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PROCESSINGXIV INTERNATIONAL MINERAL CONGRESS

NOTICE: This materlsi may be pmtededhy ooPvright law (TItle 17, U.S. Code)

POLYlCER-SURFAGTANT INTERACTIONS. IN THE

FLOTATION OF QUARTZ AND HEIlATlTE

P. $OOlasundaran end L. T.. Lee

Henry Krumb School of Mine s

Columbia University

New York, N.Y. 10027

ABSTRACT

Current mineral beneficiRtion operat~ans sometimes invol~e the use of pol1ffiersand surfactants simultaneously. Presence of polymers and surfactants togetherin the same system can lead to unavoidable interactions between the two species.The effects o~ such interact~ons on flotation are studied here for two or theindustrially important minera.ls namely quartz and helUliti te using acrylamidebased nonion1c, anionic and cati~c polymers, and dodecylamine hydroch1orid~and sodium dodecylsulfonate as surfactants. Under most conditions, flotation i~~ound to be afrected Bigniricantly by the above polymers. Depending on t:~e chargeof the polYlner in :relation to the cha1"ges of the surfactant and the substrate, thE:polymer can enhance, activate or depress flotation.

One major force of interaction between the substrate and the solution speciesis considered to be electrostatic ill nature. The possible mechanisms by whichflotation is affected by polymers are discussed here j,n terms of polymer-surfac-tant interactions at the solid-liquid interface~ polymer-surfactant complexationand po~eric bridging of particles to surfactant-armored bubbles.

The. possible use of polyacrylamide as s selective depressant for hematite inthe flotation-separation or hematite/quartz system is also discussed.

INTRODUCTION

Low quality finely dispersed ores are being subjected now to new techniquesthat' o~ten de~d an ~e uge or po1ym&rs a1ang w~th gur~actan~ co11ectors. Thu~

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October 17.231982

TorontoCanada

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.iron ore and potash, polymers and surfactants are used simultaneously (1,2).Polymera in these processes for rlocculation can sometimes arrect sub3eq~entrlotat1on operations owing to strong interactions of the polymers with thecollectors used ()-6). It is to be noted that polynlers used in otherstages or mineral processing such 8S filtration or grinding can also be carriedto flotation stage particularly if recycled water contains residual polymers atsignificant levels-

In order to fully utilize ~he beneficial effects of polymer-surfactant inter-actions as well as to control their detrimental effects, it will indeed be help-ful to have a full understanding of 'these 1nte~actions at the mineral surface.There has 1 however 1 been no detailed study of polymer-surfactant interactionsat solid surfaces although there have been a few reports on interactions in bulksolutions (7-18). In this paper, the role of polymer-eurfactant interactions onthe £lotation of single and mixed mineral systems of two industrially importantminerals, hematite ~d quartz, ere examined using combinations of anionic andcationic surfactants and polymers as well as non-ionic polymer. Results fromsingle mineral studies are usea also to explore the possibility of selectivedepression of hematite from a quartz/hematite mixture.

EXPERDAENT AL

~nera18

~emati te; Brazilian hema ti te obtained' from Bethlehem Steel Corporation wascrusb~d using a roll crusher. The -65 + 100 mesh fraction collected on e Rc-tapwas washed and deslimed several times with distilled water to a final pH of 6.Jand then stored in triple distilled water.

Quartz: Brazilian quartz purchased from Wards Natural Science Establishment wassimilarly crushed and the -28 +65 roeeh portion was passed through a magneticseparator several times to remove iron contamination. This fraction was leachedwith warm nitric acid, washed till a pH of 5.? waS obtained and then storedin triple distilled water.

Chemicals

Collectors: Sodium dodecylsul£onate (NaDDS) and dodecylamine hydrochloride(DDA-HCl } purchased from Aldrich Chemical Co.. and ~stman Koda~ Co. respectivelywere used as collectors without any further puri£icatian.

PolYmers; All the polymers were synthesized ~t Columbia Un! vers~~y using aradiation induced heterogeneous polymerization technique wi th a Co source.The ~atianic po~r (PAMA) 'was prepared from the co-monomers methacrylamidopropyl trimethyl 8Jmnoniumchloride (Jafferson Chemica;t) and acrylamide (EastmanKodak OQ~ ) and the anionic polymer (PAMS) was prepared from 2~acrylamido-2-methylpropane sulfonic acid (Lubrizol'Chemical) and acrylamide. The narl-io!licpolymer used Wag polyacrylamide (PAM). Details of the polymer synthesis andthe preparation of the various polymer-surfactant solutions have been givenelsewhere (1,9).

Flotation: For single mineral flotation, one gram of quartz or 0.5 gram ofhematite was conditioned with the necessary reagents on a tumbler at 16 r-p.mfor ten'minutes and the flotation was conducted using nitrogen in a modified

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Hall1.I!\Ond cell (.20) for 15 seconds at a gas flo" rate of 36 cm.)/min. In theca$e of mixed minerals, 0.' gram of quartz and 0.25 grams of hematite were used

RESULTS ~D DISCUSSIO~J

Hematite and quartz were chosen for this investigation because of the indu~-trial application of selective flocculation of thege minerals. In addition,the wide difference in their surface charge characteristics mskes it pos9ible t\~

isols""ve and study various forces such as electrostatic attraction/repulsion alC

hydrc.gen bonding that are responsible for the interaction between mineral£; aJ!.U

polymers and surfactants.

Hematite

The flotation behavior of hematite using sodium dodecylsulfonate under twodifferent pH conditions is shown in Figure 1 as a function or the sulfonateconcentration. It is seen that very little flotation occurs under natural pHconditions (-5.5). Evidently,. the hematite is not sufficiently positivelycharged just below its point of zero charge (-8) tCI fRcilitate adequate sulfclnat~adsorption for flotation. At pH 2..5, the flotation is, however, as 'expected,nearly complete. Since the adjustment of the mineral pulp to pH 2.5 usinghydrochloric acid changes flOt only the surface charge of the mineral but alsco th~ionic strength, the above e~eriments were conducted also at a constant ionicstrength of J x 10-2 kmol/rn (NaCl). F1otation behavior of hematite at. naturalpH end pH 2.5 \lnder these conditions was similar tc that obtained in the ab$(::n\~eof any added NaCl.

All subsequent flotation tests with hematite were conducted at pH 2.5 andionic strength J x 10-2 kmo1/mJ. Interestingly, both at pH 2.5 and 5.5,the flotation is found to go through a maximum as the collector concentrationis increased. While the initial increase in flotation with concentratiml isexpected on account of the increase in the amount of the anionic sulfor~te ad-sorbed electrostatically on the positively charged hematite, the decrease ob-served at higher concentrations is attributed to additional adsorption of sur-factants with a reverse orientation, decrease in the bubble size resulting inreduced levitation by-the bubbles, and armoring of the bubble surface by thesurfacta..'1t species. These factors have been discussed in detail elsew~.ere (. ~ '1 )

The effect of the nonionic polyacrylamide PAM on the sulfonate flotation ofhematite is illustrated in Figure 2, PAM is seen to depress the flotation urldermost, conditions, It is noted that as little as 1 mg/kg PAM addition can reducethe flotation from 90% to about 10%. In the presence of excess sulfO~ute Pft~is, however, found to enhance the flotation at intermediate polymer levels. Asa result of this dual effect, the sulfonate concentration for maxim\lIn flut.":i.tic!l

is shifted to higher levels. The above effects (..an be attributed directly tc:..the competitive adsorption of PAM on hematite as well as any complexation be-tween PAM ~d sulfonate. CoInpetition between PAM and the sulfonate for surfacesites will require higher sulfonate additions for s given sulfonate adsorptionand flotation resulting essentially in a shift of the curve tot:ards highersulfonate concenA,re.tion. CoI!1plexat1on between the polymer and the 5ulI'onate c.::::

~lso le&d to such a shift of the flotation curve since the amount of free 5Ur~a(;tJJ.nt. available to function as collector will be red\lCed by such complex.3.til~n.

Indee'l. polymer-surfactant complexes themselves can iD some cases funct,ion a$~ollector~ (5. 6). Apparently. this efi'ect is negl~gible for the hem~tit.e-PMJ-

;::ulfonI'i7.e system.

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100 .HEMATITE/HoODSNo CI Ckmol/m3)

T= 25.f28C3 -10-2080

pH=5.5to.6(Natural} ~

pH = 2.5 .

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00

60aW I... :<I0...lLL 40

~.

20

0

010~210-8 10-5 'K)-4 lO-~

NaOOS CONCENTRATION (kmol/m3)

Figure 1: Flotation of hematite using dodecylsulfonate at two different pHand ionic strength conditions.

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100HEMATITE! NaDOS! PAM

/-,IIIIII

II

II

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I/

0

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10~10-4 10-3NaDDS CONCENTRATION (kmol/m3)

10-~10-6

Figure 2: Diagram illustrating the effect of nonionic pol.Y)ncr J PAM. on the

flotation of hematite using dodecylsulfonate.

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The effect of addition of anionic PAYS is found to be much more marked thanthat obtained with PAM (see Figure J). At 1 mg/kg addition, the flotation isdepressed cCll1p1etely under all conditions and at 0.1 mg/kg addition the flots"t.ioncurve is shifted to higher sulfonate concentration range. First of all, thenegatively charged polymer is able to compete more effectively with the sulfonatethan the nonionic PAM on the positively charged hematite surface. Also, theadsorbed polymer macromolecules can be expected to ma9}= the co-adsorbed su1fon&~eand reduce the hydrophobicity of. the outer mineral surface and thus cause adepression in flotation. The polymer can also be expected to affect flotation dueto the "se1ting-out" of the surfactant. In this case the hydration of thepolymer increases the effective concentration of the sllrfactant in solution, andthereby increases flotation. Clearly the effect of "salting-out" in this caseis less than that of the depression resulting from the interaction of the polymerwith the sulfonate on the mineral surface-

The enhancement of flotation due to "salting-out" and formation of polymer-surfactant complexes can be more clearly seen in the hematite-sulfonate-cationicPAM! polymer system where the effect of direct adsorption of the polymer i'tselfshould be minimal since both the PAMA polymer and the mineral are 6imilarlycharged in this case. The results obtained at various levels of PAUA given inFigure 4 show the effect of PAMA on flotatiQrI to differ depending c.n the polymerand surfactant levels. At low surfactant levels, flotation is depressed atall polymer levels whereas at high surfactant levels, it is depressed at the lowpolymer level and enhanced at high levels. The practical implication of such widerange' of effects on the flotation plant performance should be noted. The rea~onfor this behavior can, however, be easilY seen when the cfrects or complexationon the free surfactant level and the nature of the pol~'XDer-surfactant complexesformed under various conditions are recognized. First of all, as mentionedearlier any complexation between the polymer and the 6urfactant will lead to a re-duction in tr~ free collector level. In the present case where the collectorand the polymer species are upposi tely charged, such complexation can be expectedto take place to a higher degree. Secondly, complexes formed at different sur-factant to polymer levels can possess different collector properties. At lowsurfactint to polymer ratios the oppositely charged polymer and surfactantspecies can be expected to form complexes where the surfactant 1s oriented withits charged head turned towards the polymer, and at higher ratios with a secondlayer with the charged head turned towards the solution. It is to be noted thatthe polymer with such a second surfactant layer on it can now adsorb on the posi-tively charged hematite surface and impart same hydrophobicity to it. Thus,while at very low collector levels flotation is only depressed, at higher lev~lsthe complexes with the negative sulfonate group6 acti11g as the func'tional groupsare able to float the hematite almost completely. In the presence of excesscollector, the concentration range of which corresponds to a decrease in flotationdue to the reverse adsorption or the collector, the reduction in collector leveldue to complexation coupled with the collector property of the complexes shouldthus be expected to produce the observed increase in flotation. In additic.n tothe above, the depres6ing erfect of the armoring of bubbles under excess cc,llectorconditions can also be reduced by the polymer considerably. As mentioned e'arlier,there can be significant repulsion between th~ armored bubbles and the mineralsurface with a bilayer of collector species adsorbed on it. The cationic poly-mer can, in this case, bridge the negatively charged particles 'to the similarlycharged bubble to form a flocculated mass of particles and bubbles which islevitated to the surface.

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Figure J: Diagr3Ill illustrating the effect of anionic polymer, PAIlS. on thE:flotation of hematite using dodecylsulfonate.

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Figure 4: Diagram illustrating the effect of cationic polymer, PAMA, on theflotation of hematite using dodecylsulfonate.

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QUartz

All flotation experiments with.quartz were conducted at natural pHquartz is negatively charged.

6.5) where

Figure 5 shows the results obtained for the flotation of quartz as a rurtcticnor dodecylamine concentration at vsriou8 levels of PAM. As in the case of hem~-tite, a maximum is obtained also for the flotation of quartz with aminc. Addi-tion of PAM is found to enhar.ce the flotation slightly only at the high polymerlevel of 1000. mg/kg. This relatively minor effect in comparison to that in thecase of hematite is in accord with our observation that PAMad90rb9 signifi..,cdritly less on quart2 than it does on hematite. In this case I the predomin&lteffect at 1000 nIg/kq polymer level is that due to "salting-out" of the aminerather than that due to the competitive interaction between polymer and surf~ctan.on the mineral surface.

The enhanceme:nt of que.rtz-wnine flotation by the "salt.ing-out" effect is JIIClr..:;:clearly seen when the anionic polymer PAYS is added to the system (see Fi~~e 6).The ionic PAMS is expected to have a higher tendency to undergo hydration bothbecause of the fully extended nature of the polymer ~nd the presence of thech;;..rged groups on them. In addition to the 1'salting-out" effect, direct polYITler-surfactant complexation between the anionic PA).fS and the cationic amine can alsvbe expected to enhance fJ..otat,ion. At high surfactant levels, the electrostaticbridging by the po~er of the positively charged armored bubble to the aminesaturated particle surface also_serves to favor flotation.

The effect of the cationic polymer PAUA on quartz flotation 1s shoWt'A in Figur,?7. It can be seen that PAMA acts as a depressing agent and at 10 mg/kg levelthe flotation is completely depressed at all levels of amine tested. PAMA ad$o!"ofJvery strongly on quartz and even causes flocculation of it, but the floc:3 areredispersed during stirring in the flotation cell. The adsorbed PAMA itself isnot expected to contribute towards any flotation because it is a hydrophilicpolymer. Since both PAMA and amine can adsorb on quartz, competition betwccnthe two species for adsorption sites on the mineral may partly account for thedepression. In addition, a3 in the case of hematite, flotation can be depre~sedalso due to the masking of amine that is adsorbed on the quart~ by the massiveco-adsorbed hydrophilic polymer. These effects have been discussed in detailelsewhere (19).

It is to be noted that the adsorbed polymer with its loops extending into thebulk solution can interact with the surfactant species also through the charg~,jgroups on the loops. While no favorable interaction Is expected in the case ,")fPAMA and amine, an anionic surfactant can be expected to adsorb on the PAMAcoated quartz and impart hydrophobicity to it. Such activation is in fact ob-served when the dodecylsulfonate is added to quartz in PAMA solution (see Fieur~8). While no flotation is c,btained with either dodecylsulfonate or PAMA...indivi\1

u511y, complete flotation is obtained at 100 mg/kg PAMA and 10-4 kmol/m,1sulfonate.

Quartz/Hematite Mixture

It is evident fram the above results that acrylmnide-based polymers can produ[~every significant effects when present in quartz and hematite flotation systems.Differences induced by the polymers in the flotatiol1 of such individual miner;1:!~':~an be used to de~igT\ candi tiOT\S th3t. """Pc apprt:>pri::ltO': t'c,r the Rf':JeC!"tiv*" !:,'~p(lr;'T"; '"or,

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1000 pH = 6.5 :t. 0.5

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.

.

.600

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0

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kmol/m~DCA - HCJ CONCENTRATION.

Figure 5: Flotation or quartz using dodecylaminehydrochloride in the presenceand ab9~nce or the nanianic polymer, P~.

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100 - ,--

aUARTZ/DDA-HCI/PAMS

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010~1 10-4 10-3

ODA- HCI CONCENTRATION, k mol/m'10-5

Figure 6: Diagram illustrating the effect of anionic pol~er, PAMS, on theflotation of quartz using dodecylaminehydrochloride.

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Figure 7: ~agram illustrating the effect of cationic polymer. PAUA. an theflotation of quartz using dodecylaminehydrochloride.

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Figure 8: Diagram illustrating the effect of ca~ionic polymer, PAMA, on tbe

flotation of quartz using dodecylsulfanate.

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.TABLE 1: Selective Depression of Hematite Using PAM

I'm-ffi- 2002 12:55 Linda Hal t:flb ~ H'~ p.l'r

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of systems which are of inttustrialimportance.. FoX' example, it can be see:! f!'JO

the results obtained in this study that while nonionic PAM does depress hematite-flotation in almost the entire surfactant concentration range, it does not d~pressthe flotation of quartz. In fact, if at all, PAM at high levels only enhar!.ces tr:E:

quartz flotation slightly. Based on this information, it should be possible tCJselectively depress hematite from a mixture of it with quartz using PAM. Th~results ot- studies.to.t~st this.passibi1it~ are give~ in.Table 1. It ~~ be.se~nthat when floated lnd1vldually 1.n 1.2 x 10 4 kmol/m am1:ne, 100% fl,:>tatl;:Jn 1:3

obtained for quartz and about 60% is obtained for hematite. When quartz ~)dhematite are present simultaneously, their flotation at the same amine level arelOO~ and 771 respective;i.y. The slight increase in hematite flotation is con-sidered to be due to possible entrapment of the hematite particles in the t'lo:Jtedquartz. Such entrapped mineral can be recovered if necessary by subjectu1g t:ht;flocculated quartz to a wash treatment- In the presence of 100 and 200 mg/~PAM, flotation of quartz when present alone remains at 100% but that OI~ hematiteis completely depressed from 601 to as. This selective depression of hema't.i ;:.eby PAM is again achieved when the two minerals are floated together under thesame conditions. PAM selectively depresses hematite to about 5% while compleT,eflotation of quartz is ~intained. Because of this selective depressing aeti~mof PAM, it can be considered as a potential reagent for befleficiating hematiteores. Alternatively, it is clear that possibilities for serious interference cfflotation performance by polymers used in other parts of the beneficiation schemefor filtration, flocculation, thickening etc., have to be recognized. Sincethere is marked increase in the use of polymers in mineral processing currerltly,it is clear that information on the manner Ifl which they interact with variousmiI'lerals as well as other reagents used in the plant is essential for optimumperfoI"JIlance.

SUJl.oAARY

1. Effect of nonionic and ionic polYmers on mineral flotation is investigale,jin this study for the.hematite-dodecylsulfonate and quartz-dodecylamine systems.Selective depression of hematite-quartz mixtures is also studied under selectedconditions. The effect of the polymers is discussed in terms of competitive ad-sorption at the mineral surface. complexation between the polymer and the collector,salting-out of the collector species by the polymer, and masking of the adsorl,edcollector by the m~ssive pol~er speaies.

2. Flotation of both hematite and quartz goes through a maximum as a functionof the collector concentration and is affected by all the polymers tested todifferent degrees depending on the charge and concentration ratios of variou~polymer-collector combinations.

J. The nonionic polyacrylamide, which adsorbs on hematite, depresses itsflotation with dodecylsulfonate except in the concentration range wiiere flotativfdecreases and shifts sulfonate concentration for maximum flotation to higherlevels owing to competitive adsorption and complexation of the polyme~ with th~sulfonate.

4. The anionic polyacrylemide is fOWld to depress the henatite flotation mark-edly with complete depression even at as low level as 1 mg/kg (1 p~-). Thisresults from the more effective competitive adsorption of the charged polymer 3.!itjpossible masking of the co-adsorbed sulfmate by the polymer.

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5. The cationic polymer o~ng mainly to complexation with the collectordepresses the flotation of hematite at low surfactant levels and in low dosage at.high surfactant levels. At high levels the flotation is enhsnced possibly dueto the collector property of the polymer-surfactant complex itself.

6. In the case of quartz the nonionic polymer increases quartz-amine flota-tion slightly only at the highest polymer level tested due to possible "saltlng-out" of the amine by the polymer.

? Quartz flotation using amine is enhanced markedly by the anionic polymerThis is attributed to the higher hydration tendency of the charged polymer,polYmer-surfactant complexation and Pgandwiching effect".

8. The cationic polymer interacts competitively with amine on the mineral sur-face causL~ depression in quartz flotation. . Depression, as in the case of hema-

tite-sulfonate-PANS system~ is suggested to be primarily the result of m~skingof the amine by the massive polymer species.

9. The cationic polymer activates quartz flotation using the sulfonate byproviding adsorption 91 tes for the sulfonate at the mineral surface. PAMA suIfonate complexes can possibly act as excellent collectors.

10. The use of polymer-surfactant interaction in beneficiation is investigatedby testing the selective depression of hematite from a mixture of it with quartzusing polYacrylamide under conditions indicated by the single mineral flotationresults.

A CKN CM1.EICdAENT

The authors gratefully acknowledge the support of the Chemical and ProcezsEngineering Ddvision of the National Science Foundation.

REFEREN CES

1. Sauaeundaran, P., "Fine Particles Treatment", in Research Needs in ltineralProcessing, Somasundaran, P. and Fuerstenau, D. W., ed., Columbia University,19?6, pp. 125-133. .

2. Villar, J. W. and ~we, G.A., "The 1:!.lden Mine - A New Processing Techniquefor Iron Ore", Yin.Cong-- J. , October, 197', PP. 40-48.

:3. Sanasundaran, P., "Princi pIes of Flocculati<%1. Dispersion. and Select i veFlocculatim"... in Fine Particles Processing. Sanasundaran, P., ed., A~J NewYork" 1980, Vol. 2. pp. 946-976. --

4. Usoni, L., et aI, "Se~ective Properties o~ Flocculants and Possibilities ofTheir Use in FIOt"ailon of Fine Minerals", Vlllth International Mineral Proces:"sing Coneress, leningrad, 1968, paper D-IJ

5. Ghigi, G. and Botre, C. J "Polymer CompleIes as New Collectors snd Their Usein Flot.tiCX1". Tr~s. De« (lnndon). 7.5-.. 1966. PI>. ~40.

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Trans.6. Ghigi, G., "Flotation of Quartz wi tb Some Polynlf:r Complex Col1ectl)rst'.~ (london), ~, 1968, pp. C212-2l9.

7. Rubio, J. and Kitchener, J.A., "New Basis for Selectiv-e Flocculatic,n of Min-eral Slimes", Transactions of Insti tutlon of Mining and Metallurgy (London, 86.1977, pp. C97-iOO.-'- - ~.-'

8. Saito, S. and Uizuta, Y., "Solubilization of Polymers in Aqueous CationicSurTactants", ~. Coll. lnterf. Sc., 31.. 1967, pp. 604-605.

9. Schwuger, M.J., "Mechanism of Interaction Between Ionic Surfactants andPolyglycol Ethers in Water", J. ColI. Interf. Sc., 43, 1973, pp. 491-498.-

10. Goddard, E.D. and Hannan, R.B., "Anionic Surfactant COOlplexes with CMrgedand Uncharged Cellulose Ethers", in Micellization. Solubilization and Micro-emuls~o~~_, Mi ttal, K. C., ed.. Plenum:,- 1977 ,pp. 8j5-845.

11. Jones, M.N., "The Interaction of SodiUJII fudecylsulfate with PolyethYlene

Oxide", .J. Coll. Interf. Sc. J :?]., 1967, pp. 36-42.

12. Arai, H., Mukata, M., and ShinodaJ K., "The Interaction between polynte::- ~'ld

Surfaetant: The Composition of the Complex between Polyvinylpyrrolidone and Sodl11In

Alkyl Sulfate as Revealed by Surfaee Tension, Dialysis and Solubilization", !.

Call. InteEf. Sc.J 17-,1971, pp. 22)-227.

. .A;J'ler"Polymer/Surfactant Interactions", :J

14. Goddard, E.D. and Hannan~ R.B., "Cationic polymer/Anionic Surfactant Inter-actions", J. Coll. Interf. Sc., 55, 1976, pp. 7)-79.- ~

15. Iewis. K. E. and RobinsOP. C.P., "The Interaction of Sodium fudecylsulfatewith Methyl Cellulose end Polyvinyl Alcohol", J. Call. Interf. Sc.. 32, 1970,pp. 539-546. -

}(-.. Saito, S., "Solubilization Properties of Polymer-Surfa~tant Complexes"J. QQ!l. Inte~f. Sc., ~, 1967, pp. 227-234. .

17. Ca'bane, B., "Structure of Some Po1yrner-~tergent Aggregates in Water",

J. Phys. Chem., ~.. 1977, pp. 1639-1645.

18. Kalpakci, B. and Nagarajan, R., ftSurfactant Binding to Polymer and PhaseSeparation in Aqueous Surfactant-Polymer Solutions".. presented at AIChE

Meeting, HoustonJ April, 1981.

19. Somasundaran, P. and Lee, L.T., "Po1ymer-Surfactant Interactions in Flot.!.i~.of Quartz", Separation Science and Technology, Symposium Issue, 1981.-

l,n

20. Somasundaran, P., "Foam Separation Methods", Separation and F'lrificationMethods, ~, p. 117, I 1972 '.