(

-ADSORPTION OF CHARGED AND UNCHARGED P"OLYACRYLAMIDES ON HEMATITE

B. M. Moudgil*

P. Somasundaran

..Henry Krumb School of Mines

Columbia University~ NY 10027

* Current Addr.ess: Department of Materials Science and Enginee~ingUniv~rsity.of FloridaGainesville, Florida 32611

For presentation at the SME-AIME Annual MeetingDallas, Texas - February 14-18, 198?

Abstract. Adsorption of aCrylallide tBsed homoand copolymers on hematite was investigated as afunction of the nature of the polr-er charge andfunctionality of the polymer. Effect of additionof sodium dodecylsulfonate and dodecylaminehydrochloride was also studied and was determinedto result in an increase or decrease in theamount of polymer adsor bed depending on, thecharge characteristics of the surfactant and thepolymer, pH of the suspension, concentration ofthe various species and the order in which thesespecies were added to the systell. The surfactantadsorption under given conditions on the otherband, was found not to be affected bJ thepresence of the polymer .alecules. The data isanalyzed to elucidate the mechanis. of adsorptionof polyacrylamide type polymers on hematite bothwith and without the surfactant species beingpresent in the system.

used i.-ediately after the inhibitor removalstage.

Viscosity average ~Jecul&r weight of thepolymers was estimated to be 2.5 million for PAM(nonionic polyacrylamide) 2.1 million for PAMS(anionic polyacrylamide) and 1.9 million for PAttD(cationic polyacrylamide).

Surfactants- 80dlwa dodecylsulfonate_spurchased from the Aldrich Chemical Co. and wasreported to be 99.9% pure. It was usea withoutany fu~ther purification. .

Dodecylamine hydrochloride was a product ofEastman Kodait Co. and wasllsed as received.

Inorganic reaRents -_Fisher certified NaOR andHC! were used for pH modification. ACS reagentgrade NaC!, a product of Amend Drug and ChemicalCo.pany was used for adjusting the ionicstrength.

Water - Triple~distilled water (TOW) of

specrfrC conductivity of 10-6 mho was used inthis .investigation. .-,:

Introduction

TechniquesBeneficiation or mineral fines usina floc

flotation technique i84ependent on theadsorption of the polymeric flocculant only onthe desired mdneral component. One of the Qethodsto achieve selective adsorption of polymers is bJcontrolling the interactions between the polymerand the surfactants used as collectors. Theseinteractions not only could modify the adsorptionbehavior of various colecular species on theDineral particle oot can also lead toprecipitation resulting in highe~consumption ofthe reagents. Precipitation can also adverselyaffect separation efficiency of the process. Atpresent effective separation of clays fromsylvite at Co.inco in Canada, is achievedcommercially through controlled interactionbetween the- polymeric and collector species. Itwould, however, be necessary to understand themechanism of such interactions before thisphenocena could be successfully applied tobeneficiate other complex ores. In order to studythe p~inciples which govern the effect of suchinteractions in mineral processing, a systematic'investigation of adsorption of polyacrylamidetype polymers on hematite ws undertaken.

Materials

Adsorption tests-0.4 I of -terial~.equilibrated with 3 ca3 of triple distilled ~teror 3 x 10-2 kmol/a HaCl solution in a screw capglass vial for 4 hours b, shaking at the desiredtemperature in a wrist action shaker. After 4hours of equilibration, pH ~s adjusted usingNaOH or HCl and thesuspension ~s furtherequilibrated for 2 hours. Required amount ofpolymer solution was then added and thesuspension was agitated for an additional 12hours before adding the surfactant solution.After adding the surfactant, 2 hours of furtheragitation was requtred to reach the equilibrium.At each step the teflon tape covering t~. vialwas replaced with a new piece. Afterequilibration, PH of the suspension ~s measuredusi~g a thin gla8S electrode attached to..adigital Corning pH meter (Model 125). Thecontents 'Of the vial were transferred to acentrifuge tube and were centrifuged in a IECModel B20-A centrifuge at 15,OOORPM for 10minutes. Residual amount of the polymer and thesulfonate were determined in the supernatant andadsQrption densitites were calculated. using" therespective calibration curves. 14

Analytical - the amount of C la belled

polymers was determined usin, a Beckaan_Hodel LSl00C spectrophotooeter.

Surfsctant analysis was conducted using a twophase titration _tbod (20). It was confirmedthat the polyaers employed in this investigationdid not interfere with the surfactant analysisand vice versa. " .

- . ,.Results and Discussion

Preli~inary studies were conducted to evaluatethe effect of paramcters such as agitationintensity and time which formulate theequilibriu~ adsorption test procedures. ~)so. thereversibility of adsorption of thc polyacrylamidctype polymers on hematite was invcsti-gated sincethe knowledge of the '.cxtent and of the rate ofdesorption are helpful in understanding themechanism of, the polyaer adsorption process.

Hematite- synthetic hematite 99.2-99.5% Fewas obtained from Pfizer, Inc. and its particlesize was reported to be 99% less than 5 microns.Surface area of the sa8~le was determined, usingQuantasorb, to be 8.7.. /g.

PolYmers - C14 tagged nonionic and ionic

polyacryla8ides were synthesized using radiationinduced heterogenous polY8erization technique. Adescription of the synthcsis and characterizationtechniques has becn given elsewhere. (17)

Anionic copolymers (~AMS) were synthesiz~using 2-acrylamido - 2-methylpropanc sulfonic

acid (AMPS) a product of Lubrizol Corp. as theco~nomer.

Cationic polyacrylamides (PAMD) weresynthesized using diaethyl-aminopropyl~thacrylamide (D~~P~~) as the comonoQer. Thisreagent was received in the stabilized form fro.the Jefferson Chc8ical Coapany. The hydroquiDOneinhibitor was removed b¥ passing a 50:50 aqucoussolution of this reagent through an activatedcarron column. The aqueous solution obtained was(

2

In the present investigation an attempt MaS..de to desorb the polJ8er from the hemati~esurface by decreasing the bilk concentratioa (byreplacing part of the solution above set~1e4.olids with pure salt ~tio~ or TDW) and.baking the suspension in a wrist action "'ierfor additional 12 hours. It was expected thatdesorption of the adsorbed polymer mlecuIe wouldincrease the NnewN residual polymerconcentration. A decrease in the residualconcentration on the other band would ind1ca~econtinued adsorption. From the results-presentedin Table 3 it is clear tbat desqrption of thepolymers, irrespective of their ionic nature. didnot occur under the pcesent:experimentalconditions. Stromberg e~al. (24) have re.,..tedthe desorption of polyesters from glass oaly whenthermodynamic character of the desorbing 8Dlventwas 8>re favorable than that of the adsorWngsolvent. In the present study since the solventremained essential1y unchanged thermodyDa8icallyunder all experimental conditions, adsorption ofpolyacrylamide type polymers on hema6tte 88.therefore, considered to be irreversible UDderall these conditions.

~ffect 2f ARitation on PolY1l\er AdsorPtionProperties

To determine if shaking of the polymersolution during equilibrium adsorption test8Odifies its adsorption behavior in any way,non-equ11ibriua adsorption tests in~lving onehour of agitation were conducted. One of thepolymer solutions used in the adsorption test wasshaken in a wrist action shaker for twelve hours(duration of the equilibrium adsorption tests)and the other waa kept on a bench top. Adaorptionresults obtained after one hour of agitation arepresented in Table 1. Also, to determine if thetwo agitation conditions bad resulted in anysubstantial changes in the molecular weightdiatribution of the polymers, intrinsic viscosityof the supernatants after adsorption was measuredusing a capillary viscometer. The estimated8O1ecular weights are also presented in the aboveTable. Uithin the experimental error the tworesults are similar indicating that shaking ofthe polymers did not cause changes in thestructure of the polymer molecules to affecttheir adsorption behavior on hematite.

Adsot'ption of Polyu.ers on He_tite

Adsot'ption of sC1'ylamide lased 1101:10 - aMcopolymet's on he-tite undet' diffet'ent pRconditions, is presented in Fils. 1 to 3. ~st ofthe adsorption isothet'm& are characterized 'Y asteep slope at low concentt'ations followed bf aslower uptake of the polymer at higherconcentrations. A plateau however, is not reachedwithin the polymer concentration range tested.Alao, it waa determined that up to a ceruininitial polY8et' concentration almost all thepolymer got adsor bed on the aolid, and it .sonly at biaher concentrations that a par~~ioningof the polymet' between the surface and the bilksolution was detected. This type of adsorptionbeha~or is characteristic of monolayer ttPe ofadsorption for non-pol~ric uterial and can i2described"bf the Lanaauir equation. In the useof poly_t' adsorption, however, any fit of tltedata to the Langmuir equation is prolabIyfot'tuitous since, polyaer mleculee can ..-different-conformations and exhibit varyiDcdegree of attachment to the sut'face as.~d--ptionpt'ogresses. Kot'eovet' , polymet' adsorption islenerally an irreversible process and lateralinteractions i2wteen adsor bed -polymer moleculescannot i2 ruled out thus, vioiating two of thelasic assumptions inYOlved in the derivatioa ofthe Langmuit' equation.

A number of investigators (2-3,8,10-11.21)have reported polyaer adsorption result~ tllathave i2en interpreted,on the lasis of theirap~rent agreement with the Langmi/.f.r equation. Inso~ cases this has i2en used to estimate thesaturation adsorption and'to calculate adSocptionrate constants which in tut'n have i2cn u~ todevelop poly.er adsorption mechanisms (10).According to the above discussion any infoc8Btionobtained on the lasis of Langmuir equatioa..shouldnot be considet'ed as anymore meaningful than fromthe use of an cmpirical equation and should be ofl1aited use only. '.

Adsorption isotherms generated in the prescnt.tudy were si.ilar in shape to the Lang8Uirisotherm bit they did not satisfy th-e criterio!!

~roma~~RraphiC Senaration of Polymer durinaAdsorPtion

It has been reported in the literature thatdisplacement of initially adsorbed low molecularweight fraction ~ higher molecular wei&htfraction could occur if the polymer mlecularweight distriootion is !road (1,121. To deteraineif there was any preferential adsorption ofhigher molecular weigh.t fractiona during thepresent investigation, molecular weight of thepolymer before and after the equil1!riumadsorption test was estimated. From the resultsBiven in Table 2 it can be observed that8Olecular weight estimates of-the polymer beforeand after completion of an adsorption test didnot differ froD each other significantly. This.indicated that either the 8Olecular weightdistri ootion of the polyacrylamide used was notbroad enough to result in any measurablechromatographic separation during the adsorptionprocess or, that the present system was notcapa ble of causing any su.ch separation.

DesorPtion-Reversibility of Polymer AdsorPtion -It is possible to obtain soae knowledge of the

strength of the bond formed between the polymerapecies .nd the adsorbent ~ determining theextent of desorption or the reversibility of thepoly.er adsorption process. Among other factors,the type ~f solvent has been known to affect therate and the aD>unt of desorbed pol~r ~o aconsiderable extent. Desorption normally is slowand incomplete when the polymer is adsorbed fromdilute solutions whereas, from concentratedsolutions it is rapid and frequently complete-'(IS). This prolBbly could be the result ofdifferences in the stability of the adsorbedpolymer from dilute and concentrated solutions.In the former case optimum number of bondforcl8tion can occur between the polY8er mleculesand the adsorbent. However, in the case ofabsorption from concentrated solutions, less tb.anoptimum number of bond formation due to "crowdingin" ~ other polymer molecules on the adsorbcntsurface is possible.

l

( of a linear CIA versus C relation. In fact on thebasis of large initial slope these isotherms maybe classified as of "high affinity" type, meaningt~t the affinity of the solute for the substrateis high even at very low concentrations (4-6).The region corresponding to the initial risewhere interactions between adsorbed chains andsegments within a chain are expected to beminimal, is the aost informative region. Thisregion, however, is often inaccessible because ofalDOst a vertical rise in the isother.. in thelower concentration range and due to thedifficulties encountered in getting reliablemeasurements of the polymer amount in very dilutesolutions.

Effect of pH: Modifications in variables such aspK and ionic strength can result in (i)alterations in .urface charge characteri.tics ofhematite since K+ and OK- are potentialdetermining ions and (ii) changes in polymeratructure due to hydrolysis especially underba.ic pH conditions.

Hydrolyais of polyacryla8ide-type polymerscontaining amide (-CONa2) groups has beenreported to occur under both acidic and basic pHconditions (9.16.19.22). Since hydrolysis ofaaide groups by acids bas been reported to besignificant only at temperatures higher than 100.C. it can be assumed that under presentexperimental conditions of 2S.C ~lymer structuredid not dhange in the acidic pH range. Kineticsof hydrolysis of polyacrylamides under basic pHconditions are fast enough to result in aconversion of significant number of -CONH2 groupsto -COOK groups in the following manner (13).

I.CONK2 + KOK~ RCOOH '+ NH3

Depending on the pH Which governs thedissociation of -COOK groups. a nonionic polymerauch as polyacrylamide can behave as an anionicpolymer. It is obv.ious that conformation of thepolymer aolecule will vary with the pH. Polyaerconfor88tion will also be influenced by thechanges in the ionic st~ength (18). Tbis type ofbehavior in general. is typical of allpolyacrylamide type polYllers. Tbe degree of -,

hydrolysis and overall charge characteristics.however. will also depend on the nature of thecharge and the a8>unt of functional p;oupspresent~' on a particular copolymer and can have amajor influence on the adsorption process.

One common feature of the adso~ption ofpolyacrylamide type polymers on hematite i. thatat higher concentrations of polyme~. ad80rptionis lower unde~ basic pH conditions than at acidicor natural pH (see Figs. 1-3). This may beattributed to the polymer hydrolysis ~esultiD& inthe formation of carboxylic acid functionalgroups in all th~ee types of polymers. Forexample. in the present case under the basic pHconditions. hematite is negatively cl\8rged andintroduction of any negative charges on thepdlymer backbone will result in an increase inthe electrostatic repulsion thus.~educing thepolymer adsorption. -

Adso~ption at higher concentrations undcrnatural and acidic pK conditions. was found to beve~y similar for PAM and PAlin but for PA}tS it washigher at acidic pH than that at natural pH. Ithas been repo~ted that the principal mechanismfor the adsorption of polyaerylamide type

(

polymers on oxide minerfls is" through hydrogenoonding, the bydJ:ogen &e1ng shared betweensurface oxygen atoms and oxygen or nitrogen ofthe polymer (14). In the ~se of polyacrylaaideswith charged functional groups, electrostaticinteraction also needs to be oonsidered. For thepolf8ers studied here, the degree of sulfonateand alline group substitution in the -polyacrylamide backbone was only aoout 3 molpercen't and it is possi ble that; their effect to alarge exten~. was asked by ,the large nu8ber ofhydrogen oond forming ~~ groups. Based oncharge .oonsiderations ff is expected that atacidic pH values, Where hematite is significantlypositively charged, adsorption of the anionicpolymer should be nore than in the basic ornatural pH and sheuld be lowest for cationicpolyacrylamide (PAM»). The data obtained for PAMSadsorption followed the expected trepd whereasfor PAM» the adsorption was sillilar both atacidic and at natural pH. The similarity in theadsorption behavior of PAM» under aoove pHconditions ay be attributed to the aasking'ofelectrostatic interactions ~ hydrogen bonding.Under the basic pH conditions When the solid andthe polymer are oppositely charged, theadsorption is expected to be higher than underacidic or natural pH conditions; hydrolysis ofthe polf8er however;- could have caused negativecharges on the backbone Which along withformation of neutral aaine molecules can resultin lower adsorption values. Besides changes inthe adsorption due to modifications in chargecharacteristic. of hematite and polymers;conforation of th~ poly.ers Which deterllines thesurface ooverage at a given ooncentratig;n canalso playa -jor role in the adsorption-process.For example, as a result of hydrolysis underba.ic pH condition. polyacrylamide acquiresnegative charges Which can cause swelling of thepolyger coil and therefore, an increase in thearea per molecule. This increase in the surfacecoverage per molecule can lead to decreasedadsorption density as has been o~erved for allthe three polymers under basic pH conditions.

Effect of Ionic Stren2th: Ionic strength changescan affect polf8er adsorption through (i) .

modifiCation in the solvent eower of the mediumand (ii) increased competition between-counter ions and polymer seg.ents for adsorptionat the solid/liquid interface. If polymer is core.oluble at higher ionic strength a decrease inadsorption would be expected. The increasedcoapetition between added ionic species andpelymer 8Olecules would also lea4 to reducedadsortpion. A third factor which"needs to beconsidered in the case of polyelectrolytes is thepossible aodifications in polyaer oonformation as. result of the added indifferent electrolyte.Electrostatic repulsion between chargedfunctional groups will be minimal in the presenceof salt peraitting increased coiling of tnepoly.er chain. This should lead to a.reduction inarea per 8Olecule and thereby, in increasedadsorption. .

. Adsorption of PAM (nonionic polyacrylamide) onhematite as a function of the residual polymeramount at dilferent ooncentrations of NaCl Laplotted in Fig. 4. It i. clear from the data -presented that there is no significant effect ofvarYin~ the salt concentration from 0 to S.lkmol/m !laCl on the adsorDtion of PAM on

~

4

b.-atite. Adsorption of PAMS (anionicpolyacrylaaide-a polyelectrolyte) on ~tite waBdetermined to be higher at hig~er saltconcentration (3 x 10-2 k801/. MaCI) (.e. Fig.5). This indicate. that under the presentexperi..ntal conditions changes in corifor..tionof polyelectrolytea influence the adsorption ofthe polymers 8Ore than the other factor...ntioned earlier.

-range. This intere~inl i?fect can be explainedas follows:

Adsorption of the polyacryla.ide typepolymers, ss discussed earlier, can be consideredto be irreversible. By irreversibility of pol~radsorption it is iaplied that even though thepoly.er 8Olecule as a Whole is adsorbed.irreversi~ly the individual segments in contactwith the "surface -y be in a reveisibleequilit.'iua st~e. And aince the _ber of.eg.ents in contact with the- Surface is nor..ll,very larg~, the reversibliinature of particularsegment ..y not lead to polymer desorption. Thepresence of Surfactant can, however. affect thi..ituation under condition. Where the surfactantadsorption on the 8U£face and the kinetics of itare hiah, i.e., if the kinetics of sulfonat.adsorption is faster than the pol~r --g-entaladsorptfon/desorption kinetics. Surfactant.olecules under such conditions can replacepolymer segments consequetively leading.to thedesorption of the polyaer 8Dlecule. This effectcan t. even .ore pronounced at hIah polr-eradsorption density since, under these conditionsthe numt.r of ..g-ents per polymer molecule incontact with the surface can 1e expected to 1elower than those at low adsorption density. Thisclearly .bows Why desorption of the PAHS washigher When laraer amount of polymer was presentin the systea as opposed to that at low poly.8er

.concentrations.

Effect of Teaperature: Variations in temperaturecan affect polymer adsorption through changes in(i) solvent power of the aediu8, and (ii)adsorption of the solvent 8Olecules CO8petingwith the polywer. Both factors have s1ailar rol..in monofunctional solute adsorption except thatin the case of polymers entropic effects due to(ii) can bI of considerable ..gnitude.

Adsorption of nonionic polyacryla8ide onh.-atlte at 2S., 45. an~ 1S.C is plotted in Fig.6. Similar adsorption blhavior MaS observ.d at 25.C and 4S.C howev.r, at 1S.C a trend towardshigher adsorption was indicated. This type ofadsorption behavior suggests significantinfluence of entropic effects in the adsorptionof polyacryla8ide on he..tite.

Effect of Functional Groups: Eft.ct ot 8Ulfonateor amine functional groups in the polyacrylamidechain on adsorption is illustrated i~r1&' 1. Itshould be noted that the anionic (PAMS) andcationic (PAKD) copoly.er~ contain 3 801 percentof the respective functional groups. It wasdeter8ined that adsorption of PAMS on he..tite atpH 1 was higher than of the nonionic PAM or thecationic PAKD poly.-rs. This protably can beattributed to the opposite natur- of the chargeson PAHS and the hematite surface under the givenexperi..ntal conditions.

dec lamine II drochloride - PAHS - llematite: An

increaae in polyaer (rAMS adsorption as abown inFig. 9, ..a obtained in the preaence of -..dodecyla.ine hydrochloride under natural pHconditions. Since precipitation-redissolutionpheno8ena waa ob8erved in this ayateD, theincrease in .pol,.er adaorption could also beYeoccured due ~o the precipitation in addition tothat cauaed ~ interaction between the oppositely~rged apeciea. These results heye beendiscua.ed elsewhere (17,23).

Effect of PolYmer Addition on Sulfonate.AdsorPtion on He_tite

Sulfonate adsorption on hematite under ~turalpH conditions was not affected 8ignificantlyirrespective of concentration oc the order ofpolymer addition (see Fia. 10). This indicatedthat the addition of the poly.er to a solutioncontainina particle8 with sulfonate alreadyadsorbed on them did not.. cau8e dosorption 'of thesulfoaate. These results a180 showed. that due tothe nature of the confor..tion of adsorbedpoly.er molecules enouBh surface area wasacce88ible to the 8ulfonate adsorption as .

illustrated in Fia. II.In 8U88ary, the above discussion clearly Shows

that if the pol~r and surfactant species aresimilarly charaed then, depending on tho order ofthe reagent addition, a sianificant reduction inpolyeer ad8orption cou14 occur. The adsorption ofthe surfactant however, re..ina unaffectedp~&sibly as a result of access to the uncoveredsites due to the 8tructure of the adso~~dpoly_r mlecule..

Effect of Addition of Surf."tant: on t:h~ AdRornt:ionof Anionic Polyacrylamide (PAHS) on He_tite..

~2diu. Dodecylaulfonate - PAHS - He.tite:

Effect of addition of aodiU8 dodecylsulfonate onthe adaorption of PAMS on hematite under naturalpH conditions. aa a function of order of reagentaddition is illuatrated in Fig. 8.

When sulfonate was added first (5+P) ortogether with the pol~r (~) adsorption of tbepoly.er wa".found to be reduced to the --degree fro. that of the pOlYMr alone. In thefor.er case. the surface waa contacted with thesulfonate first. leavinl lesser uncovered areaavailable for polyaer adsorption and therefore.causinl a reduction in the adsorption. In thelatter case even thouah both sulfonate andpolYMr were added si.ultaneoualy it ia possible,.that because of ~lky nature of tbe polY8er8Olecules their 8Obility and therefore. diffuaionto the solid/liquid interfacial relion ~a slowerthan that of the sulfonate 8O1ecules and aa aresult. polY88r adsorption essentially took placeon a surface which had sulfonate ~leculeaadsorbed on it. This ia co8parsble to thesituation discussed aboye (5+P) and the observed.reduction in polymer adsorption therefore. i8 notunexpected.

Addition of polYMr followed b, that ofsulfonate (P+5) also resulted in reduced polYMradsorption as co.pared to that when no sulfonatewas present in the Iylte8. The decrease was 8Ore

significant in higher pol,.er concentration

Conclusions

Based on the above discussion, the followingconclu.ions regarding adsorption of

s

(3 IDOl percent of the functional groups) thechangN occurring in the conformation of thepolymer 8k>lecules woul<! be or lesser degree thanwhat maybe required to be of sianificsnce inaffecting the flocculation process.

Ack~owledgement8

The authors would like to thank Dr. K. P.AnanthapadDBMbhan for helpful discuss1.ons andMrs. ~gina Gorelik for help in experimentation.Financial assistance from the National ScienceFoundation 'Grant No. DAR~7.9-09295) and fro. theINCO Inc.. is acknowled&ed. One of the authors(BHH) would also like to thank the OccidentalResearch Corporation for granting educationalleave to him at Columbia University.

References

1. Felter, R.E., Hoyer, R.S. and Ray~ Z.N.. 1969.L"Polv... Sci., 17, 538.

2. Fontana, B.J. and Thoaas, J.R., 1961, J.Phvs.

~ 65,480.

3. Frisch, H.L., Hellman, M.Y. and Lundberg,

J.J., 1959. J. Polvm. Chem., 38.44.

4. Giles, C.H., D'Silva, A.P. and Easton, I.A.,

1974, J. Colloid Tnterface Science. 47, 766.

s. Ciles, C.H., MacEwan, T.H., Nakhwa, S.N. and

Smith, D., 1960, J. Chem. Soc., 3973.

6. .ciles, C.H., Smith D. and Huitson, A., 1974.J. Colloid Inter.face Sci.. 47, 755.

-..7. Healy, T.W. and LaMer, V.K., 1962, J. Phvs.

~, 66, 1835.

8. Heller. ~.. 1966, Pure Appl. CheQ.. 12.249.

9. Higuchi. H. and Senju. R.. 1972. ~olym.J~. 3.370.

10. Hollander, A. 1979, MA Study of the

Interactions of Poly (Acrylamide) a~d itsCopolymers with Kaolinite,. M.S. Thesis,Columbia University, Rew York, NY.

11.Kennedy, P., Petronio, H. and Gisser, H., 1971J. Phvs. Chem., 75, 1975.

12. Kothoff, I.M. and Gutmacher, R.G., 1952, J.Phys. Chem., 56, 740. -

l3~u1icke, u. and Kl~1n, J., 197&~ ~Angewnndt~Hakromol. Che.., 69, 189. Quoted in Reference~JO

14.L1nke. V.F. and Booth. R.I., 1959. Trans.~. 217, 364. -

polyacrylamide type polymers or hematite can bereached.

The adsorption of the ionic and nonionicpolyacrylaaides on he..tite is governed pri8arily~ hydrogen bonding between the surface oxygenand the oxygen or nitrogen on the polymer.Electrostatic interactions between the polymerfunctional groups and the he..tite surface playonly a Secondary role in the present systeabecause of relatively low degree offunctionality of the copolymers.

The relatively ...11 effect of salt additionon the adsorption of PAMS - an anionic

polyacrylaaide on hematite and almost negligibleeffect of ionic strensth on the adsorption of PAMon hematite indicates that either the changes inparameters such as solvent power of the mediuQand conformation of the poly.er are notsignificant or their effects are mutuallycancelled out.

The effect of temperature on the adsorption ofpolyacrylaaide on hematite was not found to bevery significant leading to the conclusion thatentropic rather than enthalpic changes playaaajor role in the adsorption process.

Desorption tests indicated that, irrespectiveof the polymer charge, its adsorption on hematitecan be considered to 1m irreversible under thepresent experimental conditions.

Polymer adsorption was determined to beaffected significantly dependins on the nature ofthe surfactant charge, amount of the surfactantadded and the order in which the pOlymer and thesurfactant were added to the system. Thereduction in polymer adsorption in the presenceof surfactant is attriblted to the unavailabilityof uncovered area for the polymer adsorption. Theincrease in the polymer adsorption on the otherhand, in the' presence of oPpo,sitely chargedsurfactant, is probably due to electrostati~charge attraction between the polymer and thesurfactant mlecules.

The surfactant adsorption, irrespective of thepolymer addition, was not affected significantly.This is attribltedto the factor that enoagh8urface area was accessible for surfactantadsorption even after the surface was coveredwith the polymer molecul~s.

It can be expected that in the presence ofpolYiler _lecules, the surface wettability, .

irrespective of the order of reagent additionwill be controlled ~ the hydrophilic nature ofthe polfmer. One can, for example, expect thatthe presence of any of, the polymers studied, willdepress the flotation of hematite using sulfonatea. the QDllector in the acidic pH range. Theinfluence of PAMS-sulfonate interaction on theflocculation behavior of heaatite on the otherhand, is difficult to analyze because of possibleopposite effects of the changes in the polymerconformation and the polymer adsorption in thepresence of the sulfonate .olecules. Hydrophobicinteraction between the polymer and thesurfactant 8Olecules will result in a tendencytowards uncoilins of the polymer which shoulde~ance the flocculation by tridging (7), but atthe same tiDe polymer adsorption could be reducedeither as a result of reduction in the uncoveredsurface area available for polyacr adsorption~or~ desorption of the adsorbed polymer mleculesas discussed earlier. In the present case thesecond factor -y control the overall Imhavior8ince due to the low degree of copolyaerization

IS. Lipatov, Yu.S. and Sergccra, L.M., 1971:-Adsorption of Polymers, - John \'iley and Sons

New York.

16.Moe . and SlDets. C.29.

(

ins, J931.

7,.1. Pol.

6.:..-

l7.Koudgil, B.M., 1981, "The Role ofPolymer-Surfactant Interactions in InterfacialProcesses." Engg.Sc.D. Thesis, ColuabiaUniversity, New York, NY.

l8.Muller, C., Laine, J.P. and Yenyo, J.C., 1979,J. Poly-.. Sci. (Polym. Cbem.), 17, 659.

19.Pinner, S.H., 1953, J. PolY8. Sci., 10,376.

20. Reid, V.W., Longman, G.Y. aDd Heinerth, E.,

1968, Tenside, 5,90.

2l.Sato, T., 1971, J. Appl. Polya. Sci., 15,1053.

22.Smets. C. and Hesbain. A.H.. 1959. J. Pol~§.sJ... 40. 217. -

23.Som&sundaran. P. and Houdgil. 8.M.. 1981.~ffect of Polymer-Surfactant Interactions onPolymer Solution Properties." presented at theACS National Meeting. New York. Sub8itted forpublication in the Symposium proceedings.

24.Stro8berg. R.R.. Quasius. A.R.. Janek. c. andParker. M.. 1959. J. Res. Nat. Bur. Std.. 62.71.

,.,

c

...

l

~

TABLE 1

Effect of mechanical agitation on adsorption of Nonionic Polyacrylamide (PAM) onHematite under natural pH conditions.

. -2 I 3lfaC1 Conc. . 3x10 X801.

pH. 6.8Agitation tilDe . 12 Hours -Adsorption time. 1 Hour -:

.~

Initial Polymer Conc.8&fa

Agitation Msorption Density8&/g

M. Wt. of Polymerin Supernatant

62.36 x 10

62.38 x 10

62.32 x 10

62.25 x 10

2000

2§0

2000

250

17.4

'..017.56.7

No

No

Yes

Yes

TABLE 2

ChrO8&tographic Separation of Honionic Polyacrylamide (PAM) DuringAd8orption on S-tite.

P AH/HEHATITE-2 3BaCl Conc. . 3 x lO~ k801~

pH. 3.5(Molecular Wt. b~fore adsorption - 2.36 x 10'

c 6Molecular Wt. after adsorption - 2.22 x 10

tABLE 3 .»-orption of Pol,-r8

Polyiaer/H_tite-2 3NaCl Conc. - 3 x 10 mol/.

Boom Temperature - 2S.C

Adsorption T18e - 12 Hr..'Desorption Ti8e' - 12 Hr..

Initial Polymer Conc. - 1000 ~/kg

Residual Polymer Conc.after 12 Hrs. of. Adsorption

ag/q

Residual Polymer Conc. after12 Bra. of 'Desorption,' mg/kgEsti8ated Experimental

POl~ pH

PAM 4.276.989.689.59

3.726.869.68

6.S36.988.78

671726723718

470-622703

635682707

151272271269

1.76233~

238256265

248227271261

161222363

230245278

l PAM!>

8

~

PAM I H£MATtTE

I.,.~k4Ml/m3 HoC!

-0- 3.4 t. 0..-0- 6.9 t. 0.1-6- 10,0 t 0.1

~-'

D

26

24- 22

i 20[- 181>-I- 16'Viz 14IIIQz 120t= 10L

~ 8'"~ 5

,. ..:f. .. I I I I I I I J J

0 100 400 600 800 ICXX> 1200 1400 ~ ~ 2O(X)

RESIDUAL CONCENTRATION (..".,1

Figure 1. Equilibriua Adsorption Isotherm of NonionicPolyacrylaaide (PAM) on He8atite at Three~ifferent pH Values.

PAMSI HEM4TITE

Figure 2. Equilibrium Adsorption lsotbermof AnionicPolyacrylamide (PAHS) on Hematite at ThreeDifferent pH Values.

l

9

.r>-I-..Z~Z0

t~0'"0c

Figure 3. 'Equi11briua Ad.orpt1on I.other. of Cationic Po1y-acry~. (PAKD) on a_tit. at Three DifferentpH Valuea. ~

PAMIHEMA TlTE ... - 7oG .t.O.t

~CONC.k-..I~

-0-0-0- 3a1a-2-0- toG-b- 5ot

24

20

16

12

i~I-!~i

.

I . . , , , I "- ' =. ~ - ~~ -

RESIOUAL POLYMER CONCENTRATION. 1"""1'

- -.

Figure 4. Effect of Salt Addition on Nonionic polyacryla-aide (PAM) Adaorption on Hematite -tinder NaturalpH Coaditiou.l

10

Figure 5. Effect of Salt Addition on Anionic Polyacryla-aide (PAHS) Ad8orption on H_tite Under Natural

~ pH Conditions~ '

(

PAM IIHEMATITE

183 .X)-2~I/m3Ho~pHo3.3tO.2 -

-0- 25.C~ 45.C-to- 758C

~ ~..~ (>0 .'

;.;.'~c

26

2.4- 22~" 20r- IS>-.. 16U;z 14'"0z 120 "A~ 10 ~ C\)

g SI¥~ 6

4

21r. I I I I I I I I . I

g0 200 400 600 800 10>0 1200 1400 ~ \SOO 2000

RESIDUAL CONCENTRATION CMO"OI

"Figure 6.- -

Effect of Temperature on Ad.o~tion of NonionicPolyacrylamide (PAM) on He.ati~!.

l

u

0

"t...~Oftz

~

z0

;:Go«0...0

c

roL YMER IHEMATITE

~ I a3aI0-l__I/".3 NaCI

pHa7.0~O.2

-0- PAN (NONIONICI-0- PANS (ANIONlC-

9JLFONATE FUNCTlo... GRaR'14 -0- PAMO (CATIONIC-

Z ~INE FUNCTIONAL GROUPI

0

- "RESa>UAL C.ONCENTRATION (...,,-,1

Figure 7. Effect of Vari~s Functional Groups on Poly-.acrylamide-Adsorption on Hematite.

~

PAMS/SUlFONATEI HEMATITE

~

~/.?~Or

26

2.- 22~... 20r- 18>-.. 16in~ 14 I' 0 kmol 1..3 NoCI

Z 12 pH -7.11 0.2~0-t: 10 SULFONATE CONC.A. ~1/,.3~08 -0- 0

~ -0- 6.6 a 10-)C 6 -c- 6.6 a 10-3

4 I K -0- 6.6 a 10-)

2( ::y-(J . I I I I I I I I I I

0 200 400 600 800 1000 1200 1400 1600 1100 2000'

RESIOUAt. ~ONCENTRATION 1"'9/kgl

~ ~R OF

~f'Ol YMER SIA.FOffATE

I -D II nI I

~

~

Figure 8. Effect of Order of Addition of Sodium Dodecysul-fonate on Adsorption of Anionic PolyacYylamide(PAMS) on Hematite Under Natural pH Conditions.

(

2e r14

IIi20

Ie

Ie

14

12

10

.L£ ...

PAMS I AMINE I HEMATITE"(AUWE AOOED fiRST I D

/; ~ ~

/'./

~

I' 0__/.,3 Mea

ANNE COMC.1--1/,.51

-0- 0-0- 7.10-3

'.i . 0;1~..5 .t 0.1I

~

3Or

21126124- 22.... 20r- II

..to 16~z 14OS~ 12

1~ 10L

~ I..a 6~

4- 2 .

0" I I I I I I I I I I

0 200 400 100 ~ 1~ ~ 1400 1600 IlOO 2000

RESIDUAL CONCENTRATION Cia,""

Figure 9. Effect of Addition of Dodecyl..ine Hydrochloride (Added First) on -Adsorption of Anionic Polyacrylamide (PAMS) on Hematite Under NaturalpH Conditions.

SULFONATE I PAMS I HEMATITE -I' 0 _1/..3 NaCI

TOTaL ~~E CONc.- 7,10""-/..,3,H. 'l1~0.2

ORDER OF AOOITIONcSPOLYMER SULfONATE

-6-. I-0- I n-0- I I

"-

..

'; 100 r-~t: 90.,.Z 80~Z 100~'";600 c-O 0' 50..,. I0 .. 40oC-... 30~Z 200...... 10~... 0 I I . I . . . . I .

0 200 400 600 100 1000 1200 1400 1800 1800 2000

RESIDUAL POLYMER CONCENTRATION ,k,1

F;i&Ure 10. Effect of Order of Addition of Anionic Polyacrylamide (PAMS) :on theAdsorption of Sodiua Dodecylsulfonate on Hematite Under Ratural pHConditions.

~to-~ 0 "0 ~ .-

~~~I. .-+ + + + + +-. + +

SOLID

Poly_r Molecule

(~ Sulfonate Molecule --

Filure 11. Adsorption of Sodium Dodecylsulfonate Molecules on a Surface alreadyCoated with the Nonionic Polyacrylamide (PAM).

\e""5e:~ 7~ !-