~printed from The Physical O1emistryof Mineral-~a.qent Interactions inSUU:1,qe Flotation, U.S. Bureau of Mines,150IC8818, 1978

SELECTIVE FLOCCULATION OF FINES

by

P. Somasundaran'

ABSTRACT

Selective flocculation, followed by a conventional mineral processingtechnique such as flotation, e1utriation, or sedimentation, is a promisingtechnique for the beneficiation of mineral slimes. In this paper, a reviewof basic chemical and hydrodynamical aspects of dispersion, flocculation,and selective flocculation is presented along with a discussion of mechanismof adsorption of polymers with functional groups. Selective flocculationachieved in the past with sulfide minerals and the problems involved are alsodiscussed.

INTRODUCTION

In spite of the ever-increasing demand for mineral products, large&8J1.Jnts of fines and ulttafines generated during mining and milling are dis-carded today, mainly because of the inadequate technology for fines benefi-ciation. We are famii1ar with the incredible loss of mineral values asslimes in the nonmetallic minerals area. In the metallic minerals area also,there is considerable loss of mineral values as fines even though in a numberof cases fines have been claimed to be treated successfully. The Climax mineof Amax is reported, for example, to have achieved a'r~e:rY-~f; -9Q pct intheir flotation of 85 pct minus 44 ~m feed of ~lybdenit._ore,' buc. it is tobe noted that the loss is mostly in the minus 5 ~ size ftac~ion (5,9). Inthe case of Pentlandite/pyrrhotite flotation, on the other hand, c7 E7 Agarin a personal communication has indicated that there is hardly any benefi-ciation obtained in the minus 20 ~m size range. Data collected by Trahar andWarren (~) on the dependence of flotation of sphalerite particles on particlesize, in both operating mills and the laboratory (fig. 1), clearly show thatthe recovery becomes poor where the particles are smaller than about 10 ~m.

1Sl

100

i ~..;Q,

>" ~=~0 70CJtAl=CJ 80ZN

50

FIGURE 1. - Comparison of the batch

f1otation of spha1erite withdata from operating mi11s.Batch f1otation (-. - .),Anthony et a1., zinc ~ircuit atBroken HmSouth (-), (Cameraonet a1., 1979); zinc circuit atMOrning Mi11 (---) , (Gaudin, eta1., 1931). (After Traher an~'Wa'r ren (38). CoUlLte.61j, El.6 ev-i.e/tSdenUr;1:c: Pub.uc.a.t.ion Co.)

10 . 1~ -7. 5 50

PART1CI,a SZE. ".

A similar effect has been observed also for lead and copper recoveries. Ingeneral, recovery of sulfide ores in the minus 20 um size range is lower thanthat in the 100 by 20 um range; this is due partly to lower floatability offines, generally observed in all flotation systems. N. Arbiter, in a privatec~~ication, has also suggested that the lower floatability of fines ispartly due to the higher oxidation of such fines.

The opti~~ size range for flotation does depend to a great extent on thenature of the mineral. Trahar and Warren (38) report that for sulfides thesize range of ma~!mD recovery increases in ~e order, galena (6-70 um),sphalerite (8-90 um), pyrrhotite (9-40 ~), chalcopyrite (15-60 um, arsenopy-rite (15-120 um), and pyrite (20-150 um). Specific gravities of. these minerals(7.4-7.7, 3.9-4.1,4.6,4.1-4.3,5.9-6.2, and 4.95-5.1, respectively) do notshow any significant correlation with the mnn;mum or maximum limit of theoptimum size range for flotation. Evidently the fines, due either to theirsmaller size or to changes in their surface composi tion and properties,respond poorly to flotation, resulting in loss of mineral values that we canill afford. If the reason for the decreased efficiency of fines flotation isthe smaller size and the resultant lower collision and adhesion rates, theobvious solution is to aggregate the fines into coarser particles. Even ifsurface chemical changes such as oxidation are resp~ip'.1e r .aggregation of thefines before such preflotation treatments as sulfidiza~on might still bebeneficial. . .

BACKGROUND

lundamentals of Selective Ag~e~ation

For selective aggregation, first of all it is necessary that at leastone component is in complete dispersion. It is also necessary that there isa maximum possibility for aggregation among the particles of the other com-ponent, with very little aggregation between the particles of the componentsthemselves. Conditions for this b~ome evident when one examines. the proper-ties that govern interactions between the particles.

Colloidal particles in a system collide due either to Brownian motion orto external forces introduced by agitation, magnetic field, etc. Probability

152

of adhesion during such collision will be determined by the nature of thetotal interactions between them. The repulsive interactions arise eitherfrom the overlap of similarly charged electrical interfaces or from that ofadsorbed layers that prefer to be in contact with the solvent. The nature ofrepulsive interactions is, for this reason, determined to a great extent bythe nature of the medium. Attractive interactions, on the other hand, arisefrom London dispersion forces, Keesom forces, and Debye forces and also fromthe steric compatibility between the adsorbed layers; the London-Van der Waalsforces are not so much dependent on the nature of the medium as are the elec-trostatic forces. In accordance with the DLVO theory and HHF theory (14), thefollowing expression is given for the total energy, VT' in terms of the-London-Van der Waals forces, VV' electrical forces, VE' steric forces Vs' andbridging forces, VB:

VT. Vv + VE + Vs + VB

-Arlr2Q

6(rl + r2)Ro

rlr2.£ 1 + exp(-ICHo)+

4(rl + r;;E.l.21n 1 - exp(-KHc)

(1)+ (W12 + .22)lu{1 - exp(-2KHo)} + Vs + VB

19here rl and r2 are radii of the two particles, ~l and ~2 are surface poten-tials, and H is distance between their surfaces. A, the Hamaker constant,0is the average for particles I and 2 in medium 3 and is given by A - Al2 +A33 - A13 - A23. £ is the dielectric constant, and IlK is the double layerthickness. a is a factor that takes into account the retardation of Londonforcea under conditions of aggregation in secondary minimum (~). Vs can bepositive or negative, depending on the solvent power of the medium for theadsorbed layer, and VB can be considered to be always ~negative. Excluding'Vsand VB' it can be seen from equation I that VI will be ~:rActiye ~at largeand small distances, since the exponential of -KHo will bersmal~e~ .than theinverse power of Ho for large and small Ho. Typical variation of VI as afunction of distance between particles is illustrated in figure 2. Th~bottom curve is for particles with negligible electrical repulsion betweenthem and the upper curves for conditions with increasing amounts of repulsionbetween the particles. On the basis of these considerations of total energy,we can derive the following conditions for selective aggregation:

1. Both type of particles should carry the same charge so that therewill be no heterocoagulation between them. Repulsive energy should be largerin magnitude than the attractive energy.

2. Charge on the particles to be aggregated should be such that repul-sive energy between them should be less than that of the attractive energy.

Conditions 1 and 2 can be met if the potential of the component to beaggregated is in the range of t 10 to 20 mY and the potential of the other

1.53

+REPULSIONENERGY

FIGURE 2. - Sum of repu1sive and at-

tractive interactions betweenpartic1es as a function of dis-tance of separation between themunder various conditions.

Distancebetweenpartldes-

ATTRACTIONENERGY

component is about 40 or 50 mv with the same sign for the potential as that ofthe first component. This can be achieved by appropriate control of theionic composition of the medium. Aggregation achieved in this manner iscalled selective coagulation as opposed to selective flocculation that isachieved normally with the help 0 f polymers.

3. Polymers when adsorbed on the particles can essentially shift thesurface of contact between them so that the electrical nature of the inter-faces, which might not have been originAlly conducive for selective aggrega-tion, assumes a secondary role. Evidently success of the use of polymerswill depend upon selective adsorption on the mineral partic~es to beflocculated.

A major fac~or tha~ affec~s the se1ec~iviry of ~be aggrega~ion is ~hein~erference by the dissolved chemical species of one par~icle on accoUD~ ofeither i~s adsorp~ion or precipi~a~ion on ~he others. The significance ofthis effec~ was clearly shown recently by the authors for the ca1ci~e/apa~ite/olea~. sys~em (1). S~ring of one component on the o~her during 8rinding- ..will also cer~ainly reduce selectiviry. ~~-" '0' ".-

",.. " ".

Adsorption of Pol~rs and noccu1a~ion

The fundamentals of adsorption of polymers and its role in fiocculationhave been recently reviewed by Sresty and co-workars (~), and salient aspectsof their review are presented here. Adsorption of polymers on minerals andthe rate involved are dependent to a large extent on the polymer propertiessuch as the molecular weight, the nature and concentration of the functionalgroups and configuration, the mineral properties such as surface charge andoxidization state, and the solution properties such as ionic strength andsolvent power for the polymer. This dependence of adsorption on propertiesof polymer, particles, and solution can be exploited in the beneficiation ofslimes using selective flocculation.

Forces responsible for polymer adsorption arise mAin1y from electro-static, hydrogen, and covalent bonding. In the case of a polymer with a

1.54

large number of charged units, ~ectrostatic bonding is the predominantmechanism. The role of ~ectrostatic forces are illustrated in figure 3,which shows the results obtained in our study of flocculation response ofnegatively charged synthetic s~ica (Bios~-A) to anionic (Separan AP-30) andcati.onic (Nalcolyte-6l0) polyacry1a:m.1des2 ~). As can be seen from thefigure, silica particles undergo excellent flocculation in the presence of thecationic polymer. The stability of the suspension is not, however, affectedby the anionic polymer. A polymer can also flocculate similarly chargedpar~icles provided the magni.tude of the interfacial potential is not veryhigh (1!). Under such conditions, tba ~ectrostatic repulsive forces are notstrong enough to prevent the par~icles from coming within the polymer bridgingrange of each other.

100

.. NALCOLYTE - 610

. SEPARAN - AP30pH = 3.5 to 3.6

-c.

~!.Qw..J~W(I)(I)Q~0(I)

..~.;,.' '.

-"f.

~O1800 60 120

POLYMER CONCENTRATION, ppm (dry solids basis)

FIGURE 3. - Percentage of synthetic si1ica settled as a function of concen-tration of Nalcolyte-610 and Separan AP-30; reagentizinq time. 30 seconds;sett1ing time. 45 seconds (~). (Co~e4Y. CRG P4e64.)

2The suspension was conditioned with polymer for 30 seconds and allowed tostand for 45 seconds. The weight-percent of solids that settled into thebottom one-third volume fraction of the original suspension is taken as ameasure of the flocculation. Additional experimental details are given byGaudin and Maloz~ff (g).

75

155

The role of electrostatic adsorption in the selective flocculation ofgalena from some other minerals has been discussed by Yarar and Kitchener (42).They noted that galena flocculation using an anionic polyacrylamide can be pro-moted by the addition of lead nitrate and inhibited by addition of sodiumsulfide. Most interestingly, it was also observed that galena dried in con-tact with air did not undergo selective flocculation from quartz, presumablydue to the fact that in a medium containing oxidized lead salts, the zetapotential of galena will be zero and hence it can also undergo coagulationwith quartz. Similarly, no selective flocculation could be obtained with amixture of galena and calcite in the absence of other additives, since thezeta potentials of these minerals are not sufficiently high at natural pH toproduce required dispersion of fines prior to selective flocculation.

Non1onic polymers can adsorb on particles by formation of hydrogen bondswith the surface oxygen species of the mineral. Flocculation by interparticlebridging follows such adsorption of polymers when the electrical double layerrepulsion between the particles is not very strong.

Selective adsorption of polymers can also be achieved if adsorption isdue to covalent bonding between the active groups of the polymer and thecations of the mineral surface. Such flocculation of kaolin by polyacryla-mides owing to the formation of salt-type compounds by reaction between thepolymer and the Ca+2 ions present in the kaolin has been reported by Michaelsand Morelos (~).

Kinetics of Adsorption

The kinetics and nature of adsorption of polymers on particles are depend-ent on a number of interrelated properties of the polymer. the suspendingmedium. and the particles (~).

The kinetics of adsorption of polymeric molecules on mineral particlesare controlled mostly by the rates of diffusion of these molecules to the sur-face of the particles and are, therefore, influenced by agitation.

..We have observed that even the ~oncentration of ~ae' '~~lymer has a major

role in determining the kinetics of its adsorption (see~~ig 4) t~). The

6100 ppm PAA -,.p.~e ~

e-;.e>I-inz'"QZ0~

FIGURE 4. - Adsorption kinetics ofpo1yacry1amide on ka01inite. (~)

I. 5x10-'M NaCIpH - 4.~0.2

Solids. 10%Temp. - 30:0.5' C

.2 ,.," A A Q 6

0 . .1 10 100 1,000 10.000

ADSORPTION TIME. min

POL Y ACRYLAMIDE/KAOLINITE

01,gOQ ppm PAA1.0

.8

.8

.4

156

suspending medium, being a solvent for the polymer molecules, has a very im-portant role in determining rates of adsorption of these molecules on thesuspended mineral particles.

When a poor solvent is used, the rate of adsorption of the polymer isgreater, owing to the weak interaction between the polymer molecules and thesolvent. The kinetics and extent of adsorption are dependent also on thespecific surface area and chemical nature of the particles. Adsorption ratesare lower for porous particles with large specific surface, and equilibriumis, therefore, established slowly (1&, I[).

Selective Adsorption and Flocculation

Selective adsorption of polymer molecules on particles can be achievedby (1) adjusting the chemical composition of the suspending medium (deter-mines surface charge on the mineral) in order to exploit the dependence ofadsorption of ionic polymers on surface charge, (2) introducing into thepolymer active functional groups that will form complexes or salts with themetal atoms on the surface of the desired mineral, and (3) using depressantssuch as sodium silicate that would adsorb on the undesired mineral surface,thereby preventing adsorption of polymer, or using activators that induceadsorption of polymers on desired minerals.

K'Jz~~n and Nebera proposed that adsorption of ionic polymers on simdlarlycharged miner~ surfaces cannot take place if the interfaci~ potential issufficient to introduce electrostatic repulsions arising from double layerinteractions (19). A noteworthy example of the application of this principleis the selective flocculation of hematite from its mixtures with quartz usinganionic polyacrylamide (lQ). Even though adsorption of the polymer on quartzparticles is expected on account of the dominance of amdde groups in it, thestrong electrostatic repulsion between negatively charged quartz particlesand the polymer apparently prevented its adsorption on quartz surface.

It is well known that adsorption of froth flotatiop collectors and modi-fiers on particles depends on active groups present in ~h~ collec~or or modi-

. " . - .fier molecules. The chemical aspects of polymer adsorptiqu'are,- ~ severalways, s~ar to those of collectors. Thus in the past, ~lectivity has beenobtained by incorporating active groups such as carboxylate, sulfonate, andmercaptan (~, ~). Incorporation of an ~roper active group, on the otherhand, can also result in loss of selectivity, and an example illustrating thisis that of modified starches discussed by Cooke and co-~~orkers (4). Starcheshave been well known to flocculate hematite in preference to quartz. Corn-starch modified to contain aminoethy1 group was found to flocculate both hema-tite and quartz, because the presence of am!noethy1 group causes the starchto adsorb on quartz particles as well.

Response of minerals to flocculation can be enhanced or retarded whennecessary by the addition of metal cations that adsorb on the mineral parti-cles and activate or depress them. For example, separation of hematite-quartz mixture by selective flocculation using anionic p~lyacrylamide hasbeen reported to be effective after addition of calgon and sodium fluoride ~.

157

Also Attia and Kitchener have reported the possibility of depressing floccu-lation of heavy minerals by xanthates using depressants such as sodium sulfide~polyphosphates, and polyacrylates (1).

Interparticle Bridginv. and Surfaca Coverav.e

Interparticle bridging, preceded by adsorption of polymer species, resultsin the progressive buildup of the fine particles into three-dimensional net-works. A complete surface coverage of the particles by polymer molecules isreported to result in stabilization of the suspension by protected colloidaction (!I, ~). Stability of suspension resulting due to complete coverageof the particles by adsorbed polymer molecules is called steric stabilizationand can be avoided only if the net change in Gibbs free energy due to inter-penetration of the polymeric chains is negative (25). For flocculation toproceed, the increase in entropy due to release o~ solvent molecules shouldoutweigh the loss of entropy due to interpenetration of polymeric chains andincrease in enthalpy due to increased degrees of freedom attained by the re-leased solvent molecules.

The fraction of solid surface covered by polymer molecules is dependenton the time of reagentizing of the mineral with the polymer solution at agiven polymer concentration. Figure 5 shows the flocculation response of hema-tite towards Separan AP-30 as a function of time of conditioning the mineralwith the polymer solution (~). Results shown in this figure indicate that the

+pHa78... pH a 4.0

Polymer dosage = 30 ppm

. .c~u~!.

QIU~

~IUcncnQ;:j0cn

-.. -.

":~:' "

oJ\.

.

0 1,200 1~00

CONDITIONING TIME, sec

FIGURE 5. - Percentage of hematite fines settled as a function of time of re-

agentizing with Separan AP-30; settling timet 45 seconds (36). (Co~tte4Y.Na.ci.ona.t-Pub.uc.a.c.oe.6 e. Pl.LbUdda.de., 8Ita4.i.t.) -

600 2.400

158

... CHALCOPYRITE pH a 3.61

.. QUARTZ .pH a 1.0

c.i

Q

~l-I-IIaIn

InQ

~

QIn

FIGURE 6. - Percentage of quartz finessett1ed as a function of time ofreagentizing with Separan AP-30;sett1ing time, 45 seconds (36).( Co uILt ~ IJ, Na.ci.o nal;- PubUc.ac.o ~ ePubV-c..i.dade, 8Jta..6il.)

. I . I . I I . I . " I

1.~

1.20 Ib/-...~ g =~!AI...c~

z0~c...0-'~

'4~---e o-o-o:;' ~

0.00 Ib/*t.03 .

. I . I . I . I . I . I I

+1.25 +2.5 .5.0 +10.0 +20.0 .21.3- 1.77 -3.54 - 7.07 -1C.1C - 21.3 -..0

PARTlC1.E DIAMETER. Jim

,01

0 - ioo 200 300XANTHA ~ eOtit:.: pPat~ dry IOIId8 b88i8)

,.' 1... .

FIGURE 8. - Percentage,of chalcopyritefines and quartz fines set.tled asa function of concentration ofhydroxypropyl cellulose xanthate;reagentizing time, 30 seconds;sett1ing time, 45 seconds (j2).(CoulLtUlj, Na.c.i.ona.l. PubUc.a.c.oe.6 e.PubUc..ida.de., Blr.a.6il.)

FIGURE 7. - Specific flotation rate ofgalena as a function of particlesize without collector and at twoconcentrations of potassium ethyl-xanthate (12). (CoulLte6lj,AmeJLic.an Cnem.<:.c.a.t. Sode.tlj. )

.30

.10

159

metastable state corres~onding to mAYimum flocculat~on is reached within shortper~ods of reagentizing. Prolonged reagent~zing causes redis~ersion of theflocculated mass. In the case of quartz, bDwever, m~~mum flocculation isobtained only at relatively longer periods (fig. 6). Such differences intime for mAYimum flocculation can be used profitably in achieving selectiveflocculat~on.

The ~nterpart~cle bridging ~ght be more effective if polymer moleculeshave an extended chain conformation. Polymers generally assume a highlycoiled conformat~on at their isoelectric points, and a sl~ght excess of eitherthe posit~ve or negat~ve sites can sufficiently extend the polymer chain;this ~ght improve the polymer' s abi~ty to produce interpart~cle bridging.

Rvdrodvnamic Aspects

Under most practical conditions, the probability for adhesion duringco1l1sion can be A~hAnced by providing sufficient kinetic energy by stirring.Flocculation assisted by such external forces is known as orthokinetic floccu-lation. Under turbulent conditions, part~c1es undergo collisions with eachother due either to diffusion while entrained in eddies or to inertia. Forcolloidal particles Levich' s ClQ) theory predicts the collision rate underturbulent conditions, J turb' to be

- 12'1fSr3u; (~Jl/2J (2)turb

where S is a constant, ni is the initial concentration of particles, £0 isthe energy loss per second per unit volume, and v is the kinematic viscosity.Warren (40) has AY~wn"ed the role of equation 2 in determining aggregationbetWeen particles of different radii. Of particular interest is his obser-vation that even under conditions selected for equal collision rates betweenfines and fines and between fines and coarse particles, rapid coating ofcoarse with fines occurred. He concluded that probabli1ity of adhesion islarger for collision between a coarse and a fine particle (as that expectedin carrier flotation) than between fine particles ~ .

~~ "

SELECTIVE AGGREGATION OF SUL:nD~.

Selective flocculation of mineral fines, as mentioned 'earlier~ appearspromising for application in the finer size range and can be accomplished ina number of ways:

coagulation by inorganic electrolytes;1.

2. flocculation by polymers;

3. carrier flotation;

4. agglomeration with the help of hydrophobic substances.

160

To the author's knowledge, selective flocculation has been tried ~y withsulfides; hence, this method will receive emphasis hera. However, other tech-niques hava been successfully tried, at least on a laboratory scale, for oxides,and for silicates or salt-type minerals, and there is a need to determineth.ir application for sulfides. For examples Pugh and KitChener have obtainedsome selective coagulation in rutile/quartz and hematite/quartz systems byadjusting tha pH and ion1c strength so that only hematite or rutile coagulated~). . Similar coagulation has also been obtained for colored impuritiesfrom kaolin (15 s 22). Beneficiation of clay using carrier flotation on a co~~rcla1 scale by in'gelhard M1ne:rals and Chemical Corp. is well known (,ll>.Very little is known, howevers about the m8chanism by whiCh this process workssand without further research it is di.fficult to predict whether it would haveany application in sulfide syst~.

Agglomeration with the help of oil has been used by Puddington and co-workers for graphite, chalk, zinc sulfide, coal, iron ore, and tin ore inaqueous solutions (1, ~). In this process, the fines are tumbled in anaqueous solution cont~i"i"g an immiscible liquid to form capil~ry bridgesbetween rugen.tized particles and causes their aggregation. In a similarprocess, Warren Spring Laharatory is reported to have obtained good separationsfrom a lead/zinc ore (32) owing to hydrophobic bonding between reagentizedslime particles. Here -. slime fraction of the ore was dispersed by a combi-nation of sodium silicate-sodium carbonate and a polyacrylate; the fractionvas subsequently conditioned with copper sulfate, and then potassium amylxanthate was added. Floccs formed wer~ cleaned twice for improving the sepa-ration. Formation of floccs was attributed to similar reasons that gaveGaudin and Malozemoff (11) selective aggregation of galena slimes in thepresence of xanthates. ~e observation by Gaudin and co-workers (1l) that,b~ow a critical particle size of 4 ~ all particles of galena were floatableto the ~ extent (fig. 1) has in fact been attributed to flocculation of thefines.

Se1ective noccu1a~ion

Selective flocculation has been successfully ~ed during the last 2 yearson a commercial scale for the beneficiation of low-grdae '~~n .or-e by theCleveland-cliffs Iron Ore. Co. <2.) and for that of potash.~y' a' Coh1nco plantin SaskatChewan ~). While selective flocculation has been attempted on alaboratory scale for a number of nonsulfide minerals, investigation pn itsuse for systems containing sulfides have been limited ~, ~, 11, ~).Usoni and co-workers (39), for example, have studied the separation of a num-ber of metal sulfides SUCh as galena and sphale.rite from associated quartzusing both nonionic and anionic polymers as flocculants. They found predic-tion of selective flocculation on tha basis of the results from single-mineral tests to agree with the results obtained for pyrite-quartz andsphalerite-quartz mixtures using a nonionic polymer (Separan), but to failfor mixtures of galena-quartz and sphalerite-quartz using anionic Aerofloc orHercules CMC and for the mixture of Smithsonite-quartz even with Separan--tfhich had worked for all other mixtures (see table 1). The reason for thisdiscrepancy is not known. This problem (analogical to that in the flotationarea) needs careful and systematic s~udy. Selective flocculation of galena

161

TABLE 1. - Predicted possibilities for selective flocculation o~from its mixtures of various minerals and

comparison with separation obtained with actualmineral mixtures (!!l)

Separationobtained with

mineral. ~ture~

Separablepair

Conc,8/1

nocculant pH

10-210-310-2

10-3_10-210-1

10-2_10-110-3

.~~l9_-2

Aerofloc R 550.. . . . . . do. . . . . . .

. . . . . . do. . . . . . .

Hercules CMC.... . . . . . do . . . . . . .

. . . . . . do. . . . . . .

Separan NP 10..do

57957979

Galena-quartz. NoNoNoNoNoNo

10-310-1_10-2

Pyr:ite-quartz. Aerofloc R 550..do Senaran NP 10..

-

Yes10-110-210-210-210-1

10-2.-10-1

10-3_1.9-3_10-2

Sphalerite-quattz .

I Aerof1oc R 550.. . . . . . do. . . . . . .

do Hercules QIC...

. . . . . . do. . . . . . .

do Separan NP 10..1

I

do :I I

Aerof1oc R 550.1 Ido Hercules 0fC...

do Se~aran NP 10..

NoNoNoNoNoNo

YesYes

10-210-210-1

10-2_10-1~3

Smi.thsonite-quartz .

NoNoNoNoNo

10:.-1-~

10~1:

Galena-calcite

Hercules Q-IC...Nal~ ~OO

~. 1-9

--

. .10-110-2

J,,~1~-:1

Sphalerite(alo-g:e) .

Hercules CMC...Nalco 600 . . . . . . do. . . . . . .

77_i

---

10-2Nalco 600 9Pyrite-calcite .

10-1],0-:

Smithsonite-calcite .

Hercules CMC...Nalco 600

79

--

162

from quartz and calcite has been obtained by Yarar and Kitchener (42). Selec-tivity was found in this case to depend significantly upon the ions- ~resentin the suspension. Presence of divalent cations such as Ca+2 or Cu+ ren-dered quartz to flocculation with anionic polymer reagents.

As mencioned earlier, selecCive adsorpcion of the polymer is the key forthe successful application of this technique. An obvious way to generateselectivity is by incorporating complexing or chelacing agents. Attia andKitchener (2) have made some interesting scudies in this regard. They haveconsidered the possibilities of synthesizing flocculants with chelating groupsspecific to each metal.

The selectivity of both short-Chain and long-chain organic compounds con-taining mercaptan or thiol group in adsorption on sulfide minerals is wellillustrated by the extensive use of xanthates as collectors for the flota~ionof sulfide minerals. Tests with hydroxypropyl cellulose xanthate (synthesizedby reacting 1 mole of hydroxypropyl cellulose with 3 moles of carbon disulfideand 3 moles of potassium hydroxide) containing mercaptan as the active groupwas found in our work to produce good flocculation of chalcopyrite with littleeffect on quartz (see fig 8) (35-36). The results of tests with syntheticmixtures of these minerals are shawn in figure 9 as a function of concentra-tion of hydroxypropyl cellulose xanthate. Both grade and recovery of

100

-~

-0

Ci80 ~..

~a.

>=w

60~(Jw=w~

40~a.0(J~-c:

20 (J

80~-;>-Q.0u

"i.cu

1/1

.. . ~ .<- ",'

. ..

.-If."

>=cU)

~ 60

--0-- CHALCOPYRITE RECOVERY IN FIRST FLOC--0-- CHALCOPYRITE RECOVERY AFTER ONE CLEANING

. ASSAY. AFTER ONE CLEANING

. ASSAY. FIRST FLOCpH a 4.5

00 500 1pOO 1,400

XANTHATE CONCENTRATION, ppm (dry solids basis)

FIGURE 9. - Recovery and grade (chalcopyrite) of the concentrate from selec-tive flocculation of chalcopyrite-quartz mixture as a function of concen-tration of hyd roxypropy 1 cellulose xanthate; reagentizing time, 30 sec-onds; settlinq time, 45 seconds (12.). (CoUlLte.6IJ, CRC P1le.6.6.)

163

100

90.- Separen NP 10

- . Ae,ofloc R 550

Naleo 600'i.=Q,>"=

p.I \

'" .--0-,'~.,'

.I'

~,..-20

101.00

0 Afte, one cleaning6. First floc 0

10-" 10"' 1 g/L

I I I I I

10"' 1 10 101 10" g/T

1~ 10-'

.75

)(wQZ

F1.0CCULANTS CONCENTRA noN

FIGURE 11. - F1otation recovery ofspha1erite in the presence of dif-ferent f1occu1ants with potassiumamy1xanthate as co11ector andOowfroth frother at pH 9 {1,2>.

z0~c~c~IIIcn

- I.50

0 500 1,000 ~oo Sep8l'. NP 10

XANTHATE CONC.. ppm (dry solids basis) AefOfloc R 550

Nalco 800 I.-I i,

': , . .,, . '~",",:1-""c"'"' i

f- !

-c

~~~

]

FIGURE 10. - Separation index achievedfrom se1ective f10cculation ofcha1copyrite-quartz mixture as afunction of concentration ofhydroxypropyl ce1lu10se xanthate;reagentizing time, 30 seconds;sett1ing time, 45 seconds.

100

~

~

70

80

>= 50 -~.~~ ...> 40QU \.. ~ \-~ m 'J

10 ~

0 10-. 10-' 10-' 10"' 1g/L

10-' t 10 10' 10' 9IT

FlOCCULANTS CONCENTRATION

Oowfroth frother at pH 7 ~).

80

10

eo

50

40

30

FIGURE 12. - Flotation recovery of

spha1erite in the presence of dif-ferent f1occu1ants with potassiumamy1xanthate as co11ector and

164

chalcopyrite in the sediment portion were observed to improve with increasein polymer concentration. At high concentrations of polymer, however, entrap-ment of the quartz by the bulky chalcopyrite flocculants did cause a loweringof the assay. Cleaning of the product improved the grade of sediment (seefig. 10).

Kitchener and co-workers (8, 42) and Read (30) have also considered theentrapment of foreign particles-in ~he interstice; of the selectively floccu-lants to be a major problem facing the successful use of this technique. Theyhave observed that such trapped material can be released by gentle agitationmechanically or by countercurTent flow of washwater in an elutTiator.

The process of selective flocculation does thus appear to hold tremendouspotent~ when it is accompanied by flotation, e1utriation, filtration, etc.There are, however, various problems that ~1 have to be studied in thisregard. For ~x~mp1e, in the case of selective flocculation followed by flota-tion, polymeric reagents used for flocculation can affect the flotation opera-tion. Usoni, and co-workers, for example, found the flotation of sphaleriteto be enhanced by Separan NP 10, Aerof1oc R 550, and Na1co 600 up to certainconcentrations and to be depressed above those levels. This effect was higherat pH 9 than at pH 7 (see figs. 11 and 12). Possibly the increase at low con-centrations is due to a fractional surface coverage and consequent flocculation.A more complete coverage at higher concentrations can be expected to retardflocculation and possibly collector adsorption on the particulates and therebyflotation. The reasons for the activating effect at low concentrations anddepressing effect at higher concentrations have not, however, been established,and the problem warrants a systematic study.

~so, selective separation betWeen various sulfide minerals has not yetbeen investigated, co the author's knowledge. As much as selective flotationof one sulfide mineral from another is possible owing to specificity of func-tional groups at certain pH values and reagent additions, selective floccu-lation between various sulfides should also be possible. Rowever, both basicand applied research are needed before the technique of selective flocculationcan be successfully used for the beneficiation of sulfi,des.

, - . '. ,- -CLOSmG REMARKS -.;~, " .. ."-

'- 1,'-I.

Selective flocculation of oxides from oxides as well as Gf sulfides fromoxides has been successfully achieved using polymers into which funct:tonalgroups have been incorporated on a laboratory scale and, in the former case,also on a commercial scale. Using the same principle, it should be possibleto achieve selective flocculation between sulfide slimes also. An under-standing of the nature of the specificity of various polymers to sulfides andthe interactions between such polymers and collectors and the related mecha-nisms would prove beneficial for the development of the selective flocculationas a useful technique for the processing of sulfide slimes.

ACI<NOt.'LEDGrENTS

Support of this work by Particulate and Multiphase Processing Program ofthe National Science Foundation and the International Nickel Co. is gratefullyacknowledged.

165

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