Electrokinetic Applications in Hydrometallurgical Copper Extraction · 2011. 5. 26. · Copper Extraction Honours Dissertation November 2007 Loong Hey, Yoong 10447553 Supervisors:

Electrokinetic Applications

in Hydrometallurgical

Copper Extraction

Honours Dissertation

November 2007

Loong Hey, Yoong

10447553

Supervisors: Dr. David A. Reynolds

David G. Thomas

iiii Abstract

Electrokinetic leaching is a new hydrometallurgical leaching technique developed to resolve

the shortcomings of conventional methods. Conventional leaching methods typically suffer

from slow leaching rates, and electrokinetic leaching solves this by electroosmosis, which

enhances the percolation of leach solution through a heap of ore. The electrolysis phenomena,

which is also associated with electrokinetics, decomposes water to generate an acid front

across a medium. And this front was theorised to be suitable for the purpose of leaching.

This project investigates the feasibility of using water as a leach solution under electrokinetic

leaching conditions. This was done through a series of column leach tests. For each test, a

PVC column is packed with copper oxide compost, and then saturated with sodium chloride

solution. An electric potential ranging from 0 – 80 V was subsequently applied across the

column for either 2 or 4 days. After the pre-determined time, the solution within the columns

were collected and analysed for presence of copper ions. The analysis of test results was

focused on determining the relationship between the copper concentration of the solution and

the applied electric potential.

Experimental results indicate that the copper concentration of the solution after electrokinetic

leaching increased with increasing applied electric potential. However, a correlation between

these two variables could not be established. On the other hand, observations over duration of

the tests also showed the various effects on the leach solution resulting from electroosmosis,

electromigration and electrolysis. By comparison, the copper concentrations obtained from

using both water and electrokinetic leaching was found to be 10 – 70 times less than those

yielded by diluted sulphuric acid without electrokinetics. Hence, despite being demonstrated

to be possible, the use of water as a leach solution under electrokinetic leaching conditions

was concluded to be not feasible due to the low copper concentrations obtained.

iiiiiiii Acknowledgements

The author wishes to acknowledge the support and assistance of the many people that have

contributed a great deal towards the completion of this project.

Dr. David Reynolds for your valuable guidance and encouragement throughout the year;

David Thomas for your massive help in securing the copper ores and some other bits;

Matthew McInnes for supplying me the all-important copper ores;

Dr. Edward Jones for assisting me in the lab as well as the analysis of results;

Ming Wu for your valuable inputs and support;

Dianne Krikke for your advices on laboratory procedures;

Professor Andy Fourie for his generosity in providing me the EKG layers;

Hon San Leong for constructing these magnificent experimental apparatus;

All my fellow friends in the UWA School of Environmental Systems Engineering; and

Last but not least, my parents and siblings who gave me the emotional support for me to last

through 4 hellish awesome years =)

iiiiiiiiiiii Table of Contents

Abstract ..................................................................................................................................... i

Acknowledgements.................................................................................................................. ii

Table of Contents....................................................................................................................iii

Glossary..................................................................................................................................vii

Chapter 1: Introduction.......................................................................................................... 1

1.1 Purpose, Aims and Outcomes........................................................................................... 2

1.2 Significance and Innovation............................................................................................. 2

Chapter 2: Literature Review ................................................................................................ 3

2.1 Electrokinetics................................................................................................................... 3

2.1.1 Transport Processes and Reactions of Electrokinetics ............................................5

2.1.1.1 Diffusion...................................................................................................... 5

2.1.1.2 Electromigration.......................................................................................... 6

2.1.1.3 Electroosmosis ............................................................................................ 8

2.1.1.4 Electrophoresis .......................................................................................... 13

2.1.1.5 Relative Contribution of Electroosmosis and Ion Migration .................... 14

2.1.1.6 Electrolysis ................................................................................................ 15

2.1.2 Case Study – Electrokinetic Remediation............................................................. 16

2.1.2.1 Previous UWA Studies .............................................................................. 17

2.2 Hydrometallurgical Leaching of Copper........................................................................ 18

2.2.1 Hydrometallurgical Leaching Methods................................................................. 20

2.2.1.1 Heap Leaching........................................................................................... 20

2.2.1.2 Dump Leaching ......................................................................................... 23

2.2.1.3 Vat Leaching.............................................................................................. 24

iviviviv 2.2.1.4 In-Situ Leaching........................................................................................ 24

2.2.2 Leach Solutions ..................................................................................................... 25

2.2.2.1 Acids and Oxidants ................................................................................... 25

2.2.2.2 Alkalis and Ammonia-Based Reagents ..................................................... 26

2.2.2.3 Bacterially-Mediated Leaching .................................................................27

2.2.3 Influencing Factors on Hydrometallurgical Leaching........................................... 28

2.2.4 Environmental Impacts of Hydrometallurgical Leaching ..................................... 29

2.3 Electrokinetic Leaching.................................................................................................. 30

2.3.1 Electroosmosis in Electrokinetic Leaching ........................................................... 30

2.3.2 Electromigration in Electrokinetic Leaching ........................................................ 31

Chapter 3: Approach............................................................................................................. 32

3.1 Apparatus, Materials and Equipments ........................................................................... 33

3.1.1 Apparatus – Leaching Column.............................................................................. 33

3.1.2 Electrodes – Electrokinetic Geosynthetic (EKG) Layers...................................... 35

3.1.3 Copper Ores – Copper Oxide Compose................................................................ 36

3.1.4 Leach Solution – 1.0 M Sodium Chloride Solution .............................................. 38

3.1.5 Peristaltic Pump..................................................................................................... 39

3.1.6 Power Supply ........................................................................................................ 40

3.2 Experimental Procedures................................................................................................ 41

3.2.1 Packing .................................................................................................................. 41

3.2.2 Saturation .............................................................................................................. 43

3.2.3 Leaching ................................................................................................................ 44

3.2.4 Sample Collection ................................................................................................. 46

3.3 Data Analysis.................................................................................................................. 47

vvvv Chapter 4: Results ................................................................................................................. 48

4.1 Porosity........................................................................................................................... 48

4.2 Ponding........................................................................................................................... 49

4.3 Condition of Conducting Medium ................................................................................. 51

4.4 Corrosion of Electrokinetic Geosynthetic (EKG) Layers .............................................. 52

4.5 Physical Characteristics of Leach Solution.................................................................... 53

4.6 Analysis of Copper Concentration ................................................................................. 58

4.6.1 Copper Marine Aquariums Tests........................................................................... 60

4.6.2 Laboratory Analysis .............................................................................................. 61

4.6.3 Estimation of Total Copper Content...................................................................... 64

Chapter 5: Discussion ........................................................................................................... 65

5.1 Differences between Batches of Copper Oxide Compost.............................................. 65

5.2 Discussion of Experimental Observations and Results.................................................. 66

5.2.1 Electroosmosis ...................................................................................................... 66

5.2.2 Changes in Physical Characteristics of Leach Solution ........................................ 68

5.2.3 Electromigration.................................................................................................... 69

5.3 Feasibility of Water as Leach Solution........................................................................... 70

5.3.1 Comparison of the Use of Water and Diluted Acid............................................... 70

5.3.2 Applicability to Field ............................................................................................ 71

5.4 Barriers to Project........................................................................................................... 71

5.4.1 Experimental Failure ............................................................................................. 71

5.4.2 Limitations of Copper Marine Aquariums Tests ................................................... 72

5.4.3 Limitations of Apparatus and Experimental Procedure ........................................ 73

5.4.4 Size of Experimental Data..................................................................................... 73

vivivivi Chapter 6: Conclusions and Recommendations................................................................. 74

6.1 Recommendations for Future Studies ............................................................................ 75

References .............................................................................................................................. 76

Appendix 1: Electrical Equipments and Chemical Reagents............................................ 80

Appendix 2: Diagram of Leaching Column........................................................................ 81

Appendix 3: Preparation of Leach Solution ....................................................................... 82

Appendix 4: Calculation of Porosity.................................................................................... 83

Appendix 5: Laboratory Analysis Results .......................................................................... 84

Appendix 6: Estimation of Maximum Possible Total Copper Concentration ................. 85

viiviiviivii Glossary

Anode electrode at which oxidation takes place;

the positive terminal of a power supply

Cathode electrode at which reduction takes place;

the negative terminal of a power supply

Counter-ion accompanying ionic species that maintains electric neutrality

Diffusion movement of water solutes from a region of high concentration

to that of a low concentration

Electrode an electrically conductive structure that transfers electrons

Electrokinetics study of the transport of chemical species that result from the

controlled application of an electric field across a porous

medium

Electromigration migration of ionic species in an applied electric field

Electroosmosis bulk flow of pore fluid through a porous medium in response to

an applied electric field

Electrophoresis migration of charged colloidal or larger-sized particles under an

electric field

viiiviiiviiiviii Hydraulic conductivity change in hydraulic head per unit distance in a given direction

Ionic strength quantity proportional to the amount of electrostatic interaction

between ions in a solution

Point of zero charge pH at which the electrical potential at the edge of the compact

layer of the electrical double layer is 0 mV

Pore space volume volume of a designated zone that is comprised of voids

Porosity ratio of pore volume to total volume

Tortuosity measure of the effect of the flow path geometry on the

movement of fluids through porous media

Transference number the distribution of electrical conduction by ion migration

Zeta-potential electrical potential at the shear plane or slip surface between the

compact layer and the diffuse layer within the electrical double

layer

1111 Chapter 1: Introduction

Chapter 1: Introduction

Hydrometallurgical techniques are quickly gaining acceptance as a reliable and cheap method

for extracting copper from their ores. Compared to conventional extraction methods such as

froth flotation, smelting and refining, hydrometallurgical techniques are slower and generally

reserved for low grade ores or mine wastes. The hydrometallurgical leaching process, is the

first of the three major processes involved within hydrometallurgy, the others being solvent

extraction and electrowinning. Hydrometallurgical leaching, or more commonly referred to as

leaching, typically takes several months to complete, but may also be stretched up to decades,

depending on the grade of the ore that is leached.

There are many established methods available for leaching. The major ones include heap

leaching, dump leaching, vat leaching and in-situ leaching. Despite the variety, most of these

methods still suffer from slow leaching rates. A relatively new leaching methods, known as

electrokinetic leaching, attempts to solve this through the application of electrokinetics. Burns

& Wright (1993) demonstrated that electrokinetic leaching was able to enhance percolation of

the leach solution through a heap of ores by electroosmosis. This, in turn, significantly

improved the leaching and recovery rates.

The application of electrokinetics is usually associated with the electrolysis phenomena, along

with electromigration, electrophoresis and electroosmosis. During electrolysis, decomposition

of water particles takes place, and an acid front is generated. The occurrence of such reaction

gives rise to the idea that the generated acid front can be used to leach metals from ores as

well. Hence, water was proposed as a possible leach solution for leaching, but only under

electrokinetic leaching conditions.

2222 Chapter 1: Introduction

1.1 PURPOSE, AIMS AND OUTCOMES

The purpose of this project is to investigate the feasibility of using water as a leach solution

under electrokinetic conditions. Through this project, it was hoped that a safer and more cost

effective option for electrokinetic leaching will be developed. This project will also serve as a

pilot study, and create a platform for future studies to be built upon.

Specifically, the feasibility of using water as a leach solution under electrokinetic conditions

will be evaluated through a series experiments, using copper hydrometallurgy as a case study.

The desired outcomes of this project are to demonstrate satisfactory copper leaching rates

using just water as a leach solution from an electrokinetic-assisted leaching experiment. In

addition, this method must be able to show economic viability as well as environmental

benefits.

1.2 SIGNIFICANCE AND INNOVATION

The potential utilisation of water as a leach solution presents an excellent opportunity to

significantly reduce copper production costs. The innovation of this idea lies in the fact that

water is cheaper and more readily available than typical leach solutions such as sulphuric acid.

If feasible, the Australian mining sector is expected to benefit greatly from this method, with

larger profits and wider social acceptance.

Also, the success of this project will help advance today’s knowledge on both electrokinetics

and hydrometallurgy, as well as encourage the development of technological innovations.

3333 Chapter 2: Literature Review

Chapter 2: Literature Review

This project can be perceived as an expansion of ideas onto a relatively new and unknown

method of hydrometallurgical leaching – electrokinetic leaching. Electrokinetic leaching is

basically the fusion of 2 components, namely electrokinetics and hydrometallurgical leaching.

And before any attempts to evaluate this leaching method are made, it is necessary that the

concepts of its two fundamental components are understood separately.

This chapter consists of three general sections. Sections 2.1 and 2.2 describe the basics and

workings of electrokinetics and hydrometallurgical leaching of copper respectively. The

remaining section (Section 2.3) reviews several studies, before discussing the potential and

opportunities available for electrokinetic leaching.

2.1 ELECTROKINETICS

In general, electrokinetics refers to the study of the transport of chemical species that result

from the controlled application of an electric field across a porous medium. Electrokinetics

has recently made significant strides in the field of engineering, especially in issues dealing

with the environment. Some of the more developed applications of electrokinetics include:

remediation of contaminated soils/sites;

remediation or dewatering of mine tailings;

dewatering sewage sludges and waste slurries; and

consolidation super soft clays.

Electrokinetic techniques involves the generation of an electric potential difference across the

subjected medium. This can be done using electrodes, electromembranes, and more recently,

electrokinetic geosynthetic layers. For example, electrokinetic remediation uses low-level


direct current on the order of milliamperes per cubic centimetre of cross sectional area, or an

electric potential difference on the order of several volts per centimetre between the electrodes

placed in the ground to be treated (Acar & Alshawabkeh 1993).

The generated electric field may result in physiochemical and/or hydrological changes within

the medium, leading to species transport by coupled and uncoupled conduction phenomena

(Acar & Alshawabkeh 1993). There are four significant species transport processes that may

present under an electric field:

Diffusion

Electromigration

Electroosmosis

Electrophoresis

Depending on the composition of the medium, these transport processes can be accompanied

by processes such as sorption, precipitation and dissolution, and other aqueous phase

reactions in the pore fluid (Acar & Alshawabkeh 1993).

Additionally, electrolysis reactions will occur and dominate at the boundaries of the electric

field; more specifically, within the immediate vicinity of both the anode and cathode.

According to Saichek & Reddy (2005), electrokinetics, though fairly simple to implement and

operate, are governed by complex fundamental reactions. The subsequent section (Section

2.1.1.1) is dedicated to each of the transport processes and reactions that may occur under an

electric field during the application of electrokinetics.


2.1.1 TRANSPORT PROCESSES AND REACTIONS OF ELECTROKINETICS

2.1.1.1 DIFFUSION

Diffusion occurs irrespective of bulk fluid motion or applied electrical potential difference.

Diffusion can be described as the movement of water solutes from a region of high

concentration to that of a low concentration (Fetter 1993). Fick’s First Law expresses the

diffusive mass flux under a chemical concentration gradient (Fetter 1993):

x

C *DJd

∂∂⋅−= 2-1

where Jd is the diffusive mass flux;

D* is the effective diffusion coefficient;

x

C

∂∂

is the aqueous phase concentration gradient; with

C as the aqueous phase concentration; and

x as the distance.

For finely-grained porous medium such as soils, Acar & Alshawabkeh (1993) expressed

the effective diffusion coefficient as:

D* = D τ n 2-2

where D is the diffusion coefficient in free solution at infinite dilution;

τ is the tortuosity; and

n is the porosity.

Tortuosity is the measure of the effect of flow path geometry on the movement of fluids

through porous media (Fetter 1993). The tortuosity value mostly ranges in between 0.20 –

0.50 for finely-grained soil (Shackelford & Daniel 1991); while porosity typically lies

over the range of 0.1 – 0.7 (Alshawabkeh & Acar 1992).


As diffusion occurs, electrical neutrality must also be maintained (Fetter 1993). Using

sodium chloride solution as an example, (negative) chloride ions cannot diffuse faster than

(positive) sodium ions unless additional positive ions are introduced into the region where

the chloride ions are diffusing towards.

2.1.1.2 ELECTROMIGRATION

Electromigration refers to the migration of ionic species in an applied electric field

(Saichek & Reddy 2005). In the presence of the electric field, the charged ionic species

will travel towards the electrode of opposite charge. This migrational flux can

subsequently be expressed by the following equation (Acar & Alshawabkeh 1993):

x

E*uJm

∂∂⋅−= 2-3

where Jm is the migrational flux;

u* is the effective ionic mobility;

x

E

∂∂

is the electric potential gradient; with

E as the electric potential; and

x as the distance.

Although there is no sound method yet to measure the effective ionic mobility, this

variable can be theoretically estimated using the Nernst-Townsend-Einstein relationship as

follows (Shackelford & Daniel 1991):

RT

zF*Du* = 2-4

where u* is the effective ionic mobility;

D* is the effective diffusion coefficient (as discussed in Section 2.1.1.1);

z is the valence of the ion;

F is the Faraday constant (which is 9.6485309 x 104 C/mol);

R is the universal gas constant (which is 8.314510 J/K/mol); and


T is the absolute temperature.

The relationship is assumed to be true for ions in the medium’s pore fluid.

Ionic Mobility versus Diffusion Coefficient

Ionic mobility of a charged species is usually at least an order of magnitude higher than

its diffusion coefficient; and the ratio of the effective ionic mobility to the effective

diffusion coefficient of a charged species is about 40 times the charge on the species

(Acar & Alshawabkeh 1993). This is best illustrated in Table 2.1. As a result of this,

under an electric field, electromigration is the dominant contributing factor to the

transport of charged ionic species, in comparison with diffusion.

Species Diffusion coefficient

D (x 10-6 cm2/s)

Ionic mobility

u (x 10-6 cm2/s)

Effective ionic mobility

u (x 10-6 cm2/s)

H+ 93 3625 760

Na+ 13 519 109

Cu2+ 5 390 82

OH- 53 2058 432

Cl- 20 790 166

SO42- 11 413 87

Table 2.1: Diffusion coefficient, ionic mobility at infinite dilution and effective ionic

mobility in soil for selected ionic species (Acar & Alshawabkeh 1993).


Transference Number

If current in an electric field is generated solely by ion migration or electromigration in

the free pore fluid, the total current can than be related to the migrational mass flux of

each species through Faraday’s Law (Acar & Alshawabkeh 1993):

∑∑

⋅=⋅=j

n

1iii

jjjj I

cuz

c*uzItI 2-5

where I is the total current; and

tj is the transference number of the j-th ion.

The transference number describes the distribution of electrical conduction by ion

migration. For each individual ion, the transference number is dependent on its ionic

mobility, concentration and the total electrolyte concentration (Acar & Alshawabkeh

1993). From Equation 2-5, it can be deduced that the transference number of a species

will increase as the ionic concentration of that specific species increases. This implies

that electromigration will be less efficient if the concentration of the ionic species

relative to the total electrolyte concentration in the pore fluid decreases.

2.1.1.3 ELECTROOSMOSIS

Electroosmosis is the bulk flow of pore fluid through a porous medium in response to an

applied electric field. When an electric field is established along with capillary, the excess

counter-ions throughout the electrical double layer region adjacent to the medium particles

are attracted and move towards the oppositely charged electrode (Acar et al. 1995). As

they migrate, momentum is transferred to the surrounding fluid molecules via viscous

forces, producing electroosmotic flow (Saichek & Reddy 2005).


Electrical Double Layer

When a liquid is in contact with a solid, the preferential adsorption of charged species of

the liquid by the solid induces the development of an electrical double layer (Paillat,

Moreau & Touchard 2001). Within this layer, counter-ions of the solid’s surface charge

concentrate (Saichek & Reddy 2005). According to the Stern model, this layer is

constituted of two zones – the inner compact layer and the diffuse layer on top of it (see

Figure 2.1).

Figure 2.1: The electrical double layer (Paillat, Moreau & Touchard 2001).

The compact layer is directly adjacent to the surface and so the space charge density is

maximum (Paillat, Moreau & Touchard 2001). Due to this, the counter-ions are not

affected by the liquid flow and are hydrodynamically immobile. The thickness of the

compact layer is in the order of the ionic radii of the counter-ion.

At the diffuse layer, the space charge density decreases when one moves away from the

surface according to Boltzmann law (Paillat, Moreau & Touchard 2001). The

counter-ions in this layer are hydrodynamically mobile. The diffuse layer ends at the

interface where electrical neutrality of ions is observed. The thickness of the diffuse

layer is usually given by (Paillat, Moreau & Touchard 2001):


σ

εDδ0 = 2-6

where δ0 is the thickness of the diffuse layer;

ε is the dielectric constant;

D is the diffusion coefficient; and

σ is the bulk liquid electrical conductivity.

The thickness of the electrical double layer depends on the magnitude of the surface

charge of the medium, and the concentration, valence and dielectric properties of the

ions in the pore fluid (Acar et al. 1995). When the ionic concentration increases, the

electrical double layer becomes narrower. As a result, the extent of the shear force onto

the pore fluid flow will be reduced and the electroosmotic flux weakens.

The electroosmotic mass flux can be expressed as (Acar & Alshawabkeh 1993):

ew

e qC

CJ ⋅

= 2-7

where Je is the electroosmotic mass flux;

C is the aqueous phase molar concentration;

Cw is the molar concentration of water; and

qe is the electroosmotic pore fluid flux.

The Helmholtz-Smoluchowski (H-S) equation is widely accepted as a means to estimate

electroosmotic flow. The electroosmotic pore fluid flux is expressed by the H-S equation

(Acar & Alshawabkeh 1993, Saichek & Reddy 2005):

x

En

η

Dζqe ∂

∂⋅

−= 2-8

where qe is the electroosmotic pore fluid flux;

D is the dielectric constant of the fluid;

ζ is the zeta-potential;


η is the dynamic viscosity of the fluid;

n is the porosity;

x

E

∂∂

is the applied electric potential gradient; with

E as the applied electric potential; and

x as the distance.

Alternatively, the H-S equation can be expressed in terms of the electroosmotic

permeability coefficient (Saichek & Reddy 2005):

nη

Dζk e = 2-9

where ke is the electroosmotic permeability coefficient.

The H-S equation is only considered valid when the thickness of the electrical double

layer is smaller than the radius of the capillary (Saichek & Reddy 2005). This is so that

the surface of the particles can be regarded as flat.

The Zeta-Potential ζ

The zeta-potential is the electrical potential at the shear plane or slip surface between the

compact layer and the diffuse layer within the electrical double layer. The zeta-potential

is basically a complex function of the interfacial chemistry between the liquid and solid

phases, with parameters such as the type of medium, ionic species that are present, pH,

ionic strength and temperature (Vane & Zang 1997).

Obviously, surface charge determines whether the zeta-potential is negative or positive.

For negatively-charged surfaces, the counter-ions are cations. So, the zeta-potential is

negative and the electroosmotic flow is directed towards the cathode, as depicted by the

H-S equation. Conversely, the zeta-potential becomes positive for positively-charged

surfaces. Thus, the electroosmotic flow is now towards the anode.


At a certain pH value, when all the ions are in the immobile zone and the zeta-potential

is equal to zero, a point of zero charge (PZC) can be defined (Saichek & Reddy 2005).

At this point, the electroosmotic flow is zero as well. The understanding of PZC is

important as it is intricately related to the surface charge of the medium. If a solution has

a pH below the pHPZC (pH at PZC), the surface charge becomes positive. This results in

a positive zeta-potential. Alternately, solutions with pH above the pHPZC give a negative

surface charge of the medium and zeta-potential.

By varying the acidity or ionic strength, the zeta-potential can be manipulated. This, in

turn, changes the magnitude and/or direction of the electroosmotic flow. For example, a

lower pH condition causes the zeta-potential increase as the surface charge of the

medium is now higher.

Unlike hydraulic flow, electroosmotic flow is unaffected by a medium’s pore size. Figure

2.2 shows that the electroosmotic permeability coefficient for different soil types with

varying pore sizes remained relatively constant, compared to hydraulic conductivity. And

as mentioned above, acidity and ionic strength significantly influences the electroosmotic

flow. If a steady supply of redox ions is not maintained within the pore fluid, the

electroosmotic permeability may decrease, leading to smaller electroosmotic flows.

Figure 2.2: Electrokinetic permeability and hydraulic conductivity for selected sediments

(ElectroKinetic Limited n.d.)


2.1.1.4 ELECTROPHORESIS

Electrophoresis is the migration of charged colloidal or larger-sized particles under an

electric field (Saichek & Reddy 2005). Electrophoresis is a counterpart of electroosmosis.

In electroosmosis, fluid moves with respect to a solid body when an electric field is

applied, whereas during electrophoresis the particles are moving while the fluid as a

whole is at rest (Delgado et al. 2005). Hence, Smoluchowski’s theory can be extended to

describe the motion of these charged particles, and used to derive equations for both the

electrophoretic velocity and electrophoretic mobility.

The electrophoretic velocity is the velocity of the particle with respect to a medium at rest

and is quantified by the following equation (Delgado et al. 2005):

Eη

Dζve = 2-10

where ve is the electrophoretic velocity;

D is the dielectric constant of the fluid;

ζ is the zeta-potential;

η is the dynamic viscosity of the fluid; and

E is the electric field vector.

The magnitude of the velocity divided by the magnitude of the electric field strength is

known as the electrophoretic mobility (Delgado et al. 2005). Similar to Equation 2-10,

the electrophoretic mobility is expressed as (Delgado et al. 2005):

η

Dζue = 2-11

where ue is the electrophoretic mobility.


Both Equations 2-10 and 2-11 are known as the Helmholtz-Smoluchowski (H-S)

equations for electrophoresis. The effective electrophoretic mobility is influenced by

particle size, surface charge density, pH and solution ionic strength (Taylor, Zafiratos &

Dubson 2004).

2.1.1.5 RELATIVE CONTRIBUTION OF ELECTROOSMOSIS AND ION M IGRATION

The relative contribution of electroosmosis and ion migration to the total mass transport is

dependent on the soil type, water content, species type, pore fluid concentration and

processing conditions (Acar & Alshawabkeh 1993). Based on the Peclet number, Acar &

Alshawabkeh (1993) introduced a similar dimensionless mass transport number to

quantify the relative contributions:

ee

m

e k

*u

J

Jλ == 2-12

where λe is the ratio of the migrational mass flux with respect to the electroosmotic mass

flux under equal potential differences;

Jm is the migrational mass flux;

Je is the electroosmotic mass flux;

u* is the effective ionic mobility; and

ke is the electroosmotic permeability coefficient.

This dimensionless mass transport number is particularly useful in gauging the efficiency

of an electrokinetic configuration in its applicability, so that optimisation and adjustments

can be performed. For instance, the electrokinetic configuration for the dewatering of

mine tailings should be set up so that the mass transport number is at its lowest

(electroosmosis dominates).


2.1.1.6 ELECTROLYSIS

Electrolysis reactions dominate at the electrodes or boundaries of the electric field. In a

porous medium saturated with aqueous solution, the decomposition of water will occur,

generating hydrogen ions and hydroxyl ions at the anode and cathode respectively

(Probstein & Hicks 1993).

At the anode, oxidation generates an acid front (Acar & Alshawabkeh 1993):

2 H2O → O2 + 4 H+ + 4 e- Eo = -1.229 V

Reduction occurs at the cathode, producing a base front (Acar & Alshawabkeh 1993):

2 H2O + 2 e- → H2 + 2 OH- Eo = -0.828 V

where Eo is the standard reduction electrochemical potential.

This results in a steep pH gradient between the electrodes at the initial state. The pH at the

anode may drop to less than 2 while increase at the cathode to over 12 depending on the

total current applied (Acar et al. 1990).

Depending on the availability of other chemical species, secondary reactions may exist.

For example, the presence of metals in the medium results (Acar & Alshawabkeh 1993):

Men+ + n e- → Me ; or

Me(OH)n (s) + n e- → Me + n OH-

where Me refers to metals.

Due to the electrical potential gradients, the acid front will advance toward the cathode,

while the base front will travel in the reverse direction from cathode to anode (Probstein

& Hicks 1993). Since the mobility of hydrogen ions is about twice of that of hydroxyl

ions (Acar et al. 1995), protons will dominate the system and the acid front will travel

much faster than the base front. Eventually, the two fronts will meet at a zone near the

cathode, where the ions may recombine to form water (Acar et al. 1995).


For electrokinetic leaching, the generation of the acid and base front raises a couple of

important implications. Firstly, the overall low pH throughout the medium may affect the

electroosmotic flow and decrease transport efficiency by ion migration. On the other hand,

the base front may form precipitates of metal hydroxide at the cathode. This can

potentially cause clogging of the porous medium and production of unwanted

by-products.

2.1.2 CASE STUDY – ELECTROKINETIC REMEDIATION

Electrokinetic remediation is one of the major applications of electrokinetics. This technique

has been evaluated and implemented as an efficient method for extracting radionuclides,

heavy metals, certain organic compounds, mixed inorganic species and organic wastes from

contaminated soils, slurries or mine tailings (Zhou et al. 2005).

The application of an electric field over a contaminated site has several effects (Acar et al.

1995):

i. an acid front is produced at the anode that transports across the soil. Along the way, the

front desorbs contaminants from the surface of soil particles;

ii. the electromigration of available species in the pore fluid and those at the electrodes is

initiated; and

iii. an electric potential difference is established, leading to electroosmosis flushing of

different species.


2.1.2.1 PREVIOUS UWA STUDIES

In recent years, the UWA School of Environmental Systems Engineering has carried out

several studies on the electrokinetic remediation of NAPL/DNAPL contaminated sites.

Three honours dissertation relating to this topic has been completed so far by former

students of the school. All three studies investigated the transport of chemical species

through a porous media using electrokinetics.

Lee (2005) conducted a series of experiments using bucket-type electrolytic cells to assess

the transport of chloride ions through a porous sediment core sample. The study managed

to establish a linear relationship between mass transport and the applied electrical

potential difference. However, it was suggested that electrokinetics may be ineffective in

the remediation of NAPL contaminated sites.

Adams (2006) examined the mass transport of nano-scale zero valent iron (ZVI) through a

porous media matrix. A number of experiments were carried out utilising electrolytic cells

similar to those by Lee (2005). The study found that the transmission rates of the ZVI

were extremely small, if not, negligible. Adams (2006) concluded that electrokinetic

induced movement of nano-scale ZVI was not feasible in cases where hydraulic

inducement is not possible as well.

The feasibility of utilising electrokinetics to transport potassium permanganate and

nano-scale ZVI through low permeability glass and clay media was examined by Gillen

(2006). Experiments were done using three different electrolytic cell configurations – a

one-dimensional column, a two-dimensional cylinder and a two-dimensional rectangular

tank. Results indicated that the mass transport of the mentioned reagents through low

permeability porous media was successful, and the transport rates can be significantly

enhanced.


In comparison with conventional techniques, electrokinetic remediation has the advantage

of being fairly simple to implement and operate, flexible, efficient and economic (Acar &

Alshawabkeh 1993, Saichek & Reddy 2005). Furthermore, studies demonstrating the

successful remediation of mine tailings (Hansen, Rojo & Ottosen 2004, Hansen & Rojo

2006, Kim & Kim 2001) using electrokinetics has lead to the optimistic views that

electrokinetic leaching might be feasible.

2.2 HYDROMETALLURGICAL LEACHING OF COPPER

Copper is traditionally extracted from ore through processes such as flotation, smelting and

refining. However, the use of hydrometallurgical methods have been gradually becoming

more widespread, contributing to about 10% of extracted copper from ores in 1994 (Biswas &

Davenport 1994). Copper was the first metal to which hydrometallurgical processes including

leaching, solvent extraction and electrowinning were applied (Bingöl & Canbazoğlu 2003).

Hydrometallurgical methods are generally reserved for the extraction of metal from oxide

minerals or low-grade ores (Warhurst 2000). In the extraction of copper, hydrometallurgy is

most commonly used for the following minerals (Biswas & Davenport 1994):

carbonate minerals – azurite (2CuCO3·Cu(OH)2) and malachite (CuCO3·Cu(OH)2);

oxide minerals – cuprite (Cu2O) and tenorite (CuO);

hydroxy-silicate minerals – chrysocolla (CuO·SiO2·2H2O);

sulphate minerals – antlerite (CuSO4·2Cu(OH)2) and brochantite (CuSO4·3Cu(OH)2); and

secondary sulphide minerals – chalcocite (Cu2S) and covellite (CuS).

Most of the world’s copper exists as primary sulphide minerals, such as chalcopyrite, bornite

and chalcocite (Biswas & Davenport 1994). However, hydrometallurgical methods are not

preferred for such minerals as the leaching of primary sulphide minerals can be very slow

(Biswas & Davenport 1994).


Before hydrometallurgical methods can be applied, the copper ore has to be firstly crushed

and processed according to the requirements of subsequent processes. The hydrometallurgical

process can be briefly summarised into three separate steps (Biswas & Davenport 1994):

ii. Leaching of copper from ore or mine waste to produce a copper-bearing aqueous solution;

iii. Solvent extraction to produce a pure highly-concentrated copper electrolyte from the

aqueous solution; and

iv. Electrowinning in which the electroplating of pure copper cathodes from the electrolyte

occurs.

Hydrometallurgical leaching, or better known as just leaching, refers to the chemical and

biochemical processes by which solutions transfer metal compounds from a solid phase to a

liquid phase (usually an aqueous solution) from which the valuable metal component can then

be recovered by downstream processing (Bridge 2000). Copper leaching can be done in a

variety of methods. The more popular and common methods are listed in Table 2.2.

Leaching method Mineralisation Leaching time Copper leached

(tonnes/day)

Heap leaching Secondary sulphides Several months (top of heap)

to several years (in heap) 10 – 200

Dump leaching Chalcopyrite (waste)

Secondary sulphides 1 – 5 decades 20

Vat leaching Secondary oxides 5 – 10 days 50

In-situ leaching All decades 20

Agitation leaching Oxides 2 – 5 hours 100 – 200

Tailings leaching Oxides ½ – 1 day 10 – 200

Table 2.2: Comparison of major copper leaching methods (Biswas & Davenport 1994).


2.2.1 HYDROMETALLURGICAL LEACHING METHODS

This section describes four of the most common leaching methods for copper – heap

leaching, dump leaching, vat leaching and in-situ leaching. In general, each leaching method

does not differ from one another significantly.

Heap leaching is the most popular method and, hence, will be described in considerable

detail. Subsequent descriptions of the remaining methods are much shorter, as only the

major differences between each method are pointed out. The basic principles for leaching

still remain the same.

2.2.1.1 HEAP LEACHING

Heap leaching is by far the most common utilised method for copper leaching and is

particularly suited for secondary copper sulphide minerals. This method involves stacking

the leach-able ore onto a leach pad (typically 3 – 10 m high and 104 - 105 m2 in area)

(Biswas & Davenport 1994).

The ores must be crushed fine enough beforehand to allow good percolation of the leach

solution without excessive channelling taking place, whilst maintaining void spaces

essential for good air dispersion and drainage (Williams, Hunter & Arnall 2005). If the

ores are too fine, percolation of leach solution through the heap will be slow and drainage

will be poor as well. On the other hand, if the ore size is too coarse, drainage will be fast

and the copper concentration of the resulting pregnant leach solution might be too low.


Leach Pads

Leach pads are impermeable lined pads constructed of synthetic material, asphalt or

compacted clay (Warhurst 2005). These pads are designed to minimise the loss of leach

solution by optimising solution recovery and to reduce environmental impacts (Bridge

2005).

Leach pads come in several types of configuration. The configuration type to be used is

chosen according to a number of factors, including ore material properties, water

balance, land availability, ground slope and the project cost (Lupo 2006). Table 2.3

shows some of the available leach pad configurations.

Leach pad configuration Considerations

Single use (standard) pad

Suitable for variable ore types and

leach cycle times.

Typically cover large areas.

Flat topography (for geotechnical

stability).

Large ponds for storm events.

Low initial capital costs.

Incremental pad expansion costs

might be required.

Table 2.3 (cont.): Leach pad configuration types and their corresponding considerations

to be made (Lupo 2006).


Leach pad configuration Considerations

On/off or Reusable pad

Suitable for ores with short leach

cycles and consistent leaching

characteristics.

Areas with limited flat terrain.

Requires a rinsed ore site/pad.

Durable, high-stress liner system.

Suitable for a wide range of

climatic conditions.

Smaller storm pond.

Costlier (due to double handling of

ore, rinsing system and storage of

rinsed ore.

Valley fill

Best suited for hard durable ore

with good drainage. Can

accommodate extended leach

times.

Used in steep terrain (up to 40%).

Internal solution storage reduces

requirement for external pond.

Robust liner system (high

hydraulic head and ore loads).

Retaining structure for

confinement of heap.

High upfront capital cost.

Hybrid configuration

Combination of dedicated, single

use pad with partial internal

solution storage.

Combination of single use pad and

on/off pad.

Valley fill pad with a portion used

as an on/off pad.

Side-hill leach pad.

Dump leach (with no liner).

Table 2.3 (cont.): Leach pad configuration types and their corresponding considerations

to be made (Lupo 2006).


Prior to stacking of the heap, a drainage layer is usually placed on the leach pad. This

layer is generally composed of non-reactive rocks such as quartzite to ensure the layer

does not react with the leach solution and the drainage of pregnant leach solution is

adequate (Williams, Hunter & Arnall 2005).

The surface of the stacked heap is subsequently sprinkled with leach solution, or lixiviant.

The lixiviant trickles down through the heap and leaches copper from its minerals to

produce a pregnant leach solution (Biswas & Davenport 1994). Copper is recovered from

the pregnant solution via precipitation, solvent extraction and/or electrowinning.

The composition and distribution of the lixiviant varies from site-to-site, depending on

costs, the minerals to be leached, and the desired composition of the resulting pregnant

leach solution. The heap is typically leached for 1 – 4 months, before a new heap is being

placed on top of it (Biswas & Davenport 1994). The heap continues to grow larger until

the trucking of ore upwards become so expensive that the construction of a new heap area

is more economic (Biswas & Davenport 1994).

2.2.1.2 DUMP LEACHING

Dump leaching is almost identical to heap leaching, with the exception that leaching takes

place on an unlined surface and run-of-mine wastes or low grade ores are used (Warhurst

2005). Little or no crushing of ores will be performed prior to stacking and every corner

will be cut where possible to save costs (Williams, Hunter & Arnall 2005).


Evidently, dump leaching is just an effort to extract what is little left from the mine wastes.

Copper dump leaches are massive, with waste rock piled into large masses ranging in size

from 20 to over 100 feet in height (Warhurst 2005). In comparison with other methods,

dump leaching is very long term as the trickling of lixiviant through the dump can take as

long as several years (Biswas & Davenport 1994).

2.2.1.3 VAT LEACHING

Vat leaching works on the same principles as heap and dump leaching. Vat leaching is a

high-production rate method conducted in a system of vats or tanks using concentrated

lixiviant (Warhurst 2005). The ores are leached for a short period, removed and then

replaced with fresh material. Vat leaching is typically suitable for oxide ores (Biswas &

Davenport 1994).

The vats are usually run sequentially to maximise contact time between the ore and the

lixiviant (Warhurst 2005). Vats enable key environmental parameters such as temperature,

pressure, acidity and oxygen availability to be monitored and controlled to optimise

recovery rates (Bridge 2005). Also, vats may be agitated to enhance the effectiveness of

chemical reactions and improve copper recovery (Bridge 2005).

2.2.1.4 IN-SITU LEACHING

In-situ leaching refers to the leaching of ore that has not been mined and is still in the

ground (Bridge 2005). Lixiviant is injected into the ore body through pipes or by trickling

down through the fractures above (Biswas & Davenport 1994). The pregnant leach

solution is recovered from the sumps in mine workings by pumping (Bridge 2005).


The advantage of in-situ leaching is that surface disturbance is minimal as the problems

associated with mine drainage and waste disposal is reduced (Williams, Hunter & Arnall

2005). However, in-situ leaching suffers from drawbacks such as difficulties in controlling

of the lixiviant’s temperature, movement and flow, and ensuring sufficient oxygen is

available for bacterial growth (Williams, Hunter & Arnall 2005).

2.2.2 LEACH SOLUTIONS

Leach solutions, also lixiviant, are used to extract valuable metals in the form of a dilute,

metal-laden solution (Warhurst 2005). The leach solution that comes out at the end of the

leaching process is known as the pregnant leach solution, and is passed to the metal

recovery/extraction stage.

Leach solutions come in several different varieties, and is selected depending on the

minerals to be leached and the target metals to be recovered. For copper, three different

types of leaching solutions are regularly used and are described below.

2.2.2.1 ACIDS AND OXIDANTS

Acid leaching of ores and concentrates is the most common method for copper leaching.

Acids are particularly suitable to leach oxidised copper minerals such as azurite, malachite,

tenorite and chrysocolla as these minerals readily dissolve at room temperature (Warhurst

2005). For less oxidised minerals, oxidants such as ferric sulphate and oxygen are

required to accomplish leaching (Warhurst 2005).

Typical acidic leaching solutions include hydrochloric acid, sulphuric acid and ferric

sulphate (Biswas & Davenport 1994).


The following are examples of reactions between oxidised copper ores and an acidic leach

solution (sulphuric acid) (Bingöl & Canbazoğlu 2003):

Azurite Cu3(OH)2(CO3)2 + 3 H2SO4 → 3 CuSO4 + 2 CO2 + 4 H2O

Malachite Cu2(OH)2CO3 + 2 H2SO4 → 2 CuSO4 + CO2 + 3 H2O

Tenorite CuO + H2SO4 → CuSO4 + H2O

Chrysocolla CuSiO3·2H2O + H2SO4 → CuSO4 + SiO2 + 3 H2O

For non-oxidised minerals such as covellite and chalcopyrite, the use of oxidants can be

useful. For example, in a sulphuric acid-oxygen system, the following reactions occur

(Padilla, Vega & Ruiz 2007):

Covellite CuS + ½ O2 + 2 H+ → Cu2+ + S + H2O; and

CuS + 2O2 → Cu2+ + SO42-

The leaching and oxidation of chalcopyrite can be done by using an acid-ferric leach

solution and/or oxygen (Antonijević & Bogdanović 2004):

Chalcopyrite CuFeS2 + 4 Fe3+ → Cu2+ + 5 Fe2+ + 2 S; and

CuFeS2 + O2 + 4 H+ → Cu2+ + Fe2+ + 2 S + 2 H2O

2.2.2.2 ALKALIS AND AMMONIA -BASED REAGENTS

Alkaline leaching can be more effective for certain copper minerals, such as ores with

large amounts of acid-consuming carbonate rocks, as the leaching process is much more

selective (Warhurst 2005). However, this selectivity often results in low recovery rates if

the ores are not fully liberated during crushing and grinding.

The principle reagents used in alkaline leaching are hydroxides and carbonates of sodium

and ammonia, potassium hydroxide and calcium hydroxide (Warhurst 2005).


An example of alkaline leaching is ammonia leaching (Prasad & Pandey 1998):

Chalcopyrite 4 CuFeS2 + 17 O2 + 24 NH3 + 4 H2O →

2 Cu(NH3)4SO4 + 2 (NH4)2SO4 + Fe2O3

Copper can then be recovered from the pregnant leach solution by solvent extraction. The

by-product of ammonium sulphate ((NH4)2SO4) can be crystallised and removed.

2.2.2.3 BACTERIALLY -MEDIATED LEACHING

Bacterially-mediated leaching is usually applied to low-grade sulphide ores, and is much

slower than typical acid or basic leaching processes (Warhurst 2005). This method relies

on the capacity of bacteria to oxidise ferrous iron to ferric iron, which in turn oxidises

other metal sulphides to produce water soluble sulphates and sulphuric acid (Warhurst

2005).

Several requirements are needed in order to promote bacterial activity: oxygen, ammonia,

nitrogen, phosphate, suitable temperatures (approximately 30 °C), and acidity (about pH

of 2.0) (Warhurst 2005). Temperatures or pH outside the optimal range will dramatically

reduce bacterial activity.

The leaching of sulphide minerals requires the aid of oxidants. Bacterial activities with

oxygen from air are capable of producing ferric ions and sulphuric acid, which is an

oxidant (Biswas & Davenport 1994):

Pyrite 4 FeS2 + 15 O2 + 2 H2O → 4 Fe3+ + 6 SO42- + H2SO4

The ferric ions from the above reactions are then used to leach secondary copper sulphide

minerals such as (Biswas & Davenport 1994):

Chalcocite Cu2S + 10 Fe3+ + 15 SO42- + 4 H2O →

2 Cu2+ + 10 Fe2+ + 12 SO42- + 4 H2SO4

Covellite CuS + 8 Fe3+ + 12 SO42- + 4 H2O → Cu2+ + 8 Fe2+ + 9 SO4

2- + 4 H2SO4


2.2.3 INFLUENCING FACTORS ON HYDROMETALLURGICAL LEACHING

The kinetics of hydrometallurgical leaching of copper can be significantly influenced by

environmental and operational parameters. These include:

i. pH

Low pH conditions result in increased recovery rates of copper, due to the resulting

lowered activation energy of the leaching reactions (Grizo et al. 1982).

ii. Temperature

Copper recovery rates rises with increasing temperature (Whitehead et al. 2007).

Similar to the effect of a decrease in pH values, higher temperatures also lower the

activation energy of the leaching reactions (Grizo et al. 1982).

iii. Concentration of leach solution

Deng et al. (2001) found that by increasing the concentration of the leach solution, the

leaching times of copper can be reduced. This is because the increase in reactive species

allows more intense leaching reactions, and in turn, improves copper recovery rates.

iv. Availability of oxygen

For non-oxidised minerals, oxygen is important for the oxidation of compounds. Thus,

an increase in the amount of oxygen will increase the recovery rates of copper. This has

been acknowledged by Deng et al. (2001).

v. Pressure

Under optimal leaching conditions, the copper recovery rate can be improved up to

about 90% by increasing the oxygen partial pressure (Anand, Rao & Jena 1983).


Obviously, due to economical reasons and limitations, it would be not feasible and almost

impossible to maximise each of the above influencing factors in practice. Furthermore, each

of the factors may be intricately related to one another. For example, the solubility of

oxygen will decrease if the temperature is too high (Deng et al. 2001). So, oxidation of

non-oxidised minerals will be much more difficult. The optimum copper leaching condition,

hence, is to balance each of the influencing factors whilst maintaining economic feasibility.

2.2.4 ENVIRONMENTAL IMPACTS OF HYDROMETALLURGICAL LEACHING

Potential impacts of hydrometallurgical leaching operations on the environment are most

likely to be experienced as changes to surface and/or groundwater quality, due to two

reasons. Since leaching involves the extraction of metals in solution, a process failure will

lead to introduction of contaminants into the environment in liquid form (Bridge 2005).

Furthermore, the solid feed products and waste products are susceptible to chemical

breakdown on contact with precipitation (Bridge 2005).

The release of contaminants from leaching units, such as leach solution, heavy metals and

sulphides, may occur during snowmelt, heavy storms, or failures in the pile or pond liners

and associated solution transfer equipment (Warhurst 2005). In addition to direct

contamination of groundwater, releases such as acid can initiate and/or facilitate the

mobilisation of metals (Bridge 2005). If not contained, the mobilised metallic substances

can result in an increase in heavy metal concentrations in groundwater. Releases from

leaching unit may also adversely affect the natural pH of surface and/or groundwaters.


2.3 ELECTROKINETIC LEACHING

Electrokinetic remediation has been shown to be very promising in the removal of metals, not

only from soils, but also from mine tailings. Several studies have been able to demonstrate

satisfactory removal of copper from mine tailings and wastes (Hansen & Rojo 2006, Hansen,

Rojo & Ottosen 2004, Kim & Kim 2001, Rojo, Hansen & Otosen 2005). Despite the

numerous researches that have been carried out on electrokinetics, studies on the application

of electrokinetics onto mining operations have been virtually non-existent.

The success of the aforementioned studies shows that there is great potential in electrokinetic

leaching. The major difference between electrokinetic leaching and electrokinetic remediation

of mine tailings would be the size of particles. And since mine tailings are usually very fine

(Hansen, Rojo & Ottosen 2004), the ores would have to be crushed into small enough sizes if

electrokinetic leaching were to achieve comparable results to electrokinetic remediation.

Electrokinetic leaching can be viewed as the application of electrokinetics onto a conventional

hydrometallurgical leaching method. Using heap leaching as an example, this would simply

mean the installation of electrodes at top and bottom of the heap. The first known study on

electrokinetic leaching was performed by Burns & Wright (1993).

2.3.1 ELECTROOSMOSIS IN ELECTROKINETIC LEACHING

Burns & Wright (1993) were able to use electrokinetics to induce electroosmotic flow

through a vertical cylindrical column of low grade gold ore and tailings deposit. This

resulted in improved percolation of leach solution (cyanide) compared to conventional

methods, which in turn, led to increased recovery rates of gold (Burns & Wright 1993). A

simple feasibility study also showed electrokinetic leaching may have significant economic

advantages over normal heap leaching methods (Burns & Wright 1993).


2.3.2 ELECTROMIGRATION IN ELECTROKINETIC LEACHING

In 2006, Löfgren & Neretnieks demonstrated that electromigration is capable of enhanced

diffusion of an ionic tracer through the pores of a granitic rock matrix. This finding

implicates a significant advantage of electrokinetic leaching that might have over

conventional leaching methods: diffusion of leach solution into the ores.

Under an electric field, electromigration will encourage the diffusion of chemical species of

the leach solution into the pores of the ores. This subsequently increases the total surface

area available for leaching, resulting in more metals that can be leached from an ore or

mineral.

Given that both electroosmosis and electromigration can be potentially advantageous for

electrokinetic leaching, practical application of this still-experimental method in near-future is

anticipated. Despite this, the feasibility of using water as a leach solution under electrokinetic

conditions is still an unknown. It is hoped that this project will provide the evidence required

and shed some light on the feasibility of this idea.

32323232 Chapter 3: Approach

Chapter 3: Approach

The purpose of this project was to assess the feasibility of using water as a leach solution

under electrokinetic leaching conditions. And this was done through a series of laboratory

experiments, which were column leaching tests. The experiments were designed to quantify

and measure copper recovery from a column filled with copper ores subjected under a range

of different electrical potential gradients, after a pre-determined time.

Column leaching tests were proposed as these tests are commonly used by both academic and

industrial researchers to simulate actual hydrometallurgical leaching operations. Furthermore,

the apparatus required for a basic leaching test can be designed and manufactured cheaply

without too much difficulty, which was suitable for a small-scale project such as this.

Burns & Wright (1993) examined the use of electrokinetics to enhance percolation of leach

solution through a low grade gold ore and a tailings deposit by column leaching tests. The

success of the study gave a very positive indication on the suitability of leaching tests for the

purpose of this project, as well as the simplicity in incorporating electrokinetics into the tests.

The following sections will firstly describe the apparatus, materials and equipments used for

the experiments (Section 3.1), before explaining in full detail the experimental procedures

(Section 3.2). Appendix 1 shows a full list of the electrical equipment and chemical reagents

that were used. The final section of this chapter (Section 3.3) gives a brief walkthrough on the

analyses of experimental observations and results.


3.1 APPARATUS, MATERIALS AND EQUIPMENTS

3.1.1 APPARATUS – LEACHING COLUMN

Four polyvinyl chloride (PVC) cylindrical leaching columns measuring 102 mm in diameter

and 600 mm in height were constructed. Constructions of the columns were done at the

UWA School of Civil and Resource Engineering’s workshop. PVC was selected to construct

the columns due to its ready-availability, low cost, strength and high chemical resistance.

The drawback in using PVC was that the columns are not transparent. Transparent columns

can be useful for the purpose of monitoring the ongoing leaching process.

The use of ready-made PVC cylinders for construction meant that the diameter of the

columns was fixed during design. The column height, on the other hand, was forced to be

smaller than the proposed height of 1000 mm, due to initial difficulties in securing sufficient

amounts of ore. From past studies (Burns & Wright 1993, Lin & Luong 2004, Miller &

Newton 1999), the typical height-to-diameter ratios of leaching columns were usually over

10:1. However, Roman (n.d.) stated that a column height of five times the diameter can still

be accepted as well. Hence, the column dimensions used in this project were still valid.

A schematic diagram of the leaching column is shown below (see Figure 3.1). An

alternative representation to Figure 3.1 can also be found at Appendix 2.


Figure 3.1: Leaching column for column leaching tests: (a) actual; (b) schematic diagram.

Top cap

Filter plate

(with 50µm filter)

Electrokinetic

geosynthetic

(EKG) layer

Bottom cap

(with valve)

Glands

(a) (b)


The leaching column consists of:

i. a cylindrical column;

ii. a top cap;

The top cap serves to minimise evaporation of the solution inside the column, but also

has two small holes that allow some air circulation into it.

iii. a bottom cap (with valve)

The bottom cap holds up the medium within the column. A valve was fitted onto the cap

to allow solutions to be pumped into or drain out of the column.

iv. two glands; and

The glands at the side of the column allow electrodes or electrokinetic geosynthetic

(EKG) layers within the column to be connected to an exterior power supply by wires.

The glands also prevent the solution within the column from leaking out.

v. a filter plate (with 50 µm filter).

The filter plate was drilled with 5 mm holes so that solutions can pass through it easily

while holding the medium on top of it.

3.1.2 ELECTRODES – ELECTROKINETIC GEOSYNTHETIC (EKG) LAYERS

The electrokinetic geosynthetic (EKG) layers (see Figure 3.2), courtesy of Professor Andy

Fourie of the UWA School of Civil and Resource Engineering, functioned as electrodes to

generate an electric field over the medium within the column. EKG layers have the big

advantage over traditional metallic electrodes on being much more resistant to corrosions.

The layers are also flexible and can be shaped according to needs, which results in a more

uniform electric field applied between the layers.


Figure 3.2: 10 cm circular electrokinetic geosynthetic (EKG) layer.

3.1.3 COPPER ORES – COPPER OXIDE COMPOST

In the experiments, the copper ores were subjected to both leaching and electrokinetics.

Oxidised copper minerals were requested specifically for the leaching tests. This was

because oxidised minerals do not have to undergo oxidation during leaching, thus giving

much faster leaching times (Biswas & Davenport 1994).

The copper ores were provided in the form of copper oxide compost, courtesy of Matthew

McInnes of Equinox Minerals and David Thomas of Golder Associates. It was informed that

the compost contained an estimated amount of 7% of copper. Unfortunately, more detailed

information on the composition of the compost was not provided, and so the compost was

assumed to contain a high percentage of impurities and other metals as well.


The copper compost was very fine in texture and dark brown in colour (see Figure 3.3). The

compost particles were not uniform in size, and ranged from several mm to smaller than 100

µm. Due to the texture, an additional 50 µm filter was placed on top of the filter plate to

prevent the compost from falling through the holes of the plate.

Figure 3.3: Copper oxide compost.

The copper oxide compost was delivered on two separate occasions: 20 kg at mid-August

and 100 kg at mid-September of 2007. Purely by observation, it was noted that both batches

has slight differences in texture, smell and colour. Hence, the usage of two different copper

oxide compost batches is very likely to result in complications in the experimental results.

Due to the small amount (20 kg) available initially, early experiments proceeded with a

50:50 mixture of copper oxide compost and glass beads. The mixture was prepared by

weighing then mixing both the compost and beads by hand until a homogenous mixture was

obtained. Later experiments continued using the same mixture to conform to uniformity.

The glass beads ranged from 600 – 850 mm in diameter, and only served to increase the

overall mass and volume of the medium to be leached. The glass beads were slightly coarser

than the compost, but were chosen as they were chemically inert and readily available.


3.1.4 LEACH SOLUTION – 1.0 M SODIUM CHLORIDE SOLUTION

Consisted to the aims of this project, the experiments were conducted using water as a leach

solution. Specifically, 1.0 M sodium chloride aqueous solution was used as pure water

contains no free ions to allow electrical conduction. This was equivalent to a TDS value of

58442.5 ppm for the solution, and was beyond the measurable range of the TDS meter.

The leach solution was prepared by adding 58.4425 g of sodium chloride into every 1 L of

deionised water (see Appendix 3). Deionised water was obtained from a water purifier in

the lab. The solution was then mixed thoroughly with a magnetic stirrer for at least 1 hour

(see Figure 3.4).

Figure 3.4: Mixing of leach solution.

For benchmarking, 0.5 M sulphuric acid was also used as a leach solution for one of the

experiments. The acid solution was prepared by diluting 27.2 ml of 98.07% concentrated

sulphuric acid into every 1 L of deionised water (see Appendix 3). Similarly, the solution

was mixed well for at least an hour before usage.


3.1.5 PERISTALTIC PUMP

The peristaltic pump (see Figure 3.5) was used to pump fluids into the leaching column.

The pump utilises a peristaltic motion to transfer fluid contained within the clear Tygon

tubing into the leaching column. The pump itself does not come into contact with the liquid.

Figure 3.5: Laboratory peristaltic pump.

Throughout the experiments, a pumping speed 3 was set for the pump. This was so that the

time required to saturate the columns with fluid were approximately the same for all

experiments. The time needed to transfer 2 L of leach solution into a column packed with 7

kg of 50:50 copper oxide compost and glass beads mixture was about 30 – 40 minutes.


3.1.6 POWER SUPPLY

A laboratory DC power supply was used to power to the EKG layers during the column

leaching tests (see Figure 3.6). It has a dual tracking feature, and was capable of supplying

voltages up to 40 V and a maximum current of 3 A. The two outputs of the power supply

can be used either independently or in a master/slave configuration. For all experiments, the

configuration was set to ‘Independent’.

Figure 3.6: Laboratory DC power supply.

Maximum current was enabled for all experiments, while the voltage was varied. Voltage or

electric potential was an independent variable in this project. The voltage used in

experiments ranged from 0 – 80 V. Voltages higher than 40 V were accomplished by

connecting the two outputs of the power supply together in series, and then adjusting the

two output voltages until the total reaches the desired voltage.


3.2 EXPERIMENTAL PROCEDURES

The experimental procedures were broken up into four different stages:

i. Packing

ii. Saturation

iii. Leaching

iv. Sample collection

An overview of all procedures is summarised in Figure 3.7.

3.2.1 PACKING

At this stage, the column was filled with 7 kg or 50:50 copper oxide

compost and glass beads mixture. This gives the mixture a height of

approximately 500 mm, or a height-to-diameter ratio of 5:1. A piece

of EKG layer was placed into the column both before and after

packing, with the connecting wires hanging out from the glands.

The column was filled using a dry packing method. For

approximately every one inch of mixture applied, the top of the

mixture medium was pressed downwards several times using a

wooden hammering tool (see Figure 3.8). This process was

repeated until the column was packed with all 7 kg of the mixture.

Figure 3.8: Dry packing of the mixture medium in leaching column.

Dry packing was performed so that the medium within the column was at its densest state.

Wet packing was not preferred as over-saturation of the mixture was very likely to occur. At

this state, the mixture is in a slurry-like form, making further packing extremely difficult.


Figure 3.7: Flow diagram of the experimental procedures.

cathodecathode

anodeanode

Packing Saturation

Leaching Sample

collection

50:50 mixture of

copper oxide compost

and glass beads

1.0 M sodium

chloride solution

Acid front

Sample

Anode

Cathode


At the end of the packing stage, the total height of the medium was measured. With the

particle density measured beforehand, the bulk density and the porosity of the column were

calculated. After that, the packed column was mounted onto the stand.

3.2.2 SATURATION

Before the column was saturated with leach solution, the column was flushed with tap water

first. Tap water was pumped into the column from the bottom using a peristaltic pump (see

Figure 3.9). This was done to push out air from the pores of the mixture medium, as well as

remove particles that were too fine. Pumping was done at a slow rate to prevent expansion

of the mixture medium, as well as better removal of air and fine particles from it.

Figure 3.9: Flushing of column with tap water.


Eventually, the entire column becomes saturated and the excess tap water overflows from

gland at the top. The overflow fluid was initially brownish in colour, indicating the removal

of fine particles. The fluid then gradually becomes clearer. The duration of this flushing

process was fixed at 3 hours, from which a clear overflow fluid was almost guaranteed. A

clear overflow fluid was proof that most of the fine particles have been removed.

The next step was to saturate the column with the leach solution. Without draining the

column after flushing, the leach solution was subsequently pumped into the column in the

same manner as tap water. Now, instead of fixing a pumping duration, the amount of leach

solution to be pumped into the column was set at 2 L. This amount was significantly higher

than the total pore space volume of the mixture medium (see Appendix 4), and ensured that

almost all of the pore spaces in the medium were filled with leach solution.

After that, the valve at the bottom of the column was turned off and the wires of the EKG

layers were connected to the power supply.

3.2.3 LEACHING

The leaching stage starts when the power supply was turned on. The top EKG layer served

as the anode, and the bottom one is the cathode. This arrangement was done so that the

generated acid front travels from top to bottom. At the same time, cations (including copper

ions) will be attracted and move towards the cathode at the bottom as well.

The current was set to maximum, while the voltage was adjusted as required. The voltage

denoted the magnitude of the electric potential that was applied across the mixture medium.

Figure 3.10 shows the set up of the experiment at this stage.


Figure 3.10: Commencement of electrokinetic leaching using water as a leach solution.

The voltages used for the column leaching tests were determined during the initial stages of

the experimental period through discussions with the supervisor. Six tests were planned out

initially: 0, 20 and 40 V for duration of 2 and 4 days. A further three more tests were carried

out after that for expansion and better understanding of experimental data. The three tests

were 30 and 80 V for 4 days, and another 0 V for 4 days using 1.0 M sulphuric acid as a

leach solution. The test using acid as leach solution was meant for benchmarking purposes.

Over the duration of the leaching stage, the voltage and current were both maintained at the

set value and at maximum respectively. Observations of any peculiarities happening were

recorded as well. This stage finished when the pre-determined leaching time ends.


3.2.4 SAMPLE COLLECTION

Immediately after the leaching stage, the power supply was turned off and the valve at the

bottom was opened to drain and collect the leach solution from the column. The first 250 ml

of the fluid coming out were able to be collected right away off without much waiting.

Drainage after that usually became very slow, and the subsequent fluid that came out were

collected separately from the first 250 ml. Since some of the fluid was still percolating

through the medium, the low drainage rates were expected. The column was then left for at

least 24 hours so that most of the fluid drains out.

Copper Marine Aquarium Tests

The collected samples were each tested for copper immediately after collection through

copper marine aquariums tests (see Figure 3.11). The aquarium tests were used as a

qualitative indicator for the presence of copper. The aquarium tests were especially useful

in determining whether or not the experiments were giving positive results.

Figure 3.11: Testing for presence of copper by a copper marine aquarium test.

The small bottle at the left is the copper indicator, while the right one is the sample.

In this case, the colour change indicates a copper concentration of approximately 0.2 ppm.


Copper marine aquarium tests are very simple and can be conducted without any prior

preparations. The test works by adding six drops of copper indicator into a test tube filled

with 10 ml of sample. The test tube is then shaken, and the colour change of the sample is

compared with a colour scale over a white background.

The copper marine aquarium test has an effective copper measuring range of 0 – 0.4 ppm.

Copper concentration is determined using a colour scale like as follows:

The obvious disadvantages of aquarium tests were its limited range of measurement and

impreciseness. Furthermore, the interpretation of the colour change may vary between

individuals due to human perception. Hence, aquarium tests should not be used as a means

to obtain quantitative results.

Ultimately, all the samples were sent to a commercial laboratory for a comprehensive

laboratory analysis. A full cation analysis for copper was requested.

3.3 DATA ANALYSIS

In conjunction with the objectives of this project, data analysis focused on establishing a

statistical relationship between the applied electric potential and the copper concentration.

The copper concentrations were obtained from the results of the commercial laboratory’s

analyses of the samples. In the end, a statement regarding the feasibility of using water as a

leach solution under electrokinetics was formulated.

Data analysis also involved examining any of the changes to the leach solutions’ physical

characteristics, as well as any other important observations over the experimental duration.

Attempts were made to explain the observations as effects of electrokinetic application.

0 ppm 0.4 ppm

48484848 Chapter 4: Results

Chapter 4: Results

This chapter presents all physical observations during and after the experiments, as well as the

results of the laboratory analysis of samples. For convenience, the 50:50 mixture of copper

oxide compost and glass beads in a leaching column will be referred to as ‘mixture medium’

or ‘conducting medium’ from this point onwards.

4.1 POROSITY

From the measured dimensions, the bulk density, particle density and porosity of the mixture

medium were calculated (see Appendix 4). Table 4.1 shows a summary of the calculations.

Leach

solution 1.0 M sodium chloride aqueous solution

0.5 M

sulphuric

acid

Duration 2 days (48 hours) 4 days (96 hours)

Voltage

(V) 0 20 40 0 20 30 40 80 0

Bulk

density

(g/cm3)

1.638 1.635 1.670 1.626 1.629 1.644 1.607 1.629 1.651

Particle

density

(g/cm3)

2.222 2.222 2.222 2.222 2.353 2.353 2.353 2.353 2.353

Porosity

(%) 26.291 26.432 24.855 26.851 30.783 30.119 31.692 30.783 29.850

Table 4.1: Calculated values of bulk density, particle density and porosity of mixture medium.

The shading of the cells show the different batches of copper used for the experiments.

White cells indicate the first batch (received in mid-August); while

the second batch is denoted by grey cells (received in mid-September).


Bulk density was fairly constant for experiments, typically around 1.60 – 1.70. The particle

density, however, was different depending on the copper oxide compost which was used for

the mixture. The use of compost from the second batch resulted in a slightly higher particle

density, compared to that by the first batch. This, in turn, gave an increase in the medium’s

porosity by about 4 – 5%.

4.2 PONDING

For experiments in which electric potential was applied over the conducting medium, ponding

was observed at the top of the column (see Figure 4.1), after both 2 and 4 days. The

accumulation of slightly bluish fluid was seen as early as after 12 hours. The top of the

column was dry at all times for experiments with zero voltage or electric potential.

Figure 4.1: Ponding at the top of the column for 0, 20, 40 and 80 V after 4 days.

0 V 20 V

40 V 80 V


The fluid accumulated at the top of the column was found to be slightly bluish in colour in all

cases of ponding. This is likely an indication of the presence of copper(II) ions (Greenwood &

Earnshaw 1997). In addition, the amount of fluid accumulated after 2 or 4 days were

approximately the same for all voltages or electric potentials, with the exception of the

experiment for 80 volts after 4 days. This oddity was likely due to experimental failure and

will be further described in Section 5.2.1.

The amount of fluid accumulating at the top of the column was also observed to increase with

time, as shown in Figure 4.2. This was the same for all applied electric potentials or voltages.

Figure 4.2: Ponding at the top of the column for 20 V after 2 and 4 days.

The occurrence of ponding was not expected during the design stages of the experiments.

Therefore, the designed apparatus was not equipped to quantify such occurrences.

2 days 4 days


4.3 CONDITION OF CONDUCTING MEDIUM

The state and condition of the conducting medium before and after leaching were almost

identical regardless of the magnitude of the applied electric potential. Obviously, the medium

after leaching was wet, with the media at the bottom of the column significantly wetter than

those at the top (see Figure 4.3).

Figure 4.3: Conducting medium at the top, middle and bottom of the column

for 40 V after 2 days.

Top Middle

Top Bottom

Bottom


4.4 CORROSION OF ELECTROKINETIC GEOSYNTHETIC (EKG) LAYERS

On two separate occasions, the electrokinetic geosynthetic (EKG) layers were found to have

corroded: the anodes for both 40 V after 2 days, and 30 V after 4 days. In both cases, the main

body of the EKG layer appeared to have suffered no damage, displaying high durability. The

parts that were connected to the wires, however, were corroded (see Figure 4.4).

Figure 4.4: Corrosion of the EKG layers at the wire connection side.

As shown in Figure 4.4, the corroded parts were covered slightly with precipitates that were

blue-green in colour. Again, this is very likely due to the crystallisation of copper(II) salts

(Greenwood & Earnshaw 1997). Due to the weakened rubber coating (white in colour) which

protects the wire connections underneath it, the metallic parts of the electrodes were exposed

to the electrolyte (leach solution). The result of this was corrosion.


4.5 PHYSICAL CHARACTERISTICS OF LEACH SOLUTION

Several important changes to the leach solution after experimentation were observed, in

particular for applied electric potentials of 20 V and above. Changes were observed in the

form of formation of precipitates and colour changes. Table 4.2 displays a summary of the

observed changes to the leach solution. Images of the samples can be found at Table 4.3. The

‘First 250 ml’ represents the first 250 ml of fluid that drains out of a leaching column after an

experiment finishes; while ‘After first 250 ml’ denotes the subsequent fluid that drains out.

Observations on leach solution Leach solution Duration

Voltage

(V) First 250 ml After first 250 ml

0 Clear solution.

White precipitates.

Clear solution.

No precipitates.

20 Clear solution.

No precipitates.

Clear solution.

No precipitates. 2 days

40

Slightly yellowish

solution.

No precipitates.

Not available due to

leakages.

0 Clear solution.

No precipitates.

Clear solution.

No precipitates.

20 Clear solution.

White precipitates.

Clear solution.

No precipitates.

30

Clear solution.

Little white

precipitates.

Clear solution.

No precipitates.

40

Very brownish

solution.

No precipitates.

Brownish solution.

No precipitates

1.0 M sodium chloride

aqueous solution

80 Clear solution.

No precipitates.

Clear solution.

White precipitates.

0.5 M sulphuric acid

solution

4 days

0

Slightly bluish

solution.

No precipitates.

Slightly bluish

solution.

No precipitates.

Table 4.2: Summary of the physical characteristics of all samples collected after leaching.


First 250 ml After first 250 ml

NaCl solution, 20 V, 2 days

Not available


Not available


Table 4.3: Images of samples collected after the experiments.






Table 4.3 (cont.): Images of samples collected after the experiments.




H2SO4 solution, 20 V, 4 days

Table 4.3 (cont.): Images of samples collected after the experiments.


Comparison of ‘First 250 ml’ Samples and ‘After First 250 ml’ Samples

In general, samples collected after the first 250 ml that drains out from the column were

slightly clearer. For columns with an applied electric potential or voltage, the ‘after first 250

ml’ samples were either free of precipitates (for 20 V) or less yellowish (for 40 V) compared

to the “first 250 ml’ samples. Since the “first 250 ml’ samples were drained directly from the

bottom part of the conducting medium, it can be implicated that the formation of white

precipitates or the colouring of the leach solution were due to reactions near or at the

cathode. Section 5.2.3 further discusses this implication.

Effects of Electric Potential

The initial leach solutions, either sodium chloride solution or the sulphuric acid solution,

were both clear fluids with no precipitates. From Table 4.2, a general observation of the

final leach solution in response to increasing voltage or electric potential can be deduced. At

0 V, the collected solution was clear. The solution remained clear at 20 V, but white

precipitates were formed. These precipitates though, started to decrease with increasing

voltage, and by 40 V no more precipitates were observed. The leach solution at 40 V was

also yellowish.

Effects of Leaching Time

The physical characteristics of the samples from experiments with different applied electric

potentials but same leaching time were very close. The main difference was the intensity of

the physical changes. For example, at 20 V, both samples collected after 2 and 4 days were

clear solutions with white precipitates. The sample for 4 days, however, was found to

contain more precipitates. Similarly, the two samples for 40 V were quite similar, but the

sample for 4 days exhibited a more drastic colour change than that for 2 days.


The physical characteristics of the sample for the 80 V experiment after 4 days was found to

be inconsistent with those of other samples. Thus, an experimental failure was likely to have

occurred, and this will be further discussed in Section 5.3.1.

As for the experiment using sulphuric acid solution as leach solution, a bluish sample was

obtained. This means that the sample may possibly contain a significantly high concentration

of copper(II) ions (Greenwood & Earnshaw 1997) compared to the other samples.

4.6 ANALYSIS OF COPPER CONCENTRATION

The analyses of samples for copper were carried out in two ways: copper marine aquariums

tests and analysis by a commercial laboratory. Table 4.4 shows a comparison of results by

both analyses for the ‘first 250 ml’ samples.

Assuming that the density of leach solution is the same as water density, then a copper

concentration of 1 mg/L is equivalent to 1 ppm.

From Table 4.5, the results of the laboratory analysis were typically much higher than that by

the aquariums test, with the exception of 0 V. The reason for this is explained in Section 5.3.2.


Total copper concentration

Duration 2 days 4 days

Leach

solution

Voltage /

Electric

potential

Laboratory

analysis

(mg/L)

Copper

marine

aquariums

tests (ppm)

Laboratory

analysis

(mg/L)

Copper

marine

aquariums

tests (ppm)

0 V 0.29 0.30 6.83 > 0.40

20 V 11.40 0.40 5.89 0.40

30 V 10.46 0.40

40 V 21.53 > 0.40 40.57 N/A

1.0 M

sodium

chloride

solution 80 V 5.78 0.35

0.5 M

sulphuric

acid

solution

0 V 347.50 0.20

Table 4.5: Comparison of total copper concentration results by laboratory analysis

and copper marine aquarium tests.

The shading of the cells show the different batches of copper used for the experiments.

White cells indicate the first batch (received in mid-August); while

the second batch is denoted by grey cells (received in mid-September).


4.6.1 COPPER MARINE AQUARIUMS TESTS

The full results of the samples by the copper marine aquariums tests are shown in Table 4.6.

As mentioned earlier in Section 3.2.4, the effective range for the aquariums test was very

limited. This was evident in some experiments where the observed change in colour was

outside of the range shown by the provided colour scale. Furthermore, the test did not work

for samples with a strong background colour. For example, the yellowish colour of samples

from the experiment at 40 V after 4 days was found to interfere with the colour change.

Total copper concentration (ppm)


Leach solution Electric

potential

First 250

ml

After first

250 ml

First 250

ml

After first

250 ml

0 V 0.30 > 0.40 0.40

20 V 0.40 0.30 0.40 0.25

30 V 0.40 0.25

40 V > 0.40 N/A N/A

1.0 M sodium

chloride solution

80 V 0.35 0.25


solution 0 V 0.20 0.20

Table 4.6: Total copper concentration of samples by copper marine aquariums tests.

For almost all experiments, the copper concentrations for the ‘first 250 ml’ samples were

higher than the ‘after first 250 ml’. Also, the copper concentration was found to increase

with increasing electric potential for experiments with a leaching duration of 2 days; but

decrease for duration of 4 days.

Due to the inconsistency of results, coupled with the limited effective concentration range,

further analysis of the aquariums tests’ results were not carried out. As said before, the

copper marine aquariums tests are only suited for simple qualitative analysis of the samples.


4.6.2 LABORATORY ANALYSIS

Laboratory analysis of the samples was performed by the Environmental Division of the

ALS Laboratory Group. The full detailed results of the analysis can be found at Appendix 5.

The total copper concentration values for duplicated samples were averaged up to give them

an individual representation, as well as to avoid unnecessary confusion.

Total copper concentration (mg/L)


Leach solution Electric

potential

First 250

ml

After first

250 ml

First 250

ml

After first

250 ml

0 V 0.29 6.83 0.61

20 V 11.40 0.27 5.89 0.35

30 V 10.46 0.68

40 V 21.53 40.57 13.15

1.0 M sodium

chloride solution

80 V 5.78 0.80


solution 0 V 347.50 383.00

Table 4.7: Total copper concentration of samples by laboratory analysis.

For leaching times of both 2 and 4 days, the total copper concentration was observed to

increase with increasing applied electric potential, if the experiment for 0 and 80 V for 4

days were ignored. Similar to the aquariums test results, the copper content within the ‘first

250 ml’ samples were very much higher than that in the ‘after first 250 ml’ samples.

Again, the results for the experiment at 80 V after 4 days were inconsistent in comparison

with the others, indicating experimental failure. The use of 0.5 M sulphuric acid solution as

a leach solution resulted in a significantly higher total copper concentration, compared to

using 1.0 M sodium chloride aqueous solution. This was consistent with the bluish solution

colour observed, as mentioned in Section 4.5.


Ignoring the experiment for 80 V after 4 days, the total copper concentrations of the samples

were plotted against the applied electric potential (see Figure 4.5). Only the values for the

‘first 250 ml’ samples were used. This was because the increasing trend of total copper

concentration was observed only within these samples, and the fixed sample volume makes

them more suitable for comparison with each other.

R2 = 0.9993

R2 = 0.9482

0

10

20

30

40

50

0 10 20 30 40 50

Applied electric potential (V)

Tot

al c

oppe

r co

ncen

trat

ion

(mg/

L).

.

2 days

4 days

Figure 4.5: Plot of total copper concentration against applied electric potential.

The shape of the markers show the different batches of copper used for the experiments.

Square markers indicate the first batch (received in mid-August); while

the second batch is denoted by diamond-shaped markers (received in mid-September).


Effects of Electric Potential

Clearly, Figure 4.5 showed that the total copper concentrations of the leach solution

increase with increasing electric potential. However, the use of different batches of copper

oxide compost appeared to have significantly disrupted the consistency of results.

For 2 days, the copper concentration exhibited a very linear relationship with the applied

electric potential. However, the increase in copper concentration for 4 days was found to

resemble more towards an exponential function, if the marker for 0 V was excluded. The

reason for this exclusion was because of the different batch of copper used for 0 V. Also,

the copper concentration at 0 V after 4 days was higher than 20 V of the same duration,

and this contradicts the increasing trend shown by all other experiments.

Effects of Leaching Time

Comparisons between different leaching times were inconclusive. Half of the samples for

4 days were lower than those for 2 days, while the other half was higher. The copper

concentrations were expected to increase with leaching times. As the contact time between

the minerals and the leach solution was longer, more copper should be leached out.

Again, this discrepancy is likely due to the different batches of copper used. The only

valid comparison for different leaching times would be at 0 V, since both samples use the

same batch of copper. The copper concentration at 0 V was found to be higher after 4 days

than that after 2 days.


As evidenced, the usage of different copper batches for the experiments was very likely to

have adversely affected the consistency of results. This was anticipated earlier as the two

batches of copper oxide compost were found to differ slightly in appearance (see Section

3.1.3). An evaluation to compare the two batches could be useful in this project. However,

the involvement of too many variables, including leaching duration and applied electric

potential, meant that statistical tests (such as a Student’s t-test) could not be performed.

4.6.3 ESTIMATION OF TOTAL COPPER CONTENT

The copper content of the copper oxide compost was estimated to be 7% by the suppliers.

Thus, a simple estimation of the maximum amount of copper can be leached from each

column was performed (see Appendix 6).

The maximum possible copper concentration that can be obtained was calculated to be

1.225 × 105 mg/L, which were orders of magnitude higher than the obtained concentrations.

Using 0.5 M sulphuric acid solution as leach solution yielded a copper concentration of only

300 – 400 mg/L, still substantially less than the maximum possible. To achieve figures near

the maximum possible copper concentration would be virtually impossible and unrealistic.

65656565 Chapter 5: Discussio

n

Chapter 5: Discussion

This chapter discusses the problems faced during practical work, as well as explains the

results and observations from the experiments.

5.1 DIFFERENCES BETWEEN BATCHES OF COPPER OXIDE COMPOST

The use of different batches of copper ore for the experiments was speculated as the main

reason for a number of inconsistencies presented within the results. The two batches of copper

oxide were claimed to be the same and originating from the same location by the supplier.

Despite no statistical method (such as Student’s t-test) was performed (due to too many

variables) to support the claims, some of the observations and experimental results do point

otherwise.

The two batches of copper oxide compost appeared to differ by observation. Slight differences

were spotted in terms of texture, smell and colour (see Section 3.1.3). Furthermore, the

second batch of delivered compost (at mid-September) was found to contain a substantial

amount of impurities and junk, such as metal strips, paper and rocks.

The difference between the two batches of compost was compounded by the analysis of the

conducting mediums’ porosity (see Section 4.1). The second batch was found to result in a

slightly higher particle density and porosity for the medium than the first batch (delivered at

mid-August), possibly due to the presence of more impurities.

66666666 Chapter 5: Discussion

While no two different ores were used under the same experimental conditions, the analysis of

results (see Section 4.6) hinted strongly that the copper batches used might not be the same:

i. Different increasing trends of copper concentration with applied electric potential (see

Figure 4.5). Copper concentration was observed to increase linearly for a leaching time of

2 days, but exponentially for 4 days.

ii. Discrepancies between samples from experiments with the same applied electric potential.

For example, copper concentration after leaching for 4 days was lower than that after 2

days. Copper concentration was expected to be higher over a longer duration as the

contact time between the copper ores and leach solution was longer. This should have

resulted in the leaching of more copper.

5.2 DISCUSSION OF EXPERIMENTAL OBSERVATIONS AND RESULTS

5.2.1 ELECTROOSMOSIS

The accumulation of fluid at the top for columns with an electric potential applied over it

suggests the presence of electroosmotic flow (see Section 4.2). The pH over the conducting

medium was expected to be low and acidic, due to the generation of an acid front by

electrolysis. The acid front will dominate the system, due to the high mobility of hydrogen

ions (Acar & Alshawabkeh 1993).

When the pH of the leach solution becomes sufficiently low enough, specifically lower than

the point of zero charge (pH < pHPZC), the surface charge of the conducting media becomes

positive (Saichek & Reddy 2005). Therefore, the zeta-potential turns positive, while the

counter-ions at the electrical double layer are negative. By the H-S equation (Equation 2-8),

the velocity of the electroosmotic flow will be negative, or towards the anode. This results

in electroosmotic flow towards the top of the column.


n

Since the composition of the copper oxide compost is unknown, its pHPZC could not be

determined. Assume that the conducting medium contains a high proportion of copper(II)

oxide, with the pHPZC for copper(II) oxide being 9.5 (Lewis 2000). Since the pHPZC is basic,

the generation of acid front will result in electroosmotic flow towards the anode (at the top),

as explained above.

In a similar experiment to this project’s, Burns & Wright (1993) were able to enhance

percolation of leach solution through a column of low grade gold ore and a tailings deposit

through electroosmosis. In contrast to the observations in the experiments of this project, the

leach solution (cyanide) travelled downwards from the anode to the cathode. This was due

to the negative surface charge of the ores (Burns & Wright 1993).

The electroosmotic flow observed in the experiments could not be quantified as the

apparatus were not designed to do so. The occurrence of electroosmosis or ponding was not

desired. Due to fluid accumulation at the top, not all leach solution was in direct contact

with the conducting medium. This would significantly reduce the amount of copper that

could be leached out.

Obviously, the accumulation of fluid could be avoided by reversing the polarities of the

electrodes. However, this presents another problem – electromigration where the cations

(including copper ions) travel upwards to the cathode. This would make the copper much

more difficult to extract. An alternative or better way would be to use larger-sized ores. Due

to the larger pore spaces present, less capillary forces will be subjected to the leach solution,

while electroosmosis flow can be overcame by gravity.


5.2.2 CHANGES IN PHYSICAL CHARACTERISTICS OF LEACH SOLUTION

With the exception of the sample from the experiment using acid, all other samples did not

exhibit any traces of blue colour, which is a characteristic of copper(II) ions (Greenwood &

Earnshaw 1997). Hence, copper concentrations in the samples were very low. Consequently,

it is unlikely that copper ions are the reason for the formation of white precipitates at 20 V

or the yellowish solution at 40 V, due to the small amount that is leached out.

When an electric potential is applied over a conducting medium, electrolysis occurs to form

hydrogen ions and hydroxide ions. Over a conducting medium, hydrogen ions will be more

dominant than hydroxide ions due to their greater mobility (Saichek & Reddy 2005). The

formation of these two ionic species was most likely the precursor for the change in

physical characteristics of the leach solution. Conversely, it can also be deduced that the

experiments with zero applied electric potential did not observe the formation of such

substances because no hydrogen ions or hydroxide ions were generated.

White precipitates were observed at 20 V (see Section 4.5). This was probably due to the

formation of hydroxide compounds, more specifically, iron(II) hydroxides which are white

in colour and insoluble. Since hydroxide ions were produced at the cathode, the hydroxide

compounds concentrated at the bottom of the column. Hence, the white precipitates were

found mostly in the ‘first 250 ml’ samples, since the solution at the bottom was the first to

drain out.

At 40 V, due to the greater intensity of electrolysis reactions, the hydrogen ions were more

dominant compared to at 20 V. So, the influences of the hydroxide ions were significantly

reduced, leading to almost no formation of white precipitates. Instead, a yellowish solution

was formed. This yellow colour is indicative of iron(II) or iron(III) ions. Since the

hydroxide ions were less present at 40 V, it is likely that the iron ions formed salts with


n

chloride ions, giving iron(II) chloride or iron(III) chloride compounds which are yellowish

or brownish.

Assuming that the above speculations are correct, it can be said large amounts of iron were

also leached out by the leach solution. Therefore, the copper oxide compost contains a large

amount of iron compounds, and also significantly more than copper compounds.

5.2.3 ELECTROMIGRATION

As mentioned in Section 4.6.2, the copper concentrations of the ‘first 250 ml’ samples were

higher than the ‘after first 250 ml’ samples most of the time. Since most of the solution of

the ‘first 250 ml’ samples drain out directly from the bottom part of the column or medium,

it can be deduced that a high proportion of copper ions gather near the cathode.

This can be explained by the application of electrokinetics over the conducting medium.

Cations (including copper ions) travel towards the cathode due to electromigration.

5.2.4 Effects of Applied Electric Potential and Leaching Times

Figure 4.5 showed that the total copper concentration of the leach solution increased with

the applied electric potential over the conducting medium. This clearly proves that water, in

fact, can be used as a leach solution under electrokinetic conditions to extract copper from

its ores. Although the results do not clearly show a correlation, it was expected that the

copper concentration will increase with leaching time due to the longer contact time

between the leach solution and copper ores.


A conclusive statistical relationship between the (recovered) copper concentration and both

applied electric potential or leaching time could not be established (see Section 4.6.2). As

suggested, the reason for this was most likely the use of different batches of compost in the

experiments.

5.3 FEASIBILITY OF WATER AS LEACH SOLUTION

5.3.1 COMPARISON OF THE USE OF WATER AND DILUTED ACID

Despite being able to leach copper under electrokinetic conditions, the use of water as a

leach solution was highly inefficient compared to using just diluted sulphuric acid solution.

The use of acid was able to recover copper with concentrations 10 – 70 times higher than

that by water and electrokinetics (see Table 4.7).

Assuming that increase in applied electric potential does indeed increase the concentration

of copper, then an extremely high voltage or electric potential would be required in order for

water to replicate the leaching rates achieved by acid. Judging by this, it was concluded that

the use of water under electrokinetic leaching conditions is not feasible.

Due to a lack of available references, a comparative analysis of the economic benefits and

environmental impacts between using water as a leach solution with electrokinetics or just

by using acid was not conducted.


n

5.3.2 APPLICABILITY TO FIELD

While water is much safer to handle than acid, the application of electrokinetics is not.

Considering the large amounts of electricity required to achieve competitive leaching rates

by water and electrokinetics, problems such as electrical safety and high maintenance costs

will arise. Furthermore, the acidic leach solutions used in copper hydrometallurgy are

typically diluted, in which the risks presented may not be as high.

Besides that, common leaching methods such as heap leaching and dump leaching both

operate under unsaturated conditions. Since the experiments in this project were conducted

using saturated leaching columns, the complications of unsaturated conditions is unknown.

However, the feasibility of using water and electrokinetics under unsaturated conditions is

expected to be extremely low. Due to the lowered conductivity, the electrolysis of aqueous

solutions will become extremely difficult. Hence, very little acid will be generated.

Ignoring infrastructural and maintenance costs, for the use of water as a leach solution to be

more economic than using just acid, the electricity cost of the leaching operation have to be

lower than the cost difference between acid and water.

5.4 BARRIERS TO PROJECT

5.4.1 EXPERIMENTAL FAILURE

Experimental failure was observed for the experiment with an applied electric potential of

80 V for 4 days (see Sections 4.2 and 4.6). The copper concentrations obtained were lesser

than expected, roughly equivalent to those by experiments with 20 V for the same duration.


It was very likely that experimental failure occurred halfway through the experiment. From

Figure 4.1, it can be seen that some fluid did accumulate at the top of the leaching column.

However, the amount of accumulation was only roughly half of that from other experiments

of the same duration but lower applied electric potentials. This could either mean that:

i. The electric potential applied over the conducting medium stopped, and the accumulated

fluid is draining back into the column; or

ii. The applied electric potential was very low.

For either reason, the experimental failure could possibly be due to faulty EKG layers, or

improper/damaged wire connections.

5.4.2 LIMITATIONS OF COPPER MARINE AQUARIUMS TESTS

Section 4.6.1 described some of the shortcomings of using copper marine aquariums tests.

The effective measuring range of was found to be limited, while the test will not work for

samples with strong background colour. More importantly, the copper concentration results

produced were found to be very inconsistent.

The reason for the inconsistency of results is possibly due to the acidity of the sample

solutions. For the sample corresponding to the experiment using sulphuric acid solution, the

aquariums test indicated a very low copper concentration. Conversely, the laboratory

analysis showed that the copper concentration was, in fact, much higher than other samples.

From the results of the laboratory analysis, coupled with the observed bluish solution

(indication of the presence of copper(II) ions), it was concluded that the aquariums test is

inaccurate and unreliable for acidic samples.


n

5.4.3 LIMITATIONS OF APPARATUS AND EXPERIMENTAL PROCEDURE

Due to the simple apparatus design and experimental procedures, a couple of useful

variables were not measured. These include pH and conductivity. If possible, pH should be

measured at several points along the column’s length. This allows the generated acid front

to be monitored, as well as to estimate the efficiency of the leaching process. On the other

hand, mass transport rates can be determined by measuring conductivity of the conducting

medium.

Transparency of the leaching column could be useful for the observation of the leaching

reactions occurring within the medium. However, due to being expensive and hard to

construct, this feature was scrapped from the apparatus design.

5.4.4 SIZE OF EXPERIMENTAL DATA

The biggest weakness of this project is undoubtedly the small size of experimental data

collected. This was due to the severe time constraints and technical difficulties encountered

over the course of this project.

This problem was particularly evident in Section 4.6, in which correlations between the

recovered copper concentration and applied electric potential/leaching time could not be

established. In some cases, it might be necessary to repeat the experiment in order to verify

the results.

74747474 Chapter 6: Conclusions and Recommendations

Chapter 6: Conclusions and Recommendations

The feasibility of using water as a leach solution under electrokinetic leaching conditions was

evaluated through a series of column leaching tests. The idea of this project was to use the

electrolysis phenomena observed in electrokinetic applications to generate an acid front. This

front will, in turn, be responsible for the leaching of metals from their respective minerals.

This project should be considered as a pilot study and uses the hydrometallurgical leaching of

copper as an illustrative example. Experimental results show that water, or more specifically

1.0 M sodium chloride solution, was able to leach copper from the ores through electrokinetic

application. The copper concentration of the solution at the end of the experiments was found

to increase with increasing applied electric potential, albeit with no clear relationship. This

was very likely due to the different batches of ores used for the experiments.

Electroosmosis and electromigration were both observed in the experiments. In particular, the

accumulation of electroosmotic flows at the anode. Also, the application of electrokinetics

also resulted in formations of white precipitation or yellowish colour in the leach solutions.

These were likely due to the presence of hydroxide compounds and iron compounds in the

solution respectively.

Despite copper was successfully leached out and recovered, the use of water coupled with

electrokinetic leaching is currently unrealistic due to the low feasibility. A similar experiment

using just diluted sulphuric acid without an applied electric potential yielded a concentration

of copper 10 – 70 times higher than that by water with electrokinetics. For water to achieve

the same leaching rates, the applied electric potential would have to be extremely large, and

this poses issues such as safety as well as maintenance and operational costs.

75757575 Chapter 6: Conclusions and Recommendations

6.1 RECOMMENDATIONS FOR FUTURE STUDIES

Further studies into this topic should focus on increasing the overall feasibility of using water

as a leach solution under electrokinetic leaching conditions. It is also important that efforts are

made to develop better methods and leaching techniques in order to improve leaching rates as

well as the efficiency of the electrokinetic leaching process.

Alternatively, this project can be expanded to investigate the possibility of using a variety of

different sources of water as a leach solution, including sea water and groundwater. The use of

such sources, if possible, may represent huge cost savings towards the mining industry. Work

could also be done to optimise the electrokinetic leaching process by varying the size of the

ores or using different concentrations of salty solution. Also, modelling of the electrokinetic

leaching processes could be useful.

Ultimately, the priority of future studies is to implement water as a feasible leach solution to

use for electrokinetic leaching. Although this project currently suggests that this was not

feasible, it must be noted that this field is still in its infant stages, and there is still lots of room

for improvement.

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80808080 Appendices

Appendix 1: Electrical Equipments and Chemical Reagents

Packing /

Quantity Model / Brand name

Electrical Equipments

Conductivity, TDS, pH, mV,

temperature meter 1x TPS WP-81

Electronic balance (up to 300 g) 1 x AND FX-300

Electronic balance (up to 21 kg) 1 x AND GX-20K

Magnetic stirrer

with PTFE coated plate 1 x IEC CH2081-008

Peristaltic pump 1 x Masterflex L/S model 7519-10

Power supply 1 x Powertech Model MP-3092

Water purifier 1 x Elga Option 3

Chemical Reagents

98.07% concentrated sulphuric acid 5 L Univar Analytical Reagent A8301-5L

Sodium chloride 5 kg Univar Analytical Reagent A464

Copper marine aquariums test lab 55 tests Red Sea

Miscellaneous

Rubber Coating 450 ml Heavy Duty Flexible Rubber Coating

PLASTI DIP

Table: List of electrical equipments and chemical reagents used in the experiments.

81818181 Appendices

Appendix 2: Diagram of Leaching Column

Top cap

Filter plate

(with 50µm filter)

Electrokinetic

geosynthetic

(EKG) layer

Bottom cap

(with valve)

Glands

82828282 Appendices

Appendix 3: Preparation of Leach Solutions

Leach solution: 1.0 M sodium chloride aqueous solution

Molar mass of sodium chloride NaCl = 58.4425 g/mol

Hence, to produce 1.0 M sodium chloride solution NaCl (aq), the weight of sodium chloride

NaCl (s) needed for dissolution in 1 L of pure water

= Volume x Molarity x Molar mass

= 1 L x 1.0 M (mol/L) x 58.4425 g/mol

= 58.4425 g

A 1.0 M sodium chloride aqueous solution has an equivalent TDS of 58442.5 ppm.

Leach solution: 1.0 M sulphuric acid

Molar mass of sulphuric acid H2SO4 = 98.0785 g/mol

Density of sulphuric acid H2SO4 = 1.84 g/cm3

= 1840 g/L

Hence, to produce 0.5 M sulphuric acid H2SO4 (aq), the volume of 98.07% concentrated

sulphuric acid H2SO4 (l) needed for dilution in 1 L of pure water

ml 27.2

L 0.0272

g/L 1840% 98.07

g/mol 98.0785(mol/L) M 0.5L 1

gravity Specificacid edconcentrat of percentage Mass

massMolar acid diluted ofMolarity Volume

==

×××=

×××=

83838383 Appendices

Appendix 4: Calculation of Porosity

Height4

DiameterπVolume

2

××=

Volume

MassdensityBulk =

Particle density was estimated simply by Archimedes’ principle.

density Particle

densityBulk 1Porosity −=

VolumePorosity volumespace Pore ×=

Leach

solution 1.0 M sodium chloride aqueous solution

0.5 M

sulphuric

acid

Duration 2 days (48 hours) 4 days (96 hours)

Voltage

(V) 0 20 40 0 20 30 40 80 0

Mass

(kg) 7 7 7 7 7 7 7 7 7

Height

(cm) 52.3 52.4 51.3 52.7 52.6 52.1 53.3 52.6 51.9

Diameter

(cm) 10.2 10.2 10.2 10.2 10.2 10.2 10.2 10.2 10.2

Volume

(cm3) 4274 4282 4192 4306 4298 4257 4355 4298 4241

Bulk

density

(g/cm3)

1.638 1.635 1.670 1.626 1.629 1.644 1.607 1.629 1.651

Particle

density

(g/cm3)

2.222 2.222 2.222 2.222 2.353 2.353 2.353 2.353 2.353

Pore

space

volume

(cm3)

1124 1132 1042 1156 1323 1282 1380 1323 1266

Porosity

(%) 26.291 26.432 24.855 26.851 30.783 30.119 31.692 30.783 29.850

Table: Calculated values of bulk density, particle density, and porosity for all experiments.

84848484 Appendices

Appendix 5: Laboratory Analysis Results

The following table lists out the Sample IDs of each sample tested.

Leach solution Duration Applied

electric voltage Sample Sample ID

0 V First 250 ml Q3588-01

First 250 ml

Q3268-01

Q3588-02

Q3588-03

Q3588-04

Q3588-05 20 V

After first 250 ml Q3588-06 Q3588-07

2 days

40 V First 250 ml Q3268-02

Q3588-08

Q3588-09

Q3588-10

First 250 ml

Q3588-11

Q3588-12

Q3268-03

Q3268-04

Q3268-05

Q3268-06 0 V

After first 250 ml Q3268-07

Q3268-08 Q3268-09

First 250 ml Q3268-10

Q3268-11 Q3268-12

20 V


Q3269-02

Q3269-03

Q3269-11

First 250 ml Q3269-04 Q3269-05

30 V After first 250 ml

Q3269-06

Q3269-07

Q3269-08

Q3269-09

Q3269-10

First 250 ml Q3269-12

Q3270-01 Q3270-02

40 V


Q3270-04

Q3270-05

Q3270-06

First 250 ml

Q3270-07

Q3270-08

Q3270-09

Q3270-10

Q3270-11

1.0 M sodium

chloride aqueous

solution

80 V


Q3271-01

Q3271-02

Q3271-03

First 250 ml Q3271-04 Q3271-05 0.5 M sulphuric

acid solution

4 days

0 V After first 250 ml Q3271-06

Table: Sample IDs of each sample corresponding to each experiment.

Matrix: WATER REG REGWorkgroup: EP0704025 EP0704025001 EP0704025002

Project name/number: BD0002 04/09/2007 04/09/2007Q3588-01 Q3588-02

Analyte grouping/Analyte CAS Number Units LOR

ED040T: Total Major AnionsSulphate as SO4 2- 14808-79-8 mg/L 1 <10 30Sulphur as S 63705-05-5 mg/L 1 <10 <10

ED045G: Chloride Discrete analyserChloride 16887-00-6 mg/L 1.0

ED093T: Total Major CationsCalcium 7440-70-2 mg/L 1 62 125Magnesium 7439-95-4 mg/L 1 13 26Sodium 7440-23-5 mg/L 1 20800 20800Potassium 7440-09-7 mg/L 1 170 65

EG005T: Total Metals by ICP-AESCopper 7440-50-8 mg/L 0.01 0.29 11.4Manganese 7439-96-5 mg/L 0.01

Client sample ID (2nd):Site:

Purchase Order:

Sample Type:ALS Sample number:

Sample date:Client sample ID (1st):

REG REG REG REG REG REG REG REGEP0704025003 EP0704025004 EP0704025005 EP0704025006 EP0704025007 EP0704025008 EP0704025009 EP070402501004/09/2007 04/09/2007 04/09/2007 04/09/2007 04/09/2007 04/09/2007 04/09/2007 04/09/2007Q3588-03 Q3588-04 Q3588-05 Q3588-06 Q3588-07 Q3588-08 Q3588-09 Q3588-10

29 29 31 33 32 90 90 89<10 <10 10 11 11 30 30 30

125 124 127 44 44 2 2 126 26 26 <1 <1 <1 <1 <120500 20400 21700 21200 20900 24700 24700 2430053 52 53 62 63 64 64 64

11.5 11.5 11.7 0.32 0.21 22.1 22.6 21.0

REG REG REG REG REG REG REG REGEP0704025011 EP0704025012 EP0704025013 EP0704025014 EP0704025015 EP0704025016 EP0704025017 EP070402501804/09/2007 04/09/2007 04/09/2007 04/09/2007 04/09/2007 04/09/2007 04/09/2007 04/09/2007Q3588-11 Q3588-12 Q3587-01 Q3587-02 Q3587-03 Q3587-04 Q3587-05 Q3587-06

19 17 <10 <10 <10 <10 <10 <10<10 <10 <10 <10 <10 <10 <10 <10

269 279 282 280 258 258

102 102 2 2 2 1 1 228 28 <1 <1 <1 <1 <1 <121700 21400 194 181 170 162 144 14267 65 <1 <1 <1 <1 <1 <1

7.45 6.950.13 0.11 0.17 0.18 0.14 0.19

REG REG REG REG REG REGEP0704025019 EP0704025020 EP0704025021 EP0704025022 EP0704025023 EP070402502404/09/2007 04/09/2007 04/09/2007 04/09/2007 04/09/2007 04/09/2007Q3587-07 Q3587-08 Q3587-09 Q3587-10 Q3587-11 Q3587-12

<10 <10 <10 <10 <10 <10<10 <10 <10 <10 <10 <10

259 270 250 248 254 265

2 2 2 1 1 2<1 <1 <1 <1 <1 <1140 142 143 140 143 142<1 <1 <1 <1 <1 <1

0.14 0.14 0.22 0.17 0.17 0.21

False

CERTIFICATE OF ANALYSIS

Work Order : EP0704025 Page : 1 of 7

:Amendment 1

:: LaboratoryClient Environmental Division PerthGOLDER ASSOCIATES

: :ContactContact MR ED JONES Michael Sharp

:: AddressAddress PO BOX 1914 WEST PERTH WA AUSTRALIA 6872 10 Hod Way Malaga WA Australia 6090

:: E-mailE-mail [email protected] [email protected]

:: TelephoneTelephone +61 9213 7600 +61-8-9209 7655

:: FacsimileFacsimile +61 08 9427 7611 +61-8-9209 7600

:Project BD0002 QC Level : NEPM 1999 Schedule B(3) and ALS QCS3 requirement

:Order number ----

:C-O-C number Q3587 Date Samples Received : 06-SEP-2007

Sampler : ---- Issue Date : 13-SEP-2007

Site : ----

24:No. of samples received

Quote number : PEN-002-06 BQ 24:No. of samples analysed

This report supersedes any previous report(s) with this reference. Results apply to the sample(s) as submitted. All pages of this report have been checked and approved for

release.

This Certificate of Analysis contains the following information:

l General Comments

l Analytical Results

NATA Accredited Laboratory 825

This document is issued in

accordance with NATA

accreditation requirements.

Accredited for compliance with

ISO/IEC 17025.

SignatoriesThis document has been electronically signed by the authorized signatories indicated below. Electronic signing has been

carried out in compliance with procedures specified in 21 CFR Part 11.

Signatories Accreditation CategoryPosition

Alan Foley Senior Chemist - Inorganics Perth Inorganics

Environmental Division Perth

10 Hod Way Malaga WA Australia 6090

Tel. +61-8-9209 7655 Fax. +61-8-9209 7600 www.alsglobal.com

2 of 7:Page

Work Order :

:Client

EP0704025 Amendment 1

GOLDER ASSOCIATES

BD0002:Project

General Comments

The analytical procedures used by the Environmental Division have been developed from established internationally recognized procedures such as those published by the USEPA, APHA, AS and NEPM. In house

developed procedures are employed in the absence of documented standards or by client request.

Where moisture determination has been preformed, results are reported on a dry weight basis.

Where a reported less than (<) result is higher than the LOR, this may be due to primary sample extract/digestate dilution and/or insuffient sample for analysis.

Where the LOR of a reported result differs from standard LOR, this may be due to high moisture content, insufficient sample (reduced weight employed) or matrix interference.

When date(s) and/or time(s) are shown bracketed, these have been assumed by the laboratory for process purposes.

CAS Number = Chemistry Abstract Services number

LOR = Limit of reporting

^ = Result(s) reported is calculated using analyte detections at or above the LOR. (eg. <5 + 5 + 7 = 12).

Key :

LOR for samples (13-24) raised for Sulphate/Sulphur and Copper due to the limited volume of sample supplied. Dilutions were made to perform the analysis.l

LOR for samples (1-4) and (11-12) raised for Sulphate/Sulphur, due to the high amount of Sodium present.l

LOR for samples (2-9) raised for Manganese due to the high amount of Sodium present.l

This report has been re-issued to include Total Copper results.l

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Analytical Results

Sub-Matrix: WATER Q3587-01 Q3587-02 Q3587-03Client sample ID : Q3587-04 Q3587-05

04-SEP-2007 15:0004-SEP-2007 15:0004-SEP-2007 15:00Client sampling date / time : 04-SEP-2007 15:00 04-SEP-2007 15:00

EP0704025-001 EP0704025-002 EP0704025-003LOR UnitCompound CAS NumberEP0704025-004 EP0704025-005

ED040T: Total Major Anions

Sulphate as SO4 2- 1 mg/L <10 30 29 312914808-79-8

^ Sulphur as S 1 mg/L <10 <10 <10 10<1063705-05-5

ED093T: Total Major Cations

Calcium 1 mg/L 62 125 125 1271247440-70-2

Magnesium 1 mg/L 13 26 26 26267439-95-4

Sodium 1 mg/L 20800 20800 20500 21700204007440-23-5

Potassium 1 mg/L 170 65 53 53527440-09-7

EG005T: Total Metals by ICP-AES

Manganese 0.01 mg/L 0.15 <0.10 <0.10 <0.10<0.107439-96-5

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Sulphate as SO4 2- 1 mg/L 33 32 90 899014808-79-8

^ Sulphur as S 1 mg/L 11 11 30 303063705-05-5


Calcium 1 mg/L 44 44 2 127440-70-2

Magnesium 1 mg/L <1 <1 <1 <1<17439-95-4

Sodium 1 mg/L 21200 20900 24700 24300247007440-23-5

Potassium 1 mg/L 62 63 64 64647440-09-7


Manganese 0.01 mg/L <0.10 <0.10 <0.10 0.18<0.107439-96-5

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Sulphate as SO4 2- 1 mg/L 19 17 <10 <10<1014808-79-8

^ Sulphur as S 1 mg/L <10 <10 <10 <10<1063705-05-5

ED045G: Chloride Discrete analyser

Chloride 1.0 mg/L ---- ---- 269 28227916887-00-6


Calcium 1 mg/L 102 102 2 227440-70-2

Magnesium 1 mg/L 28 28 <1 <1<17439-95-4

Sodium 1 mg/L 21700 21400 194 1701817440-23-5

Potassium 1 mg/L 67 65 <1 <1<17440-09-7


Copper 0.01 mg/L ---- ---- <0.10 <0.10<0.107440-50-8

Manganese 0.01 mg/L 0.12 0.14 ---- --------7439-96-5

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Sulphate as SO4 2- 1 mg/L <10 <10 <10 <10<1014808-79-8

^ Sulphur as S 1 mg/L <10 <10 <10 <10<1063705-05-5


Chloride 1.0 mg/L 280 258 258 27025916887-00-6


Calcium 1 mg/L 1 1 2 227440-70-2

Magnesium 1 mg/L <1 <1 <1 <1<17439-95-4

Sodium 1 mg/L 162 144 142 1421407440-23-5

Potassium 1 mg/L <1 <1 <1 <1<17440-09-7


Copper 0.01 mg/L <0.10 <0.10 <0.10 <0.10<0.107440-50-8

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Analytical Results

Sub-Matrix: WATER Q3588-09 Q3588-10 Q3588-11Client sample ID : Q3588-12

04-SEP-2007 15:0004-SEP-2007 15:0004-SEP-2007 15:00Client sampling date / time : 04-SEP-2007 15:00

EP0704025-021 EP0704025-022 EP0704025-023LOR UnitCompound CAS NumberEP0704025-024


Sulphate as SO4 2- 1 mg/L <10 <10 <10 <1014808-79-8

^ Sulphur as S 1 mg/L <10 <10 <10 <1063705-05-5


Chloride 1.0 mg/L 250 248 254 26516887-00-6


Calcium 1 mg/L 2 1 1 27440-70-2

Magnesium 1 mg/L <1 <1 <1 <17439-95-4

Sodium 1 mg/L 143 140 143 1427440-23-5

Potassium 1 mg/L <1 <1 <1 <17440-09-7


Copper 0.01 mg/L <0.10 <0.10 <0.10 <0.107440-50-8

85858585 Appendices

Appendix 6: Estimation of Maximum Possible Total Copper

Concentration

Estimation of copper content in copper oxide compost: 7%

Each column contains 7 kg of 50:50 mixture of copper oxide compost and glass beads. So, 3.5

kg of copper oxide compost were used for each experiment.

Hence, for each column, the total copper content = 7%

= 7% × 3.5 kg

= 1.715 kg

= 1.715 × 106 mg

The pore space volume available in each column ranges from about 1100 – 1400 cm3.

Hence, approximately 1.1 – 1.4 L of fluid can be filled into the pores of the volume.

Assume that each column is saturated with 2 L (taken as upper limit) of leach solution.

So, the maximum possible total copper concentration that can be obtained from the column

mg/L 101.225L 2

mg 101.715

5

6

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Documents

Electrokinetic Applications in Hydrometallurgical Copper Extraction · 2011. 5. 26. · Copper Extraction Honours Dissertation November 2007 Loong Hey, Yoong 10447553 Supervisors: