References Puddington. I.E.. and Sparks. B.D.. 1975. "SphericalAgglomeration Process." Minerals Science Engrneering, Vol. 7.No.3.Rao, T.C., and Bandopadhyay. P.. 1980. "Processing of IndianCoal Fines," Fine Particle Processing. P. Somasundaran. ed.,AIME, New York.Rao. T.C., Vanangamudi. M., and Hanumantha Rao, K.,1982. "CharacteriStic Curve for the Coal. Agglomeration Process...International]. Miner Process.

Rao. T.C.. Vanangamudi, M.. and Hanumantha Rao. K.,1982, "Kinetic Study of Agglomerate Growth in Coal-OilAgglomeration Process, Fuel.Sarkar, G.G.. et aI.. 1976, "Studies on the Applicability of OilAgglomeration to Various Coal Beneficiation Problems... 7thIntemational Coal Preparation Congress. Australia.Stock. D.I., 1950, "Micro Spherical Agglomeration of BariumSulphate... Nature, Vol. 170. p. 423.Swanson. A.R.. Bensley, C.N., and Nicol, S.K.. 1977. "SomeFundamental Aspects of Selective Agglomeration of Fine Coal...2nd Intemational Symposium on Agglomeration, Atlanta. GA,p.939.

Bandopadhyay, P., Rao, T.C., and Sinha, P.R., 1979, Benefici.ationofCoal Fines in India," World Coal, May.Bensley, C.N., Swanson, A.R., and Nicol, S.K., 1977, "The Ef.fect of Emulsification on the Selective Agglomeration of FineCoal,"lnt.]. Miner Process, Vol. 4, p. 17~.

Capes, C.E., 1980, "Principles and Applications of SizeEnglargement in Liquid Systems," Fine Particle Processing, P.Somasundaram, ed., AIME, New York.Capes, C;E., et aI., 1979, "Pilot Plant Testing of the SphericalAgglomeration Process in Coal Preparation," Proc. Imt.Bnquet. Agglom. Bien. Confr., Vol. 16, p. 7~.

Capes, C.E., McIlhinney, A.E., and Coleman, R.D., 1970,"Beneficiation and Balling of Coal," Trans. SME-AIME, Vol.247, p. 2~~. '

Capes, C.E. et al., 1976, "Application of SphericalAgglomeration to Coal Preparation," 7th International CoalPreparation Congress, Australia.Nicol, S.K., and Swanson, A.R., 1979, "Ultrafine CoalRecovery from Preparation Plant Tailings," 8th InternationalCoal Preparation Congress, USSR.

Y.H.C. Wang and P. Somasundaran

Abstract-A detailed study of camn flotation of kaolin clayWJ"tag calcite showed the major benefication mechant:fm to beenhanced aggTegation between anatase and calcite under intenseagitat"on conditions, To develop an undeTstanding of this selec,tl've aggregation, surface charge chaTactemt,Cs of kaolinite,anatase, and calcite were stum'ed under SImulated flotationconditions, Zeta potential of aU these minerals tended tOUlaTds aconstant negative mille in oleate solutions undeT certain condi,tions possibly due to adsorption OT precipitation of oleate onthem, HOWeveT, whereas the zeta potential of anatase in theoleate solutions was not influenced by the agitation level, that ofkaolinite was found to be strongly dependent on the agitatiOnintensity, The effect of oleate on zeta potential of kaolinite wasTeduced by an increase in agitation intensity, It is sfJggested thatoleate is much more firmly bound to the surface of the anataseand that this preferential attachment is Tesponsible foT the en-hanced selective aggregation of the anatase WIth calCIte,Agitation level plays a majoT TOle in cameT flotation since in-tense agitation is consideTed to enhance both the chemisoTptionof oleate on anatase and preferential detachment of cala'umoleate preCl:pitate from the kaolinite surface, aU of thisproducing a large diffeTence in the surface propeTties of anataseand kaolinite, and hence in theiT tendency to aggregate withcalcite.

1961; Green. Duke, and Hunter, 1961). However. very little isknown about the process itself and the mechanisms involved. Adetailed study of the basic aspects of carrier flotation- has beenmade in this investigation with the aim of understanding thisprocess so that it could be made useful for the beneficiation ofother ores.

Results of the first phase of this work. which included carrierflotation of anatase from kaolinite using calcite and oleate un-der various conditions. suggested the major mechanism involvedin carrier flotation to be enhanced aggregation between fineanatase and coarse carrier particles (Wang and Somasundaran,1980). Other than for the speculation that the anatase mighthave a lower surface charge than the kaolinite under the optimumconditions (Sennett and Young. 1979). the reasons for the selec-tive aggregation between the carrier particles and anatase haveremained obscure.

In this work. surface charge characteristics of calcite. anataseand kaolinite in oleate solutions are determined under relevantconditions and their role in causing the selective aggregation isexamined. Zeta potential of anatase and kaolinite conditionedat different agitation levels is Studied and the effect of theagitation intensity on electrokinetic and carrier flotationbehavior of the system is discussed.

IntroductionY.H.C. Wang, member SME, is research associate, and P.Somasundaran, member SME, is professor, Henry KrumbSchool of Mines, Columbia University, New York, NY. SMEpreprint 81-132, AIME Annual Meeting, Chicago, IL, Feb. 22,1981. Manuscript Feb. 1981. Discussion of this paper must besubmitted, in duplicate, prior to Aug. 31, 1983.

Carrier flotation. also known as ultraflotation. is one of thetechniques that is useful for the beneficiation of fmes. Thistechnique has been commercially used by Engelhard Mineralsand Chemicals Corp. to remove anatase impurity from kaolinclay with coarser calcite added as carrier (Green and Duke.

197o-Transac;tions Vol. 272 SoCiety of Mining Engineers of AlME

fect on the yield of agglomerates. At lower dosages of oil (10%)the yield is extremely low and considerable increase in yield isobtained when the level of oil is equivalent to 15% by weight ofcoal present (Fig. 2). Funher increase in the dosage of oil has aninsignificant effect on yield. At 20% and 25% oil dosages. theyield is same even with increase in agglomeration time whereasat lower oil dosages the yield shows an increasing trend withtime. Even though the yield does not increase with time athigher levels of oil dosage. the growth of agglomerates takesplace. At higher oil dosages quite bigger allomerates are formedup to 25% oil level. Beyond this. agglomerates are not formedas distinct spheres. but coal mass in the form of amalgam withoil has been found.

The ash content of the agglomerates is almost the same at dif-ferent periods of agglomeration at a particular furnace oildosage. However. the ash content is decreased when the furnaceoil dosage is increased from 10% to 25%. The reason for this isdue to the increased amount of oil present in the agglomerates.When the level of bridging liquid is low. the agglomerates arequite voluminous in the form of flocs. With increase in oildosage. the agglomerates are well formed with distinct sphericalshape. As more oil is available at the surface of the spheres withincreased oil dosage. bigger agglomerates are formed.

Effect of Degree of Agitation

The results obtained at three levels of degree of agitation(900. 1200 and 1400 rpm of impeller speed) at different periodsof agglomeration are given in Table 5. On comparing the yieldof agglomerates at different rpm. at two minutes agglomerationtime. the yield is drastically reduced with increase in rpm.Though the yield with other periods of agglomeration is almostthe same at all rpm. an increase in yield with time is noticed atall levels of agitation. In the initial periods. the agglomerates areloosely bound and the higher degree of agitation makes thembreak easily. After a cenain time. the agglomerates formed arecompact and. hence. the yield remains constant with increase indegree of agitation. The ash content of the agglomerates alsoremains constant with increase in rpm.

Conclusion

For a successful agglomeration, there is a maximum limit tothe pulp density of the slurry beyond which the separation ofcoaly matter from the mineral constituent is difficult. The yieldincreases with increase in pulp density up to a cenain level andthen decreases in the range below the critical pulp density. Themaximum yield that can be obtained increases with increase infurnace oil dosage to some extent and then remains constant.The degree of agitation has more effect on the size distributionof the agglomerates than on the yield and ash content. It is alsoconcluded that aU the variables tested have no significant effecton the ash content of the agglomerated product. 0

Summary

Acknowledgements

The financial support of CSIR for the research project "Opti-misation of Process Variables in Oil AgglomeTation Process" un-der which this research program was carried out is gratefullyacknowledged. ThankS are due to Central Coal WasheriesOrganization for supplying coal samples used in this investigationThe authoTS wish to thank Shri G.G. Sarkar. Deputy Director.Central Fuel Research Institute for his valuable suggestionsduring the course of this inveStigation.

From the process operation point of view the following impor-tant observations may be made from the results discussed above.

. The agglomeration process needs less time (5 min) at a

moderately high pulp density (20%). Below or beyond this levelof pulp density the maximum yield can be attained only withconsiderable increase in agglomeration time.

. Beyond the minimum agitation required. an increase in

agitation does not have a significant eff~t on the maximumlevel of yield or the time at which the maximum yield is attainedin the ranges studied.

. Low level of furnace oil (10%) gives a maximum yield ofonly about 25% even with 15 minutes agglomeration time.whereas 15% furnace oil level with 15 minutes agglomerationtime gives the maximum yield (about 88%) that can be ob-tained with the coal. Beyond this level of furnace oil, thismaximum value is reached even at two minutes agglomerationtime. Hence. a moderately high furnace oil level (15-20%) cangive a maximum yield with less time.

Table 5-Effect of Degree of Agitation on Yield and Ash Content of Agglomerates at DifferentPeriods of Agglomeration

(Sample: Dugda-1 Washery slurry)TIme of Agglomeration {in minI

2 5 . 1271.64 82.14 92.78 93.0716.99 17.12 17.26 18.0461.72 78.21 64.40 92.2116.~ 11.23 11.51 11.43320M 78.28 ..85 90.4211.01 11.43 11.04 11.43

Degree ofagitation (In rpm)

900

18

94.001846

92.4918.15

92.5718.15

Yield %A8h%

YIeld %A8h%

Yield %A8h%

1~

Transactions Vol. 272-1-Society of Mining Engineers of AlME

Table 1-Comparison of Zeta Potential of Anatase in ClaySupernatant with that in Reference Solutions

Experimental

Materials

CaCI2kmoUm3

Zet. potentl.' of anatase (mY)In N~CO3.Na2SI03 solutions

pH Ha-Olaatekglm3

Clay~t

-31.0-46.4-58.1-62.2

Aele-solution

-31.4-47.2, -45.9

-581

-64.8

1.8 x 10-47.4 x 10-67.4 x 10-67.4 x 10-6

8.510.110.110.1

-0:52.33

ner .in clay supernatants prepared by dispersion of the kaolinclay in sodium carbonate-sodium metasilicate solutions for 30minutes at 2000 rpm (Wang and Somasundaran, 1980) andremoval of the residual clay by centrifugation at 12,000 rpmusing an IEC refrigerated hign speed model B-2A centrifuge.

Results

The resultS obtained for the effect of clay dissolved species,oleate, and agitation on the zeta potential of various mineralsare given below.

Clay Supernatant

Flotation feed was prepared from kaolin clay obtained fromEngelhard Minerals and Chemicals Corp. by removing the + 20j4n fraction (Wang and Somasundaran, 1980). Chemical analysisof the kaolinite indicated the impurities to be 2.26% Ti02' 0.5%F~03, 0.03% P205, and the rest to be kaolinite. The X-raydiffraction powder pattern of the sample was characteristic ofthat for kaolinite. Impurities, since they were present in smallamounts, did not appear in the X-ray diffraction pattern. Thepanicle size distribution of the kaolinite sample, determinedusing a Sedigraph 5000, showed the sample to be 100% -151ArDand 90% - 2 lArD.

Pure synthetic anatase was purchased from Gallard-SchlesingerChemical Manufacturing Corp. The sample was specified by thecompany to be 99.9% Ti02 and 0.48 lArD in diameter.

Crystalline calcite, Iceland Spar Variety from Chihuahua,Mexico, was purchased from Ward's Natural Science Establish-ment Inc. This sample was crushed using a steel hammer,ground using a disc pulverizer, and further wet ground to - 20 j4nusing a porcelain ball mill.

Surface area of kaolinite, anatase, and calcite determinedusing nitrogen adsorption technique was 13.2, 12.2, and 1.1

m2/g respectively.Triple distilled water was used for preparing all the solutions

used in the electrophoresis experiments. Sodium oleate solutionwas prepared by mixing excess amounts of sodium hyroxide witholeic acid, a laboratory grade reagent purchased from FisherChemical Co. The rest of the reagents used for the preparationof electrolyte solutions and for pH modification were ofanalytical grade.

The effect of soluble species released from clay on the chargecharacteristics of anatase was investigated by determining thezeta potential of anatase in kaolin supernatant. The data ob-tained in kaolinite supernatants at various pH values and calciumand oleate concentration is given in Table 1 along with that ob-tained in corresponding reference sodium carbonate-sodiummeta silicate solutions. The results show that the species in-troduced into the solution either by the dissolution of or by theion exchange from the kaolin clay do not cause a measurablechange in the surface charge characteristics of anatase underthe tested conditions.

Procedure

Oleate

Zeta potential of calcite at pH 10.1 is shown in Fig. 1 as a func-tion of oleate concentration. Calcite is seen to become highlynegatively charged upon the addition of oleate even at a concen-tration of 0.3 kg/m3 with no change upon funher oleate ad.

+40pH.10.11.1 I 10-3 kmol/m3 C03

1.9 11o-3kmol/m3SiO;+20

>e

-Joct~ZI&JI-0Q.

octI-I&JN

\

0

-20

-40

-60

!-eo. I I I I I

0 0.4 0.8 1.2 1.6 2.0 2.4CONCENTRATION OF SODIUM OLEATE, kg/m3

Fig. 1-Zeta potential of calcite at pH 10.1 in sodium carbonate-sodium metasilicate solutions (1.1 x 10-3,1.9 x 10-3 kmol/m3)as a function of sodium oleate

For the electrokinetic experiments. first a 0.03 wt. % of con.centrated suspension of anatase or kaolinite was prepared byultrasonic agitation (at 100 watts for 30 sec.) and then diluted toa concentration of 0.0015% with solutions of sodium carbonateand sodium metasilicate adjusted to desired pH values and thenstirred for 30 minutes. This was followed by the addition ofcalcium chloride and sodium oleate and triple distilled water tomake the total volume of the suspension to 100 cm3 (3.38 oz). Ineach case pH was adjusted. if necessary. following the reagentadditions. Sodium carbonate and sodium metasilicate were ad.ded since they are the dispersants used in carrier flotation andtheir fmal concentrations were estimated to be 1.1 X 10-3 and1.9 X 10.3 kmol/m3 respectively. For tests with anatase andkaolinite only. calcium chloride also was added to simulatecalcium that would have been released from calcite if it waspresent in the system. Its concentration was calculated from thedata for the solubility product of calcium carbonate and theconcentration of the carbonate that was added into the system.The 100 cm3 (3.38 oz.) of a sample was then stirre4 in a 150 cm3(5.1 oz.) beaker at 335 rpm using a magnetic Stirrer with a 3.8cm (1.5 in.) Stirring bar (67 cm/s). For the tests to determine theeffect of agitation intensity. the suspensions were. on the otherhand. prepared by stirring 200 cmJ (6.76 oz) of the suspensionin a 250 cm3 (8.5 oz) beaker fitted with a baffle assembly (4 baf.fle plates of 0.63 cm in width) at 2000 rpm using a 2.54 cm (1 in.)diameter propeller (top speed 266 cm/s). At the end of thestirring. pH was measured and zeta potential was determinedusing a Zeta meter.

For tests with calcite. the solution containing sodium car.bonate and sodium metasilicate was prepared at the desired pHand a known amount of calcite was added directly to it. Afterthe addition of sodium oleate to this suspension and adjustmentof pH. if necessary. it was diluted to 0.015%. and stirred for 50minutes and used for the electrokinetic measurements.

Tests conducted to determine the effect of dissolved clayspecies involved conditioning of the minerals in a similar man-

Transactions Vol. 2~1971Society of Mining Engineers of AIME

+40 +40pH-tO.1

1.1 x 10-3kmol/m3 CO;

1.9 x 10-3 kmoll m3 SK>;

CoCt2

+20 +20

>E

oJc

~

Z

1&1

t-

fc~1&1

N

>E 0

-ic~z -20I&J.-

~

c -40.-I&JN

-60 -60 ~~-Q ~-- , ,- 1 8

-eo I I I I I I

0 0.4 0.8 1.2 1.6 2.0 2.4

CONCENTRATION OF SOOIUM OLEATE. k9/m'

FIg. 2-Zeta potential of wtatase at pH 10.1 In aodkJm C8b0nat.

sodium metasllicate solutions (1.1 x 10.3.1.9 x 10-3 kmol/m3)and calcium chloride (simulated calcite supernatant) as a func.tion of sodium oleate

-eo I I I I I I

0 0.4 0.8 1.2 1.6 2.0 2.4CONCENTRATION OF SODIUM OLEATE, kg/m3

Fig. 3-Zeta potential of kaolinite at pH 10.1 in sodium c.bonat&sodium metasilicate solutions (1.1 x 10.3.1.9 x 10-3 kmol/m3)and calcium chloride (simulated calcite supernatant) as a func-tion of sodium oleate

dition. Such a sharp dependence on concentration is charac.teriStic of precipitation and, in this case, is considered to resulteither from surface precipitation of calcium oleate or thecoating of the calcite panicles with calcium oleate precipitate.

Variation of zeta potential of anatase and kaolinite at thesame pH-with oleate concentration is shown in Figs. 2 and S. Inboth cases, the magnitude of the negative zeta-potential is foundto increase with increase in oleate concentration and to attain aconstant value of about - 65 m V . Since this value is close to thatobtained in the case of calcite, surface precipitation of calciumoleate is considered to take place in the case of anatase andkaolinite allo.

Agitation Intensity

Since the agitation that was used for the preparation of rhesuspensions for the above electrokinetic rests was mild in compar-ison wirh that used during the conditioning srep prior to carrierflotarion. it was necessary to investigare rhe effect of theagitation level and this was done by conducting selected electro-kinetic tests at rwo different stirring speeds (67 and 266 an/I).

Fusr. electrokinetic dara for anatase prepared at the twoagitation levels is given in Fig. 4. In the tesred range. the changein agitauon intensity did not produce any significant variarionin the zeta potential of anatase.

+40 +40 ":c'" . . ',. ~~'I

0 67 em/.

A 266 em!.0 67 cm/l

6 266 cm/l+20 +20

: pH c 10.1

1.1 K 10-3kmol/m3 CO;

1.9 K 10'"3 kmol/m3 510;

CoC12

--~ ~ pH -10.1

1.1 a 10-3 kmol/m3 CO;1.9 a 10.3k~l/m3 SlO;

CaC12

>E 0

Jc~z -20'"I-

~~ -40I-I&J

>E

oJc(~Z!&I...0a..

~!&IN'-

-60 -60

r:---A ---;;: !'. i..c'. ~'a

~O-"a---Q---~_.~ :;: .""t)."8'."O'"" 9._-~'OO!'""'O - -"

-eo' . . I I .

0 0,4 0.8 1.2 1.6 2.0 2.4

CONCENTRATION OF SODIUM OLEATE, kg/m'

FIg. 5-Zeta pot-.tiaI of kUnte at ~ 10.1 in ~ c&-oo sodium metasilicate solutions (1.1 x 10-3, 1.9 x 10-3 kmoUm3)

as calcium chloride (simulated calcite supernatant) as a func-tion of sodium oleate at two different speeds of reagentizing of

kaolinite suspensions

-eo I I I I I I

0 0.4 0.8 1.2 1.6 2.0 2.4CONCENTRATION OF SODIUM OLEATE, kg/mS

FIg. 4-Zeta potential of .-tase at pH 10.1 ., eoolwn C8b0r8te-sodium metasillcate solutions (1.1 x 10-3, 1.9 x 10-3 kmol/m3)and calcium chloride (simulated calcite supernatant) as a func-tion of sodium oleate at two different speeds of reagentizing ofanatase suspensions

Society of YNnQ e of ANe1172-~ Vol. 272

0

-20

-40

0

-20

-40

Corresponding results obtained for kaolinite are given in Fig.5 and Table 2. It can be seen that the magnitude of the zetapotential of kaolinite does decrease with an increase in stirringspeed under all conditions. This change in zeta potential withincrease in agitation intensity is significantly higher when oleatewas present in the solution: - 71 mV to -50 mV at pH 8.5 and-65 mV to -52 mV at pH 10.1 in comparison to -40 mV to- 37 m V and - 52 m V to - 46 m V, respectively in the absenceof oleate.

If coating of the particles with calcium oleate is the majorphenomenon in the present system, the differences observed inthe effect of agitation intensity on the zeta potential of differentminerals can be due to possible differences in the strength of ad.hesion of the oleate to the mineral surfaces and resultant detach.ment of the precipitate in some cases. This possibility is furtherexamined next.

Discussion

highest speed used in stirring prior to deCtrokinetic test. Theobservation that the removal of anatase from clay by carrierflotation was higher at higher agitation levels further supportsthe mechanism discussed above. Furthermore. solids con-centration (28%) used in flotation tests is higher than thatused in electrokinetic tests. Detachment of the weakly attachedoleate from the kaolinite surface due to scrubbing also can beexpected to contribute towards selectivity in flotation. The elec-trokinetic results obtained during this study for anatase andkaolinite as a function of oleate concentration under differentagitation levels clearly suggest that the oleate uptake by themineral particles is responsible for aggregation. Selective aggre-gation occurred between anatase and calcite even though anatasewas more negatively charged than kaolinite under high agitation.The oleate on the mineral surface is able to induce aggregationowing to oleophilic (hydrophobic) interaction between adsorbedfIlms on different particles. The attractive forces resulting fromthe hydrophobic interaction are shown to be much greater thanthe van der Waals force; the total attractive forces are thus able toovercome the electrostatic repulsive force (Wang and Somasun-daran. 1982). The seleCtive aggregation observed in carrierflotation is possibly similiar to the "shear flocculation" occurringduring intense stirring mineral suspensions (Warren, 1975;Warren, 1975;jarrett and Warren, 1977).

The basic reason for the selectivity in aggregation is proposedhere to be the stronger attachment of the oleate to the anatasesurface than that of it to the kaolinite. The possibility of strongbonding of oleate to anatase is in accord with the chemisorptionhypothesis proposed in the past (Sherwood and Rybicks, 1966) forthe oleate/anatase system. Elevation in pulp temperature due tothe intense agitation observed during conditioning will enhancesuch chemisorption of oleate. Carrier flotation results obtainedhere (Fig. 7), which show improved separation at higher pulptemperatures. support the above contention. Similar adsorptionto oleate on kaolinite is unlikely. Oleate has not been observedto undergo chemisorption either on kaolinite or its major constit-uents. silica and alumnia. There can be some uptake of oleateon kaolinite in calcium solutions under the pH conditions studied,panicularlyat the edge surfaces. This possibly is induced by anyactivated adsorption at such surfaces. Evidently such uptake isnot of a major consequence, at least under high agitation con-ditions.

Summary

1) Electrokinetic tests showed the zeta potential of calcite to at-tain a large negative value of - 65 m Vat pH 10.1 u~n contact-

ing it with oleate solutions containing 1.1 X 10-3 kmol/m~Na2CO-, and 1.9 X 10 - -' kmol/m-' Na2S10-,.

2) Anatase and kaolinite also acquire similar values in theabove oleate solution containing in addition 7.4 X 10-6kmol/m-' of calcium chloride. This is attributed to the adsorbedoleate and/or calcium oleate precipitate on the mineral sur-faces.

- -Table 2-Zeta Potential of Kaolinite Prepared Under Different

Agitation Conditions

System: KaolIN.. In Na2COS-N82S1O3 Solution (1.1 x 10-3,1.9 x 10.3 kmoi/m3j endSilnuleted Celclte Supem8tant

DH - 1.5 10.1

A~i..tion

If selective aggregation between anatase and calcite is thereason for the success of the carrier flotation, there are twomajor questions that need to be answered. What are the forcesresponsible for the aggregation between the above two mineralsand why is it selective? Aggregation depends on the nature of in-teractions between the particles. the two major types of interac-tions being the electrostatic interactions and London-van derWaals attractive interactions. While the former can be repulsive(or attractive) in nature. it is sufficient for the total energy of in-teraction between the two entities to be negative for the aggre-gation to take place. In the present case, all the three mineralswere found to acquire a large negative charge in oleate solutions.Selective aggregation under such conditions clearly suggestssel~ctive surface modifications that enable certain mineral com-ponents to acquire an additional attractive force in order to over-come the electrostatic repulsive force between them. Coating ofthe panicles by oleate either due to surface precipitation or ad-sorption or attachment of bulk oleate precipitate can indeedmodify the surface for av:y;r~ation.

Oleate has been suggested in the past to chemisorb on calcite(Peck and Wadwonh. 1963) and anatase (Sherwood and Rybicks,1966). Oleate adsorption on clay is possible because of its activa-tion by the calcium species in solution. In addition. nucleationleading to surface precipitation of Ca-oleate on all three solids,which are partially hydrophobic due to initial oleate adsorption.can also result in surface modification. Precipitation of Ca-oleateis expected to occur in all cases here, since the solubility productof Ca-oleate (10 - 15.7 to 10 - 15.4) (Fuerstenau and Palmer.

1976; Jung. 1976; Du Rietz. 1964) is exceeded for the range ofoleate (10-3 to 10-2 kmol/m3) and calcium (7 X 10-6kmol/m3) present in the system. Funhermore. the attainment ofconstant value for the zeta potential of all the minerals whencontacted with oleate under low agitation supports such a possi-bility that a single species might have coated the mineral surfaces.

Indeed. carrier flotation was selective since anatase wasremoved by calcite in preference to kaolin and the reasons forthis become evident while examining the effect of agitation in-tensity on the magnitude of the zeta potential change due tooleate. It was observed during the current investigation that in.crease in agitation intensity minimized the zeta potential changedue to oleate but only in the case of kaolinite (Fig. 5 and Table 2).Zeta potential of anatase remained unaltered upon increasingthe agitation (Fig. 4). This is attributed to the easier detachmentof calcium oleate precipitate from the kaolinite surface. Ap-parently oleate is much more strongly bound to the anatase sur-face than it is to the kaolinite. Aggregation between panicles,evidently induced by the surface modification caused by adsorbedor attached oleate, can take place under intense agitation con.ditions only between anatase and calcite and not betweenkaolinite and calcite. Possibility for such selective detachment ofcalcium oleate which can induce aggregation is even higher incarner flotation than during the electrokinetic tests sinceagitation during the conditioning of the mineral before flotationwas much higher than that corresponding to 266 cm/s, the

SOCiety of Mining Engi~a of AIME Transactions Vol. 272-1173

5) The magnitude of the ma ~ential change is reduced in thecase of kaolinite when the suspension is subjected to a more in-tense agitation. Agitation level was found to have no such effecton the zeta potential change of anatase.

4) The difference in the effect of agitation intensity is attribUtedto weaker binding of the oleate to kaolinite surface than toanatase surface and preferential removal of the oleate from thesurface of the kaolinite under intense agitation conditions. Thesuggested strong binding of oleate on anatase as well as calcite isin agreement with chemisorption mechanism that has been con-sidered in the past for oleate and these minerals. Observed sharpincrease in temperature during conditioning prior to carrier flo-tation can be expected to enhance such chemisorption.

5) Presence of oleate on anatase rather than on kaolinite underintense agitation conditions contributes towards selective aggre-gation between calcite and anatase due to oleophilic interactionsthat apparently predominate over the electrostatic repulsive in-teractions between the similarly charged anatase and calciteparticles.

6) The surface modification of anatase and calcite induced byoleate uptake on them and resultant selective aggregation be-tween them, in addition to any homoaggregation betweenanatase particles themselves, is proposed to be a major mechan-ism of carrier flotation. 0

Acknowledgment

Suppon of the Chemical and Processing Engineering Divisionof the National Science Foundation (ENG-7825213 and CPE.8011013) is acknowledged.

Fuemenau, M.C., and Palmer, B.R., 1976, "Anionic flotationof Oxides and Silicates," Flotation, M.C. Fuemenau, ed.,AIME, New York, Vol. 1.Garrels, R.M., and ChriSt, C.L., 1965, Solutions Minerals andEquilibria, Harper and Row, New York.Greene, E.W., and Duke,j.B., 1961, Mining Engineering, Vol.10, p. 792.Greene, E. W., Duke, j.B., and Hunter, j.L., 1961, US Patent2,990,958, July 4.

jarrett, R.G., and Warren, L.j., 1977, Proc. Australas. Inst.Min. Metall. Vol. 262, p. 57.

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D.G. Foot. Jr. and J.L. Huialt

Abstract- The Bureau of Mines dewed a direct flotationmethod for treating low-grade carnallite (KCI8MgCI286H20)and sylvinite (a mixture of KCI and NaCl) ores characterized bya high content of water-insoluble impunties. The procedureconsists of flocculation-depress,on of the insoluble slimes;decomposition leach (camaUite only); potash Tougher, cleaner,and recleaner flotation; and final product leaching. The tech-nique eliminates the neceSSIty of removing the water-insolubleslimes by mechanical or flotation desliming. Laboratory resultsdemonstrated that the direct flotation procedure, when com-pared with conventional techniques, yielded equiwlent or im-proved flotat,on results with equal or less reagent consumptions.The direct flotation method recovered 81- 6% of the solid phaseKCI from carnallite ore and 79.7% of the KCI from sylvinlte ore'"n final products containing 60..5 and 60.9% K20, respectively.A flowsheet incorporating the desm.bed flotation procedure ispresented.

that the nation's mineral needs can be fulfilled in a manner thatreduces waste and ensures minerals and metals are processed,used, and recycled at acceptable economic, social. and environ.mental c~. In accordance with this mission, a research programwas conducted to investigate anew. direct flotation method(patent application serial number 348, I 17) for recovering potashwithout prior removal of insoluble slimes. Methods were devisedthat are effective on both high-insoluble-slime-bearing carnalliteand sylvinite ores.

The Permian Basin near Carlsbad, NM, has been a sourCe ofhigh-grade sylvinite ores during the last 40 years. As these high-grade sylvinite ores are depleted, low-grade sylvinite ore, con-taining abundant insoluble slimes, and carnallite ores arebecoming the future sources for potash production. These orescontain 1-8% water-insoluble slimes, which must be removed

D.G. Foot, Jr.. member SME, is a metallurgist and J.L Hula«.member SME, is research supervisor, both with USBM's SaltLake City Research Center in Utah. SUE preprint 81.74, SUE.AIME Annual Meeting, Chicago, IL, Feb. 1981. Manuscript Jan.7, 1981. Discussion of this paper must be submitted, induplicate, prior to Aug. 31,1983.

Introduction

The mission of the Bureau of Mines minerals researchprogram is to help improve minerals processing technology so

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