLD TOTALS

Copper Cathode Capacity

(tonnes/ year)

There has been extensive research done to technologically Unprove and make

electrorefining operations more efficient and productive. Experts have corne to bener

understand the importance of parameter control in electrorefining. Factors such as

current density, addition agent concentrations and electrode specifications must be closely

monitored to ensure high quality deposits. New technologies such as on-line

computerized monitoring and control systems are allowing refineries to better control

these parameters and increase their profits.

Process automation in area such as electrode handling has not only lead to

increased production, but also to increased safety since workers are not required to

physically handle the electrodes [8,10,11]. Old equipment which has completed its useful

life is being replaced with superior technology that requires less maintenance. One

current trend is the increasing use of unlined precast polymer concrete electrorefining

cells [8]. Companies such as Inco Limited are replacing their old concrete and leadl PVC

paralined cells with new polymer concrete cells. In addition to simpler maintenance and

installation, these cells benefit from high acid and temperature resistance.

In industry the use of permanent stainless-steel mother blank cathodes continues

to increase. Schloen [8] writes that nearly a quarter of the world's major copper

ref'ineries now use stainless steel cathodes in their tankhouses. Advantages to using these

blanks include the exclusion of starter sheet manufacture!, and wnsistent vertical hanging

of the sheets within the plating cells. Electrode verticality is important for maintaining

cathode purity, avoiding short circuits and maxhhhg current efficiencies [12].

Additionally, anode-cathode spacing can be reduced and cell inspections are less

demanding.

Process improvements are always desirable, yet they can often have a substantial

price tag. For o k refineries, the capital costs of upgrading are potentially high and so

there can be considerable reluctance in replacing old technology, especially if its still in

good working condition. However, in many instances the retum on investment in new

technology can be high and imrnediate.

In industry, the basic layout of an electrorefuiery is quite similar from one

operation to another, though there can be quite distinct differences in equipment design

and the degree of automation. A flow sheet for a typical copper electrorefining operation

such as the one at CCCR is show in Figure 2-1.

BUSE8 COPPER 1

Figure 2-1. Flow sbeet of a typicai copptr elecîrorcfïning o p t i o n [ 131.

At the Inco operation, blister copper from the Copper Cliff Smelter is sent by rail

to CCCR. There it is M e r refined in anode himaces to lower the sulphur and oxygen

content, and then cast into anodes (0.OOl-O.003 % S and 0.054.396 0) [Il]. The cathode

starter sheets are plated on ground titanium blanks for 24 houn in stripper cells (160 in

total). After this period, the titanium blanks are pulled and loaded onto a stripping

machine that automatically strips the copper starter sheets off the blanks. These starter

sheets are then fitted with hanging loops and square copper crossban, ready for use in

the 1436 commercial cells. The rnajority of the electrolytic cells are the lead and PVC

lined concrete type which are slowly being replaced with polymer concrete cells. Each

ce11 holds 33 anodes and 34 cathodes.

The tankhouse, operiiting at an average cumnt density of 183 A/m2, has a 28 day

anode cycle and a 14 day cathode cycle. After 14 days the cathodes are removed,

washed, weighed, inspectai and strappeû for market sale. Cathodes not passing

inspection are soid as lower grade or are recycled to the anode fumace. Afkr 28 days

the anodes are rernoved and the cell is sluiced to coliect the anode slimes that contain

precious metals that requh further r e w g . The anodes are also washed to remove any

adhering slimes. The remaining d e scrap (approximately 20 46) is reverted.

2.3.2 Prduction of Reclaimed Acid at CCCR

The tankhouse electrolyte, approximately 40 to 45 g/L Cu2+, 20 to 22 g/L Ni2+,

and 155 to 165 g/L H2S04, is heated to maintain a temperature of about 66°C. Glue.

Tembind and chloride are continuously added to the electrolyte to help in plating smooth

cathode deposits. The target concentration levels for these addition agents in electrolyte

are around 5, 150 and 20 ppm, respectively.

Each &y 3% of the tankhouse electrolyte is bled via the 170 segregating cells for

electrolyte purification (decoppering and evaporation/nicltel sulphate production) in the

acid plant. The segregating cells function in a fashion similar to the commercial cells

except that they have a bottom-in/bottom-out buik elecnolyte flow pattern. This pattern

gives diminished convective mixing in each cell resulting in a decreasing C3'

concentration as one moves from the bonom of the cell to the surface of the electrolyte.

It is at the top of the segregating ceil, that approximately 1 to 2 Umin of segregated

electrolyte solution (about 26 g/L Cu2+) is bled for purification.

Purification of the segregated electmlyte solution involves a seria of steps. From

the receiving tank, the segregated solution is batch run through two liberator circuits.

In the first circuit, the copper in solution is electrowon, effectively lowering the Cu2+

concentration to about 14 g/L. In the second circuit, the Cu2+ concentration is lowered

M e r to a concentration of about 3 5 fi. This solution is then vacuum fed to the

stem evaporaton where water is boiled off in six hou cycles at temperatures

approaching 220°F. From the evaporators, the solution is circulated through cooling

coils to cool the solution to a temperature of 150°F. AAer cooiing, the solution is

centnfbged to remove the precipitated nickel sulphate.

Electrotyte purification sewes three main purposes. Fust, copper is removed and

recovered. Second, arsenic, bismuth and antimony are removed from the electrolyte by

electrowinning them into an impure copper cathode deposit that can be reprocessed.

Finally, nickel sulphate (contaminated with iron, cobalt, copper, arsenic, antimony and

bismuth) is precipitated from the concentrated solution via evaporation, and separated by

centrifugation. The nickel sulphate can be sold for eiectropiating and other chemical

uses. Apart from precipitated solids, the other end product of purification is a high

strength sulphuric acid, called reclaimed acid, containing approximatel y 1000 g/L H2S04.

For raisons explained in the foliowing section, this reclaimed acid is recyclai to the

tankhouse.

2.3.3. IJ-e of Tapbbpye Owration at CCCR

The addition agent combinations and concentrations useâ in industry Vary from

refinery to refinery. Glue and chionde are the universal electrolyte addition agents,

followed by thiourea [8]. The choice of addition agents used in the Copper Cliff

tankhouse maices it somewhat unique since it is one of only two major copper

electrorefiners worldwide not ushg thiourea as an addition agent (Table 2-3). The

reluctance in using thiourea cornes h m the fact that it is a suspected carcinogen [14,15]

as well as a source of suiphur contamination in the cathodes [13]. Additionally, Avitone,

a hydrocarbon based sodium sulphonate product [13.14,16] which is used quite

extensively in the copper refining industry, is not used at the Copper Cliff tankhouse.

Table 2-3. Cornparison of Capacity, Current Density and Addition Agents Between Major Producers Worldwide [8]

Inco Litnitcd CCCR, Canada

Falconbridge Ltd, Kidd Crcck, Canada

Noranda CCR Rcfmery, Canada

Corp. de1 Cobrt de Chilc, Chuiquicarnata

Corponicion del Cobrc de Chile, P o t d o s

Mansfclder Kupfcr & Messing GmbH, G m .

National Iranian Cu Industries Co, Inn

Kosaka Smclting & Refining Co, Japan

Mitsubishi Matcrisls Corp, Japan

Nippon Mining and Mctals Co, Hitachi, Japan

Nippon Min. and Met. Co, Saganoseki, Japan

Onahama Smciting and Rtfining Co, Japan

Sumitorno Mct. Min. Co. , Nishibara, Japan

Sumitorno Meta1 Mining Co. Ltd, Toyo, lapan

Minero P m , Pcru

Palabra Mining Co, South Africa

Asarco Inc, Texaa, USA

Coppcr Range Co, Michigan, USA

C p Miruni Mining Corp, Arizona, USA

Kenneou Utah Coppcr Rchcry, Utah, USA

Magma Metals Co, Arizona, USA

Phcips Dodge Rtfhing Corp, Texas. USA

Zambk Cons. Cu Mines Ltd, Muhiira, Zun.

glue, Tembind, Cl

glue. thiourea, Cl

glue, thioum, Avitont. CI

gluc, thiourca, Avitone

glue, thioum, Avitonc, CI

gluc, thiourea, Cl

gluc, thiourca, Cl, Magnafloc

gluc, thiourea

glue, thiourca, Avitonc, Cl

glue, thiourcri, Avitone, Cl

glue, thiourea, Avitonc, Cl

glue, thiourca, Avitont. Cl

duc, thiourea, Avitont. Cl

glue, thioum. Avitonc, Cl

glue. thiourca, CI

glue, thiourca, Avitonc, Cl

M

glue, thiourca, Avitont. Cl

glue, thiourca, Avitone

flue, t hhum, CI

flue, ihiour#r, CI

glue, thiourca, Avitant, Cl

glue, thiourw, OrLan, C l

Another unique aspect of the operation is that the tankhouse employs a current

density of 183 A h 2 . As nich, it is the lowest cunent density operation among major

producen 181. The advantage in using a relatively low current density is that the ORC

brand copper cathodes produced at CCCR are of the highest quaiity found in the world

[17. The ORC brand cathode specifications weU exceed those set out by the London

Metals Exchange (LME) for high gracie copper (Table 2-4). However, it m n o t be

overlooked that since CCCR does operate at such a low current density, the production

rate of cathode copper is also low since the cathode plating rate is directly dependent on

the current density .

Table 24. Cornparison of LME Specifications for High Grade Copper Cathodes to ORC Cathodes [lq

Group

1

2

3

4 1

5

6

Impurity 1990 Data for ORC Cathodes mm)

T Se, Te, Bi - group total 3 ppm max Se - Se + Te 3 ppm Te - any one element 2 ppm max Bi

Cr, Mn, Sb, -group total 15 ppm max Sb O. 1 Cd, As, P -Sb 4 ppm, As 5 ppm As O. 1

Pb c 5 ppm Pb 0.2

Fe < 10 ppm Fe 1.7

- -

The practice of rezycling reclaimed acid is another notable feature of the Copper

Cliff tankbouse operation. RecIaimed acid is not oniy recyclexi to maintain the tankhouse

electrolyte acid batance, but also because it contains organic decomposition products

believed to be beneficial to plating. Although residual glue is completely destroyed in

the evaporation stage o f electrO1yt.e purification, Tembind demonstrates an unusually

resiIient nature. Reclaimed acid assay indicates that it contains approximately 1 g/L

Tembind andlor Tembind decornposition products. Based on previous lab and plant

experiments performed at CCCR, it is generally agreed that Tembind andfor its

dccomposition products are largely rrsponsible for reclaimed acid's deposit-enhancing

properties [9].

In the 19403, Fischer [18] coined the term 'electrocrystallization' to describe a

process of crystallization when mass üansfer is accompanied by charge transfer. Since

the field of electrocrystailization is largely experimental, the theory behind it is often

expressed by cornparison with physical crystallization. Unlike physical crystallization,

electrocrystallization takes place in the presence of foreign atoms and with transfer of

charge 161.

Electrocrystallization is the result of a direct or indirect (usually both to some

extent) electrochemical influence on physical crystallization [19]. If the value of the

electrode potential determines the type of nucleation and the growth kinetics, then a

direct electrochemical influence exists, Indirect influences couid involve alteration of the

local reaction environment (ie. pH) and hence the reaction product. An example of this

could include codeposition of metal oxides/hydroxides resulting fiom a hydrogen

evolution side reaction in unbuffered solution [19].

The simple cathodic reduction in the electrocrystaüization of copper is as foilows:

Cu" + 2e-+ Cd'. 0.1)

The heterogeneous charge transfer reaction takes place at the electronic and ionic

conductor interface. This interfixe region consists of the three near electrode layen: the

electrical double layer with outer Helmholtz plane (0.5nm < (p, < 1 nm), the Nemstian

diffusion layer ( lpm c 6, < 100prn) and the Prandtl (hydrodynamic) boundary layer

(0.lmm < 6, < lmrn).

The elecaical double layer and the resulting potential field is caused by charge

sepration (Fig 3-la). The Nemstian diffusion layer (defined by the assumption of a

linear profile) develops due to concentration gradients at the electrode surfaces (Fig 3-

1 b). The Nernstian difision layer thickiess (6,) is related to the mass transport

coefficient (kJ and the diffision coefficient (D) by the equation

kL = DibN . 0.2)

The Prandtl boundary layer (dehed by the assumption of a linear profile)

develops due to localized velocity differences in elcctrolyte convection (Fig 3-lc). As

the electrode surface is approached, the velocity of the bulk elecwlyte is increasingly

retardeci. ElectrocrystaUîzation may be affected by changes in any of these layers which,

in practice, do interact with each 0th [19].

Before hydrated Cd+ ions in solution become incorporated into the copper metal

lanice they must undergo convective diffusion, electro~tion, surface diffision,

dehydration, nucleatioo and p w t h [2]. The steps (Fig 3-2) in the overail process are:

cd+- -, 0.W

CJ',, + 2e* + C d f . 0.3)

Figure 3-1. Electrolyte layers at the electrode/electrolyte intehice: (a) the electrid double layw at a d o d i c surfoce. The v, piane is the "outcr Helmholtz plane"; (b) the concentration boimdary hyer and Nernst diffusion layer thickness, b,.; (c) the fluid bomdary layer and îhe Prandtl boundary hyer thickness, b,+ [19].

The electrode potentiai may exert an influence over any of these steps [19]. Charge

msfer, electric fields and the presence of molecules and ions adsorbed at the cathode

surface can greatiy infiuence the nature of elatrodeposited copper [q.

INTERFACE chugc uiarfcr

ELECTRODE clectronic cluata conductioo

hem iiphcricil

growth centres pyramidrl

EL ECTROLY TE ionic

conduccion

Figure 3-2. Simplified schemtic showing various steps assaciated with the electrocrystailizatioa of a solvated copper cation onto a cathode, including idealired growth geometries [19].

The linear rate of electrcicrystalliraiion, v, is directiy related to current density,

j , by the equation

v = jV,/nF (3.4)

where V, is the molar volume, n is the number of moles of electrons involved in the

electrochemical reaction. and F is the Faraday constant. Thus, the importance of currrnt

density distribution is evident with higher localized values leadhg to a higher growth

rate, different growth type or the possibility of side reactions [19].

The amount of metal deposîted per unit area is given by Faraday's law:

" = q/hF 0.5)

where m is the ratio of the mass per unit area to the molar mass (w/M) and q is the

charge density at the electrcxie surface. In tems of local current density the expression

would be

rn = jdt/nF. 0.6)

3.1.2. Ove ipotential in EJectrocwmtioq

The equilibriurn between the electrode surface and the electrolyte with which it

is in contact may be characterized by the reversible electrode potential or E,.

Electrocrystallization is made possible by a dnving force called the overpotential q ,

w hich is the magnitude of deviation from equilibrium electrode potential. Overpotential ,

also called overvoltage or polarization, results from the 'slownessn of the reaction

process occumng at an electrode (ie. discharge/formation of ions). It can be expressed

as

i, = E - E , . (3.7)

Overpotential is dinctly related to chernical potentiai (p) and the change in Gibbs free

energy (AG) as follows:

7 = A&nF

i ) = A G I M A

where m is the amount of material pet unit area of elecaode, A (191.

In the above equations the total overpotential is a complex parameter that may be

separated into five additive tenns: charge transfkr overpotential q,, diffusion overpotential

qd, reaction overpotential r),, crystallization oveptential q,, and m e resistance

overpotential 7, [6]. Unfortunately, great difficulties arise in providing a quantitative

analysis of the partial ovefpotentials and so the total overpotmtiai is used.

The overpotential affects the nature of the electrodeposit. Chia and Su [20]

conducted studies that showed that increases in the overpotential nsulted in decreased

grain &es. Walsh and H e m 1191 m t e that the general trend is towards inaeasing

roughness as the overpotential is increased. As overpotential is increased, the kinetics

as well as the deposit morphology change. The current density inmeases due to the

increased rate of charge transfer as approxirnated by Tafel kinetics:

i = j,,qp(-@WRI) O- 10)

where j, is the exchange current density, a, is the cathodic msfer coefficient, R is the

gas constant, and T is the absolute temperature. As the overpotential increases, the

overail rate of reaction becomes increasingly influenced by the rate at which copper

cations reach the cathode [19].

Metal deposition requires that the system m u a be disturbed k m equilibrium

either directly by applying a potentiai field, or indirectly by aitering the

electrocrystailization environment through temperature or e lm1yte composition

changes. By varying the eIectrode potential the degree of supersaturation in

electrocrystalhation processes can be contro11ed. Poor conirol of potenthi distribution

cm lead to changes in deposit morphology and growth rate, or result in undesired side

reactions [ 191.

3.1.3. Wéct of OveFbotential on N u w o n and Growth

For electrocrystallization to be possible there must be active deposition sites

available on the electrode surface. The Kossel and Stranski hypothesis says that the sites

of high available energy on the crystai surface have a higher probability of atom

incorporation [2 11. For growth to proceed, adsorption and nucleation at these active sites

must first take place.

In the absence of any crystal of a metal, thne dimensional nucleation must fust

occur [6]. The size of the new crystal is dependent on the rate of three-dimensional

nucleation. Observing thrre-dimensional nucleation in electrocrystallization or physical

crystallization shows a similar trend. In physical crystallization, a metal which is

solidified fkom a high temperature liquid will have a smaüer grain size than the same

metal which is solidified from a startiDg point closer to the equilibriurn temperature,

since the former has a much greater the-dimensional nucleation rate [6]. In

electrocrystailization, an increase in the current density or inhibition intensity (resulting

in higher overpotentid) yields a higher nucleation rate and thus a smaller grained deposit

Pl-

However, if the total overpotential is not large enough to support three-

dimensional nucleation, then only oncdimensionai (new row generated at an existing

crystal plane) and twoaimensional nucleation (new plane is generated at a crystal

d a c e ) occur. The growth of a Mgle crystal arises through cornpetition between

vertical growth (dependent on the rate of two-dimensional nucleation) and horizontal

growth (dependent on the rate of onedimensional nucleation). In this case, as is

sometimes seen with copper deposition, small additions of inhibitors or the presence of

other foreign ions in the eleztrolyte may still resuit in a large grained deposit 161.

Ln industrial applications two-dimensional nucleation is the predominant

electrodeposition process. Two dimensional nucleation on a perfect crystai surface is

only possible if the criticai overpotential is exceeded. As the overpotential increases the

number of dislocations increase. On an imperfect crystal with dislocations (step, kink,

hole, edge vacancies), growth may be possible at a lower overpotential than required for

two-dimensional nucleation, if those dislocation sites are not inhibited 161. However,

because of their inactive nature, the morphology of the deposit is largely influenced by

impurities in the electrolytic solution. Eichorn and Fischer [22] demonstrated that an

increase in inhibitor concentration resulted in a decrease in the thickness of the growth

layers. Additionall y, the layers develop at a fister rate when the apparent overall current

density is kept constant.

In industrial deposits many crystals develop at the same the. The growth of a

single aystal can be directly infiuenced by the presence of other neighbouring,

developing crystals. Lateral grow.tti of crystals ceases when crystals impinge on one

another or when local current density is lacking (ie. as when dendrites are present).

Listed are the main crystal growth types associated with polycrystalline electrodeposits

[18]:

field-oriented isolated (Fi) fieldaiented texture

basis-oriented reproduction (BR) unoriented dispersion (UD)

- twinning intermediate (2)

These five types of deposits (Fig 3-3) are defined by metaiiographic structure and not

crystallographic texture. For example, FT and UD deposits can have the same

cry stailographic textures though their rnetaiîographic structures differ.

FI types are common at low inhibition. As the current density is increased

whiskers, prismatic crystals, dendrites and eventually powder deposits are produced. FI

types can be identified by direct extemai obsemation unlilce the remaining four types.

BR types are common at moderate inhibition ancüor current density 161. There is

sufficient time to ailow for good lateral growth, however, the crystals may eventually

grow to a size that eatrap electrolyte and impurhies as occlusions withïn the deposit.

Allowed to proceeû, the roughness increapes and degradation to an FI type is possible.

FT types are common at strwg inhibition andfor high current density. Elongated

crystals are arranged perpendicular to the substrate, forming a compact void-free deposit.

UD types are common at an even higher înhiiition andlor current density. Numerous,

s m d crystals form a compact, void-free deposit. The first four types of deposits are

formed by twdimensional nucleation, while the UD type is fomed by threedimensional

nucleation, which is observed only when the overvoltage is quik high (61.

FI : field ociented isolated crystals BR : basis reproduction FT : fieid oriented texture type UD : unoriented dispersion type

Figure 3-3. Diagram showing d i f f m t types of polycrystaiiine electrodeposits as a hction of j/CM?+ and inhibition intensity [4].

Two additional deposit types exist that occur under specific conditions and so are

considend apart k m the above five. One is the nodular deposit (N) and the other is the

rhythrnic larnellar structure (RL). Nodulation develops when fine electricai conducting

or semi-conducting solids in the eleztrolyte adhere to the deposit surface [23]. The RL

structure occun when the inhibitor, whose tmsfier to the electrode surface is diffusion

controlled, is entrapped or reacts at the sudace of the cathode, and is later consumed

afkr sufficient swace coverage is achieved [6]. Microxopic analysis of the RL

smcture shows a distinct oscillating or sinusoida1 growth pattern [5].

The coordinates in Figure 3-3 are j/C&+, the ratio of apparent cathodic current

density to bulk concentrations of metac ions to be discharged, and inhibition intensity.

If the Nernst diffusion layer thickness, 6,, is M y to Vary because of hydrodynarnics

changes, the coordinates should be j&. where j, is the diffusion limiting current density,

and inhibition intensity. The meaning and influence of the first coordinate of Figure 3-3

is simple to understand since it varies in the same direction both as the total overvoltage

and of i ts different parts [6]. The inhibition intensity is a complicated parameter that is

related to the addition agent(s) concentration in solution or adsorbed at the electrode

surface. They are responsible for changes in deposit morphology as well as

overpotential. Addition agents are further explained in Section 3.2.4.

3.2.1. Current Density

Current density in electrorefining can be dehed as the amount of current per unit

area of cathode. In industry, refmeries usually operate in the range 180 to 250 Mm2

[24] at an appiied ceil voltage of 0.25 to 0.3 V, though periodic cumnt reversai (PRC)

has permitîed the use of current densities up to 300 A/m2 [a. Discharged cations can

either form nuclei or grow as part of existing crystal planes on the cathode. The current

den* determines the rate of cation formation and discharge since the theoretical rate

at which copper is electrochemically plated on cathodes is b t l y related to cathode

current density. Therefore, in production it is desirable to operate at as high a cumnt

density as possible. As well, higher current density deposition produces denser

nucleations [24]. In a general overview, Devaaj and Seohadri [26] wrote that increasing

the cunwit den sity decreased current efficient y, increased hardness and increased cathode

overpoten tials.

The curent density employed in copper electrorefining cannot be increased

indefinitely. If the current is steadily increased, eventually a point of "limiting current"

is reached. This is the point where the maximum rate of transport is achieved given by

the following equation [27, a form of Fick's first law of diffusion:

-dQ/dt = DcJd (3.14)

where dQ/dt is the flux or rate of diffusion of ions to an electrode, D is the diffusion

coefficient, c, is the cation concentration in the buik, and 6 is the Nernst difision layer

thickness. Converting equation 3.14 to an equation for cumnt yields:

-dQ/dr = ilnF.

Finally. taking equation 3.15 and expressing i it in its limiting form gives:

i, = nEDcJ6

where i, is the limiting current [271.

As the current density is incnased, the electrolyte at the cathode surface becornes

increasingly depleted of cations. At limiting m a t dentity, the reduction of copper

cations at the cathode occurs so rapidly that the copper cations in the electrolyte at the

cathode surface are completely depleted. This can aiso result in unfavourable situations

such as unwanted metal codeposition due to selectivity andlor hydrogen evolution which

lowers current efficiency [28]. Figure 3-4 shows the dationship between current and

overpotential, and the various regions of deposition control. Also shown is the transition

h m copper deposition to hydrogen evolution at limiting cunent density. In an

expriment by Fukunaka et al. [29], spongy dendrites were clearly formed together with

hydrogen gas bubbles at extremely high overpotentials, though it was concluded that it

was impossible to tell whether the formations were rehted to hydrogen gas evolution.

Re ion of mus transiet (diffusion) controllrd Cu depoiition

Figure 3-4. Gmph of q vmus i showing deposition rcgions as related to i,Cu" [19,27J.

At high cunent density in copper electrorefïnhg, the dissolution of metallic

copper at the anode may becorne so rapid that the copper cation concentration in the

anode slime layex becornes supersaturateci causing crystallimtion of cupric sulphate

pentahydrate, CuSO4.5H,O. This passivating layer impedes the dissolution of the anode.

Anode passivation is less lh1y when the copper concentration is low (40 g/L),

temperature is high (60 to 65"C), and good electmlyte circulation across the anodes is

main tained [Z].

The ratio of current density to cathodic lirniting cumnt density is vitai to

electrodeposition. The limiting current density for an average commercial electrorefining

operation having convective rnixing between the electrodes is about 450 Mm2 [Il] to as

high as 675 Mm2 [30]. In order to produce smooth cathodes, refineries operate at

between 30 to 50% of the limiting current density or between 200 and 250 MmZ.

However, it is possible to obtain satisfactory cathode deposits at high current density

provided that the current density to limiting current density ratio is kept within

satisfactory limits by simultaneously increasing both [4,24]. As seen in equation 3.16,

a decrease in the Nernst diffusion layer thickness increases the limiting current density.

This can be achieved by enhancing the electrolyte agitation between the electrades so that

the diffusion layer is made thinner. Figure 3-5 shows the effet of reducing the diffusion

layer thickness on limiting cumnt.

The change in deposit morphology brought about by changes in current density

and overpotential has important te!chnological implications. Whiie metal powders may

be deliberately manufactured by inducing high cumnt density and overpotential, cathode

electrorefining requires smooth, void-fke deposits which are favoured by a relatively

lower overpotential 1191. Figure 3-6 shows the different growth morphologies that are

obsemed at various regions on the overpotential vernis cumnt c w e .

Figure 3-5. Graph of i) vmus i, showing the effat of d d g the 6, on i, [27].

~ s D t r i b , tapers iid blackr 4

Figure 3-6. Deposit morphoIogies o h a d aimg the 11 v m i m e [19].

3.2.2. ~v&odypPpiics - Mass w e r

Hydrodynamics is another important factor in the electrodeposition of copper.

Copper cation mass transport h m anode to cathode is achieved through a combination

of diffusion, hduced migration and natural convection. Difision involves the movement

of the cation dom a concentration gradient such as the one pictwed in Figure 3-7.

Migration involves the movement of the cation because of the potential gradient (electric

field), and it is the mechanism by which elecfric charge is conducmi through the

electrolyte. However, migration forces are electrostatic and do not dimiminate between

different ions in solution. As a result, migration does not contribute much to the copper

cation transport [31].

Convection is the movernent of the cation due to mechanical forces. Cation

concentration gradients exist in the electrolyte layers adjacent to the electrode surfaces.

These concentration gradients result in diffant specific gravities for surface and bulk

electrolytes. The specific gravity of the electrolyte at the anode surface is greater than

the specific gravity of the bulk electmlyte which is in tum greater than the specific

gravity of the electrolyte at the cathode. As a resuit of this, the elecmlyte flows dom

at the anode and up at the cathode with respect to the buik [13,30]. This is nsponsible

for the development of natural convection between the electrodes (Fig. 3-7). Despite

fluid flow in the bulk elmolyte, the layer immediately adjacent to the elecuode is

stationary. Thus, elecaon receiving, copper cations mut flow through the bulk via

convection, and through the stagnant layer via difision. This convection with diffision

process prevents the solvateci copper ion concentration h m falling to zero.

In electrorefîning, as the impure copper anode dissolves, other insoluble metah

and compounds form a slime that either adheres to the anode or deposits on the ce11

bottom. The slime layer that forms on the anodes during electrorefining impairs the

mass transfer within the system. Electrolyte within the porous slime layer is stagnant and

so the diffusion of cations is rate controlling [13]. If operating near limiting current

density, the presence of the slime layer can intensifj cation supersaturation and result in

anode passivation as explained in Section 3.2.1.

Figure 3-7. Nnniral convection and concentration profiles in cqper electrorehing [13].

Though naturai convection asures some degree of rnixing behveen electrodes,

mechaniai electrolyte or electrode agitation *in be helpful in lowering concentration

gradients at the electrodes and ensuring constant addition agent supply between

electmdes. This, however can be impractical and costly on an industrial scale. A more

practical approach to enhancing hydrodynamics is to manipulate the flow direction

(perpendicular, parallel) of the electrolyte. Elcctrolyte flow parallel to electrodes, as

found in channe1 ceils [32], oui greatly decrease the Nernst difision layer thickness, di,,,,

at the electrodes. The resulting inaease in limiting current density, as was seen in Figure

3-5, allows for smooth copper piating at higher current densities than would be allowed

in conventional perpendicular flow cens.

3.2.3. o. ion

Electrolyte copper and acid concentration, as well as the presence of addition

agents and impurities within the electrolyte can have a great impact on the morphology

of electrodeposited copper. Theoretically, a higher copper concentration in the

electrolyte yields a higher mass transfer rate and a lower overpotential. The Limiting

factor for copper concentration in the electrolyte is the copper cation oolubility that

increases with incnasing temperature and decnases with increasing acid concentration.

It should ais0 be noted that an increase in the copper cation concentration Iowers the

electrical conductivity of the electrolyte since copper cations are less mobile than

hydrogen cations. Despite all this, Ogata et al. [3] mote that otha snidies indicated that

there was no appreciable change in the shapes of electrodeposits plated at identical

cumnt densities but different copper cation concentrations.

Increasing the acid concentration d t s in an increase in the electrolyte electrical

conductivity because acid supplies highly mobile H+ cations [33]. However, the effect

of acid concentration on the morphology of electrodeposited copper was not examinecl

until quite recently. Fukwiaka et al. [29] found that the addition of an excess amount of

H,SO, greatl y increased the cathodic overpotentiai and induced three-di mensional

nucleation resulting in rounded precipitates, even at lower overpotentials. T'his may have

been the result of strong H,O+ adsorption on the cathode surface and no contribution to

migration.

The concentrations of impurities in the electrolyte must be controlled to ensure

that their interference with plating is rninimized. Physically , their levels are controlled

by electrolyte purification as in the technique dexribed by Biswas and Davenport [25].

Electmchemically, selectivity ensures that impurities and other metai ions do not plate

at the cathode. Metals such as gold and platinum do not dissolve in sulphate electrolyte

and so do not plate ai the cathode. Silver undergoes some dissolution and minor plating,

but it is largely precipitated as a selenide. These metals are more noble than copper and

would plate at a lower voltage than that requireû for copper, therefore, it is important

that they form an insoluble anode residue [13,2!Q

Sulphur, selenium and teîiurium are present in the anode as insoluble compounds

(selenides, tellurides and sulphides of glver and copper) and do not electmchernically

dissolve, much like the noble metals. Lead and t h form insoluble sulpbates that

precipitate as anode slimes. Arsenic, bismuth, cobalt, iron, nickel and antimony are al1

less noble than coppet and tend to dissolve in the electroIyte. Signincant axnomounts of

arsenic, antimony and bismuth revert to siimes, largely a resuit of compound formation

with copper in the anode. The thrrt can combine to form menate pncipitates which

often becorne the major source of deposit contamination [34]. Braun et al. 1351 wrote

that these three elements can be incorporated into a cathode deposit by electrolytic

codeposition (unlikely since electmlyte potentids and impurity concentration are too

low), anode slimes occlusion, electrolyte occlusion, or direct precipitation h m solution.

Therefore, regardlas of selectivity or how well controiled an electrorefining

operation is, there will inevitably be some degree of codeposition, or occlusion of

suspended slimes and impurity-containing electrolyte droplets in the cathode deposit.

3,2,4, Addition Agents

Inhibition, hindering of the cathodic process, occun because of the presence of

addition agents different from Cu2+ or the conespondhg adatom (adsorbed Cuo atom not

yet part of a metal crystal) at the electrode surface, in the diffusion layer or in the double

layer [6]. It is widely documented that addition agents play a vital role in producing a

cathode depont of acceptable quality. They help to modify the crystal size and structure

of the deposit, improve brighmess, widen the operating range of pH, temperature or

current density [36], as well as improve ductility, d u c e interna1 stress, harden and

d u c e surface tension to induce gas bubble detachment in deposits 111. To achieve

adsorption on copper, addition agents should contain radicals or groups such as sulphur,

the arornatic ring, double bonds (ie. C=N; C =C), triple bonds (ie. C =C) or polawd

groups (ie. -NHJ [5].

Common addition agents used in copper electrorefïning rnay be inorganic or

organic. Inorganic cations such as Na+ do not disharge at the cathode and, therefore,

have a negligible inhibiting effkct. Inorganic anions can alter the double layer and thus

the charge transfer overvoltage. These could include activation anions (Cr Br, r),

intermediate anions (NO3', S0:) and inhibiting anions (BF,', NH,SO$, CIO,') [6].

Organics (ie. glue, Tembind, thiourea, Avitone) in electrolytic solution can be strong

inhibitors if they adsorb at the electrode and do not have an affinity for water. They can

minimally inhibit and even be activating agents if they adsorb at the electrode and have

an affinity for water. Organics could also be minor activating agents if they have an

afinity for water, but do not adsorb at the electrode. Ultimately, they can be totaily

ineffective if they neither adsorb nor have an afinity for water [6].

Though the mechanism by which addition agents work is poorly understood, and

that their behaviour as inhibitors is complex [4], it is generally accepted that most of

these addition agents infiuence the cathodic reaction largely by physical or chernical

adsorption at the cathode Nface. Adsorption could nsult from molecular charge eflects

or it can resuit h m specific adsorption (betwem electrodes and ions of like charge)

where the contact adsorbing ion is partly oblivious to the charge of the metal [2]. It is

believed that preferential adsorption of addition agents occun on active cathode growth

sites where the current density is highest [36,37]. Growth sites experience higher

localued current densities because they are closer to the anode relative to the nimundhg

area of the cathode. Bockris and Ranirnney [38] support the theory that organic

additives are consumed at the cathode by their own diffusion iimiting flow. They

theorize that the consumption of inhibitor occurs by ratedetefminiag mass transfer in

solution to the electrode, followed by adsorption at the electrode surface.

These addition agents can af'f'ect the cathodic process in several ways. This can

include lowenng local current density, and ultimately cumnt efficiency, by

simultaneously reducing with the desired metal ion. Addition agents cm also

contaminate the metal deposit with their decornposition products. They fan alter the total

overvoltage by inducing changes in one or more of the partial overvoltages. Most

important, addition agents can alter the metal and crystal structure of the deposit, thereby

making them usehl in cathode leveliing and grain rrfining [6]. Described in hnher

detail are the four addition agents that are of interest in this thesis: glue, Tembind

(ammonium lignin sulphonate) , thiourea and chloride.

3.2.4.1. Glue

Glue is the most common of all addition agents [8,16]. This universal addition

agent is a biopolymeric organic compound @rotein) consisting of high molar mass

(10,000 to 250,000 rnolar mass units), long chah amino acids (Fig 3-8) [37. It is

derived from, among other things, animal bone and conneztive tissues. It is generally

accepted that only glue molecules with a certain molar mass (grrater than 10,000 uni&)

are useful in moderathg electrodeposition and behave as the "active" glue in solution

1371. By definition, active glue refers to those molecules which have the ability to form

a resistance kyer on the cathode [39].

R O CHz-CHt-CHa O H

l I I I 1 II I

Figure 3-8. Chernical formula for glue (51.

Glue molecules adsorb to active, negatively charged growth sites on the cathode

[37. The O and the N (preferentially) tenninals of the peptide chahs (-CO-NH-) are

chemisorbed io the cathode, increasing the limiting current density of diffision and

decreasing the charge transfer exchange current density (51 when added in typical

amounts (1 to IO m a ) [l6]. The admbed molecules c h g e the nature of the diffision

iayer at the cathode and potentially alter the sUTface =ta potpitials.

Glue works best as a grain refiner, when used alone in concentrations of 5 to 10

ppm [Ml. Up to 20 ppm it decnases roughness, though no change is observed in

deposit structure (FT type) [5]. It increases cumnt density and produces smoother

deposits up to a lirniting concentration after which the bulky nature of the molecules

hinders efficient deposition due to visconty increases in the double layer (361. Excess

glue concentrations can lead to rough, striateci and brittle deposits 1401. O'Keefe and

Hunt [34] found that increashg the glue concentration in the 7.5 to 30 ppm range gave

increasingiy less ductile deposits.

In acid sulphate electrolyte, glue, by itself is a strong cathodic poladr, which

at typical indusaial concentrations (3 to 10 ppm) can increase polarization by 30 to 50

mV [13]. At just 3 ppm the overall wervoltage is approxirnately doubled [5]. According

to Blechta et al. [39] the overpotential induced by glue addition first inmeases. Cher

time, less active long chah molecules undergo rapid hydrolyses to more active medium

size molecules. After reaching a peak, the overpotential decreases exponentially with

time due to the lower hydrolyses of medium size molecules to short molecules that are

unable to form a resistance barrier at the cathode surface. This gradual hydrolysis (over

one to six houn) in hot electrolyte causes the active glue to lose its effectiveness as a

polarizer over time (161. Studies done at CCCR concluded that glue was completely

decomposed in electrolyte when subjected to heating at 9S°C for 1.5 to 2 hours [39,41].

Saban et al. [37J clah that after 40 to 80 minutes of nomial tankhouse operation

(dependhg on the mass transfer rate), glue is degraâed to molecules consisting of less

than 10,000 atomic mass units (mu). The study goes on M e r to state that the criticai

giue mass is around 3700 mu below which it loses most of its activity. Glue is also

consumed by incorporation into the deposit and adsorption onto slimes. Hence, glue must

be added continuously to an elecmefiniag circuit in order to maintain the des- glue

activity. However, additional molar mass distribution and glue degradation rate studies

will be necessary before accurate models can be made for electrorefining operations.

3.2.4.2. Tembind (Ammonium Ligidphooate)

Tembind is produced by Temfibre Inc. (Timiskaming) as a by-product of its wood

processing operation. The chernical name for Tembind is ammonium lignosulphonate.

Lignification, a major process that occurs during plant maturation, is the formation of

a network of complex three-dimensional phenol based (ie. benzene ring) polymers [42].

The structure of a typical lignin is shown in Figure 3-9.

Figure 3-9. StniEture of 1ign.h [451.

Typically, Tembind is maintained at a concentration of approximately 150 ppm

in the electrolyte. M o u s studies conducted at CCCR show that by itself Tembind acts

as a depolarizer in electrolytic solution (431. ûverall, though, the mechanism by which

it works in electrorefining is not well known, though it might be speculated that it

adsorbs due to charge effects or some specific physical characteristic of its complex

molecular structure [ 14,441.

Though not widely used in industry [8] Tembind does play an important role in

cathode production in the Copper Cliff tankhouse. Even without glue, its addition to

electrolyte results in an acceptable cathode sudace, significantly better than without

addition agents [44]. Apart fiom any cathode levelling benefits it may have, it is also

considerd to be a buffer for glue fluctuations in the electrolyte [14].

Unlike glue, Tembind demonstrates high resilience in the presence of sulphuric

acid electrolytes and/or high temperatures [43]. After two hours of heating at 95"C,

Tembind reaches a constant concentration, approximately 75 % of its initial concentration,

in synthetic electrolyte [41]. CCCR rechimed acid, an acid plant end-product produced

by high temperature evaporation, contains high levels (1000 ppm h m analysis) of

Tembind, despite having an H,SO, level of around 1000 g/L. If acid düution is taken

into account it appears that very linle Tembind is destroyed during reciaimed acid

manufacture*

Kezping this is rnind, it is thought that Tembind and its decomposition products

play an important d e in cathode production Snce reclaimed acid is recycleci to the main

tankhouse electrolyte. Persorne1 directly involved in copper electrorefining at CCCR

believe that reclaimed acid is essential in produchg high quaüty cathodes [14], and

experiments that w a e carried out to address ihis appear to support the idea [46].

Electrolytes prepareû with reclaimed aciû, compared to eîectrolytes prepared with new

acid, produce better cathodes (471.

Published information on Tembind was quite limited since its use is not

widespread in the electrorefining industry. Thus, the bulk of the information available

at the time this thesis was written, was largely confîned to that found in Inco references

(ie. monthly reports).

3.2.4.3. Thiourea

Thiourea is a common addition agent often used in conjunction with glue. AU but

wo of the worlds major refineries utilUe thiourea in cathode production [8]. Iu

chernical formula is given in Figure 3-10a. Unlike glue and Tembind. which are

cornprised of large molecuiar structures, the thiourea rnolecule is srnail. It is not totalïy

consumed by electrolysis, but also undergoes a time dependent deterioration in electrolyte

[32]. In copper suiphuric acid elecwlytes, thiourea complexes with Cu+ to produce (Cu-

th)+, and reduces Cu2+ to Cu' aiso fomhg dithioformamidine in the proces (Fig. 3-

lob) 151. The (Cu&)+ complex slowly degrades over a matter of days.

T h i o w has an inhibithg effect in the double layer and is strongiy selective, but

it adsorbs unifody over the entire cathode surface. Thiourea molecules are oriented

on adsorption and change the dipole configuration of the double layer. ûniy the > C =S

dipole is believed to influence the potential across the double layer [20]. When thiourea

is present in electrolyte the nst potential of the copper elecaode is more positive, due

to surface sulphidization (51. It also increases the limiting cumnt density.

Figure 3-10. Chemicai formuiae for (a) ihiourea (b) dithioformamidîne [36).

Literature contains varied views on the effect of thiourea on overpotential. Chia

and Su [20] wrote that thiourea increased overpotentiai drastically, more so than glue.

In their experiment, 100 ppm thiourea was used which is well outside the operating range

for indusaial practice. There was also no mention of the electrolyte acid concentration

that was used. Krzewska et al. [48] found that at temperatures higher than 40°C the

effect of thiourea concentration on cathodic polarization was insignificant. At 200 A/m2

W m d et al. M m t e that the charge transfer overvoltages were decreased at low

thioufea concentration (< 1 pprn) and increased at high concentration (> 2 ppm).

Fabricius and Sundholm 1161 found that oniy at cathode overpotentiais of les than -100

mV, thiourea had a depolarizing effect on copper deposition. At more negative

potentials, thiourea concentrations of less than 10 mg/L had no signifiant efiect on

poiarization.

m e r studies showed that addition of small amounu of thiourea (0.2 to 2 ppm)

in electrorefining electmlytes significantiy deimased grain size and roughness in deposits

[32] [71 while not significantly affecthg the overvoltage when compareil against pure

solution [5]. At a concentration of vound 5 mg/L t h i o n decreased cathode cunent

efficiency, though it still improved deposit quality 1361. Thiourea levels in electrolyte

must be closely monitored since overdosage leads to a rapid deterioration in cathode

deposits. De Maere and Winand m found that thiourea greatly increased the three-

dimensional nucleation rate. At levels greater than 3 ppm the deposit structure changes

from FT to UD, with the possibility of nodulation [SI. At concentrations above 5 mg/L,

Afifi et al. [36] found that thiourea increased current efficiency but also prornoted

nodulation and rough deposits due to increased precipitation of CuS and for S on the

electrode. Smith et al. [32] observed that copper deposits became dark and brittle when

the thiourea concentration approached 8 rng/L.

Despite its grain refining properties when used in combination with other

particular addition agents (ie. glue), thiouna is not a satisfactory additive when used by

itself in electrolyu 141. m e r drawbacks associated with using thiourea include the

conmbution of up to 10 ppm sulphur in cathodes 1131 and its reputation as a suspected

carcinogen [2 11.

Chloride (as HCl or NaCI) is another common addition agent used in copper

electrorefining eiectroiytes. The chloride ion has a s r d i radius (0.99A vs 1.70A for

SO?'). The addition of chloride ion to pure copper sulphate electrolyte results in a

decrease in potential [49]. It is usually maintained in the range of 10 to 50 pprn in

electrolyte, with typical concentrations being between 20 to 30 pprn [13].

For rnany yean, it was believed ihat the main function of chloride in

electrorefining electrolyte was to suppress the dissolution of silver by lowenng its

solubility, thus precipitating AgCl [7]. A mon recent study has shown that silver is in

fact precipitated as a selenide which has a lower solubility than AgCl [50]. According

to another stud y, chloride serves to reduce antirnony contamination, perhaps b y

precipitating antimony oxychlondes, though there is great speculation that this may not

be the actual mechanism (341. Another theory is that the chloride ions in the double

layer could act to complex antimony ions and prevent their codeposition by altering the

overpotentials necessary for reduction (341.

Studies show that exceedhg critical chloride ion concentrations in electrolyte

causes detenoration of the cathode deposit including CuCl precipitation [S, 133 11. If

CuCl deposits at the cathode, the active surface area decreases, giving rise to higher local

cunent density and overpotential tint couid lead to dendrite or nodule formation. As the

chloride ion concentration rnoved h m 20 to 40 ppm, deposits changed fiom uniform to

crystalline; they became uneven and more nodular 1491. On the other hand, Blechia and

Wang 1231 found that increasing the chloride concentration from 20 ppm to 50 ppm

improved the cathode surface very slightly. The differences between these two studies

may be explained by the fact that the former involved electrowinning using silver-lead

anodes and titanium cathode blanks, whereas the latter involved typical copper

electrorefining using copper anodes and copper starter sheets.

O'Keefe and Hurst [34] found that 15 pprn or higher chloride, alone, in solution

decreased grain size and gave very rough and irregular deposits that had a powdery,

faceted appearance. At 30 ppm chloride and low current density (133 A/m3 they

produceci a "lacy" deposit witnessed in other studies. Finely divided CuCl may have

represented a barrier to grain growth and increased the nuclcation rate. In the same

study, chlonde addition gave the most ductile deposits [34]. Lakshmanan et al. [49]

obsewed that the effect of chloride ion concentration depended on operating current

density: lower current densities gave ridged growth sauctures while higher current

densities have pyramidal type growth. The source of chloride ions (NaCl, CaCl,, MgCI,

and FeCl,) was not a factor in deposit morphology.

UnliLe thiourea, where an inmase in concentration leads to higher sulphur

contamination of the cathodes [13], increasing chloride concentrations does not always

lead to higher chlorine concentrations in the cathodes [71. In one study, spectroscopie

analysis of the deposit suggested that regardless of the chlonde concentration (in the 7.5

to 30 pprn range) the concentration in the double layer or the adsorbed concentration

remains fairly constant regardiess of the bulk concentration [34].

3.2.4.5. Combined Effect of Addition Agents

nie effect of each addition agent alone in solution cannot simply be added to

detemine their combined effect on cathode overpotential and deposit morphology . For

example, the cathodic overpotentiai observed in the presence of glue and thiourea is not

simply the sum of the overpotentiais observed in the presence of those additives

separately [48]. Thus, the combined effect of various addition agents can Vary greatly

depending on the combination that is used.

Though extemal referenca citing Tembind are rare, various Inco CCCR monthly

reports and memoranda contain information on Tembind and its behaviour in the

presence of other addition agents such as glue. Tests done at CCCR showed that

Tembind decreased the glue polarization in synthetic electrolyte. Glue polarization was

dccnaxd by approximately 50 percent regardless of the Tembind concentration in the

electrolyte [41,43,52]. Blechta and Wang [23] found that the glue-Tembind system was

quite forgiving. Wide glue and Tembind fluctuations still gave similar cathodes of

acceptable d a c e quality. Blechta and Wang [23] also found that various glue-thiourea

cornbinations gave rougher deposits when compared to the glue-Tembind combinations.

The best iesults for the glue-thiourea combination was achieved using high glue (5 ppm)

and low thiourea (5 ppm) [23].

Chlonde is well ncognued for impfoving and brightening cathode deposits when

combined with organic additives. However, the synergistîc effm of chloride and

organic additives are still not weil understd [SI]. Dependhg on the combination of

addition agents in electrolyte, chloride ion addition can have varying effects on

overpotential and deposit quality. At constant giue concentrations, chlonde addition first

decrrases total overvoltage, bottoms out and then inmeases with increasing chlonde

concentration [SI. When combined with glue, 20 to 40 pprn chlonde gives the lowest

values of intemal deposit stresses [SI. O'Keefe and Hurst [34] found that chloride (30

ppm) and glue (15 ppm) together in electrolyte produced a similar deposit to glue alone

(15 ppm). However, the ductilities of the deposits plated in the presence of glue and

chloride were lower than those for the deposits plated with only chloride present, and

they improved as the glue concentration was lowered.

Krzewska et ai 1481 wrote that adding chloride to an electrolytic solution

containing glue, thiourea or a combination of the two, caused a considerable polarization

increase. Further increases in any of the additives did nothhg to change the polarhation

potential. When combined with thiourea or a glue/thiourea containing electrolyte,

moderate chioride addition improves deposit quaüty [SI.

When a high chioride concentration (50 ppm) was used in combination with glue

(50 gfton of deposited copper or "g/tdcW) and thiourea (40 g/tdc), the crystal size

increased with deposit thickness and both t h and two-dimensional nucleation rates

decreased [7J. De Maere and Winand [n also found tbat UicreaSing the concentration

of these three additives at the same time did not significantly change the metallographic

stnicture of the reference deposit (35 ppm chlonde, 50 g/tdc giue and 40 g/tdc thiourea).

Furthemore, the chioride concentration had less influace on metallographic structure

than the glue or thiourea concentrations. When oniy one additive concentration was

changed, low glue (25 gltdc) or high chloride (50 ppm) were most detrimental. Aiso.

increasing the thiourea (80 g/tdc) or glue decreased the influence of chloride ions.

W i w i d [SI States that no k t correlation can be found between overall

ovenioltage changes due to addition agents and changes in a deposit's metailographic

structure. While a combination of additives may significantly alter the overvoltage

compared to pure solution, that same combination may not generate a signifiant change

in the metallography of the deposit. On the other hand, a combination of additives may

not markedly alter the overvoltage compared against pure solution, yet may produce a

radically different deposit.

Based on the precedhg information an expenmental project was proposeci. The purpose

of the project was to address the following objectives:

Examine and compare the effects of various addition agents, including rec1aimed

acid, alone and in combination, under weli controlled conditions on cathode

polarization.

Examine and compare the effect of various addition agents, including reclaimed

acid (plant and synthetic), alone and in combination, on copper cathode

morphology, using lab sale electrorefining ceils.

Examine the correlation between polarization results (ie. overpotential changes

due to various addition agents and their combinations) and deposit morphology.

Compare the effect of thiourea and hm-used addition agents, with respect to both

cathode polarization and cathode morphology.

Determine whether desireû cathade morphology can be produced at high cumnt

density without using thiourea.

Examine and identify, using dialysis and spectrometric techniques, the organic

species present in reclaimed acid and how they are related to Tembind.

The purpose of these tests was to produce copper cathodes and to analyze the

effects of different addition agent combinations on deposit surface appearance,

crystallography and hardness. These tests studied the effect of CCCR tankhouse addition

agents (glue, Tembind, and chlotide) and thiourea, as well as CCCR Acid Plant

reclaimed acid and synthetic reclaimed acid made using the procedure outlined in Section

4.4.1.

Lab scale electrorefining cells were used to plate copper cathodes using various

combinations of addition agents. The lab sale set-up (Fig. 4-1) allowed simulation of

plant operathg conditions such as temperature, anode, cathode substrate, electrolyte

composition, current density, electrode spacing and continuous addition of additives.

Two lab Sue electrorefining banks were used, each containhg four separate

electrolytic ceus. The two banks were made of HW thick CPVC. Each celi in a bank

was comprised of an electrolytic @Ming) compartment, and an electrolyte storage

compartment where addition agents (glue, Tembind, thiourea, chioride) were added.

Figure 4-1. Expcsimenîai set-up for the 1ab d e electrorefbhg ceus.

4.2.2.1. Electmlyte and Addition Agent Make Up

The synthetic electrolyte was made up in 24 L batches using distilled water,

magent grade sulphuric acid and cuprîc sulphate pentahydrate to give appmximately 40

g/L Cu2+ and 155 g/L H#O,. Prior to each eiectrorefining test, the appropriate arnount

of addition agent(s) was addeû to the electroiyte to give desind initial concentrations.

Semi-synthetic electroIyfe was pnpand by taking acid plant reclaimed acid, diluthg it

to 155 g/L sulphuric acid using distilled water, and adding an appropriate amount of

CuSO,.SH,O to give 40 g / L Cu2+.

Since glue can degrade quite readily in solution a special procedure was followed

to produce consistent batches of glue solution. The glue was ground using a mortar and

pestle, and sieved using a #2S screen. One gram of the sieve undersize was added to LOO

mL of distilled water heated to 50°C on a hot plate/stirrer. The solution was stirred for

one-half hour, ensuring that the glue cornpletely dissolved. After the heating period, this

solution was diluted with distilled water in a volumeaic flask of predetermined size to

give the desued concentration. The unused portion of the glue solution was refrigerated

to minimize degradation.

Tembind, thiourea and chloride did not require any special preparation since they

readily dissolved in aqueous solution. Measured arnounts Tembind and thiourea were

dissolved in volumetric flasks using distilled water. When used, measured amounts of

chloride were added directly to the electrolyte as solid sodium chloride.

4.2.2.2. Electrode Reparation

AU lab anodes (110 x 50 x 10 mm) (Fig. 4-2) were machined from a single

tankhouse anode that was pou& thicker than a reguiar anode to allow for machining.

Since anode chemistry is a major factor in copper elecûorefining, this procedure was

foîiowed to eliminate the influence of anode composition. Assay analysis of the

laboratory anodes showed tbat the composition fell within acceptable limits (Table 4-1).

The lab anodes were scrubbed with a suitable abrasive cleauser to remove any cutting oil

residue. The anodes were then thoroughly rinsed with distilled water. Afkr rinsing, the

anodes were dipped in a 1 5 sulphuric acid/distilled water solution, rinsed with distilled

water again and wiped dry.

Figure 4-2. Dcawings of the Lob anode and cathode showiag dimensions.

The cathodes (1 15 x 60 mm) (Fig 4-2) were cut from a plant starter sheet. Using acrylic

spray, the side of the cathodes not M g the anodes were coated prior to plating to

ensure that copper did not plate on the back side of the cathodes. The plating surfaces

were lightly abraded with 6M) sandpaper to remove any surface impurities. The cathodes

were then dipped in a 1 :5 sulphuric acid/distilled water solution, rinsed with distilled

water and wiped dry. The cathode weights were recorded both before and after plating.

Table 41. Assay Analysis of the Laboratory Anodes m m )

1

43 & M A As Au Bi Ca0 339 585 < 152 < 70 < 55 < 9 439 < 98

I

Co Cr,O, Cu Fe fr K Li Mg0 < 44 < 40 98.2 % 559 < 4 6 3 Cl72 < 5 232

I

Mn Mo Ni P Pb Pd Pt Rh < 3 c 72 4089 <262 C l 4 3 Cl69 <230 c 2 6 0

1

Ru S Sb Se SiO= Sn Te Zn CS86 < 9 3 < 146 < 909 1090 < 79 <239 C 4 6

4.2.2.3. Laboratory Copper E l e c t r o M î

The electrodes were supported by stainless steel hanging wire that passed through

predrilled holes in the celis and electrodes. The anodes were placed within the

electrolytic compartment 29 mm from the cathodes. The cathodes were 10 mm wider

than the anodes and were positioned 5 mm lower in the electrolyte to minimize edge-roll

formation. In position, the lower 65 mm p o r t h of the cathodes were imrnersed in the

ekmlyte.

Each celi (Fig 4-3), with a volume of 400 mL, had an independent electrolyte

circuit. The electrolyte was pumped h m the electrolyte storage cornpartment by a

variable speed penstaltic pump to the electrolytic compartment. As the electrolyte passed

through the 6.4 mm I.D. diameter, 316 SS tubing (chosen for its good heat transfer

properties) it was preheated by the water bath surroundhg the ceil. From the electrolytic

compartment, the elecmlyte overflowed into the storage compartment to maintain a

constant electrolyte level in the plating compartment.

- 3 l b S i 4.8 mm LR

Omilow Hok

6.4 mm

Eiccuordiniag CcU i . 3.2 RIUI CPVC

Figure! 4-3. Cross4cctionai drawing of a lab plating c d showing dimensions.

The eight electrorefining cells (four in each bank) were nui simultanemsly . Each

ce11 was filled with e1ectroIyte contalliing various combinations/concentrations of addition

agents. The water bath cornpartment that held the two banks (Fig 4-4) was insulateci to

d u c e heat loss. The water was circuiated and kept at a constant temperature by a Cole-

Parmer immersion circulator. A fixed water level in the bath was maintained using a

. . - . . . - - - - - . - . -. . . .

float level controlier (located in the bath) that activated the opening and closing of an

electromagnetic valve on the 10 L nalgene bottle containing dinilled water.

Glue, Ternbind and thiourea were pumped by four fixed speed (20 rpm) peristaltic

pumps using small diameter (0.51 mm I.D.) tubing. Flow of the addition agents was

controiled by a GE Fanuc Series One junior programmable controlier that intermittently

activated the peristaltic pumps. The fine tubes carried addition agents h m s d 3 0 rnL

viais to the pumps which pumped the agents through the fine tubing to the electrolyte

storage compartments. Elecûical power was supplied by a Xantrex 2OV quad DC

rectifier which delivered a constant current to the cells which were connected in series.

Figure 4-4. hwing of the iaboraîory elac~ro~tfïnïng ceU bank and hot WOter brth showing dimensions (plan view).

4.2.2.4. Cornparbon of Lab and PLnt Rirameters

The lab d e electrorefining parameters were carefully selected, keeping in rnind

those used in practice at the Copper Cliff ER tankhouse. Table 4-2 lists the parameters

used in the îab scde tests and those used at the tankhouse.

Tabh 42. Lab and Electrorefining (ER) Tankhouse Operathg Parameters

glue concentratîon target 5 PPm 3-6 ppm

Tembind concentration target 150 ppm 120-170 ppm

thioureri concen~rotion taqet 0.2 ppm, 2 ppm NA

chloride concentration target 20 ppm 20 PPm

anode p h t ( m e 4 ~ h t

cathode p h t (Cu!) p h t

anode dimuisiol~g 110 x 50 x 10 mm 0.91 x 0.91 x 0.04 m

mode to uthode surfirce spacing 30 mm 30 mm 1 1

cathode p W g cycle 1 &Y 14 âays 1

ctarmt dwsity 300 A/UI~ 183 A l d

1

Every effort was made to simulate the tankhouse operation, however, considering

the degree of d o d g , it was not always possible nor Ralistic. Ultimately , it can be

- - -- - -

bottomlia, toplout

66°C

- - - p p p p p -

electrolyte flow pattern L

electrolyte temperature

- - - p-p - -

bottodin, toplout

66OC

said that the o v d results are specific to this piece of equipment and may or may not

reflect actuai plant opemtion. However, the results do provide valuable information that

is narssary in plamhg nasonable pilot plant tests.

In the experiments, synthetic electrolyte was used in place of plant electrolyte.

This was done to e l i d t e the presence of addition agent decomposition products or

other impurities that might have influenceci the electrorefining process. The glue and

Tembind addition rates for the Iaboratory equipment was incruiscd by an amount

equivalent to the ratio of lab to plant current density . Theoretically . it was assumed that

the percent increase in current density would yield an equivalent increase in the rate of

copper deposited and hence an equivaient increase in the rate of addition agent

consumption. This assumption was indeed verified during pretrial testing by determinhg

glue and Tembind levels in the electrolyte after plating.

Since thiourea is not used in the tankhouse, it was neceSSary to rely on addition

agent information fmm other refineries to determine addition rates 183. Based on

published figures, it was decided to utilize the same additiodconcenaation ratio for

thiourea as is used for glue in the tankhouse. Thus, to maintain the desired concentration

of thiourea in elecholyte, the addition rate was appropriately adjustecl based on this ratio.

Unforninately, since thiom is not used in the tankhouse, there was no available rnethod

for thiourea determination and the exact concentration after plating could only be

speculated.

4.2.2.5. %ope of Work

After extensive preliminary test work dealing primady with cathode preparation

(masking the back of the cathode to prevent plating) and equipment commissioning, a

total of eight series of tests were conducted. The lab equipment consisted of wo banks

containing 4 ceils each for a total of eight ceus. To monitor the feproducibility, most

of the experiments were run in dupücate (ie. same conditions in each bank) w, each series

yielded four results (exceptions will be noted whenever applicable). Concentrations and

combinations of various addition agents were selected in most instances to match those

used in the polarization experiments.

The standard experimental conditions were as follows:

During commissioning, all eight plating cells were run using the identical

conditions employed in the CCCR tankhouse (5 pprn glue, 150 pprn Terhbind, 20 pprn

chloride, 183 N m 3 . The resuiting cathode deposits demonstrated that the plant

conditions wuld k duplicated in the lab cells and tbat aU eight cells gave identical

results when the identical parameten were hcorporated. Additional preliminary testiag

involved operating at various current densities (250, 300 and 350 A/m2) using otherwise

identical plant conditions. Besides checking the reproducibility between the cells, the

purpose of these tests was to determine the most appropriate current density to use in the

lab cells,

Given the greater degree of parameter control in the lab cells, it was possible to

operate at much higher current densities than in the plant and still produce good

cathodes. From these preliminary tests it was determined that operating the plating cells

at a current density of 300 A/m2 was the most suitable level for lab scale operation. At

this current density, the "cushionn afforded by better control was effectively removed

making the system much more responsive to changes in addition agent

concentrations/combinations. This current density value was identical to the value used

in the cathodic polarization tests described in the Section 4.3.

Two different electrolytes were made up for the laboratory electrorefining tests:

Synthetic electrolyte: solution of reagent grade mlphuric acid, distilled water and dissolved reagent grade CuSO,.SH,O (composition: H2S04 - 155 g/L , Cu2+ - 40 gfL)

Semi-.rynthetic electdyte: solution of (10%) reclaimed acid electrolyte (solution of acid plant reclaimed acid, distilled water and reagent grade CuS04.W20; composition: H2S04 - 1% g/L, Cu2+ - 40 gL) and (90%) synthetic electrolyte

Reclaimed acid is a CCCR add plant product (@I000 g / L H2S04, @I000 ppm

Ternbind). Synthetic reclaimed acid* batches were also made using reagent grade

sulphunc acid as well as regular and dialysed Tembind* to give concentrations sidar

to plant reclaimed acid.

(*sec Section 4.4.1 for procedures)

The experimental series were as follows:

Series A:

Senes B:

Series C

Series D:

Senes E

Series F:

Series G:

Series H:

no additives: 5 pprn glue; 150 pprn Tembind; 5 pprn glue + 150 pprn Tembind

identical to A, with addition of 20 ppm chloride to ail 8 ceiis

identical to A, except semi-synthetic electrolyte used in al1 8 ceils

identical to A, with addition of 2 pprn thiourea to all 8 cells

identical to A, with addition of 0.2 pprn thiourea to ail 8 ceUs

identical to A, with addition of 20 pprn chloride and 0.2 pprn thiourea to

ceîis 1 - 4; ceils 5 - 8 are identical to ceiis 1 - 4, except semi-synthetic electrolyte is used

2.5 pprn glue + 50 pprn Tembind; 2.5 pprn glue + 150 pprn Tembind; 10 pprn glue + 50 pprn Ternbind; 10 ppm glue + 150 pprn Tembind; 5 pprn glue + 50 ppm Tembind; 2.5 ppm glue + 50 pprn Tembind + 20 pprn chioride; 5 ppm glue + 50 ppm Tembind + 20 pprn chloride; 10 pprn glue + 50 pprn Tembind + 20 ppm chloride

no additives; 150 ppm Tembind; 150 pprn Wysed Tembind; 5 pprn glue + 150 pprn Tembind; 5 ppm glue + 150 pprn dialysed Tembind; no additives + semi-synthetic electrolyte; no additives + 10% synthetic RA; no additives + 10% synthetic RA (made usîng dialysed Tembind)

The resulting cathode deposits were judged by simple visual observation (naked

eye) , pbotornicrographs of polished cross-sections and microhardness measurement . For

photomimgraphy, the samples were sectioned tranmersely about one centimetre above

the bottom to avoid edge effects. However, in some cases, it was necessary to section

closer to the centre of the deposit depending on the severity of edge efkcts. The sections

were mounted in plastic and polished for metallographic examination. The etchant used

to reveai the microstructure was potassium dichromate. Photomicrographs were taken

near the centre of the NI thickness of the section using 50 x magnification.

Microhardness measurements were iaken on some samples of the starter sheet and

each deposit using a Beuhier Miclonet II equipped with a Vicken diamond indenter and

an indentation load of 100 grams. One reading was taken on the starter sheet sampIes

and three readings were taken on each sample deposit.

USng a gaivanostatic method (constant cumnt), cathodic polarization tests were

performed to determine overpotentials specinc to various combinations of addition agents

in synthetic electrolyte. The equipment used for the polarization tests, was a proven

apparatus that bas been in use for several yean at the Inco Limited Copper Refinery for

glue analysis of plant electrolytes. In the d y 1990's. polarization tests were carried

out at the Copper Refbery using this equipment. The findings [39,52] showed that:

i) i n d g the Cu2* concentration (35, 40 and 45 g / L ) in real and synthetic

electmrefining electrolytes (containhg 100 pprn Tembind and glue decomposition

products) decreased the polarization (7 to 30 mV) at glue concentations ranging from

O to 10 ppm.

ü) increasing the Ni2+ concentration h m 15 to 27 g/L in synthetic electrolyte

(containing 100 ppm Tembind and glue decomposition products) had no effect on the

polarization at glue concentrations ranging from O to 10 ppm.

iii) increasing the H,SO, concentration h m 100 to 200 g/L in synthetic electrolyte

(containing 100 ppm Tembina and glue decomposition products) increased the

polarization (3 to 12 mV) up to 5 ppm glue concentration, after which the polarhtion

decreased (3 to 5 mV) up to 10 ppm glue.

iv) incrasing the temperature from 40 to 65 O C in real electrol yte resulted in a substantial

decrease in polarization (20 to 50 mV) at glue concentrations ranging h m O to 10 ppm.

V) increasing the current density in 150 N m 2 intervals from 150 to 600 A h 2 in reai

electrolyte with 5 pprn glue increased the polarization about 50 mV at each interval.

From the above test results it was concluded that with respect to polarization

nickel has no effkct, sulphwic acid concentration has a smal l effcct, copper has a

medium effect. and temperature and c m n t density have a medium-large effect [41,52].

For the sake of wnsistency, aiI polarization measurements (for the present series of

tests) were done at constant Cu2+ and H,SO, concentrations (40 and 155 g/L.

respectively), 65 'C and 300 A/m2 current density (set Section 4.3 -2). The only variable

was the combination/wncentration of addition agents.

The apparatus (Fig. 4-5) consisted of an electr01ytic celi with a platinum working

electrode, copper anode and copper reference electrode. The cell had a water heated

jacket, two inlets for electrolyte and rinse solution, and a drain. The flow of electrolyte

and rinsing solution was controlled by electrornagnetic valves. mer pieces of equipment

included an electrornagnetic stirring plate (American 20). an MS Lauda water bath with

immersion heater and circulator, EG&G PAR Potentiostat/Gdvanostat (mode1 273). a

Compaq 386/2ûe cornputer and an Epson LQ-5 10 printer.

Figure 4-5- Set up of the gaivanostatic equipment used for cîthodic poiarimîion measurements.

The tests studied the individual and synergistic effects of glue, tembind, Cl- ion,

thiourea and reclaimed acid on cathodic poIarization. The electrolyte and addition agent

solutions were made up as explained in Section 4.2.2. The 250 mL simples were made

up by adding to the electrolyte, hown amounts of addition agents in various

cornbinations. A constant current was applied between the copper anode and the

platinum cathode imrnersed in the electrolyte samples. The potential between the cathode

and the copper reference electrode was then recorded by the computer. The potential

shift, the difference between potential measurements at 0.1 min and 2.5 min, was then

recorded [39]. The start time elirninated the nucleation period of copper on the platinum

electrode so that only the plating of copper on copper was measured. The time interval

for the potential shift was also chosen such that the potential achieved a steady state

value.

A current density of 3 0 Mm2 and temperature of 65°C was used since it gave

the highest sensitivity [52]. Each sample test was repeated twice for a total of three runs

lhat were averaged to yield a potesitiai ciifference specific to a pariicular addition agent

combination. The test repeats w a e done to check the reproducibility. Subsequent to

each overpotential meanirement nui, the platinum cathode was cleaned by reversing the

current. A printout of the resuïts was generated by the cornputu and p ~ t e r . ARer each

test, the electrolytic ceU was flush& with distiîied water to wash out any residual

electrol yte.

The purpose of this series of tests was to determine the organic composition of

reclaimed acid produceci by the acid plant at Inco's Copper Refinery. Attempts were

made to anaiyze nclaimed acid, and determine and compare its phenolic content to that

of Tembind using dialysis and spectrometric methods. Since Tembind is a

lignosulphonate, and lignin has a high phenolic (phenols are high molecular mass

molecules) content that cm be determined effectively using spectrometric methods

[42,52], dialysis and spectrometry initially appeared to be promising modes of analyses.

Diafysis was used in an attempt to isolate and recover heavy molecular organics

in Tembind and reclairned acid. Once obtained, the organics were to be compared and

related by studying their effects on cathode morphology when used in laboratory plating

tests (see Section 4.2). Additiunally, two synthetic reclaimed acid batches were made

using Tembind (regular and diaiysed) and sulphuric acid for cornparison with plant

reclaimed acid via phting tests. The three spemometric techniques included ultraviolet

spectrometry 0, infrared spectrometry (IR) and nuclear magnetic resonance (NMR)

spectrometry. Gas chromatographylmass spectrometry (GC/MS) was also msidered,

but was consequently excluded since the high a d strength of reclaimed acid would have

damaged the apparatus. Nonetheles, the other three spcctrometric analyses were &ed

out on samples of ngular and dialysai Tembind in solution as weii as reclaimed acid

where possible. Ultimately, any usefid results h m these analyses were to be M e r

investigated via plating tests.

for MPly& and Synthetic R-ed Acid Produch 4.4.1. proCedures *on

Dialysis was perfomed on solutions of reclaimed acid and Tembind using

Spectrum Spectra/Por0 (mwco 1000) dialysis membrane. A 25 mL sarnple of plant

reclaimed acid was fint neutrali.zed with 10 N NaOH and checked using litmus. The

neutralized sample was then poured into the dialysis tubing and put in a distilled water-

filled beaker. The dialysis was ailowed to continue unal there was no evidence of brown

discolouration in the distilled water that was periodically changed. After dialysis, the

contents of the dialysis tubing were fütered through 0.45 pm papa to collect the "fluffy"

precipitate. The precipitate was dried in the oven at 5S°C for 1 &y, while the remaining

dialyseci solution was rotovapped to remove the water.

The Tembind solution was made up by dissolving 4 g of Tembind in 25 mL of

H,O. This solution was poured into the dialysis tubing and put in a distilled water-filled

beaker. The dialysis was allowed to continue until there was no evidence of brown

discolouration in the distilled water that was periodically changed. After dialysis, the

contents of the dialysis tubing were freeze dried.

The process was repeated using another 4 g of Tembind. A 0.1 g sarnple of the

freeze dried product was dissolveci in deuterated water @,O) for analysis in the NMR.

Another 0.5 g of the freeze dried product was mixed in 500 mL of 1000 g/L H2S04 and

refluxed for three hours to produce a synthetic reclaimed a d . A second batch of

synthetic reclaimed acid was made using pure Tembind. These two synthetic recMmed

acid batches together with the remainder of the dialysed/freeze dried Tembind were used

in a few electrorefining tests using the lab d e equipment. The purpose of those

experiments was to compare the effects of regular and didysed Tembind as well as

regular and synthetic reclairned acid on deposit morphology.

4.4.2. Roeedures for S+rometric Amly~e~

Ultraviolet (UV) spectmmetry was camed out using a Beckman DU-65 UV

spectrometer. The W spectrometer measured light radiation emitted by sample electrons

that were excited to higher energy States [53]. Absorbance scans were performed in a

particular range (200 to 700 nm for this test) depending on the sample, and recorded as

spectra. A 0.04 g sample of Ternbind was dissolved in 100 rnL of distilled water. A

small amount this solution was poured into an analysis via1 and analyzed against a

distilled water standard in the W spectrometer. A sample of rezlaimed acid was also

poured into an analysis via1 and aMyzed against a 1000 g/L H,SO, standard. After

examination of the first two W spectra, the process was repeated using a sample of

Tembind at double the concentration, and a sample of reclaimed acid at one half the

concentration, or 500 g/L. The resuiting specm were also examined.

The infrared (IR) spectmmeûy M was d e d out using a Bomem Michelson 100

infraed spectrometer. The IR spectmmeter measufed the infiared radiation generated

by the excitation of molecular bonds in the samples. A 0.002 g sample of Tembind and

0.2 g of KBr were combined and ground using a clean mortar and pestle, and transferred

to a srnail plastic vial. D r , the standard, acted as a binder as weii as a hydroscopic

window. A small amount of the ground mixture was then poured from the vial into a

compacting machine. Ten tonnes of pressure were applied to the sample to produce a

very thin wafer suitable for analysis in the IR spectrometer. The wafer was placed in

the apparatus which anaiyzed the Tembind against the KBr. After analysis in the IR

spectrometer, the spectra were examined. Reclaimed acid, king a high acid liquid, was

unsuitable for analysis using this technique.

The nuciear magnetic resonance (NMR) spectrometry test was d e d out using

a Varian Gemini 2000 NMR spectrometer. This spectrometric method was used to

determine the types and proportions of particular hydrogen atoms (ie. as in the benzene

ring) present in the reclaimed acid and Tembind samples. The samples were dissolved

in deuterated liquids @,O, CD,CI, comprised of the hydrogen isotope) to ailow for an

accurate analysis wiihout interference from the hydrogen atoms present in water.

First, a 25 mL sample of reclaimed acid was neutralized with NaOH and checked

using litmus. Fifty millilitres of deuterated chloroform (CD2C13 was added to the

reclaimed acid sample. The contents were shaken well, allowed to settle and then

decanted leaving the organic phase. This procedm was repeated three times after which

the three organic containing portions were combined and rotovapped to remove the

water. The tiny fraction of resulting solid was redisso1ved in 2 mL of CD,Cl,. A small

volume of this solution (0.7 rnL) was transferred to a thin anaiysis tube and analyzed in

the NMR. After analysis, the graphical printout was examined.

Tembind and dialysed Tembind were also analyzed by NMR. Small portions of

both were dissoIved in 40 to give solutions of appmximately 0.1 g/L. A srnali volume

of each solution (0.7 mL) was transferred to a thin analysis tube and anaiyzed in the

NMR spec trometer . A fter anal y sis, the spectra were examined.

C H A ~ R 5

RESULTS AND DISCUSSION

The effect of addition agents on cathode physical quality (morphology) was

examined by testing one agent at a time as well as various addition agent combinations.

The concentrations were selected on the basis of documented industrial practices. The

deposit produced in additive-free was used as the "basew case. It should be noted that

most experiments were carried out in duplicate, with good to excellent reproducibility

of the results. The cathodes were evaluated by naked eye and microscopically.

Photographs (acnial size) of the electrodeposits are show in Appendix C (îabelled

A : . . Hg), w hile correspondhg photornicrographs (50 x magni fication) of various deposit

cross-sections are shown in Figure 5- 1. The photomicrographs are labelled in the sarne

fashion as the acnial size photos with the addition of an "m" in the label (ie. Alm mAl).

When plating was conducted in the absence of any agent, the deposit was

relatively coarse but nodulcfree (Al , AS; Hl). Addition of glue alone at a typical

industrial level of 5 ppm provided smooth, fine-grained background deposit with high

ndges (striation) and small irregular nodules at numerous locations dong the ridges (A2,

A6). Addition of 150 ppm Tembind produced a fairly smootb, relatively dense deposit

which was definitely better than the deposit produced in the absence of agents (A3, A7;

H2). Thiourea alone at 0.2 pprn produced a coane cathode covered with smail, sharp

nodules. Moreover, the deposit was not uniform, exhibithg a higher degree of

coarseness and nodulation in the upper part of the cathodes (El, ES). Increasing the

thiourea concentration to 2 ppm resulted in a h e r texture, pronounced mini-dation and

rounding of the small nodules (Dl, D5). Chlonde used alone at a concentration of 20

ppm had, by far, the most pronounced and detrimental effect (BI, BS). The entire

cathode was covered with sharp, branched dendrites. In summary, onIy Tembind, as a

single addition agent, improved the quaiity of the deposii when compared with a deposit

produced in additive-free electrolyte.

Since chloride had such a pronounced effect on both polarization (see Section 5.2)

and morphology when added to additive-free electrolyte, it was worth exarnining iu

effect on cathode quality when combined with other addition agents. Two identical tests

with chlonde at 20 pprn and glue at 5 ppm yielded different results (B2, B6). This was

one of only two cases of poor reproducibility, and was Wrely due to contact shorthg or

shorting of the former depont with conductive slimes at the ce1 bottom @2), as

witnessed in pretrial commissioning. As a resuit, the latter deposit (B6) was considered

to be representative. This deposit was much worse than the deposits produced with glue

alone (A2, A6). The suspect deposit (B2) was different, but was also of poor quality.

The Tembind-chloride combination resulted in pronounced deterioration of the deponts,

with large, rounded nodules covering a large proportion of the suiface (B3.87). On the

CHAPTER S - RESULTS AND DISCUSSION 72

other hand, adding chloride to electrolyte containing 0.2 pprn thiourea visibly reduced

the grain size and produced a smooth, uniform deposit (FI).

Other two-addi tive combinations tested were as follows: glue-Tembhd at various

concentration levels (A4, A8; G 1 4 5 ) , glucthiourea (E2, E6) , and Tembind-thiourea

0 3 , D7). The Tembind-thiourea(2 ppm) combination produced a slightly rough deposit

with visible fine striation which was typical of thioumnly deposit, but missing in the

Tembind-only deposit. The glue-thiourea(0.2 ppm) combination produced a dense

deposit with very fme striation, which was superior to the deponts produced from

electrolytes containing either glue or thiourea alone. Glue (2.5- 10 pprn range) and

Tembind (50 and 150 pprn levels) combinations produced acceptable fine-grained,

nodule-fie deposits with variable amounts of pitting. Macroscopically, the deposits did

not differ considerably. Al1 in dl, deposits produced from electrolytes containing both

glue and Tembind, regardles of their levels (within the tested ranges) were either

comparable or finer than those produced from electrolytes containing either glue or

tembind alone.

Examination of three-agent combinations revealed the pronounced beneficial effect

of adding chloride to the giue-Tembind combinations (GGG8). The sarne is m e for the

Tembind-thiouna(O.2 ppm) and Tembind-thiourea-chlonde combinations (U, E7).

Addition of 20 pprn chloride to the 150 pprn Tembind and 0.2 ppm thiouna combination

resulted in a very smooth, nodule-free, but lightly pitteû deposit (F3). This fine pitting

is Wrely more noticeable bere than in other deposits because of their extreme smoothness.

On the other hand, adding chloride to a 5 pprn glue and 0.2 pprn thioulea combination

lead to coarsening of the deposit (E2, E6; F2). The deposits produced in the glue-

Tembind-thiourea(2 ppm) electrolyte did not differ significantly h m those produced in

the Tembind-thiourea(2 ppm) eiectroîyte (D3, D4, D7, D8). The two smoothest, nodule-

free deposits were obtained in 150 ppm Tembind, 0.2 ppm thiourea and 20 ppm chloride

electmlyte (F3) and in electrolyte using the identical combination with the addition of 5

ppm glue (F4).

In other tests, the effect of reclaimed acid (using rmi-synthetic electrolyte) was

examined for various addition agent combinations. The beneficial effect of reclaimed

acid was evident in the deposit made using only glue. The presence of reclaimed acid

in semi-synthetic electrolyte containing only glue gave acceptable deposits (C2, C6)

which were striation-free and profoundly smoother than those deposits (A2, A6) produced

under identical conditions but in the absence of reclairned acid. As for other deposits

produced in additive-free elecüolyte (A 1, AS), the presence of reclaimed acid gave

mixed results (C 1, CS; H6). This was the only other situation where reproducibility was

not good. The presence of reclaimeù acid did not appear to improve the cathode deposits

(Cl, C5) though the deposits did differ in appearance from additive-ffee, synthetic

electrolyte deposits. Deposits produced in the semi-synthetic electrolyte (Cl, CS) were

irreguiat with fine, scattered nodules, whereas the deposits produceci in synthetic

electrolyte showed a homogeneous, but rough tutme (Al, AS). The other deposit (H6)

showed that the presence of reclaimed acid did improve the cathode quality. The most

probable cause for this discrepancy was most b l y due to insufficient drying time (les

than 24 hours) for the acrylic m a h g used in these two "Cm series cathodes (Cl, CS)

CHAPTER 5 - RESULTS AND DISCUSSION 74

compared to ail the other cathodes. This statement is supported by O ~ S ~ N ~ ~ ~ O R S from

pre-trial debugging that clearly showed that improper masking agents and drying times

lead to signifiant depont deterioration very similar to that witnessed with these two

particula. 'Cm series cathodes (C 1, CS). In light of this, the "Hm senes cathode (H6)

was taken to be repfesentative.

For deponts produced in Tembind, and glue-Tembind electrolytcs (A3, A4, A7,

AB), the presence of reclaimed acid using identical additive combinations appeared to

have little, if any, smoothing effect, giving deposits that were quite nmilar (C3, C4. C7,

CB). A similar trend was true for the thiourea(0.2 pprn)-chloride, glue-thiourea(0.2

ppm)-chloride, Tembind-thiourea(O.2 ppm)-chloride, and the glue-Tembind-thiourea(O.2

ppm)-chloride combinations (T 1 -F4). The addition of reclaimed acid to these

combinations also gave very similar deposits (FS-FS), but subtle differences were noted.

The two combinations where Tembind was absent, gave slightly smoother deposits (F5,

F6) and there was no pitting in the four additive combination deposit when reclaimed

acid was present (F8). These observations indicate that the presence of reclaimed acid

was most beneficial when Tembind was not present. As such, this fïnding provides

support for the belief that Tembind decomposition products give reclaimed acid its

deposit enhancing properties.

The last Sefies of tests compared the effect of dialysed Tembind with regular

Tembind. The tests also compared the effet of plant reciaimed acid with two synthetic

reclaimed acids, one made with reg& Tembind and the other with dialysed Tembind

(the procedure for Tembind dialysis and synthetic reclaimed acid production is given in

C ~ E R 5 - RESULTS AND DISCUSSION 75

Section 4.3). Observations showed that both 150 pprn dialysed and regular Tembind

gave simiiar deposits in the p e n c e of, and in the absence of, 5 ppm glue (HZ-HS).

Furthemore, deposit analyses showed that the three types of reclaimed acid (plant.

synthetic made with Tembind and dialysed Tembind) all gave very sirnilar deposits (H6-

Hg). This finding would also support the suggested relationship between reclaimed acid

and Tembind. As for dialysed Tembind, its deposit enhancing characteristics appear to

be unchanged relative io ngular Tembind. This indicates that long chained Tembind

molecules play an important role in deposit enhancement, though the effect of smaller

moIecuIar weight Tembind molecules cannot be discounted.

5.1.1.2. Microscopie Characterization

Selected electrodeposits were submitted for microscopie evaluation. Examination

of polished cross-sections under the microscope was particularly useful in assessing

deposits which looked simila when inspecteci by naked eye but revealed differences when

examinai under the microscope. The photomicrogaphs were taken at 50 x mapification

and are shown in Figure 5-1. They are oriented such that the starter sheet is located at

the bottom of the photo and the electrodeposit on top.

Microscopic examination of deponts plated h m eleztdytes that contained a

single additive or no additive at aii confirmed the observations performed by the naLed

eye. While deposits produced in electmlytes with no additives (mils), with 5 pprn glue

(mA6), with 20 pprn chloride (m), or with thiourea (0.2 acd 2 ppm) (mD5; mE5)

were unacceptable and had irregular microstructures, elecectrolyte containhg 150 pprn

Tembind produced an acceptable deposit with a stable microstructure (mA7). The

chloride-only, glue-chlonde and the Tembind-chloride eleztrolytes produced very

dendntic and nodular structures which were clearly evident (-5- mB7). From the

backgrounds (ara surrounding the growths) it appears that the dendrites and nodules

formed &er the initiai period of three dimensional nucleation (UD type growth) began

to progress to two dimensional nucleation (FT type growth).

Decreasing the thiourea concentration h m 2 to 0.2 pprn increased the degree of

porosity i n the deposit (mD5; mE5), however the addition of 5 pprn glue gave a better

microstructure with 0.2 pprn thiourea than with 2 pprn thiourea (mE6; mD6). In the

former deposit (mE6), the crystals were elongated and columnar, and more tightly

packed than in the latter deposit (mD6) which appexs to have a microstnicture alrnost

identical to the one produced in the absence of glue (mD5). The addition of 150 pprn

Tembind or a glue-Tembind combination to electrolytes containing 2 and 0.2 pprn

thiourea yielded deposits with rnicrosmictures that had significant porusity, as well as

irreguiar crystal sizes (mD7, mD8; mE7, mE8). Furthemore, the deposits produced in

2 pprn thiourea (mD7, mD8) generally had srnalier crystals while the other deposits

(mE7, mE8) had larger, elongated crystals. This is an interesthg finding since it was

not obvious after the deposits were examined by eye and found to be very sirnilar.

In tests where various levels of glue and Tembind were tested (mA8; mG 1-mGS),

photornicrographs revded that the finest, rnost uniform microstructure was obtained at

2.5 ppm glue and 150 pprn Tembind, while the worst one was obtained at 2.5 pprn glue

CHAPTER 5 - RESULTS AND D~SCUSSION 77

and 50 pprn Tembind. Increasing the Tembind h m the 50 to 150 pprn level had a more

profound effect on deposit microstnicture than an incfeasing glue concentration. Similar

tests (mB8; mGbmG8) examined the effect of chloride (20 ppm) in wnjunction with

various glue-Tembhd combinations. In each case, the addition of chloride gave larger,

columnar crystal microstructures of mixed FT and BR type.

Unaided visual observation of the "Fm senes found that ali the deposits ranged

from acceptable to the smoothest produced in the electmplating experiments. In half of

the series (mF1-mF4), ail electrolytes contained both 0.2 ppm thiourea and 20 ppm

chloride, as well as variable combinations of glue and Tembind. The second half of the

series (mF5-mF8) ut i l id identical combinations of additives and was canied out in the

semi-synthetic electrolyte. The addition of Tembind resulted in smoother deposits (mF3,

mF4, mF7, mF8) than without (rnF1, mF2, mF5, mF6).

Microscopie evaluation confirmed what was observeci with the naked eye, but with

more clarïty. The addition of glue to the thiourea(0.2 ppm)thloride combination

resulted in a increase in crystal size, though macroscopically the deposits were quite

similar (mF1, mF2). These two Tembind-fke ekctrolytes gave deposits (mF 1, mF2)

with much larger crystals (BR type structure) than the two Tembindcontaining

electrolytes which gave deposits (mF3, mF4) with fine, stable crystals (UD and FT type

structures). Si& d t s were obtained when the tests were carried out in semi-

synthetic elecmlyte (mFS-mF8). However, the deposits (-1, mF2) produced in

Tembhd-free synthetic electrolyte appear to have a larger crystal size than those deposits

CHAPTER 5 - RESULTS AND DISCUSSION 78

(mFS , mF6) produced in semi-synthetic electrolyte containhg 10 % reclaimed acid . This

grain altering effect is not M y evident f m ~ k e d eye observation.

The H-series compared the effect of reg& and dialysed Tembind, as well as

plant and synthetic reclaimed acids. The dialysed Tembind electrolyte gave a deposit

(mH3) with a microstructwe that was very similar to regular Tembind (rnA7). The

microstructure was comprised of thin, elongated FT crystals with a few BR crystals

scattered throughout the matrix. The gIue(5 ppm)-Tembind( 150 ppm, dialysed)

combination yielded a deposit (mHS) microstructure very similar the identical

combination using regular Tembind (mA8). The presence of glue appears to slightly

increase crystal size and give a microstructure with crystals that are not as neatly onented

as with Tembind (regular or dialysed) alone.

The microstnicture of the deposit (mH6) produced in the presence of plant

reclaimed acid differed slightly from the microstructure of the deposits (rnH7, mH8)

produced in the presence of the two synthetic reclaimed acids. The former exhibits

elongated BR crystals, while the latter two exhibit simifar crystal structures that are

comparatively srnaiier (FT and BR mixture) than the former. AU thre!e microstructures

show improved crystai o r d e ~ g without the large messes present in the microstructure

of the deposit produced in pure synthetic elemlyte. These resiiits M e r confirm the

beneficial effects of reclaimed acid on deposit quality, as well as the link between

Tembind and reclaimed acid.

Figure 5- 1. Photomimgraphs of pofished etectrodeposit cross-sections.

CHAPTER 5 - RESULTS AND DISCUSSION 80

Figure 5-1 (cont.). Photomicrographs of polished electrodeposit cross-sections.

Microhardness measurements were iaken on the electrodeposit samples as weîi as

a few of the starter sheets. The Vicken Hardness Numbers 0 for the sarnples are

given in Appendix A. For the most part, a large number of the deposits had a VHN in

the range 60 i. 5, which was similar to the starter sheet measurements. Comparing the

photornicrographs in Figure 5-1 with the VHNs reveals that the electrodeposits in the

VHN range 60 * 5, had crystal structures that varied from FT to BR types and the

crystal sires were usually of medium size.

Though the VHNs did not Vary in wide ranges, there does appear to be some

correlation between crystal ske and hardness. An increase in crystal size appears to lead

to a drop in the hardness of the deposit. Deposits show in mB8, rnF1 and mF2 ail

exhibited large BR crystal structures and their VHNs were measured to be in the range

45 f 5. Conversely, a decrease in crystal size appears to increase the hardness of the

elec~odeposit. Deposits shown in mB5, rnB6 and mB7 were a i l highly nodulated and

dendritic, however it was possible to carry out hardness measurements on cathode

background areas (the plating areas sunoundhg these growths). The photomicrographs

show that these areas exhibit very fine, compact UD and FT crystal structures, and

correspoadingly high VHNs (ie. 1 17 for mB7). Deposits shown in mF3, mF4, mF7 and

mF8 also exhibit small and compact UD and FT crystal structures, and have reiatively

high VHNs.

5 - RESULTS AND DISCUSSION 82

Thus, there is an evident trend between crystal size and hardness. As crystai

structure changes from UD to FT and finally to BR, the resulting increase in crystal size

generally resuits in a lower VKN. The stable UPFï structures exhibited the hardest

deposits, followed by average hardness deposits with a stable FT-BR structure. The

deposits that demonstrated hill BR stnicturing had the largest crystals and the lowest

values for hardness.

Cathodic overpotential was measured through the determination of potential shift

(PS) as explaineû in Section 4.3.2. The impact of addition agents on cathodic

overpotential was studied in two different ways:

i) examination of the effect of concentration of various agents on the direction and

magnitude of overpotential.

ü) examination of the effect of a single addition agent and of various combinations of

two, t h e and four addition agents at fîxed concentrations on the âirection and magnitude

of overpotential.

The values for overpotentiais in Figure 5-2 are given as PS values, in millivolts,

relative to a Cu refaence elecûode. These values are the averages of thne runs

(Appendix B) cxmied out for each addition agent combination. Judging by the results,

the reproducibility of the proceûure was excellent.

Vohimt 1 Rccfrimd kid

'km blnd

Figure 5-2. Graphs showing the change in PS (mV) as a function of concentraiion for each addition agent as well as reclPimad acid.

in the first series, concentrations mges of pure agents varied depending on a

given agent (see Appendix B). For ewnple, it was found h m tankhoux experience

and published literatwe that glue and thiourea display an active nature at low

concentrations (icss than 10 ppm), whereas Tembind has a usefbi operating range of

between 50 and 200 ppm. Active chioride concentrations f d in the 10 to 40 ppm range.

CHAPTER 5 - RESULTS AND DISCUSSION &

This information was used to detmnine the concentrations for testing. Thus, the effects

of glue, Tembind, thiourea and chloride were examined in the ranges O to 15 ppm, O to

200 ppm, O to 10 ppm and O to 40 ppm, respectively.

The effect of reclaimed acid, containhg decomposition products of Tembind, was

also studied. in these tests, varying amounts of plant reclaimed acid, in addition to fresh

acid, was used to make semi-synthetic electrolyte batches ranging h m O to 20 percent

reclaimed acid. These ranges correspond to presumed mkhouse conditions with respect

to reclaimed acid fluctuations. Although thiourea is not a CCCR tankhouse-used addition

agent, it is a common additive used in conjunction with glue at most other major copper

refineries worldwide [8]. Thus, it was agreed that studying the effect of thiourea on

cathodic polarization would be usefûl.

Tested alone, glue was the only addition agent that increased the cathodic

polarization compared to additive-free electrolyte. It not only increased the polarization.

but also affected it in a more dramatic fashion than the other addition agents. lu effect

was most pronouncd when increased h m 2 to 5 ppm, which coincidentally corresponds

to the normal operating ranges in the tankhouse. This particuiar increase in

concentration lead to a more than eight-fold încrrase in polarbation. Tembind had an

opposite and far les pronounced effect on cathodic polaruation compared to glue.

Chlonde behaved much Wre Tembind though its depolanting effect was siightly pater.

Thiourea also acted as a cathodic depolarkr. Mihile thiouna dairrased the polarization

at 0.2 ppm, ïncreasing the concentration to 2 pprn resulted in an overpotential increase

relative to 0.2 pprn though, overail, the polarization still decnased compared to additive-

free electrolyte. Further increases in thiourea concentration up to 10 pprn gave similar

effects as obsemd at 2 ppm.

These muîts are in fairly good agreement with published literature. It is widely

written in the literature that glue inmeases polarization quite substantidly when used

alone in electrolyte [13,39]. Winand et al. [5] wrote ihat at just 3 ppm glue, the overall

overvoltage is approximatel y doubled.

Literature contains varied views on the effect of thiourea on overpotential. Chia

and Su [20] wrote that thiourea increased overpotential drastically, more so than glue.

In that expriment a 100 pprn thiourea concentration was used which is well outside the

reasonable operating range for industrial practice. Also, the electrolyte acid

concentration was not given. Knewska et al. [48] found that at temperatures higher than

40 O C the effect of thiourea concentration on cathodic polarization was insignifiant .

Winand et al. [5] wrote that at less than 1 ppm thiourea the charge transfer overvoltage

decreased, while at greater than 2 ppm thiourea the charge transfer overvoltages

increased. This final obsentation would best support, though not M y , the behaviour of

thiourea observed in Figure 5-2.

As for chloride, its behanour in these experiments is supported weli by literature.

Lakshrnaaan et al. [49] wrote that at concentrations of greater than 1 pprn alone in

copper electrolyte, chloride acts as a depolarwr. O'Keefe and Hurst [34] m t e that

chioride acts as a cathode depolarizer until it exceeds a certain level (this level is not

stated) .

Examination of CCCR literature containing references to Tembind revealed, in

a monthly report [54], that prwious tests indicate Ternbind will increase polarization

slightly in glue fkee electrolyte. However, this report does not clearly specifi the

composition of the electrolyte, or whether it contains any other additives such as chioride

that could result in an overall increase in polarization.

The second series of polarization experiments used fixed levels of addition agents

as follows: 5 pprn glue, 150 pprn Tembind, 0.2 pprn thiourea and 20 pprn chloride. In

addition to the tests using these "baselinew concentrations, several experiments were run

at 2.5 and 10 pprn glue, at 50 pprn Tembind, and at 2 pprn thiourea. Examination of the

combinai effects of various addition agents on cathodic overpotential (Table 5-1)

revealed some unexpected and previously unknown behaviours. In Table 5-1 the

potential measurements for different addition agent combinations are given as U S values

(APS = PS pure electrolyte - PS electrolyte containing additives) to simplify cornparison.

For a complete lia of PS values refer to Appendix B.

Different addition agent combinations, al1 containing glue, gave different values

for the overpotential. Whereas 5 pprn glue alone in electrolyte yielded an overpotential

incrrase of 26.5 mV over the additive-fiee electrolyte, the addition of 20 ppm chloride

(typical industrial coucentration) to glue-containing electrolyte nearly doubled the

overpotential to 46.8 mV. This was surpnsing since chloride alone in electrolyte acts

as a depolarber. Addition of Tembind to gluocontairhg electrolyte dso had a ciramatic

effect which was opposite to that of chlonde. Whüe chloride addition enhanced the glue

polarization, Tembind nullüied the glue effect. The addition of 150 ppm Tembind

CHAPTER S - RESULTS AND DISCUSSION 87

(normal tankhouse concentration) to the glue-containing (5 ppm) elecmlyte reduced the

APS h m 26.5 to -2.9 mV. Results were timilar (-0.6 mV) when the combination

included 2.5 pprn glue and 50 ppm Tembind. Increasing the glue to 10 ppm while

maintaining 50 pprn Tembind resuited in a APS increase to 5.2 mV.

Table 5-1. Polarization Results

Addition Agent Combination

und Concentration

no addition agents

g

T tho. 2

th2

CI

g2.5, TSO

8. T g10, T50

g, th0.2

g* th2 g, Cl T, Cl T, th0.2

Addi tioo Agent Coinbition and Concentration

+ conceatraîions are giue (5 ppm), Tembind (150 ppm), chloride (20 ppm) des5 sîated otherwise

As seen in the first set of experiments, thïourea alone in electrolyte has a

depolaRPag efféct, even when present in concentrations of les than 1 ppm. Ln this

second series of tests thiourea was added at two concentration levels, 0.2 and 2 ppm to

CHAPTER 5 - RESULTS AND DISCUSSION 88

electrolyte containing 5 pprn glue. As expected, in both instances, the thiourea decreased

the APS from -1.3 mV at 0.2 pprn to -2.9 mV at 2 ppm. It is worth noting that the

addition of 2 pprn thiourra has the same effect as the addition of 150 ppm Tembind to

electrolyte containing 5 pprn glue.

Chloride had such an unexpected and profound effet on polarkation when used

in combination with glue, it was decided to study its effect on polarkation when

combined with Tembind and thiouna in electrolyte. In each of the the cases exarnined

(150 pprn Tembind, 0.2 pprn thiourea, 2 pprn thiourea, each with 20 ppm chlonde

added), chloride addition counteracted the depolarizing effcct of Tembind or thiourea to

varying degrees. Chionde and Tembind together in electrolyte resulted in a APS of 6.6

mV as compared to -3.1 mV for the solution with Tembind alone. The addition of

chloride to the solutions containing 0.2 and 2 pprn thiourea also counteracted the

depolarization but to a Iesxr degree. For the 0.2 pprn thiowea-containing solution, the

addition of chioride changed the APS from -6.7 to -5.0 mV, while for the 2 pprn

solution, chloride addition changed the APS from -4.3 to -2.8 mV. In other words,

chloride addition resulted in a polarizing effect, although the effea was far les profound

than in the case of the giucchloride combination. Thus, in summary, chloride acts as

a depolarizer when used alone, however, in combination with glue, Tembind or thiourea,

a polarizing e f k t is observed.

In the combinations of 150 ppm Tembind and 0.2 pprn thiourea, and 150 pprn

Tembind and 2 pprn thiourea the results were as anticipateci. The A P S values were -4.9

and -4.2 mV, respectively. In other words, their combined effect yielded values that

CHAPTER 5 - ~ S U L T S AND DISCUSSION 89

were in between their values when present individually in electrolyte. M e n 20 ppm

chloride was added to these two combinations, the resuit was a polarizing effect, yielding

U S values of 3.1 and -1.6 mV, respectively.

When exarnining the effect of three or four addition agents in combination, again

the profound effect of chloride stands out, especially in the presence of glue. For

example, while a combination of glue (5 ppm) and Tembind (150 ppm) yielded a APS

of -2.9 mV, the addition of 20 pprn chloride to the same solution yielded a APS of 24.7

mV. Additionally, whereas combinations of glue-thiourea (0.2 ppm) and glue-thiourea

(2 ppm) yielded APS values of -1.3 and -2.9 mV, addition of 20 pprn chlonde yielded

APS values of 41.5 and 40.7 mV, respectively. The same is true for glue-Tembind-

thiourea (0.2 pprn) and glue-Tembind-thiourea (2 ppm) combinations. The measured

APS values for these combinations were -3.6 and -2.2 mV respectively, while the

addition of 20 pprn chloride to the same solutions yielded APS values of 14.4 and 7.7

mV respectively. Thus, in combination with glue, chloride substantially enhanced

polarization when compared to sirnilar, chloride fne electrolytes.

Variation of glue concentration in the preseace of chloride and Tembind has a

similar though smaller effect on polarization. For example, inmashg the glue

concentration from 2.5 to 10 ppm in the pnswice of 50 pprn Tembind and 20 pprn

chloride increased the APS by a factor of five, while a similar increase in the glue

concentration when present alone increased the U S by a factor of about eight. In the

absence of glue, chloride loses it polarîzation-enhancing ability, as demonstrated by the

two Tembind-thiourea-chlonde tests. Since chloride is routinely added to tankhouse

electrolyte, its fluctuation may have a signifiant, previously unrecognued effect on the

quaiity of the cathode deposit. Momver, fluctuation of chloride in the plant electrolyte

may have a previously unrecognized effect on the accuracy of glue determination in plant

sarnples by the present method that utilizes overpotential measurements.

Fixed-concentration polarization tests carried out in semi-synthetic electrolyte

(containing 10% acid volume from plant reclaimed acid + 90% acid volume h m pure

acid) gave patterns and results similar to those obtained using identical additive

combinations in pure synthetic electrolyte. The results for those tests can be found in

Appendix B.

0 5.2.1. Com~gçisoo of Cathodic P o l n ~ ~ o n and Macrodepo& OuaUtv

Table 5-2 was constructed to illustrate and compare the effect of various addition

agents, alone and in combination, on both cathodic polarization and deposit quality, and

thus determine any possible correlation. The tests were arranged in order of decreasing

overpotential .

From the Table 5-2 it appuvs that glue alone or a combination of chloride and

glue gives a high overpotential. The absence of glue and chIoride more or less leads to

a Iow overpotential. Cornparison of the macIOdeposit quality rating and the U S values

in Table 5-2 indicates that there might be a slight correlation between overpotential and

deposit quality. Overall, the positive mge of APS values (polarkition relative to

additive-* solution) appears to give better deposits, than when the A P S values were

in the negative range (depolarking effect). However, close inspection of the resuits

shows that exceptions do exist. For example, the glue ody, glue-chloride and Tembind-

chloride tests gave quite poor deposits, despite having higher overpotentials.

Additionally, the glucTembind and Tembind only tests gave acceptaMe deposits despite

the negative APS values.

Table 5-2. Macrodeposit Quality Rating and Cathode Polarization

Addition Agent C m b i d o n s and Concemîmîiom +

g10 TSO g

g g T g T g2.5 TSO

T g10 TSO

T

g2.5 TSO g 8 T il T il

T g T

T

T

Test I.D.

- G8 82, B6 F2 A2, A6 B4, B8 F4 G6 B3, B7 G3 F3 Al, AS, Hl G1 E2, E6 DO, D8 A4, A8 D2, D6 A3, A7, FI2 E4, ES D3, D7 Dl* D5 E3, E7 F1 Bi, BS El, ES

* concentrations art glue (5 ppm). Tembmd (150 ppm), chloride (20 ppm) uniess sîatd 0t)lCiWiSe

The glue(l0 mm)-Tembind(50 ppm)-chloride combination gave the highest A P S

(51.9 mV) and a very good deposit. The Tembind-thiourea(O.2 ppm)-chloride

combination gave a considerably lower overpotential (APS = 3.1 mV) yet gave a deposit

of high quality also. Other addition agent combinations whose overpotentids fell in

between those values gave deposits that varied in quality from very good to very poor.

The glue-chloride combination, which gave the second highest APS (46.8 mV), gave one

of the poorest deposits. Chloride, on its own, yielded the second Iowest APS of -6.6 mV

and gave a pmr, highly dendritic deposit.

Thiourea at 0.2 and 2 ppm gave APS values of -6.7 mV and -4.3 mV,

respectively , and gave Iow quality deposits. On the other hand. the thiourea(0.2 ppm)-

chloride combination gave a APS of -5.0 mV and a deposit better than those produced

in thiourea alone. Tembind on its own yielded a A P S of -3.1 mV, yet gave acceptable

deposit quality . Combinations of glue-thiourea(0.2 ppm) , glue-Tembind-thiourea(2 ppm)

and glue-Ternbind gave U S values of -1.3 mV, -2.2 mV and -2.9 mV, respectively,

with depont qualities king very good, bad and good. Moreover, combinations of glue-

Tembind, glue-thiourea(2 ppm) and Tembind alone give almost identicai APS vaiues, yet

the deposits were good, bad and good, respectively.

Thus, the results contained in Table 5-2 couid support the observation that there

is a correlation showing that as the APS d m , the deposit quality deteriorates.

However, there are visible exceptions that cm maire the prediction of deposit quality

based on overpotential measurements unreiiable.

CHAPTER 5 - RESULTS AND DISCUSSION 93

0 Evaiuation S m 53.2. pohnution and &lectrod~~~@

The polarization and electroplating tests yielded a large amount of interesthg and

usefui information. Therefore, in order to diow for a quick and simplified evaluation

of these nsults a condensed table (Table 5-3) was constructed. The table outlines the

results for the various tests that were evatuated hy four methods (polarization,

microscopy , macroscopy , hardness). The remainder of the test results uui be found in

the appropriate Sections or Appendices.

Table 5-3. Cathode Polarization and Electrodeposit Evaluation Summary

thin, elongated, FI' crystais tint UD crystai background, irrrgular growtha thick, clongated, iargt FT-BR crysuils srnail, imguhr FI'-BR ~rt. lr

- - - -

smooih. dense 1

I

hmvy noduiation

, v e y d* compact, some

very imooth* compact rom tiny p h coam no additives

g2.5, TSO

mccaKI, small FT-BR crystd~ snirill UD-Fï-BR mcdium

mughncas, some tiny pits dense, very fine rtsiations

coanc, finc striation imguinr FT-BR

crystals medium FT-BR cry-b

fauly smooth. dase. fine striation coanc, fine striation

rcccsses, small irrcgular FT-BR crystais

LYiy smooth, 1 55.7 1 4 dense, fine striation

rtccsscs, medium Fï-BR crystais rtcerscs. smalI UD-FT-BR

r e c c s ~ , s d UD-BR crptals

coane, fine striation rough. fine striation. somc piüing rough, loosc* finc nodules, striation

lwu* m g , striation, finc nodulation iüghtiy rough, &lu

m m * irreguiar BR c r y d medium, Fi'-BR

fine, UD cryrtsl background,

coanc, loosc, 54.4 1 loosc, arcgulu BR cr~stafs

* concentrations art glue (5 pprn). Tcmbind (150 ppm). chlonde (20 ppm) unlcrs stated othcimst

Whereas there was a slight trend when cornparhg polarization with macrodeposit

quality, there does not seem to be a trend between microstructure and polarbation.

Crystal shape, sïze and arrangement appears to be largely detefmined by the combination

and concentration of addition agents. The presence of thiourea most often has a

decreasing influence on crystal size, whiie combinations involving chloride mostly favour

an increased crystal size than without chloride. As hardness measurements and

rnicroscopy indicated, larger crystai deposits are more k l y to have lower hardness

values. Additionally, both large and small crystai sizes can lead to variable quality

deposits, from dendntic and c a s e to very smooth.

In this =ries of tests, the primary assumption was that Tembind decomposition

products exist in reclaimed acid and contribute to improving deposit quality. Literature

on glue degradation as weil as rechhned acid assays supported this assumption quite

well. nie idea of using dialysis to separate large and s d molecdar weight

components (ie. short chained sugars, rneîai ions, etc.) in Tembind and reclaimed acid

was pmued. The prospect was that higha rnolecular weight organics cornmon to

Tembind and reclairned acid rnight be possible to extract and compare using ihis method.

While it was possible to dialyse Tembind and collect a high molecular weight product

the same was not possible with reclaimed acid due to the extremely srnall amounts, if

any, of large molecuiar weight organics present.

Thus, it was not possible to perform a comparative analysis of dialysis products.

However, the dialysed Tembind product was used in some plating tests to compare it

with regular Ternbind. Additionaily, synthetic reclaimed acids using regular and dialysed

Tembind were made and used in plating to compare with plant reclaimed acid. Those

test results are discussed in Section 5.2.

Other ways of anaiysis were then punued. Literature (421 offered an initial idea

that involved using gas chromatographylmass spectrometry as a method of analysis.

Further consideration of this pa~ticular method indicated it would be unsuitable due to

the extremely high acid content of reclaimed acid that could damage delicate components

of the GC/MS. Other specnometric techniques were then considered and pursued.

These included IR, W and NMR spectrometry. Unfortunately, these methods were also

fond to be unsatisfactory approaches for determination, largely due to the high acid and

small organic content in nclaimed acid, as well as the complex nature of Tembind. The

spectra from the spectrometric tests were vague and poorly defined. As a result no

usefûî diagnostic information could be deduad to advance the present knowledge, and

W, IR and NMR spectrometry were labelied not suitable and so abandoned.

CHAPTER 6

CONCLUSIONS AND RECOMMENDATIONS

In general, the r d t s and trends observed in the thesis experiments agree well

with what is written in literature. However, due to the specific nature of the conditions

(ie. addition agent combinationslconcentrations) fond in individual studies such as this

thesis, data and results cannot be directly interchanged between them. To answer

specific questions, expenrnents that employ specific conditions are warranted. As such,

this thesis, LiLe other studies, is unique because of the specific equipment and parameters

used to carry out the experimentation.

lectrore[iPino Tests 6.1.1. Laboratory COQ-œr E

i) Only Tembind, as a single addition agent, improves the quality of electrodeposited

copper when compared with a deposit produced in additivçfree electrolyte. Glue,

thiourea and chloride atone in electrolyte give deposits bat are of a poorer quality (ie.

awne, nodulated, dendritic) tban with no additives at dl.

ii) Combinations of glue (2.5 to 10 ppm) and Tembind (50 to 150 ppm) produce

acceptable, nodule-fne deposits that mac~oscopieaily do aot differ considerably.

Regardless of their levels, the glue-Tembind combination gives comparable or fher

deposits than can be pduced using glue or Tembind alone.

iii) Thiourea is an excellent addition agent that, uwd in proper combinations and

concentrations, has the potential to give deposiu of a greater quality, and in some cases,

much greater than those produced using various combinations of glue, Tembind and

chloride only. The combination of 5 pprn glue and 0.2 ppm thiourea produces a dense

deposit with very fine striation that is superior to the deposits produced h m electrolytes

containing either glue or thiourea alone. By far, the srnoothest, nodule-free deposits

were obtained in 150 ppm Tembind, 0.2 ppm thiourea and 20 ppm chloride electrolyte,

and in electrolyte containing that identical combination in addition to 5 ppm glue

(identical addition agent combinations in semi-synthetic electrolyte give similar deposits).

Microscopic observations show that these deposits have a fine and densely packed crystal

structure.

iv) The presence of reclaimed acid in semi-synthetic electrolyte containing only glue

gives acceptable deposits which are striation-fkee and profoundly smoother than those

deposits produced under identical conditions but in the absence of reclaimed acid.

Furthemore, the benefit of reclaimed acid is only apparent when Tembind is not present

in the electrolyte, and has an effect similar to that of Tembind.

V) Deposits pduced in the presence of synthetic reclaimed acid (made using Tembind

and sulphuric acid) are similar to those produced in the presenœ of plant reclaimed acid.

This finding, together with conclusion (iv), nipports the suggested relationship between

reclaimed acid and Tembind.

vi) Dialysing Tembind does not appear to change its deposit enhancing characteristic,

since dialysad Tembind givs deposits similar to reguiar Tembind. ~ h e microstructures

are also very simiiar. This seems to indicate that long chained Tembind molecules play

an important role in deposit enhancement, though the effect of srnaller molecular weight

Tembind molecules cannot be discounted.

Mi) Microscopie examination of electrodeposits confirms what is observed with the naked

eye but with more clarity. Some deposits which rnacroscopically appear quite similar,

c m in fact exhibit quite distinct microsmictures depmding on the addition agent

combinations and concentrations use& Microscopy can be usehl in assessing the relative

stability of outwardly similu deposits which couid be important when selecting ideal

addition agent combinations and concentrations. It can also be helpful in diagnosing

problems (such as poor addition agent control or the presence of contaminants for

example) encountered in daily operations by allowllig one to observe abnorrnalities in

deposit microstructure.

viii) Mîcroscopic exarnination shows that the only noticeable difference betwezn the

synthetic and semi-synthetic electmlyte produced deponts occun in the absence of

Tembind. In the Tembind-fke depon~, the presence of reclaimed acid appears to

de- crystal size in the deposits mrnpared to the deposits produced in the absence of

reclairned acid. This grain a l t e ~ g effect is not M y evident with naked eye

observation.

ix) The addition of 5 pprn glue to a 150 pprn Tembind-contahing electrolyte appean to

slightly incnase crystai sU+ and give a microstructure with crystals that are not as neatly

ordered. Inmashg the Tembind concentration h m 50 to 150 pprn has a more profound

effect on deposit microstructure than an increasing glue concentration, resulting in a more

stable crystal structure. The addition of chlonde to electmlyte containing glue and

Tembind results in a larger, columnar crystal microstructure, but the overall deposit is

smoother than without chlonde.

X) The presence of synthetic reclaimed acids gives deposits that have somewhat smaller

crystal structures than a deposit produced in the presence of plant reclaimed acid.

However, in general, the presence of reclaimed acid (plant or synthetic) in electrolyte

gives microstructures that show improved crystal ordering without the large recesses

observed in deposits produced in pure synthetic electrolyte. This finding also lends

support to the proposeû link between Tembind and reclaimed acid.

xi) There is an evident trend between crystal size and hardness. Generally, as the crystal

size increases the hardness decreases, with the deposits exhibithg the kgest crystals

giving the lowest W s . The Vickers Hardness Number for the average starter sheet

is in the range 6015, which is the approximate ange for most of the laboratory dqmsits,

though 44.5 was the lowest and 117 the highest.

xii) There is no obvious correlation between crystal size and deposit quality. Acceptable

deposits can have both smaü and large crystal sizes and the same is me for poor

deposits.

i) Glue is the only addition agent that, when present alone in electrolyte, increases the

cathodic polarization compared to additive-free synthetic electrolyte. It not only

increases the overpotential, but also does it in a much more dramatic fashion than

Tembind, thiourea, or chloride, al1 of which have an opposite (ie. depolarking) effect

on cathodic overpotential when used alone in electrolyte. The glue effect is most

pronounced when increased from 2 to 5 pprn, which corresponds to normal tankhouse

operating conditions.

ii) The addition of 150 pprn Tembind (typical tankhouse concentration) to an electrolyte

containing 5 pprn glue nullifies the glue polarization effect. The addition of 2 pprn

thiourea (typical industrial concentration) to an electrolyte containing 5 pprn glue has the

same effect on glue poiarization as 150 ppm Tembind.

iii) Chlonde alone acts as a depolarizer. Chloride in combination with glue, Tembind

or thiourea has a polarking effect. Addition on 20 pprn chloride (typical tankhouse

concentration) to an electrolyte containing 5 pprn glue results in a near doubling of the

overpotentid compared to glue done. Addition of chloride to Tembind and thiourea

containing solutions also increases the polarization relative to the same electroiytes

without chloride, though the effect is far less pronounced than in the case of the glue-

chloride combination. Even in three and four addition agent combinations chloride

substantially enhances the polarization when compared to sirnilar chloride-free

electrol ytes.

iv) Since chloride is routinely added to tankhouse electrolyte, its fluctuation may have

a signifiant, previously unrecognized effect on the quality of electrorefined copper.

Moreover, the fluctuation of chloride in the plant electrolyte may have a previously

unrecognized effect on the accuracy of glue determination of plant samples by the present

method that utilues potentiai shift measurements.

v). Polarization tests carried out in semi-synthetic electrolytes containing 10 percent acid

content from plant reclaimed acid give sirnilar rrsults to those obtained with the pure

synthetic elecmlytes. The presence of reclaimed acid in semi-synthetic additive-free

electrolyte resdts in cathoâic depolarization compmd to pure synthetic. Its effect on

plarization is simiiar to Tembind.

vi) A definite correlation was observed between cathodic polarization (potential shifi -

U S ) and deposit quality. A higher or positive APS results in good quality deposits,

while a lower or negative APS resuits in poorer quality deposits. Notable exceptions are

CHAPTER 6 - CONCLUSIONS AND RECOMMENDATIONS 103

deposits produced from electrolytes containing glue only, glue-chlonde and Tembind-

chloride, where cathode quality is much worse than could be predicted h m the APS-

deposit quality trend. Thus, the prediction of deposit quality based on overpotential

measurements can be unreliable.

6.1.3. Dialvsir and Speetmrnetric~lvsa of Reefaimed Acid and Tembigé

i) Using dialysis it was possible to recover a high molecular weight product from regular

Tembind. However, dialysis could not be successfully performed on reclaimed acid due

to either the small arnount of organics present or because of the small physical size of

the decomposition products themselves. As a result, dialysis was not a viable method

for isolating and comparing the organics in reclaimed acid.

ii) Ultraviolet (UV), infiared (IR) and nuclear magnetic resonance (NMR) spectrometry

dong with gas chromatographylmass spectrometry (GCIMS) as attempted in this project

were not viable methods of analysis for determining the organic composition of reclaimed

acid. The reasons for failure at this point could, for the most part, only be assumed and

likely due to the high acid content or srna11 organic content in reclaimed acid, as well as

the complex nature of Tembind.

i) in view of the profound effect that chloride had in both the polarization and plating

tests, m e r testing on the influence of chloride concentration on glue activity should be

famed out using the galvanostatic equipment. This will ensure that chloride fluctuations

in tankhouse electrolyte are not giving erroneous glue measurements. Additionally,

laboratory andlor pilot plant testing should be undertaken to observe the effect of variable

chloride concentrations on cathode quality. The range of chloride concentrations tested

should be in the normal industrial range of (O to 40 pprn). Although none of the

laboratory tests were done using plant electrolyte, it can be assumed that chloride

fluctuation will affect polarization and cathode quality in the Copper Cliff tankhouse

(since it profoundly affécted polarization and cathode quality in synthetic electrolyte

containing glue and Tembind).

ii) Since thiourea had a signifiant levelling effm on laboratofy cathodes when it was

used in certain combinations, it is worthwhile to test thiourea in the tankhouse pilot ceils

at normal andor higher current density levels. The use of thiourea* should be in

addition to the present addition agent conditions, as weli as h the absence of glue since

laboratory cathodes did not seem to benefit noticeably h m glue addition when Tembind,

thiourea and chloride were ail present in the electmlyte. From laboratory tests (two

thiourea concentrations were tried, 0.2 pprn and 2 pprn), it appears that the thiourea

concenaation should be kept very Iow, around 0.2 ppm when useû in combination with

CHAPTER 6 - CONCLUSIONS AND RECOMMENDATIONS 105

the prescnt tankhouse addition agent conditions. This low concentration should also help

minirnize sulphur incorporation in the cathode deposits. (* Prier to testing, the health

concem concemittg thiourea shoulà be appropnately oddressed by the health Md s@ery

comminee tu enrure thor employees will mt be subjected to k d t h tfskr.)

iii) Additional information can be gained by microscopie evaluation of cathodes, thus.

it may be useful to carry this out routinely for cathodes (good and poor quality) being

proâuced in the tankhouse. The absence or presence of an addition agent(s) visibly

affects crystal structure. An archive of indexed photomicrographs might prove to be

very helpful in problem diagnosis since it can be referred to during episodes of poor

quality cathode production that are related to such things as addition agent problems or

electrolyte contamination. The viability of such an approach is subject to economic

feasibility, however, the procedure for producing and photographing polished cathode

sections is quite simple, and should be possible to cany out on site at minimal cost.

iv) In view of the beneficial effects of even small amounts of reclaimeû acid on cathode

production, the recycling of reclaimed acid should continue. However, considering the

effect that reclaimed acid bas on cathodic polarkation, the hapbazard recycling of slugs

of reclaimed acid directly to the tankhouse electr01yte should be avoided. Rerouting

reclaimed acid to the slimes thickener in the tankhouse, for example, will help minimize

disruptive fluctuations in electmlyte composition.

APPENDm A. J~ABORATORY ELECTROREFINING DATA AND m m

Table A-1. Vickers Hardness Nurnbers for Electrorefined Copper Deposits

*57.1,51.7, 48.9 (10% RA)

'60.8.61 -6. 70.6(10% RA)

APPENDICES 108

Table A-2. Laboratory Electrorefining ûperating Data

ppm glue

ppm Tcmbind

pprn chloride

1 Suri 1.17 2.1

'Fi* 1.17 1.6

C (1-8: 10 % RA)

pprn Tcmbind

Sun 1.17 1.4

Ftnirh 1.17 1.4

Suri 1.17 1.4

Fini* 1.17 1.3

pprn thiourca

F (5-8: 10 % RA)

pprn glue

ppm Tembind

pprn i h i w m

pprn cbloridc

G

APPENDICES 109

Table A-3. Laboratory Electrorefined Cathode Data

- Btf - 35.6

60.5

35.7

(O. 8

40.1

36.8

60.9

37.5 œ

AP~PENDM B. Cathodic P o l a ~ o n Data and Rem& a8 œ

Table El. Potential Shifts (PS - mV) for Various Addition Agent Combinations

* Reclaimed Acid (5%)

Rechimcd Acid ( 15 56)

* Recîaimtd Acid (20%)

glue (2)

I chloride (a)

Tembind (150), thiourca (0.3)

Tcmbind (150), chbride (20)

thiouna (0.3, chloridc (20)

glue (3 1, Tembind ( 150), thiourea (2)

duc (5), Tcmbind (150), thourai (0.2)

due (5). Tcmbmd (150). chloridc (20)

glue (lO), Tcmbind (50). chloride (=>O)

glue (5). tbiourra (0.3). chloridc (20)

APPENDICES 112

A l - no addition agents A2 - 5 pprn glue

A3 - 150 ppm Tembind A4 - 5 ppm glue, 150 ppm Tembind

Figure C-1. Photographs of Laboratory Electrorefined Deposits (@ actual site).

APPENDICES 113

AS - no addition agents A6 - 5 ppm glue

A7 - 150 ppm Tembind A8 - 5 ppm glue, 150 ppm Tembind

Figure C-1 (cont.). Photographs of laboiatory Electmtehed Deposits (@ achial &)

B1 - 20 pprn CI' B2 - 5 pprn glue, 20 pprn CI'

B3 - 150 ppm Tembind, 20 ppm 84 - 5 ppm glue, 150 ppm Cl- Tembind, 20 ppm Cl-

Figure C-1 (cont.). Photognpbs of Laboratory Electrocenned Deposits (@ actuai &)

B5 - 20 ppm Cl' 86 - 5 ppm glue, 20 ppm Cl-

B7 - 150 ppm Tembind, 20 pprn Cl-

B8 - 5 pprn glue, 150 pprn Tembind, 20 pprn Cl-

Figure C-1 (corn). Photographs of Laboratory EiectrotetIned Deposits (@ achial size)

CI - 10% RA C2 - 5 ppm glue, 10% RA

C3 - 150 ppm Tembind, 10% C4 - 5 ppm glue, 150 ppm RA Tembind, 10% RA

F i p C-1 (cont). Photographs of kbontory Eleztrorehed Deposits (@ actuai size)

C5 - 10% RA C6 - 5 ppm glue, 10% RA

C7 - 150 ppm Tembind, 10% C8 - 5 ppm glue, 150 ppm RA Tembind, 10% RA

Figure C-1 (font). Photopphs of Labontory EIoçtrorcfined Deposits (@ actual size)

D 1 - 2 ppm thiourea D2 - 5 pprn glue, 2 ppm thiourea

D3 - 150 ppm Tembind, 2 ppm D4 - 5 ppm glue, 150 ppm thiourea Tembind, 2 ppm ihiourea

APPENDICES 119

D5 - 2 ppm thiourea D6 - 5 pprn glue, 2 pprn thiourea

D7 - 150 ppm Tembind, 2 ppm D8 - 5 ppm glue, 150 ppm thiourea Tembind, 2 ppm thiourea

Figure C-1 (cont.). Photographs of Laboratory ElecîmrefÏned Deposits (@ rd e)

El - 0.2 pprn thiourea E2 - 5 pprn glue, 0.2 ppm thiourea

E3 - 150 ppm Tembind, 0.2 E4 - 5 ppm glue, 150 ppm ppm thiourea Tembind, 0.2 ppm thiourea

E5 - 0.2 pprn thiourea E6 - 5 pprn glue, 0.2 ppm thiourea

E7 - 150 ppm Tembind, 0.2 E8 - 5 ppm glue, 150 ppm ppm thiourea Tembind, 0.2 ppm thiourea

F 1 - 0.2 pprn thiourea, 20 pprn Cl-

FZ - 5 ppm glue, 0.2 pprn îhiourea, 20 pprn Cl-

F3 - 150 ppm Tembind, 0.2 ppm F4 - 5 ppm glue, 150 ppm Tem, thiourea, 20 ppm 0 0.2 ppm thio, 20 ppm Cl-

-

Figure C-l (cont.). Photographs of Lboratory Electroretined Deposits (@ actuai

F5 - 0.2 ppm thiourea, 20 ppm F6 - 5 ppm glue, 0.2 ppm thio, Cl-, 10% RA 20 ppm Cl-, 10% RA

F7 - 150 ppm Tem, 0.2 ppm F8 - Sppm gl, 150ppm Tem, 0.2 thio, 20 ppm Cl-, 10% RA ppm thio, 20ppm CI-, 10% RA

G 1 - 2.5 ppm glue, 50 ppm G2 - 2.5 ppm glue, 150 pprn Tembind Tembind

G3 - 10 ppm glue, 50 ppm G4 - 10 ppm glue, 150 ppm Tem bind Tembind

Figure C-1 (cont.), Photograpbs of Laboratory ElectrorefÏned Deposits (@ a c t d size)

G5 - 5 ppm glue, 50 ppm G6 - 2.5 ppm glue, 50 ppm Ternbind Tembind, 20 ppm chloride

G7 - 5 ppm glue, 50 ppm G8 - 10 ppm glue, 50 ppm Tembind, 20 ppm chloride Ternbind, 20 ppm chloride

Figure C-1 con^). Photographs of Labr~ to ry Electrorefbd Deposits (@ aclurl size)

Hl - no addition agents H2 - 150 ppm regular Tembind

H3 - 150 ppm diaiyzed Tembind H4 - 5 ppm glue, 150 ppm reguiar Tembind

Figure C-1 (COIIL). Photographs of Laboratory Electrorehed Depossits (@ actuaî 90e)

HS - 5 ppm glue, 150 ppm H6 - 10 % regular RA dialyzed Tembind

H7 - 10% synthetic RA H8 - 10% synthetic RA (regulafïembind) (dialyzed Tembind)

Figure C-l (cont.). Photognphs of LabotPtory Electrorefmed Deposits (@ actual s i z )

. . D . R. Turner, Plating bath chemistry considerations, Electrodepoation Technolopv. Theory and Practice, Vol. 87-17, L.T. Romankiw, Ed., 1986,417- 423.

J.O'M. Bociais and A.K.N. Reddy, Madem Electfochemistrv. Volume 2, Plenum Press, NewYork, U.S.A., 1970.

Y. Ogata, K. Yaniakawa and S. Yoshirawa, Concentration depuidence of the morphology of electrodeposits and a criterion for the rnorphological change of copper electrodeposits, Journal of Apg1ied gectmchemistry. Vol. 13, 1983,611- 6 17.

R. Winand and P. Harlet, High current density copper electrorefining. f n 9 . '0 Vol. 101, 1992, 33-44.

R. Winand, G. Troch, M. Degrez and P. Harlet, Industriai ekctrodeposition of copper . Problems connected to the behaviour of organic additions, p~~lications of Polarization Measurements in the Contm 1 of Metal Dewsibo n (Process

. . Metallurgy, Vol. 32 I.H. Warren, Ed., Elsevier, Amsterdam, Netherlands, 1984, 133-145.

R. Winand, Electrocrys~tion - theory and applications, Bmest Peters International Svmoosium - Hydromet&rgv. Theop and Practice, Hydrometailurgy 29, W.C. Cooper and D.B. Dreisinger, Eds., 1992, 567-598.

C. de Maere and R. Winand, Study of the influence of additives in copper electrorefining , simulating industrial conditions, Coowr 95ICobre 95. Vol. III.

t ro re f in iud udro- of C-, W.C. Cwper, D.B. Dreisinger, LE. Du*, H. Hein and G. Ugarte, Eds., 1995, 267-286.

J.H. Schloen and W.G. Davenport, Electrolytic coppa refining - world tankhouse operating data, Qpper 95fCobre 95. Vol. III - Electrorefinine and H v d m m e u v of Conter. W.C. Cooper, D.B. Dreisinger, J.E. Dutrizac, H. Hein and 0. Ugarte, Eds., 1995, 3-25.

P. Tyroler (Inco Limited, retiredl and S. Sanmiya (hco Limited, Rocess Technology), private communication, 1995.

J.H. Schloen, El~ctfoIytic copper refïning reviewed, CIM Bulletin, Vol. 79, 1986, 102-107.

B.R. Conard, Çppper. N i u d Cobalt Electrgmetallurer, Montreal, Canada, 1990, 3-31.

J.H. Schloen, Electtolytic Copper Refining - Tank room data, Çpp-r 91ICobre of Co-, W.C. Cooper,

D.J. Kemp, G.E. Lagos and K.G. Tan, Eds., Pergamon Ress, Oxford, England, 1991, 491-507.

V.A. Ettel and B.V. Ti, Electrolytic refining and winning of metals, Comp rehens ive Treatise of Electrochemistq Vol. 2, LO'M. Bockris, B.E. Conway, E. Yeager and R.E. White, Eds., 1981, 327-379.

B. Rogers, Inco Limi ted, Process Technology , private communication, 1995.

B. Whittaker, Inco Limited, Process Technology , private communication, 1995.

G. Fabricius and G. Sundholm, The effect of additives on the electrodeposition of copper studied by the impedance technique, Journal of A~olied Electrochemistry, Vol. 15, 1985, 797-801.

W. F. Whittaker , Cathode quality control and productivity improvement - Inco ' s Copper Cliff Copper Refinery, The Mineral, Metals & Materials Society, I.P. Hager, Ed., 1992, 701-711.

lvtische Abscheidung u H. Fischer, Elektro nd Elektrokristallisation von Metallen, Springer, Berlin, 1954.

F. C. Walsh and M .E. Herron, Electrocrystaihation and electrochemical control of cry stal growth: huidamental considerations and electrodeposition of metals, Journal of Physics D: ADplied Ph* Vol. 24, 1991, 217-225.

E.H. Chia and Y.Y. Su, Organic Additives: A source of hydrogen in copper cathodes, &Q@ of Metals. Vol. 39, 1987, 42-45.

W.K. Burton, K. Cabrera and F.C. Frank, Role of dislocation in crystal growth, N a m , Vol. 163, 1949, 398-399.

G. Eichom and H. Fischer, Uber die Bildung widimensionder Netzebenenkeime der Gleichrewichstsfrombei der inhibierten ElektrokrisîaUisation, Z. Phvs. C m , Vol. 61, 1968, 10-15.

V. Blechta and 2.2. Wang, Inco memomdum to D. W. Krueger, CCCR Rocess Tedmology , February , 1992.

D.P. Barkey, R.H. Muller and C. W. Tobias, Roughness development in metal deposition, J o u d of the Electrochemia Sc&&, Vol. 136, 1989, 2199-2206.

A.K. Biswas and W.G. Davenport, m t i v e Metallm~ of Co=, 2nd Ed., Pergmon, Oxford, England, 1980, 295-323.

G. Deveraj and S.K. Seshadri, hilsed electrodepsition of copper, P m n . Surface Finishing, Vol. 79, 1992, 72-78.

hernical Sc J.O'M. Boclais and D.M. Drazic, Electro-C iencb Taylor & Francis, London, Great Britain, 1972.

S.J. Wallden, S.T. Henriksson,P.G. Arbstedt and Th. Mioen, Electrolytic copper refining at high current densities, Journal of Metalg, Vol. 1 1, 1959, 528-534.

Y. Fukunaka, H. Doi and Y. Kondo, Structurai variation of electrodeposited copper film with the addition of an excess amount of H,SO,, Journal of the

trochemical Society, Vol. 137, 1 990, 88-93.

N. Ibl , Optimization of copper electrorefining , J3ectrochirnica Ac@, Vol. 22, 1977, 465-477.

D. Plechter, Jndustrial mtrochemistry, Chapman and Hall, London, 1984, 17.

G.R. Smith, F.X. McCawley, P.B. Needham, Jr., and P.E. Richardson, Electrorefining copper at high current densities, Bureau of Mines R m r t o f

U.S. Department of the Interior, 1979.

D.C. Rice and W.G. Davenpon. Physiuxhemicai propenies of copper electrorefining and e lectro~innin~ e l e c t r o l ~ , M e m c a l T-ctions B, Vol.

T.J. O'Keefe and L.R. Hurst, The effect of antimony, chloride ion, and glue on copper electrorefining , J o d of ADplied a e c a o ~ h e m Vol. 8, 1978, 109- 119.

T.B. Braun, J.R. Rawling and K.J. Richards, Factors affécting the quality of electrorefined copper, m c t i v e Me- of Copmx - Pvrometallurgy and

c Re-, Vol. 1, J.C. Yannopoulos and J.C. Agarwal, Eds., 1976, 5 1 1-524.

S.E. Afifi, A.A. Elsayed and A.E. Elsherief, Additive behaviour in copper electrorefining, Joumd of M W Vol. 39, 1987, 38-41.

M.D. Saban, J.D. Scott and R.M. Cassidy , Coilagen proteins in electrorefining: rate Constants for glue hydrolysis and effects of molar mass on glue activity, &tallur&a.l Transactions B, Vol. 23B, 1992, 125-133.

J.OtM. Bockris and G. Ranimney, Fun-ental &pects of Electro- . . çrystallizatio~ Chap. II, Plenum Pnss, NewYork, U.S.A., 1967.

V. K. Blechta, 2.2. Wang, and D. W. Knieger, Glue analysis and behaviour in copper electrolyte, Metallqgjcal Transactions B, Vol. 24B, 1993, 277-287.

J.B. Mohler, Copper suiphate plating - Part 1 Simple addition agent control, a . .

etal F i a , Vol. 85, 1987, 121-122.

V. Blechta and Z.Z. Wang, presentation - Eiectrochernical technique for glue and Tembind analyses, Apnl 199 1.

F.A. Mellon, K. W. Waldron and R.R. Selvendran, The potential of pyrolysis/gas chromatographyf mass spectmmetry for detennining the progress of lignification: an investigation of maturing asparagus sclerenchyma tissue, (&pic mas^ Soectrometry, Vol. 29, 1994, 556560.

Inco Monthly Report, CCCR Process Technology, March 1991, 15.

V. K. Blechta, Inco Limited (retireci), private communication, 1995.

Laurentian University Chemistry Department, h o w n source, 1996.

Inco Monthly Report, CCCR Process Technology, NovlDec 199 1, 14.

D.W. Knieger and P.M. Tyroler, Inco memorandum to L. Kowal, CCCR Rocess Tezhnology, Jaauary, 1992.

S. Knewska, L. Pajdowski, H. Podsiaddy and I. Podsiadsly, Metallur@cai ons B, Vol. lSB, 19û4, 451-460.

REFERENCES 132

V.I. Lakamanan, D.J. MacKinnon and J.M. Bnnnan, The effect of chlofide ion f Aml' in the electrowinning of copper, J o u d O ied Electrochemistry, Vol. 7,

1977, 81-90.

haracterization of Inco Coqper Anodes. A& Slimes and Nodul@ed Cathodes (Presentation Notes), C m , 19%.

S. Ywn, M. Schwartz, CEF and K. Nok, Rotating ring-disk electrode studies of copper electrodeposition: effect of chloride ions and organic additives, Plating

d Surface Finishi~ig, Vol. 81, 1994, 65-74.

Electrcxhemical Methods for Glue and Tembind Analvses, Quantitative analyses of active Tembind in CCCR electrolytes by galvanostatic technique, Inco Project Report No. 306.53, Process Technology , Copper Refinery Tankhouse, 199 1.

H. Joly, Laurentian University, Chernistry department, private communication, 1996.

Inco Monthly Report, CCCR Process Technology, MayIJune 1991, 15.