. . .

P. Somasundaran

Henry Krumb School of MinesColumbia University

New York I New York 10027

VOL. 71, No. 150 t 975 PACES 1-15

flotltion, I technique widely u.d for the concentretion or purifica-tion of plrticulltes, is dictated mlinly by the interfacial properties of

the solid/liquid/gas system and chlnges in those properties due to Id-

sorption of various inorganic Ind organic reagents. Basic principles

governing the Idsorption process(1s) Ind the resulting flotation Ire reoviewed in this introductory paper. Examples are discuaed to show the

effects of relevlnt controilible verilbles such IS solution pH; collector

structure and concentretion; ionic strength; concentrltions of floc-

cullnts, depreGlnu, and Ictivltors; Ind conditioning tempereture.

P. Somasundaran

again the basis for separation, but the adsorbed material is col.lected selectively with a liquid (instead of air) that is immisci-ble with the bulk aqueous solution. At present, froth flotationis the only technique that has significant industrial application,and is therefore emphasized in this paper. Precipitate flota.tion, which appears to hold promise for future applications, isalso discussed.

METHODS

For froth flotation. a pulp of the particulates is first con.ditioned with the appropriate reagents. It is then agitated us-ing impellers in a cell such as the one shown in Figure I. Airis sucked in or sometimes fed into the cell near the impeDerlone. The air bubbles. now dispersed by the impeller. collidewith particles and are attached to those that are hydrophobicor have acquired hydrophobicity and rise to the cell top wherethey are removed by skimming. Figure 1 is a schematic repre-sentation of a typical industrial flotation cell.

As opposed to froth flotation which uses turbulent condi-tions. foam separation techniques generally consist of aerationat a low flow rate. and the separation of the foam containingthe collected material is followed by its breaking using variouschemical, thermal or mechanical methods (5). A strippingmode in which the descending feed is introduced into thefoam and an enriching mode in which part of the foamate isrecycled to the top of the flotation column are recommendedfor increasing the recovery and grade. respectively. of the

product (see Figure 2).

}. large variety of chemical species ranging from moleculesand ions to micro-organisms and minerals can be separatedfrom one another or concentrated from solutions using flota.tion processes. Even though the mechanisms involved in theflotation or the nonflotation of each species with various reoagents are not fuUy established, the flotation pro~sses can beconsidered to be primarily the result of the tendency of cer.tain surfa~ active species to concentrate at the liquid/gasinterfa~ and the tendency of some other species or particlesto associate with or adsorb these surface active species. Thelarge number of flotation processes tested have been classified(Table I) according to the size (molecular, microscopic, ormacroscopic) of the flotated species and the mechanism (con-sistent with natural or acquired surface activity) of flotation.Thus, there is foam fractionation for the separation of surfaceactive species such as.detergents in aqueous solutions, andfoam flotation for that of naturally surface active organismsand proteins. Techniques based on the tendency of variousspecies to associate with surfactants are: ion flotation for theseparation of ions, micro flotation and ultraflotation for veryfme particulates, and froth flotation for the separation of min-erals that possess mostly polar surfaces. In addition to thesetechniques, there are also certain nonfoaming flotationmethods such as oil.flotation (2), bubble fractionation (3) andsolvent sublation (4), for which adsorption at the interface is

Henry Krumb School of Mines, Columbia University, New York,New York 10027.

AIChE SYMPOSIUM SERIES2

TABLE 1. FLOTATION TECHNIQUES CLASSIFIED ON THE BASIS OF MECHANISM OF SEPARATIONAND SIZE OF MATERIAL SEPARATED It I

Mechanism

Natllrat surfec8 activity

Size Range

MiuOtCOt)ic

F08m flOClcionIX:micrOOfpni."s. prOteins

In essoc~tion with surf8C8Ktiw agentl

Mecroscopic

Froth flot.tion of nonoo~miner."

ex:sulfur

Froth flotationex:miner.'s such .s silic.

Precipitate flotation{1st.nd 2nd kind}

Microfloutlon. colloid IIo~tion.ultra flotation

ex:P8rticuletes in _ste weter. clay.

micrOOf't8nisms

Molecular

Fo.m fractionationIX:dltlrgents from aqueous

solutions

Ion flot8tiOn. molecul.r

floutlOn, Idsorbingcolloid flotation

,.:5rl+, Pbl+, Hgl +, cyanide

.x:f.ric hydroxide

ReprInted from CtNn SurfKft 1970. Courtesy of Marcel ~ker Inc

Cq, tite, and oxidized sulfides; and long chain amines ror quartz,potash, reldspars, mica, etc.

Two recent reviews on xanthate-galena systems by Gutier.rez (7) and Granville et al. (8) deal with the different mech-anisms and the problems involved in the study or the flotationchemistry or sulfide minerals. Xanthates are considered toadsorb on sulfides such as galena due to chemical rorces be-tween the polar head and the surrace resulting in metal xan.thates. Mechanisms involving the rormation and adsorption ordixanthogen, xanthic acid, etc. have also been proposed. Theeffect or the oxidation of sulfide mineral surfaces on flotationhas received considerable attention. Gutierrez (7) noted in

BASIC PRINCIPLES

SELECTIVE HYDROPHOBICITY

As mentioned earlier. froth flotation of minerals or precipi-tates is possible if they can be preferentially wetted by gasrathe. than by water. Only a very smaU fraction of the min-erals such as sulfur is naturaUy hydrophobic. Precipitates ofthe second kind (6). formed by reaction between ions and cer-tain organic reagents. are also hydrophobic. Hydrophobicityhas to be imparted to most other minerals and precipitates inorder to float them. Towards this purpose. a surfactant thatwill selectively adsorb on the material to be floated is added tothe suspension in water and conditioned by agitation. Thissurfactant. called a collector. possesses at least one nonpolarand one polar portion. Owing to chemical. electrical. or phys-ical attraction between the polar portions and the surface sites.the collectors adsorb on the particles ~'ith their nonpolar endsoriented towards the bulk solution. thereby imparting hydro-phobicity to the particles. Collectors that are commonly usedinclude short chain alkylxanthates for base metal sulfides; longchain fatly acids and their alkali soaps for phosphates. berna-

No. ISO, Vol. 11 SOMASUNDARAN

this connection that due to the porosity of natural plena evenfreshly ground galena will possess oxidized layers, and hence,results reported for such systems do not necessarily determinethe effects of oxidation of the galena surface on flotation.The reaction of xanthate with the oxidation products ofgalena on the surface through an ion-exchange process is con-sidered to be the major adsorption mechanism responsible forthe xanthate flotation of galena. Previous identification ofdixanthogen on plena is attributed by GranviUe et al. to itsformation during the evaporation of lead xanthate in ether orCSz onto a surface. Their tests, however, do not conclusivelyidentify the species responsible for flotation, because theamount of dixanthogen observed on the mineral could havebeen sufficient to cause flotation. Adsorption mechanisms forsulfide flotation systems have been discussed elsewhere byFinkelstein et al. (9) and hence are not covered in this paper.

Unlike xanthates on galena, alkyl amines, sulfonates, andsulfates are considered to adsorb on minerals primarily due toelectrostatic attraction between the polar head of the coUectorand the charged surface sites on the mineral. These electro-static forces, which are not u strong as the chemical forces in-volved in xanthate adsorption, are assisted by the associativeinteraction among the long alkyl chains that normally contain8 to 20 carbon atoms (10-12). Because electrostatic forces arethe basic cause for the selective adsorption in these cases, it isimportant to understand the electrical nature of the mineral/solution interface and the mechanisms governing its origin.

The electrical nature of the particle/solution interfal% is theresult of either a preferential dissolution of lattice ions u inthe case of silver iodide, or of the hydrolysis of the surfacespecies followed by pH-dependent dissociation of the surfacehydroxyls as in the case of silica (I I) and alumina (13):

OH-- M(HzO)Surtace -- - MOHSwf8c:8 ~

under conditions of zero surface charge on the mineral. As-suming that potential differences due to dipoles remain con-stant, the total double layer potential is considered zero whenthe surface charge is zero; such a condition is called the pointof zero CM'Ke (pzc). For oxides, the activities a. and a~ willbe that of hydrogen ions in the solution under considerationand that at the point of zero charge, respectively. Similarly,Q- and a~ will be the activities of hydroxyl ions under corre-sponding conditions. Thus the oxides will carry a positivecharge in solutions that are more acidic than that a pzc and anegative charge in solutions that are more alkaline. Sin~ thesystem IS a whole must be electric:a1ly neutral, the mediumsurrounding the particles must contain an equivalent amountof ions, called counter ions, of charge opposite to that on thesurfa~ of the particle. Owing to the attraction by the chargedswface sites, these counter ions will not be uniformly distrib-uted in the solution phase, but will be adsorbed at the oxide-solution interfa~. This gives rise to an electrical double layerconsisting of one layer of surface charge and another layer ofcounter ions. However, because of thermal agiution, this sec-ond layer extends as a diffuse layer over a finite distan~ fromthe particle surface. A schematic represenution of this elec-trical double layer is given in Figure 3.

Point of zero charge of a mineral is an important dwacter-istic because the adsorption of various organic and inorganicions will be governed by the location of the solution properties(as pH) with respect to the pzc. Typical pzc values are givenin Table 2. It is important to note that these values are af-

--H.

0 e0

e

SURFACECH4Rj STERN

PLANE

.-

~:0

00::; 00

cn~

0

e POTENTIAL-\!) DETERMINING IONS

HYDRATED0 COUNTER IONS

0 NEGATIVE CO-IONS

SHEARPLANE.

'110

..J~t='zw...0a..

"'a~

- M°Sutt.~ + H2O

The lattice ions are considered as (surface) p>tential determin-ing ions for AgI type solids, whereas H+ and OH- are the cor-resp>ndinl ions for oxide minerals. For minerals sudt ascalcite (J 4) and apatite (J 5, J 6), both of the above mecl1a.nisms can be operative since the lattice ions can undergo pt'Cf.erential dissolution as wen as reaction with H+ and OH-. Inthe case of these mmerab, the lattice ions H+ and OH- andcertain complexes of the lattice ions with H+ or OH- can bep>tential determining. Silicate minerals with layered structuresuch as that of clays, on the other hand, are negatively charledunder most natural conditions due to the substituion, for ex.ample, of AlJ+ for Si4+ in the silica tetrahedra.

The surface p>tential '" a in these systems is given by

8 01 STANCE-where a. and a_are the activities of the positi~ and negativepotential determinina ions in the solution with valencies Z.and Z - (inclusive of sign), and a: and a! are their activites

Fia. 3. Schemauc representation or the double layer accordiRI toStem's model.

RT a. RT a-~o . Z- F Ino or -z F ino

. a. - a-

4 ADVANCES IN INTERFACIAL PHENOMENA AIChE SYMPOSIUM SERIES

TABLE 2. POINT OF ZERO CHARGE OR ISOELECTRICPOINT OF VARIOUS TYPICAL MINERALS

pzc or i~

pH 2-3.7pH 6.0pH 9.0pH 12.0pH6

Ref.

11-1920132115

Min..-als

OU8rtl, 5i02Rutile, Ti02Corundum, A120)M~n..i8, MgOFluor8patite Inetur811

CasIPO.I) IF, CHIFluor8P8tite Isyntheticl 22

HydroxY8P8tite. Cas (P041]10HI. Synthetic

Calcite CaCO]Barite B8S04Silver iodide AgISilver sulfide At1S

22

pc. 4.4. pF 4.6.pHPO. 5.22

pH 7-7.15.pHPO. 4.19-4.48

pH9.5PBa 6.7PAt 5.6PAt 10.2

,.232.25

fected by the presence of impurities (26.27), previous historyincluding pretreatments (28), method of storing and aging,the extent of aging (17,29, 30) that it undergoes in an aqueoussolution. and the pH (17). Table 3 gives values reported forthe point of zero charge or isoelectric point- of alumina. Itcan be seen that the pH ranges of plC and iep are wide, namely3 to 10. indicating the magnitude of the problem. Variationsin the source or method of preparation including mechanicaltreatments and washing and drying. and the presence of sur.face defects and of adsorbed and structural impurities produceconsiderable changes in the plC. Common cleaning procedures

.Isoelectric point (iep) refers to die conditions under which the elec.trokinetic potentia!, commonly termed zeta potential (the potentia!that manifests in die region of shear between die liquid and the solidwhen one is moving relative to die other), as determined by electro-kinetic experiments is zero. The surface potentia! tJI 0 need not be zerowhen the zeta potential is zero, particularly in the presence of $pecif-icaUy adsorbing ions. Therefore pzc and iep need not be the same.

such as leaching in acidic (35) and hot solutions (36) have alsobeen found to alter the interfacial properties drastically. Fig-ure 4, for example, gives values reported for the zeta potentialof quartz leached with different acids; the variations when us-

TABLE 3. POINT OF ZERO CHARGE OR ISOELECTRIC POINT VALUES REPORTED BY VARIOUS WORKERS FOR ALUMINA 1281

Material

Synthetic upphire

Tr.tment

L~hed in HCI,_ltIed, nor~in -ter

L~h~ in 6% HCI,_ltIed, dried .t120.C. nored dry

~hed in HCI,_ltIed in _ter.nd dri~.t 120.C

~h~ in HCI,_hed, di8lytit,nor~ dry

Method

Str~ingpotentia'

IEP

9.4

R.narkl

Hydroxylat8d

surf-

Author.

Modi IndFu8rlteneu 13'1

Dobi8. It II. 1321 Synthetic S8pC)hir. EI8Ctr~sis 8.7 Dehydr.ted wriece

Johansen .~Buchanan 1331

N8w,.1 COf'Undum MicroelectrOOlmOsis 8.4 Dehydrated surf-

Schulyenborg endSenger 1341

Natu,.' coNndum Microelectro-phorlli.

3.0 Polym8fiation 8ndpl'0b8bly par-tially d.,ydl'atedsurface

Chromatograpttlcalumina

As r8C8iYtd Titration 10.0

Reprinted from C"'n Surl-, 1970. Courtesy of Marce' Oe~ker Inc-

Microelectro-phor..i.

7.5-8.2

H..-czynlka endProazynaka[cited in 1261 )

Holm.. Fllm.fuled Ground. not c..ned.[cited in 126) ) synthetic stored in _t.. for

IIpphirt Ibout a day

sSOM AS UN DA RANNo. 150. Vol. 71

SOL

SURFACE POTEN-TIAL DETERMINING 0 CO-IONSIONS

SPECIFICALLY 0 COUNTER IONS<:> ADSORBING r. c""" COLLECTORDEHYDRATED \.~,.. CATIONS

COUNTER IONS

ing different leaching media are evident here. It has beenfound recently that the pzc of quartz can be raised from below2 to as high as 6 by leaching it in hydrofluoric acid solution(35). Upon aging the HF-leaclted quartz in water, the pzc canbe brought to its original value but only over a period of sev.eral days. Washing minerals with hot solutions produces sim-ilar long-term effects (36). For example, the zeta potential ofalumina contacted with a 2 X 10-1 N KNO1 solution changedfrom about - 35 mv at pH 9.4 to about - 52 mv at pH 9.35,

after the suspension passed through a cycle of heating to 90°Cand cooling to room temperature. The original value of zetapotential was not attained for days. The implication of thisshould be noted on the usual procedure of cleaning mineralsby leaching in hot acid solutions.

In flotation clternistry research, the adsorption of organicand inorganic ions at the mineral/solution interface is of con-cern. The adsorption density r 6 in the plane 6, which is at adistance of closest approach of counter ions to the surface, isgiven by the Stem-Graharne equation

Fig. S. Schematic representation of adsorption of a Ionl chain anionicsurfactant (a) individuaUy at low concentrations and lb) withlateral association between chains at higher co.ncentrations.

.t~.!.RT

r, = 2rCexp

where' is the effective radius of the adsorbed ion, C is thebulk concentration in mole/crn3, ~ is the standard freeenergy of adsorpti~ is the gas constant, and T the abso-lute temperature. ~G~I is the driving force for adsorptionand can be considered to be made up of a number of terths.each term for a given type of interaction that is responsible forthe adsorption (40,41).

~ = dG:'ec + dG~ + dG:-c + dG:-s

+4Gft+4Gfl.o

~ is the electrostatic interaction term equal to zFIlI6where z is the valency of the adsorbate, F the Faraday con-stant and 1t16 the potential at the S plane; ~G~em is the chem-ical term due to any covalent bond formation between adsor-bate and adsorbent; ~G~-c is due to the cohesive chain-chaininteraction that could occur between the surfactant speciesupon adsoprtion; ~G~-I is similar to ~G:-c and is the van derWaals interaction between the hydrophobic chain and the hy-drophobic sites on the mineral surfa~; ~Gf. is due to hydro-gen bonding; ~Gl\o is due to hydration or dehydration of theadsorbates or adsorbents upon adsorption. One or more of theabove terms can predominate for each system. l'hus, thechemical term is considered to be the predominant term forthe adsorption of xanthates on galena, and the electrical andthe chain-chain interaction terms are important for the adsorp-tion of alkylsulfonates or aikylsulfates on oxides such asalumina.

The adsorption of surfactants on alumina has been recentlystudied in detail (12,41). At low concentrations of surfactantand low surfa~ potentials, the surfactant ions are individuallyadsorbed and the for~ of attraction, responsible for adsorp-tion, between these ions and the mineral surfa~ is mainly elec-

trostatic (see Figure 5). When the concentration of the re-agent is increased, the adsorbed ions begin to associate to formtwo-dimensional aggregates called hem;m;ce/les. Unde{ thiscondition, the adsorption is due, in addition to the electro-static forces, to favorable energetics of removal of alkyl chainsfrom aqueous solutions (42). The above adsorption mecha-nism is formulated on the basis of the experimental observa-tion that interfacial properties such as adsorption density, zetapotential, flotation recovery, contact angle, sedimentationrate, etc. undergo a marked change at a given surfactant con-centration that is dependent upon pH and hence upon the sur-face ootential of the oxide particles (12), solution temperature(43), chain length (10,11,44,45), and chemical compositionof the surfactant (45) and the solution (46 to 48). Adsorptiondata for the alumina/dodecylsulfonate system is given in Fig-ure 6. Sharp increase in the slope of the adsorption isothermalong with those of other parameters at an adsorption densityof 10-11 mole/cm1 can be clearly seen L"l this figure.

The mode of adsorption of the previously-mentioned sur-factants on soluble salts such as sylvite is not established.Fuerstenau and Fuerstenau (50) have proposed that adsorptionin these cases is governed by matching the size of the polarhead of the collector with the constituent ion of the solidwhich carries the same charge as the polar head of the coUec-tor. Thus amine adsorbs on sylvite (KCl) and not on halite(NaCl), due to comparable sizes of the aminium ion and K.

ion. This theory, however, fails to explain. for example, whythe anionic aikylsulfate as a collector should distinguish be.tween KCl and NaCl; it floats the former but not the latter.According to an alternative theory proposed by Rogers andSchulman (51), adsorption is governed by the hydration prop-erties of the solid; the one with the larger negative heat ofsolution is the most amenable to flotation. This theory cannotexplain why a particular mineral such as KCl will be floated bycertain collectors like alkylsulfate but not by carboxylates or

AIChE SYMPOSIUM SERIESADVANCES IN INTERFACIAL PHENOMENA6

Particularly interesting in this ooMection is a recent sugges-tion by Sorensen (55) that in the case of the anionic flotationof simple salts such as fluorite. hydrogen bonding between theoxygen of the collector and fluoride species is active and thatit is wisted by the electron resonance of the pow groups. thestructure of which must be compatible with the geometry ofthe mineral crystal. Correlation that exists in several cases be-tween adsorption and insolubility of oompounds formed be-tween the collector and the chemical oonstituents of the solidsuggests yet another mechanism dependent essentially on whatcould be considered as the precipiution of sud\ oompounds at

the mineral/solution interface.While mud\ emphasis has been placed in flotation researdt

on collector adsorption on the mineral. the role of the ooUec-tor species adsorbed on the bubble has been largely neglected.Using a semi-empirical model. it has been shown for thequartz.amine system at neutral pH that the collector adsorp-tion density at the liquid/ps interface can be several timeshigher than that at the solid/liquid interface (see Figure 7).Furthermore. recent studies have shown that collector migra-tion at the liquid/air interface is several times faster than thatfrom the bulk aqueous solution to an interface (57). Duringthe contact of an air bubble with a particle. it is therefore pos-sible for the species adsorbed on the bubble to migrate to thesolid/gas interface and thus establish the desired adsorption forthe attachment of the bubble. It must be noted that such amigration is dependent upon the presence of a sufficient quan-tity of coUector ions on the bubble surface at the time of cOn-tact with a particle and therefore upon the kinetics of adsorp-tion of the collector species at the liquid/air interface. Thestrong correlation that exists between flotation and the

- -10-6 10" 10-4 10'" - 1~'2

CONCENTRATION, mole/liter

Fit. 7. Adsorption density of dodccyllrnmonium acetate at differentinterfaces lafter Somasundaran (56)!. Reproduced by permis-sion of AmeriaR Inst. Min. Met. EftlJl. (AIME).

phosphates. The authors have alternative explanations for cer-

tain exceptions.Fatty acids are widely used collectors. Adsorption of

oleate on hematite, apatite, fluorite, calcite, varite, etc. hasbeen attributed in neutral and alkaline solutions to chemicalbonding between the oleate and the mineral surface species.In addic solutions, oleic acid formed would indeed predpitatedue to its very low solubility in water. Infrared studies havebeen considered to provide evidence for the formation ofchemical bonds between oleate and fluorite (52) and oleateand hematite (53). It remains questionable as to whether thechemical states identified by such spectroscopic tectU\iqueson samples which have been subjected to various treatmentsfor the spectroscopic analysis itself can be considered to beidentical to the original chemical state of the oleate adsorbedon the mineral in an aqueous solution. Recently, it was shownthat the oleate-oleic acid complex which forms in the neutralpH ranse was hishlY surface active and therefore was pro-posed to be responsible for the maximum hematite flotationwhich was observed in that pH range. This mechanism is dis-cussed elsewhere (54).

One mechanism of adsorption that probably governs theadsorption in various rnineral-collector systems, including pos-sibly some that had been attributed in the past to chemicaland electrostatic mechanisms, is that based on the similarityin geometry between the mineral crystal and the coUector.

7SOMASUNDARANNo. iSO, Vol. 71

kinetia of adsorption at the liquid/air interface for thehematite-oleate system is discussed elsewhere (54). The mi-gration of collector species from the bubble/liquid interfaceto the solid/gas interface caMot be expected to be nonselec-tive with respect to various minerals because the adsorptiondensity at the interface of the bubble and the mineral particle(with possibly several layers of water molecules strongly at-tached) will be essentially detennined by the surface prop-erties of the particle.

From Young's equation relating the three interfacial ten-sions '11,., '1"., and '1" to the contact angle 9, one obtains thecondition that '1", - '1" must be smaller than '11,. for a largecontact angle and thereby good flotation (56). The larger thevalue of '11,., the lower is the froth stability the above condi-tion can be fulfilled only by keeping '1". small and '1" as largeas possible. Because the adsorption of surfactant at any inter-face will only decrease the interfacial tension there, it is clearthat the above condition can best be satisfied by allowing thetransfer of surfactant species from the bubble surface (or fromthe gaseous phase) to the solid/gas interface. Perhaps for thisreason, Wada (58), on passing the collector into the cell in thefonn of an aerosol with the gas stream, obtained optimumflotation at reagent concentrations as low as lis to I/aO ofthose used in the conventional process.

FROTHING

Nonionic surfactants. generally slightly soluble, monohy-droxylated compounds such as cresol, are added to induce thedesired froth stability during flotation. particularly when thechain length of the collector is relatively small. Sulfide flota-

zQ(/)ZLiJ..-

LiJU

~

~(/)

CONCENTRATION OF SOLUTE

Fig. 8. Diagram illustratin& the correlationbetween froth stability and surfacetension lowerin& due to the additionof a surfacunt (after Cook (.59)).Reproduced by permission of JohnWUey-lnterscience.

tion using short-chained alkylxanthates invariably requires theaddition of a frother. The desired concentration of the frotherin the system is approximately that at which there is a signifi-cant change in surface tension with concentration so that arestoring force is available to prevent the rupture of bubblessubsequent to any local extension of the surface (see Figure 8).It is also necessary that the diffusion of the surfactant speciesfrom the subjacent surface to the locally extended surfaceregion is not fast enough to reduce the difference between thesurface pressure in the vicinity of the extended region andwithin it because this difference is mainly responsible for therestoring force.

In addition to providing froth stability, the frother can playanother role that must be taken into consideration in thestudy of flotation mechanisms. Similarly to collector speciesadsorbed on the bubble, frother species also can migrate fromthe bubble surface to the particle/solution/bubble contact lineand particle/bubble interfacial regions and co-adsorb on theparticle along with the collector species (60 to 62). Suchfrother adsorption can be favorable for flotation, possibly be-cause the neutral frother molecules adsorbing among the ioniccollector species can shield each adsorbed collector ion fromrepulsion by others (63) and thereby enhance the overall ad-

sorption of surfactant.

ACTIVATIONActivators enhance the flotation of a mineral by collectors

that will not float it in their absence. Examples include cal-cium activated flotation of quartz using oleate, and coppersulfate activated flotation of sphalerite with xanthate at rel-atively high pH values. Activators normally act by adsorbingat the mineral-solution interface, thereby providing sites foradsorption of the collector species. Adsorption of the acti-vators is attributed to electrostatic attraction between themand the mineral surface in such cases as calcium adsorption onnegatively charged quartz. Bivalent ions such as calcium, uponadsorption on minerals, are capable of reversing the sign of theStern potential and thereby cause the adsorption of collectorsthat have a charge of the same sign as that of the mineral. Insome cases, activators have been effective because of their re-actions with collectors to form compounds of low solubilityproduct. This aspect is discussed in a paper by Fuerstenau

(64).

DEPRESStONReagents that prevent the adsorption of collectors on min-

erals and thereby retard their flotation are known as depres-sants. Uke an activator, a depressant often reverses the Sternpotential of the mineral, but the resulting potential in this caseis of same sign as that of the charge of the collector ion so that

collector adsorption is reduced.Polymers such as starch can also depress flotation, but as

discussed in detail later, in this case collector adsorption is en-hanced by the depressant (65). The decrease in flotation ob.tained in spite of the increased collector adsorption can be

attributed to the peculiar structure of the coUector-stardtclathrates formed with a hydrophilic exterior-

8 ADVANCES IN INTERfACIAL PHENOMENA AIChE SYMPOSIUM SERIES

DEACTIVATION

Deactivators prevent activation, generally, by interactingwith the activators to form an inert species of a stable ioniccomplex. Addition of cyanides for the deactivation of copperin the xanthate flotation of sulfides is a well-known exampleof this type of deactivation reaction.

Fig. 10. Flotation of alumina as a function of pH with CF )(CF1)6COOK and CH)(CH1)6 COOK as collectors in 2 x 10-)mole!1 KNO) solutions (after Somasundaran and Kulkalni(45) J. Reproduced by permission of Institute of Mining andMetallurgy (IMM) London.

considerably (45). In the case of perfluoro-carboxylates, anadditional advantage is their better pH tolerance, comparedwith any corresponding hydrocarbon homologue, attributed tothe reduced tendency of the former to hydrolyze in acidicsolutions (see Figure 10). However, their current cost is pro-hibitive for any application in flotation processing. Uke per-fluoro compounds, silyl reagents are also reported to be highlysurface active (66). While geometrical modifications in thestructure such as distribution of the methyl groups into var-ious branches in general reduces the surface activity, additionof active groups at appropriate points in the surfactant mole-cule, so that the distance between the groups will correspondto the distance between active sites on the mineral surface, canbe beneficial. The role of Zwitter ions in flotation is discussedby Gupta and Smith (67). A better understanding of the roleof chemical constitution of the surfactant in flotation will in-deed be highly beneficial for developing tailor-made flotationreagents with desired selective adsorption properties.

EFFECT OF VARIABLES

There is a large number of variables that affect flotationprocesses. These variables originate from the physical andchemical nature of the ore, its storage, its preparation includ-ing grinding, the chemical constituents that may be present inwater, reagents added and the type of flotation cell used. It isrelevant to examine here only the physicochemical variablesthat affect the interfacial processes. The nature of the min-erals and other components in the ore wiU indeed govern theinterfacial processes, but there is very little control that onecan exercise on this. However, with the composition of theore known, a knowledge of the effect of controUable variablescan be helpful to obtain maximum process efficiency.

CHAIN LENGTH Of THE COLLECTOR

Increase in length of the nonpolar part of a surfactant in-creases its adsorption at interfaces, thus generaUy enhancingthe flotation of minerals. Results in Figure 9 for the flotationof quartz at natural pH using aikylammonium acetates of vary-ing chain length show an increase in flotation with an increasein chain length (10). The chain length effect on flotation wasascribed to the increased adsorption at the solid/liquid inter-face owing to lateral interaction among the adsorbed speciesto form two-dimensional aggregates and at the liquid/gas inter-face. The length of the chain is often limited by solubilitywhich decreases with increasing chain length. If very longchain surfactants are to be introduced into the flotation ceU,it can be done through an oil emulsion.

CHEMICAL STRUCTURE Of THE SURfACTANT

Substitution of hydrogen in CH1 or CH3 groups of the sur-factant with fluorine increases surface activity and flotation

18C 16C~eo!~ i

060'101t-

~ 40-'16-

20I

COLLECTOR CONCENTRATION

It can be seen from Figure 9 that flotation recovery is alsostrongly dependent upon the concentration of the coUector.This effect is not due to the dependence of the mechanicalproperties of the foam on collector concentration because theparticular case reported in Figure 9 is for Hallirnond tube testsfor which such effects are absent.

Rubin and co-workers (68), among others, have observedthe dependence of precipitate flotation on collector concentra-tion. A collector to colligend (copper species in this case)ratio of one was found necessary to get nearly complete re-moval of copper. For foam separation techniques, the mostsuitable surfactant concentration is the lowest one that pro-vides the desired foaming properties (69 to 71). Transiency ofthe foam found desirable for effective extraction (72) is higher

10-8 10.7 10.6 10.' 10-4 10'S 10-2 10.1 1

CONCENTRATION, mole/liter

Fic. 9. The effect of alkyl chain length on the flotation of quaru inalkylammonium acetate solutions (after Fuerstenau, Healey,aJKI Som.sundaran (10)). Reproduced by permission of Amer-ican (nst. Min. Met. Engrl. (A(ME).

No. ISO, Vol. 71 SOMASUNDARAN 9

pH

Fig. 12. Flotation of calcite with dodecylammonium acetate (DDAA)and sodium dodecylsulfate (DDSO4) solutions (afterSomasunda.ran and Alar (14»). From Journal CoUoid andInterface Science 24, 439 (1967). Reproduced by permis$ionof Academic Press Inc.

at lower coUector con~ntration. An ex~ss of coUector hasbeen reported to reduce the flotation of minerals (45) and pre-cipitates (73). In particulate flotation this is sometimes due toa reduction in the size of the bubbles to such a level that theyare not capable of levitating the large number of particles thatcaUect on them (45). Adsorption of a second layer of coUec-tor (at high con~ntrations) with an orientation opposite tothat of the flfst layer, or adsorption as micelles can also de-crease flotation, but this is less likely since only a small frac.tion of the surface need to be hydrophobic for flotation tooccur (see Figure 11).

SOLUTION pH

pH is a major controlling factor in the separation of oxides,silicates, etc. Proper choice of pH and the type of coUector isin fact a requirement for selective flotation of one mineralfrom another. The effect of pH iUustrated in Figure 12 is forthe flotation of calcite with an anionic and a cationic collectoras a function of pH at two concentrations (14). The isoelec-tric point of calcite is in the pH range 8 to 9.5 (14). It is evi.dent that significant flotation with an anionic collector is pos-sible only below the isoelectric point when the particles arepositively charged, and with a cationic collector only abovethe isoelectric point when the particles are negatively charged.

The pH will also influence flotation through its effect oncollector hydrolysis. A typical example of this is the amineflotation of quartz in basic solutions. A critical pH-coUectorcon~ntration curve for the incipient flotation of quartz withdodecylammonium acetate is given in Figure 13. Quartz isnegatively charged above pH 2, and therefore it should be pos-sible to float it with a cationic collector above this pH. It canbe seen from Figure 13 that flotation ceases once the pH ex-ceeds 12. This observation was ascribed to the fact that atthis pH most of the collector was in the form of neutral mol-ecules which do not absorb on quartz (see Figure 14). It mustbe noted, however. that neutral molecules can act as excellent

122 4 6 8 ...0

pHFic. 13. Critical-pH concentration curves for incipient vacuum flota-

tion of quaru usina dodecylammonium acetate solutions (75).

ADV ANCES IN INTERFACIAL PHENOMENA AIChE SYMPOSIUM SERIES10

1)0

102I I I I I I I

~

f ~J80

ae60QIAJ~

g40...J ':"MAXIMUM

RNH2

,...' "~

AI/

II

~~

20f . .-:-~~~--:~~-Jin(OH '. (. ) - I' I n(OH)z(s)

0.2

.0 2 4 pH 6 8 10 12

FiC. 15, Efrect or pH on zinc notation usina sodium laurylsulfatc atcoUector ratios or 0.2. I, Z. and ) from I x 10-4 molc/bterzinc (II) solution. In the halched reSion, nolalion orZn(OH)2 precipitate occurs (ICter Rubin Ind upp (78)1.Reprinted rrom Se'pGrgrion SC;,ltce' 6 )57 (1971). ColUtesyor Marcd Dekker Inc.

I

0" -

00" I- (j.eo" I J I I I I I10 0 8 10 12 14

pHFil. 14. Concenuation of neutral molecules (M) and ions (I) in a 2

2 x 10-i mole!1 (A) and 2 x 10-4 mole!1 (8) dodecyiammo-mum chloride solution as a function or pH. Solid lines indi-cate the maximum solubility (after Gaudin l76»). From110141;011, 2nd Edit., by A. M. Gaudin (1957). Used with per-mission or McGraw-Hill Book Co.

collectors when present along with ionic surfactant species.This is supported by the observation that maximum flotationof hematite with oleate was obtained in the PoH range in whichhalf of the oleate was present in the neutral form (57). Thiswas attributed to the significantly higher surface activity ofthe I : I acid-soap complex formed in this pH range and its ad.sorption at various interfaces. Fuerstenau and Yamada (63)obtained an increase in flotation of alumina with dodecylsul-fate upon the addition of dodecylalcohol. They ascribed theflotation increase to an increase in the total adsorption of thesurfactant species at the solid/liquid interface facilitated bythe screening of the repulsion among the ionic parts of theadsorbed surfactant species by the neutral alcohol moleculescoadsorbed between. There is, however, no direct experi-mental evidence available yet to support such a hypothesis.There has been observed an increase in flotation of alumina,but not hematite, owing to the dissolution of methane andbutane in sodium dodecylsulfonate solutions (76, 77). Thereason for this selective activation is not yet established.

The effect of pH on ion flotation and precipitate flotationhas been discussed in an earlier publication (1). The selectedpH of the solution may in fact determine whether the process

will be ion fl~tation or precipitate flotation; thus zinc is re-moved from solution by ion flotation below pH 8 and by pre-cipitate flotation above pH 8 (see Figure I S). It can also beseen from Figure 1 S that ion flotation is influenced by collec.tor concentration to a greater extent than precipitate flotation.Grieves found precipitate flotation to be most efficient whenthe sign of the charge of the precipitate was opposite to thatof the collector and when the amount of soluble species was ata minimum (1). Microflotation of organisms is also reportedto be highly sensitive to pH (79. 80); thus. flotation of E. coliusing lauric acid and alcohol is maximum in the pH range of 4to 8 (79).

IONIC STRENGTH

If the adsorption of the collector on the particles is pri.marily due to electrostatic attraction of the coUector speciesto the charged mineral surface. a significant increase in ionicstrength will decrease its adsorption on solids because the ad-sorption of the collector ions must take place in competitionwith other ions that are similarly charged. This effect isclearly shown by the results obtained recently for the cat-ionic flotation ofquartl (46) (see Figure 16). In this case.potassium nitrate, added to increase ionic strength. acu as adepressant. An increase in ionic strength by the addition ofuni-univalent electrolytes has in general been found to be det-rimental to froth flotation. An exception has been noted reocently for hematite flotation using oleate (81). In this case,an increase in KNO) concentration from 8 X 10-5 to 2 X 10-1mole/liter was found to increase flotation from about 28 to9O'ro at an oleate concentration of 1.5 X 10-5 mole/liter. Con-ditioning was carried out at 2SoC and pH 8.0. When the con-ditioning was carried out at 95°C. the effect of an increase inionic strength was. however. found to be detrimental. If the

I I, 1" II 1

II

.j lAM... I

~. I

~Q)-:: -~~ 100E-

Z -4

Q 10

~cr-I- _£,Z lO-WuZ

SOMASUNDARAN iiNo. 150. Vol. 71

100

80

If

0601w 1too

940l~1

1.5 . 1O-4~. OOA

20

0K5 K5 K53 Kj"- K)-t

K~3 CONCENTRATION, mole/ liter

Fil. 16. Flotation of quartz as a function of KNO) concentration atnatural pH of S.B in I.S X 10-4 mole/l dodecylammoniumacetate solutions (46).

quantities sufficient to reverse the effective charge on the alu.mina particles, thus promoting the cationic surfactant to ad.sorb and to make the particles hydrophobic. Bivalent cationssuch as calcium can similarly activate the anionic flotation oforiginally negatively charged particle.. It has been reportedthat alkaline earth ions such as calcium can function most ef-fectively in the pH range where they are in the hydrolyzed sol.uble form. Fuerstenau et al. (84, 85) studied the role of iron,aluminum, lead, manganese, and calcium in the anionic flota-tion of quartz as a function of pH and found that each cationbegan to activate flotation when the solution pH correspondedto the beginning of metal ion hydrolysis and ceased the activa.tion at the precipitation pH of the metal hydroxide (see Fig-ure 20).

added salt contains multivalent ions of the same sign as that ofthe collector ions, depression is more marked due to the ten-dency of the multivalent ions for stronger specific adsorptionand resultant larger competition with the collector ions. Thiseffect is clearly illustrated by the results of Modi and Fuer-stenau (82) reproduced in Figure 17. Evidently, the presenceof bivalent sulfate ions is more detrimental to the anionic flo-tation of alumina than the monovalent chloride ions. If thebivalent ions are of opposite charge to that of the particle andthe collector ions, then activation of flotation can occur dueto charge reversal of the particle caused by the adsorbed bi-valent ions. Thus, as shown in Figure 18, Modi and Fuer.stenau (82) obtained flotation of alumina, positively chargedin water at pH 6, using a cationic surfactant after the additionof bivalent sulfate. Their electrokinetic results (31), repro-duced in Figure 19, show that the sulfate ions can adsorb in

.it..~!,!. ',' I. I100 0 NaCl

6 NozSO..eOr

80

~ I- 60

Q!AI~«0 40..JI&.

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ALUa8IA0 NoC1.. NoZSO.0 RSO.No

-80r pH 6.5i '. . . ." .1-1 -& -s -. -s -Z -I

10 K) K) K) K) K) K)

ELECTROLYTE CONCENTRATION. mole/ life'

Fil. 19. Effect of addition of NaCl. Na1S0.. and Na dodecylsulfo-nate on the ~etl. potential of alumina at pH 6.S (after Aplanand Fuerstenau (81) J. Reproduced by permission of Amer-ican 1nst. Min. Met. En,q. (AlME).

20

ALUMINA-s

4 . 10 M RSO. ~pH6

0 I I I I I

-7 -6 -S -. -3 -I -110 10 10 10 10 10 10CONCENTRATION OF ADDED SALT, mole/liter

Fic. 17. The depression of notation of alumina by NaCI and NatSO.with sodium dodecybulfatc IS collector It pH 6 [after Modiand Fuerstenau (82)). Reproduced by permission or Amer-ican Inst. Min. Met. Engrl. (AIME).

QUARTZpH - 5.8

ADVANCES IN INTERFACIAL PHENOMENA AICbE SYMPOSIUM SERIES

80l~ ~

60 ~- t~ r-C 40 ,0 r-

~ ~20l

02 4 6 8 10

pHFig. 21. Effect of addition of alum on the flotation of illite UDnI so-

dium laurylsulfate as collector. . -no alum;. -6.25 lng/Ialum; e-50 mg/l alum (after Rubin and Erickson (92}J. Re-printed from Wale' Res. 5437 (1911) by Rubin and Erickson.Reproduced by permission of Pergamon Press inc.

The effect of ionic strength on precipitate flotation can alsobe expected to be of a similar nature. Sheiham and Pinfold re-port a decrease with increasing ionic strength in the precipitateflotation of strontium using dodecylpyridinium chloride. hexa-

decyltrimethylammonium chloride, and a dialkylammoniumchloride (87). As expected, they did not observe such an ef-fect in the precipitate flotation of "the second kind" of nickeland palladium with nioxime (88,89) because the collector at-tachment to the colligend is a part of the precipitation processand independent of electrostatic attraction between the col-lector species and the precipitate. Ion flotation also should beretarded by an increase in ionic strength because the colligendions will now have to compete with other inorganic ions for at-tachment to collector ions. Rubin et al. (78, 90) and Grieves(9 J) have observed the interference of ionic strength to theion flotation of zinc, copper, and orthosphosphate, respec-tively. Indeed, in ion flotation and other foam separationtechniques, the effect of ionic strength on foam stability anddrainage can be a governing factor. The foam separation ofsurfactants is assisted by an increase in ionic strength becauseof the enhancement of their adsorption on the bubbles, atleast below the critical micelle concentration.

meric type reagents such as starch. Figure 22 illustrates the ef.fect of starch on the flotation of calcite using oleate (65). Itcan be seen that the addition of even a small amount of starchdecreases the flotation of calcite drastically. As mentionedearlier, starch does not reduce flotation by inhibiting the ad.sorption of the surfactant on calcite particles. In fact, the ad.sorption of oleate on calcite was found to be higher in thepresence of starch than otherwise. Similarly, the adsorptionof starch was also enhanced by oleate (see Figures 23 and 24).Thus even though the particles adsorbed more surfactant in

~0

0~..-<{0.oJ~

FLOCCULANTS AND DISPERSANTS

Complete flotation of a material can be achieved in severalcases by adding auxiliary" reagents. For example, Rubin et at.found that the flotation of illite, titania, and B. cerew withsodium laurylsulfate was increased to almost 100% by addingalum (92-94). Figure 21 shows the typical effect of alum onmicroflotation. It is not clear whether the increased flotationis due to charge reversal of the coUigend particles or simplydue to their flocculation. In the froth flotation of minerals,flocculation is valuable only if it is selective. Such selectiveflocculation followed by flotation has been found to be usefulfor the large-scale separation of fine hematite from quartz (95).

Separation by flotation is affected by the addition of poly-

00 4.5 9 13.5 18

CONCENTRATION OF STARCH, ppm

Fig. 22. The depression of calcite notation using sodium oleate bystarch (after Sornasundaran (6.5»). From Journal Conoid andInterface Science J 1 (4). 19. Reproduced by permission ofAcademic Press Inc.

SOMASUNDARANNo. ISO. Vol. 71 13

10.4

~

IAJ...U-J«u

~

~-0 -E 10

0IAJm~0(/)0<t

IAJ...«IAJ-J0 -

100 I ~ I ~ I ~ I ~ I l~ l~5

CONCENTRA T ION OF STARCH, ppm

Fic. 23. Effect of Starch addition on the adsorption of oleate on cat.cite at natural pH of 9.6 to 9.8; vertical lines indicate thestandard deviation due to the variation in scintillation count-ing (after Sornasundaran (65»). From Journal CoUoid andInterface Science J 1 (4). 19. Reproduced by permissionof Academic Press Inc.

with a hydrophilic exterior and a hydrophobic interior. Mu-tual enhancement of adsorption is possible owing to the forma-tion of a helical starch-oleate clathrate with the hydrophobicoleate held inside the hydrophobic starch interior. The hy-drophilic nature of calcite in the presence of starch and oleateresults from the fact that the adsorbed oleate is obscured fromthe bulk solution by such wrapping by starch helixes whoseexterior is hydrophilic and possibly also by simple overwhelm-ing of it by massive starch species.

CONDITIONING TEMPERATURE

In the case of flotation dependent on the physical adsorp-tion of the collector, adsorption and hence flotation can beexpected to decrease with an increase in the temperature ofconditioning (reagentizing) while for flotation dependent onchemisorption the reverse is true. There has been actually verytittle work done on the temperature effects on froth flotation.Flotation of hematite with oleate (96) and fluorspar (97) hasbeen reported to increase on heating the pulp. Recent resultsfor hematite flotation using oleate, however, Mve shown thisto be true only at low ionic strengths (81): Above an ionicstrength of 2 X 10-3 N flotation was found to decrease mark-edly with increase of reagentizing temperature.

Effect of temperature on flotation can affect the perfor-mance of foam separation by its influence on foam drainage,transiency, and adsorption at the liquid/gas interface. Suchmultiple effects might be responsible for the absence of anydefinite trend in the effect of temperature on foam separa-tions. For example, while an improvement in flotation withtemperature is reported by Grieves for the foam fractionationof ethylhexade cyldimethylammonium bromide (98), andMa1me and Pinfold for the precipitat~ flotation of the rustkind of strontium with a cationic collector and of the secondkind of nickel with. nioxime (87,99), tittle or no effect is re-ported by the latter authors for precipitate flotation of thesecond kind of palladium with nioxime (100), and by Rubinand co-workers for the ion flotation of copper(l) using sodiumlalirylsulfate (90). Clearly, more work under a wide range ofcontrolled conditions is needed in this area to elucidate themechanisms involved.

the presence of starch. they remained hydrophilic. This effectwas ascribed to the helical structure: that starch assumes in thepresence of hydrophobic species and under alkaline conditions.

1200 .~ --

~~~~ ~ ~.--b '

~

CONCLUSION

Froth flotation phenomena are governed by the propertiesof the various interfaces formed between the solid, liquid, andgas phases. Attachment of a bubble to a particle for its levita-tion takes place if the free energy change is favorable for dis-placing the solid/liquid interface with solid/gas interface. Sur-

factants are added to help to meet this criterion by adsorbingat various interfaces. The role of adsorption at various inter-fa~s is now well recognized. Mechanisms of adsorption ofsurfactants on minerals are understood in many cases with the

help of experimental tools such as electrokinetic techniques,adsorption isotherm determinations and spectroscopic tech-niques. However significant these techniques are in elucidatingadsorption mech2nisms, they must almost always be used withsome reservation, because a direct application of some of the

~ 1000~4U~ 8000~

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0

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~ 2001~ :(/)

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SODIUM OLEATE CONCENTRATION, mole/liter

Fig. 24. Effect of oleate addition on the adsorption of starch on cal-cite at various pH values (after Somasundaran (65»)- FromJOlUnal Colloid and Interface Science J1 (4), 19. Repro-duced by pennission of Academic Press Inc.

14 ADVANCES IN INTERFACIAL PHENOMENA AIChE SYMroSIUM SERIES

techniques can very weU be the cause for frequent misinterpre-tation, particularly when one is dealing with heterogeneous,natural minerals. Electrokinetic experiments provide only anaverage measurement for the whole solid particle. Further-more, the measured property depends upon the type of pre-treatment and storage that the mineral has received. Spectro-scopic techniques can also cause misinterpretation if it is notrecognized that the surface species can undergo significantchanges during the preparation of the sample for the analysis.

E~n today, flotation practice leans rather more on expe-rience than on a meaningful scientific undentanding. It ap-pean that the effects and interactions of a large number ofvariables, including the chemical constituents present in a nat-ural flotation system, need to be recognized. studied. and un-derstood if the knowledge gained from research on the physicalchemistry of the mineral-solution-gas system is to be of anysignificant application in actual froth flotation practice.

LITERATURE CITED

1. Somasundaran, P., S~poralion ond Purifico/ion M~llrod.r. I, 117(1972).

2. ui. R~. w.. ~nd D. w. Fucr~tenau. Trans. AI."E. 241. S49(19681; See ~I~o R~8h~van. S.. and D. W. Fuentenau,AIClrESymp. ~,. No.. 71 (197S).

3. Sh.h, G. N.. and R. Lcmlich,lnd En,.. Ch~m. FuIIdG~nlols, 9.35011970).

4. Sheibm. I.. and T. A. Pmfold. ~pt1rvlion Sa., 7.43 (1972).S. Goldber8. ~.. and E. Rubin. Ind. En,.. "'~m. houu D~sip

D~II~/op..6,195(1967).6. Pinfold. T. A.. ~pGlV/ion Sri.. 5. 379 (1970).7. Gutierrez. C..."in~rvISa. En,., 5,108 (19731.S. GrAnville. A., N. P Finkelstein. ~nd S. A. Allison. r,ons. IMM. 81,

Cl (1972).9. Finkelstein. N P..S A. Allison. and V. M. ~veU.AIClrESymp.

S~,. No. 150.71,165 (197S).10. Fuenten~u. D. W., T. W. Healey, and P Somasunduan, rrvns.

AJ."£. 229. 321 (1964).II. Somasundaran. P.. T. W. Healy. and D. W. Fuer~tenau.J. Pltys.

Ch~m..68,3562(1964).12. Somasundaran. P..~nd D. W Fuerstenau.ibid.. 70.90 (1966).13. Yopp~, J. A.. and D. W. Fucntenau,J. Colloid Sa.. 19.61 (1964).14. Somasund~ran, P., ~nd G. E. Agar,J. Colloid In/~'foc~ Sci.. 24.

433 (1967).IS. Somasundaran. P..ibid., 27.659 (1968).16. Somasund~ran. P.,and G. E. Alar, ibid.. 252. 348 (1972).17. KulkarnI, R. D..~nd P. Sornasundaran, in "Oxide- Electrolyte

Interfaces:' Am. Electrochem. Soc., 31-44 (1972).18. Gaudin. A. M.. D. W. Fuentenau. r,ons. AIM£. 202. 66 (19S5).19. Iwasaki. 1., R. R. B. Cooke,~nd H. D Choi.ibid..120. 394

(1961).20. Berube. Y. G.. and P. L deBruyn.J. Colloid In/~'fo« Sri., 27.

305 (1968).21. Robinson. M.. J. A. Pask.. and D. W. Fuerstenau. 1. A~'. C~rvmic

Soc., 47, 516 (1964).22. Saleeb. F. Z. and P L deBruyn. El~ctrocrnol Ch~m. fnl"foc.

E/~ctroclr~m., 37.99 (19721.23. Buchanan. A. S..and E. Heym~nn.Proc. Ro}'oISoc.. A195.1S0

(1948).24. Overb~ek. J. Th. G., in Colloid Sci~nc~. H. R. Kruyt. (ed.), Vol. 1.

ElseVIer. New York (19~2).25. Freyberger. W. L. aad P. L deBruyn.J. PIt yr. Chtm.. 63,1475

(19S71.

26. Parks. G A.. Ch~1PI. R~p., 65.177 (1965).27. D~ju, R. A., and R. B. Bhappu. "A Chcmiallnt~rprctation of

Surface Phenomena in Sitiate Minerals:' New M~~iQ) StateBureau of Mines and Mineral Resources Circ. No. 89 (1966).

28. Somasunduan, P., in Cle.n Swfaces Th~;, P,~panrion.ndo..,.cterlurion 10' /nrul.c;.1 Srudin, Matcd Dekker,p. 285-306 (1970).

29. Smith. R. W..and N. Trivedi, Tnns. A/ME. 156.69 (1974).30. Puks,G. A.,A~. Min~ra/0Iist,51. 1163 (1972).31. Modi, H. J.. and 0 W. Fuerstenau.J. Phys. CIr~m.. 61, 640

(1951).32. Dobias. B.. Spurny, and E. Freudlova. Coll~ction Cl~ch. Ch~m.

COnllnU1l.. 24, 3668 (1951).33. Johansen. P. G.. and A. S. Buchanen.Austr'8l. J. CIr~m.. 10.3980

(1957).34. $<:huylenborgh, J., and A. M. H. Sanaa, R~c. Trap. Clrim.. 68,

999 (1949).35. Ku1kuni. R. D., and P. Somasundaran, paper presented at 164th

meetina of A.m. Chem Soc., New York (1972).36. Somasundaran. P., and R. D. Kulkarni, J. Colloid /nterf.~ Sri.,

45.591 (1973).37. Li. H. C., Sc D. thesis. Mass. Inst. Tech..C.mbridp (1958); Li.

H. C., and P. L. d~Bruyn. Swfac~ Sci., 5. 203 (1966).38. Zucker, G. L., D.E.$<:. thesis, Columbia Univ.. New York (1959).39 Cited in Joy. A. S.. and R. M. ~nscr, Trans. /MM. 15, Cl 94

(1966).40. Haydon. D. A.. and F. H. Taylor. hoc. 1~ /nt~m. COlli". ofS".

fac~Activity,Vol. 1.p.157(19601.41. Fuerslcnau. D. W.. in Th~ CIr~mistry of Bio~f«es, M. Hail.

(ed.).Vol. l,p. 143(1971).42. Lin, I. J., and P. Somasundaran. J. Colloid /nlerf.~ Sri., 31.731

(19711.43. Somasundaran. P., and D. W. Fuerstenau, Trans. A1ME.152. 275

(1972).44. Wakamatsu. T.. and D. W. Fuerstenau. in AdsorpfiOfl from So1&l-

lion. Adv. Chern. ser.. No 79.161 (1968).45 So~sundaran, P., and R. D Ku1kuni. Trans. /MM (London). 82.

C163 (1973).46. Somasundaran. P.. Trans. A/ME. 255. 64 (1974).47. Onoda, G. Y.. and D. W. Fuerstenau, 711r /nttn!. Mineral PI'oceu.

inl Con"., Vol. /, p. 301, Gordon and Bteach. New York(1964).

48. HoPSlock, D. M.. and G. E. Apr, Tram. A/ME, 241. 466 (1968).49. Somasundaran, P.. PhD. thesis. Univ. California. Berkeley (1964).50. Fuerslenau, D. W.. and M. C. Fuerslenau. Trans. A/ME. 204. 302

(1956).51. Rogers, J.. and J. H. Schulman, "Proc. Secood Intern. Conar. of

Surflce Acuvity:' Vol. 3. p. 243, Butterworth;, London(1957).

52. Peck. A.. S.. and M. E. Wadsworth, Proc. 711r /nl~'n. Mineral Pro-cessi", Con, p. 259. Gordon and Breach. New York (1965>-

53. Peck. A. S., L. H. Raby. and M. E. Wadsworth, T,.ns. A/ME. 238,301 (1966).

54. Kulkarni, R. D., and P. Somasundaran. A/ChE Symp. ~r. No.150,71 (1975)

55. Sonnsen. E..J Colloid /nt~'faa Sci.. 45. 601 (1973).56. Somasundaran, P.. Trans. A/ME. 241.105. (1968).57. Kulkarni. R. D.. and P. Somasundaran. to be published.58. Wada. M.. paper presented at the IV Intern. Auft)ereil..KoUoquium,

Forsch. Aufbereit.. Freiberl (Sachs). (1966).59. Cooke. S. R. B.. in Advanc~s in Colloid Sci~nc~, Vol. III, H. Mark,

and E. J. W. Verwey, (ed.), p. 326, Interscience, New York(1950).

60. Schulman, J. H.. and J. Leja, KolIoid.Z.. 136. 107 (1954).61. Leja, J.,Proc. 2nd/nt~'n Con".. Swfac~AclilliIY. London, 3,

27) (1957).62. Schulman. J. H.. and J. Leja, inSwf.cePltenomeM i" Ch~mistry

No. ISO, Vol. 71 SOMASUNDARAN IS

98. Grie9Cs. R. B.. and R. K. Wood. AIChE J., 10.456 (1%4);Grieves, G. B., and D. BMttacharya. J. A"'. Oil Ch~",., 41.114(1965); Grieves. R. B., and D. BhattacMrya,J. WGt~r Pollut.Co/lrrol FN.. )7.980 (1965).

99. Mune. E. J.. and T. A. Pinfold.J. Appi. Ch~",.. 11.52 (1968).100. -,ibid.. 140.

DISCUSSION

Emesto Valdes-Krei&: How do collector ratios studied in abatch ~ll reprodu~ in a continuous system? We have ob-served that true concentration in a batch cell are often not re-corded, but rather their initial values are given. The adsorp-tion capacity of the mineral and the continuous aeration maymodify the conclusion derived.

P. Somasundann: PhysiQI chemistry of froth flotation hasbeen studied in the past using batch tests with no correspond-ing continuous tests for comparison. The best comparisonthat is possible is between laboratory batch tesU and large-scale plant continuous tests. The ratio of collector to col-ligend is in general found to be rugher under p~t conditionsthan under the laboratory test conditions. For example, whilean oleate con~ntration of only S X Iv-4 mole!1 was neededto obtain nearly complete flotation of hematite at pH 1 to 8 ina laboratory batch test using Denver ~ll, a ooncentration ofS X 10-3 mole!1 is reportedly used in the plant during oondi-tioning for the notation of the same ore. We found concentra-tion for similar flotation. but of a different type of hematite,in a HaIlimond ~ll to be S X 10-5 mole!l. The need for in-creased dosage under a larger-scale condition might be due tothe presence of various additional colligends (that compete forthe co~ctor), particularly slimes that might often be presentin higher amounts in a large-scale operation.

Flotation results are usually reported in tenns of the initialsurfactant con~ntration rather than the equilibrium bulkconcentration. In an ordinary laboratory flotation test theequilibrium bulk concentration will be lower than the initiaiconcentration and such differences could indeed affect the in-terpretation to some extent. Reported effects of such vari-ables as solution pH and interpretations based on them, how-ever, can be expected to be in seneral valid for a given flotationsystem. Moreover, in the case of HaUimond tube tests (thathave been widely used to study the physical chemistry of flo-tation), surface area of the solid available for surfactant de-pletion by adsorption is very small, and hence equilibriwnsurfactant concentration will be very close to that of the in-itial concentration. It might be noted that results obtained foradsorption tests during flotation research (which use rugh sur.face area systems) are usually reported in tenns of equilibriumbulk concentration. It will indeed be advisable to check theequilibriwn concentration for all tests if available time per-mits the required chemical analysis.

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63. Fuerstenau. D. W., and B. J. Yamlda. r,.lIs. A/ME, 213, SO(1962). .

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131 (1973).67. Smith, R. W., and S. C. Gupta, A/OlE Sy1/lP. Ser. No. /50,71,94

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E/lf. Pro"., 55, 42 (19S9).72. Robertson, G. H., and T. Vermeulen. "Foam Fractionation of

Ru.wth Elemeau:' Lawren~ Radiation Lab. Report,UCRL.19525 (1969).

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J.C. Lamb,fll,Biotech. E/If., 8,f31 (1966).80. Rubin, A. J.. ibid.. 10,89 (1968).81. Sornasundaran. P., and R. O. Kulkarni. paper presented at the

103rd Ann. AWE Mcctinl, Dallas (1974).82. Modi, H. J., and D. W. Fuerstenau, TraIlS. A/ME. 217, 381 (1960).83. Aplan, F. F.. and D. W. Fuerstenau, Froth Flotation, 50th All- .

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Proceu Desip DeHlop.. 5,368 (1966).91. Grieves, R. B., in "AdsorptiYe Bubble Separation Techniques,-

R. ~mlich (ed.), p. 175, Academic Press, New York (1972).92. Rubin. A. J.. and S. F. Erickson, WGIIr Res.. 5, 437 (1971).93. Rubin, A. J..and D. C. Haberkost,SepaIVtion Xi., 8, 363 (1973).94. Rubin, A. J.. and S. C. Lackey. I Am. Water Worb Assoc., 60,

1156 (1968).95. E/lf. MllIiIII/.. 175(11), 140 (1974).96. Bjome. C.. and J. Keeley,Millill, EIII., 65 (1964).97. DorenfekS. A. C.. in "Froth F1ot~tion. 50th A.nni'YersMy Vol..

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