11/ FLOTATION / Reagent Adsorption on Phosphates

Rubinstein J (1995) Cohtmn Flotation: Processes, Designsand Practices. New York: Gordon and Breach.

Schubert Hand Bischofberger C (1979) On the optimiza-tion of hydrodynamics in flotation processes. In: Las-kowski J (ed.) Proceedings of the 13th InternationalMineral Process Congress, pp. 1261-1287. Warsaw:Elsevier.

Wills BA (1992) Introduction to Mineral Processing Techno-logy, 5th edn, pp. 558-575. Oxford: Pergamon Press.

Xu M, Quinn P and Stratton-Crawley R (1994) Graph-ite/chalcopyrite separation using a rapid column cell.In: Yalcin T (ed.) Innovations in Mineral Processing,pp. 181-186. Sudbury, Ontario, Canada.

Xu M, Quinn P and Stratton-Crawley R (1996) A feed-lineaerated flotation column. Minerals Engineering 8(10):1159-1173.

Yang DC (1988) A new packed column flotation system,column flotation '88. In: Sastry KVS (ed.) Proceedingsof the International Symposium on Column Flotation,pp. 257-265. Phoenix, USA: SME.

Yoon RH, Adel GT and Lurtrell GH (1988) A process andapparatus for separating fine particles by microbubbleflotation together with a process and apparatus forgeneration of microbubbles. US patent no. 5761008.

Yoon RH and Luttrell GH (1989) The effect of bubble sizeon fine particle flotation. Mineral Processing and Ex-tractive Metallurgy Review 5: 101-122.

Young FR ([989) Cm'it"ti/»,. London: Mc~r;t\v-Hill.Zhou ZA. Xu Z and Finch JA (1994) On the role of

cavitation in particle collection during flotation - acritical review. Minerals En.~ineerin.1,' 7 (9): [07 -~-1084.

Zhou ZA, Xu Z and Finch JA (199.') The minimumrecovery zone height in flotation columns from par-ticle-bubble collision analysis. TranSllctions of the Insti-tution of Mining and MetaIIurg)' 104: C 1 02-C1 06.

Zhou ZA, Xu Z and Finch JA (199.') Fund.tmental stlldy ofcavitation in flotation. In XIX International MineralProcessing Congress, vol. 3, pp. 93-97. San Francisco,USA: SME.

Zhou ZA. Xu Z and Finch JA (1996) Effect of gas nuclei onhydrophobic coagulation. journal of Colloid InterfaceScience 179: 311-314.

Zhou ZA, Xu Z, Finch JA and Liu Q (1966) Effect ofgas nuclei on the filtration of fine particles withdifferent surface properties. Col/oids &. SllYfaces 113:67-77.

Zhou ZA, Hu H, Xu Z et al. (1997) Role of hydrodynamiccavitation in fine particle flotation. Internatio,ral jollY-nal of Mineral Processing 51: 139-149.

Zhou ZA, L1nglois R. Xu Z et al. (1997) In-plant testing ofa hydrodynamic reactor in flotation. 111: Finch JA,Rao SR and Holubec I (eds) Processi,rg of ComplexOres, pp. 185-19.~. Sudbury. Canad.t; CIM.

Reagent Adsorption on Phosphates

and subsequently the interactions between the surfac-tants and the mineral particles. The interactions inmineral-solution system include dissociation, micell-ization and precipitation of the surfactant, dissolu-tion of a small amount of solids followed by hydroly-sis, complexation and precipitation of the dissolvedspecies, and the interactions betWeen dissolved min-eral species with surfactant in the bulk in variousforms. The dissolved species, including those intro-duced due to dissolution from all the minerals presentin the ore and those from the water source, fresh andrecycled, are the major elements that affect thewater chemistry. While impurities introduced fromwater can be controlled to some extent, the chemicalspecies released into the system due to dissolutionfrom the minerals cannot be avoided. In systemscontaining soluble or sparingly soluble mineralswhere the extent of dissolution is markedly higherthan that in most oxide/silicate systems, the ef-fect of dissolved mineral species can be drastic. Un-derstanding the mineral-solution-surfactant chem-ical equilibrium under different physicochemicalconditions is critical for developing reagent and pro-cessing schemes for separation.

P. Somasundaran and L. Zhang. Columbia University,NY. USA

Copyright @ 2000 Academic Press

IntroductionAdsorption of surfactants on, minerals is the basicprocess governing flotation. It is controlled by variousphysicochemical processes in the pulp involving inter-actions among the mineral particles, surfactants, dis-solved inorganics, solvent species and other additivessuch as polymers. Adsorption can be considered asselective partitioning of the surfactant adsorbate intothe interfacial region, resulting from the more ener-getically favourable interactions between the adsor-bate and the solid than those between the former andthe species in the bulk solution. The interactionsleading to adsorption include chemica" bonding, elec-trostatic interaction, desolvation of the surfactant po-lar group and the mineral surface species, hydrogenbonding, van der Waals interactions, etc.

Water chemistry plays an important role in theadsorption process by affecting the surfactant-solution equilibria, the mineral-solution equilibria

11/ FLOTATION / Reagent Adsorption on Phosphates 1563

Phosphate is one of the most important mineralsprocessed by flotation techniques. Flotation is ef-ficient for the beneficiation of phosphate ores withsilicate gangues, but those with carbonaceous gan-gues are difficult to separate by flotation tech-niques. The low selectivity has been attributed to thesimilarities in the surface chemical properties of theconstituent minerals. These properties, in turn, areinfluenced by the water chemistry of the surfactant-mineral systems. In this section the effects ofwater chemistry on the surfactant-solution equilib-rium, the mineral-solution equilibrium, the surfac-tant-mineral interactions in the separation of phos-phate and associated minerals are discussed. Methodsto manipulate and control the solution chemistry toachieve selectivity in flotation are also examined.

tion to form ions (01-) at high pH values and exist asneutral molecules (HOI) at low pH value. In theintermediate region, the ionic and the neutral molecu-lar species can associate to form ion-molecule com-plexes ((OI)zH-). As the surfactant concentrationis increased, micellization or precipitation of thesurfactant can occur in the solution. In addition,surfactant species can associate to form otheraggregates such as the dimer (Oli-) in premicellarsolutions. Also, long chain fany acids such as oleicacid have very limited solubility, which is a sensitivefunction of pH. The pH of precipitation of oleic acidcalculated as a function of total oleate is shown inFigure 1.

The solution equilibria of oleic acid (H01) areexpressed as below:

HOI(liquid) = HOI(aq)pK"'1 = 7.6 (Kso1: solubility product)

Water Chemistry of FlotationReagentsLong chain fatty acids such as oleic acid are amongthe commonly used reagents for the flotation of ox-ides, silicates and salt-type minerals. Flotation ofthese minerals using fatty acids is affected greatlyby solution properties such as pH, since weakly acidicfatty acids undergo association interactions that caninfluence their adsorption and flotation properties.For example, oleic acid species will undergo dissocia-

H01(aq) = H+ + 01-pKa = 4.95 (Ka: acid dissociation constant)

201- = (OIMpKd = - 3.7 (Kd: dimerization constant)

HOI + 01- = (01)2H-pKad = - 5.25 (Kad: acid-soap formation constant)

The species distribution of oleic acid as a function ofpH based on the above equilibria at a given concen-tration is shown in Figure 2. It can be seen from thisfigure that:

-51. The pH of the precipitation of oleic acid at the

given concentration is 7.45.2. The activities of oleic monomer and dimer remain

alrnQst constant above the precipitation pH anddecrease sharply below it.

3. The activity of the acid-soap (OI)2H- eXhibitsa maximum in the neutral pH range.

~>~ -6G~..G~

"0a -7

~

~~"c... , - - ~ = 2.51 x 10-'

-8

-9

2 4 6 8pH Oleic acid precipitation

10

The surface activities of the various surfactant spe-cies can be markedly different from each other. Ithas been estimated that the surface activity of theacid-soap (01)2H- is five orders of magnitude higherthan. that of the neutral molecule (H01) and aboutseven orders of magnitude higher than that of theneutral molecule (H01) and about seven orders ofmagnitude higher than that of the oleate monomer01-.

The existence of salt will also affect the surfac-tant-solution equilibria by changing the surfaceactivities of the various surfactant species, the criticalmicelle concentration and the solubility of the surfac-tant, and the solvent properties of the solution.

Figure 1 pH of oleic acid precipitation. (From Morgan LJ. Anan-thapadmanabhan KP and Somasundaran P (1986) Oleate ad-sorption on hematite: problem and methods. International Journalof Mineral Processing 18: 39. Copyright: Elsevier Science.)

II / FLOTATION / Reagent Adsorption on Phosphates1564

-~01-

, ;01)22-

1~:~/L. "/ '"I

-//

trolthe dissolution of calcite and apatite in water aregiven in Table 1.

In the case of carbonaceous phosphate minerals,apatite, calcite and dolomite will dissolve in water,followed by pH-dependent hydrolysis and complexa-tion of the dissolved species. Since these minerals aresparing soluble, the dissolved species have a markedeffect on their interfacial properties.

It should be noted that, from theoretical consider-ations, depending on the solution conditions, the sur-face of apatite can be converted to calcite and viceversa through surface reactions or bulk precipitationof the more stable phase. The stoichiometry of theequilibrium governing the conversion of apatite tocalcite can be written as:

"I "

m.!uGI -60-atGI

.c~-0'Z: -8'>.~.!;01,g -10 ,

3 4 8 8 10 t2 13

pH

CalO(PO4)6(OHh(S) + lOCO~-

= lOCaCO3(S) + 6PO~- + 20H

It can be seen from this equation that, dependingon the pH of the solution, apatite can be converted tocalcite if the total carbonate in solution exceeds a cer-tain value. In fact, the amount of dissolved carbonatefrom atmospheric CO2 does exceed that required toconvert apatite to calcite under high pH conditions.

Surface conversion due to the reaction of the dis-solved species with the mineral surface can be pre-dicted using stability diagrams for heterogeneousmineral systems. This is illustrated in Figure 3 for thecalcite-apatite system. The activity of Ca2 + in equi-

librium with various solid phases shows that the pointof interception for calcite and apatite is pH 9.3.Above this pH, apatite is less stable than calcite andhence conversion of apatite to that of calcite can beexpected in the calcite-apatite system. Similarly,apatite is more stable than calcite below pH 9.3. It isto be noted that Ca2 + in equilibrium with calcite inan open system (open to atmospheric CO2) is signifi-cantly different from that in a closed system. Also,

FIgure 2 Oleate species distribution as a function of pH. Totaloleate concentration = 3 x 10-5 mol L -1. (From Ananthapad-manabhan KP and Somasundaran P (1980) Oleate chemistryand hematite flotation. In: Yarar B and Spottiswood OJ (eds)Intetfacial Phenomena in Mineral Processing, p. 207. New Yort(:Engineering Foundation.)

It is clear that, to understand the adsorption of

reagents on solids, the effects of concentration,

pH, ionic strength and activities of the various poss-

ible reagent species on the adsorption process need to

be taken into account.

The Effect of Water Chemistryon Mineral-Solution EquilibriumWhen mineral particles are in contact with water,they undergo dissolution, the extent of which is de-pendent on the type and concentration of chemicalsin solution. The dissolved mineral species can under-go further reactions such as hydrolysis, complexa-tion, adsorption and precipitation. The complexequilibria involving aU such reactions can be expectedto determine the interfacial properties of the mineralsand their flotation behaviour. The equilibria that con-

Table 1 Equilibria controlling the dissolution of calcite and apatite in water

K.K.,

100.'103-310-12.810-12.

cr". + tCOicr. + 001-

Cr. + HaCcr.+~

~CaH~+.,t CaC~aq)~CaOH+ + H+.,t Ca(OHh + 2H +

10'10210"10'10'10'

Ca2++HP~-CaHPO.(aq)Ca2 + + ~POiC82+ + 2F-C82+ + F-

+:t CaHPO.(aq)+t CaHPO.(s)+:t CaWPO.++:t CaF2(s)+t CaF ...

Calcite~(S) ~Ca2+ +001- 10-8..~- + H + ~ tiCOa- 1010.aHC~- + H + ~H~ 1oe~

COa(g) + HaC ~ ~ 10-1.5

ApatiteCa,oCPO.),(F,OH)2(S) ~ 10 Ca2 + + 6 ro:- + 2 (F, OH)-ro:- + H+ +:tH~- 10'2.3H~- +H+ ~HaPOi 1072HPOi + H + ~ H3PO. 1oz.2Ca2+ +HaO +:tCaOH+ +H+ 10-12.8Ca2 + + 2HaO +:t Ca(OHk + 2H + 10-22.8

F- + H+ ~HF 10"1

-118

.1

3

1

04

.

II/FLOTATION/Reagent Adsorption on Phosphates 1565

0

+-NeU'0~'>°fl~

8'-J

-2

-4

-6

-8

-100 2 4 86 10 12 14

pH

FIgure 3 pH dependence of activity of Ca2 oj. in equilibrium with

calcium oleate (dotted line: O~ = 10-0 kmol m-3). calcite (open

(closed lines) and closed (dots and dashes) systems) and apatite(dashed lines). (From Ananthapadmanabhan KP and Somasun-daran P (1984) The role of dissolved mineral species in calcite-apatite flotation. Mineral and Metallurgical Processing 1: 36.)

The surface conversions in the calcite-apatite systemhave been proved experimentally; electrokinetic dataobtained for the calcite-apatite system in water and inthe supernatant of each other are shown in Figure 4.When apatite is in contact with calcite supernatant, itszeta potential is seen to shift to that of calcite and viceversa, suggesting surface conversion of apatite to cal-cite and calcite to apatite, respectively.

The zeta potential data obtained in mixed super-natants of calcite and apatite also show the effectof dissolved mineral species. If supernatants of calciteand apatite are combined as a 1 : 1 mixture, the twominerals have almost identical surface charge charac-teristics in the basic pH range (Figure 5).

The surface conversion of apatite and calcite is fur-ther supported by the result of electron spectroscopyfor chemical analysis (ESCA) measurements. The re-sults in Figure 6 show that, when apatite is condi-tioned in the supernatant of calcite at pH ,.., 12, itssurface exhibits spectroscopic properties characteristicof both calcite and apatite. This behaviour is attributedto the precipitation of calcite on the apatite.

Dissolution equilibria of sparingly soluble min-erals playa major role in determining the surfaceproperties of these minerals and in turn, adsorption ofreagents on them.

in the absence of atmospheric CO2, apatite has a widerstability region than in the open system. AtmosphericCO2 can thus be expected to play an important role inthese types of mineral-solution equilibria and in op-erations dependent on interfacial properties.

eo

~I "\I ~40

>g~;c

i.a~

,~>:§e'+;cQ)-0Q..G~N

20

0\"

\\

~\-20

'a

Figure 4 Illustration of the effect of supernatants on the zetapotential and isoelectric point of calcite and apatite:2x10-3kmolm-3KNOa. Open circles. calcite in water; opentriangles. apatite in water; filled triangles. apatite in calcite super-natant; filled circles. calcite in apatite supernatant. (From Anan-thapadmanabhan KP and Somasundaran P (1984) The role ofdissolved mineral species in calcite-apatite flotation. Mineral andMetallurgical Processing 1: 36.)

-40

5 6 7 8 9 10 11 12 13

pH

Figure 5 Illustration of the similarity in zeta potentials of calcite(circles) and apatite (triangles) in mixed supernatants. (FromAnanlhapadmanabhan KP and Somasundaran P (1984) The roleof dissolved mineral species in calcite-apatite flotation. Mineraland Metallurgical Processing 1: 36.)

1566 II/FLOTATION/Reagent Adsorption on Phosphates

in equilibrium with Ca2 +-oleate, Ca2 +-oleate can beexpected to precipitate.

Depletion isotherms of oleic acid on both francoliteand dolomite has been observed to be a two-regionlinear isotherm with a change of slope at about10-4 kmol m-3 (Figure 7). Simultane~us analysisof the dissolved mineral species in the supernatantsof the samples used in the adsorption experiments(Figure 8) shows a s~ decrease in the concentrationsof both Mg and Ca species when oleate concentrationexceeds 1.0 x 10-s kmol m -3 in the case of francolite

and 3.0x10-skmolm-3 in the case of dolomite.This suggests that bulk precipitation of calcium andmagnesium species can occur under such conditions.

Major chemical equilibria for the precipitationof Ca and Mg species by oleate can be given asfollows:

"Wi (A)~

ei Ie

'5..~.QE~

.s

.i Ic$ (8).5

---~/"-~~KCa(OI)2 = 3.81 X 10-13y2+ + 2 01- = Ca(01)2

KMi(0I12 = 1.58 X 10-11+ 2 01- = Mg(01)2Mg"

The onset of the precipitation of Ca(OI)2 and Mg(OI)2is calculated from the solubility products given aboveand marked in Figure 8. The calculated oleate con-centrations at the onset of precipitation are in goodagreement with experimental observations.

It is postulated that, in the case of oleate adsorptionon dolomite and francolite, different mecha-nisms govern the adsorption process. In the low con-centration range «10-4kmolm-3), the adsorption

295(C)

290 280 275285Binding energy leV)

Figure 6 ESCA spectra of C(1s) peak of apatite conditioned incalcite supernatant at pH - 12. (A) Apatite in water; (B) calcite inwater; (C) apatite in calcite supernatant. (From Ananthapad-manabhan KP and Somasundaran P (1984) The role of dissolvedmineral species in calcite-apatite flotation. Mineral and Metallurgi-cal Processing 1: 36.)

The Effect of Water Chemistry onAdsorption of Reagents on MineralsChemical equilibria in aqueous solutions containingboth the minerals and the surfactants can be expectedto be much more complex than in either of the indi-vidual systems discussed above. In addition to surfac-tant adsorption at the solid-liquid interface, interac-tions between dissolved mineral species with varioussurfactant species can be expected. All these interac-tions can affect the surfactant adsorption and thesubsequent flotation.

As indicated earlier, oleic acid has a very low solu-bility and adsorption of oleate, in some cases, is infact precipitation of the surfactant in the interfacialregion. In Figure 3, the activity of Ca2 + in equilib-

rium with various solid phases is plotted. If, at anystage, activity of Ca2 + in solution is greater than that

Figure 7 Depletion isotherms of '.C-labelied oleic acid on fran-colite (squares: pH = 8.2) and dolomite (circles: pH = 9.2). Temp-erature, 25°C; S;L = 0.3; 1= 3 X 10-2 kmol m-3 KN~. (FromSomasundaran P, Xiao L and Wang D (1991) Solution chemistryof flotation of sparingly soluble minerals. Mineral and MetallurgicalProcessing 8: 115-121.)

II/FLOTATION/Reagent Adsorption on Phosphates 1567

E"0 5 X 10-3

ac0.~ 10-3

0(.)

~~"CC: Calculated onsetu of Caol2 ppm.

10-5 I 10-5 -II . "'~-.!! No oleate 10-5 10-- 3 x 10-- = No oleate 10-5 10-- 3 x 10--a (A) Initial K oleate concentration (kmol m-') is (B) Initial K oleate concentration (kmol m-')

Figure 8 Dissolved Ca (squares) and Mg (circles) levels from (A) francolite (pH = 8.2) and (B) dolomite (pH = 9.2) suspensions asa function of oleate concentration. (From Somasunda:ran P, Xiao L and Wang D (1991) Solution chemistry of flotation of sparinglysoluble minerals. Mineral and Metallurgical Processing 8: 115.)

..E

- ~0 .

E~c0~e

~QC8Q~"0C~~"0~'0U)

10-- 10-.Mgol2pptn.

pletion of oleate owing to the precipitation of calciumoleate. In the case of apatite flotation, the depressionis due to phosphate and carbonate species in solution.The adsorption of these ions on the surface calciumsites reduces the sites available for oleate adsorptionwhich, in turn, lowers the hydrophobicity of the sur-face and so depresses the apatite flotation. Calciumoleate precipitation, in this case, does not occur toa significant extent due to the low concentration ofoleic acid used in flotation. The above observationsclearly show that water chemistry plays a crucial rolein the flotation of apatite-calcite systems.

In addition to reagent complexation and precipita-tion, other reactions that occur in the bulk solutioncan take place in the interfacial region. For example,hemimicellization at a solid-liquid interface is aphenofl1enon that drastically affects the adsorp-tion of collector reagents on solids.

Flotation is a dynamic process. In addition tothe equilibrium effects associated with the waterchemistry, it can also influence the adsorption kinet-ics of surfactants on the solid surfaces. Anionic condi-tioning is a unit operation that precedes rougherflotation and skin flotation of phosphates in Floridaflotation plants. The effect of water chemistry onoleic acid adsorption on francolite during anionicconditioning has recently been studied in detail. Inorder to identify the effect of process variableson the adsorption, the experiment was carried outunder both laboratory and plant conditions (Table 2).

The kinetics of oleic acid adsorption on francoliteunder both laboratory and plant conditions, usingdistilled water and plant water, is shown in Fig-ure 10. The adsorption density and kinetics are quitedifferent depending on the conditions and the

of oleate on both minerals occurs mainly due tochemical bonding on surfaces without any precipita-tion. At an intermediate concentration of about10-4kmolm-3, the solubility limit of Ca and Mgoleate can be reached in the interfacial region but notin the bulk solution, suggesting surface precipitationof oleate on both minerals. In the high concentrationrange (>5 x 10-4 kmol m-3), oleate depletion maybe dominated in the case of both minerals by theprecipitation of Ca and Mg species with oleate, on themineral surface and in the bulk solution.

From the above discussion on apatite-calcite con-version, it is clear that a flotation separation schemedesigned on the basis of the surface properties ofa single mineral is not likely to perform satisfactorily.The effect of dissolved species of calcite andapatite on fatty acid flotation of both minerals has infact been studied using mineral supernatant solutionscontaining various dissolved species. The flotationresults are shown in Figure 9. Both supernatants ofcalcite and apatite are found to depress the calciteflotation by oleic acid in the tested pH range, withapatite supernatant exhibiting a greater depressingeffect. Similar results have also been obtained forapatite flotation. The supernatants of calcite and apa-tite depress the apatite flotation under all tested pHconditions.

Studies on the dissolved species responsible for theobserved effect revealed that, for calcite flota-tion, the depression role of apatite supernatant resultsfrom the combined effects of calcium species andthe phosphate species in solution, while the depress-ion role of calcite supernatant is mostly that of thecalcium ion and possibly some carbonate ions. Thedepression due to calcium ion is caused by the de-

x 10~

10-3

-1~-~~

1568 II / FLOTATION / Reagent Adsorption on Phosphates

100

80

-g 60..~0

ii:

~ 40

20

00 2 8 10 12 144 6

(81 PH(A) pH

(C) 4 5 6 7 8 9 (D) 4 5 8 . 7 8 9

pH pH

Figure 9 (A) Effect of apatite supernatant (squares) on calcite flotation. K oleate 10-. krool rn-3; 1- 3x 10-2 kmOI rn-3 KNO3.Circles. water. (B) Effect of calcite supernatant (squares) on calcite flotation. K oleate 10-. kmol rn-3;1 = 3x 10-2 kmOI m-3 KNO3-Circles, water. (C) Effect of calcite supernatant (squares) on apatite flotation. K oleate = 2 x 10-8 ~ m-3; 1- 3 X 10-2 krnol m-3KNO3. Circles. water. (D) Effect of apatite supernatant (squares) on apatite flotation. K oIeate=2x10-8krno1m-3; 1=3x10-2 kmOI m-3 KNO3- Circles. water. (From Ananthapadmanabhan KP and Somasundaran P (1984) The role of dissolved mineralspecies in calcite-apatite flotation. Mineral and Metallurgical Processing 1: 36.)

water. Under laboratory conditions, the adsorption inplant water is significantly lower than that in thedistilled water. It is proposed that this is due toreagent loss resulting from the dissolved species inplant water precipitating the oleic acid. In contrast,under plant conditions, the adsorption behaviour of

oleic acid in plant water and distilled water is similarand adsorption densities are lower than those underlaboratory conditions. The high solid/iiquid ratio un-der plant conditions will reduce the adsorption den-sity on the solids because of the much greater solidsurface on to which the reduced total amount of

Table 2 Comparison of laboratory and plant conditions

Laboratory conditions Plant conditions

Conditioner Wrist-action shaker

pHWatelSolidTime

9.1-9.5Distilled and plant water10 (2 9 sample)120 (except for kinetics)

Lightnin Labmaster L 1 U08. four-bladedcruciform propeller operating at 350 rpm9.1-9.5Plant water72 (1000g sample)3 (except for kinetics)

r(%)(min)

11/ FLOTATION / Reagent Adsorption on Phosphates 1569

3.0 x 10-1

~Q-D- -

~

0~p

J. 10j, .-;1 - -.'

--.;~~-,

rf" 2.E"0E?: 2.'Vic~

'Cc,2 1.~..0II)

'Ca'C 1.'ua,"e(5 5.

., . . . . I . . . . , . . , . . , .. . . , . . . . ,

0

0 10 20 30 40 50 60

Conditioning time (minI

Figure 10 Kinetics of oleic acid adsorption on francolite in distilled water and plant water under laboratory and plant conditions. Opensquares, distilled water in laboratory conditions; filled squares, plant water in laboratory conditions; open circles, distilled water in plantconditions; filled circles, plant water in plant conditions. Oleic acid concentration: 8.1 x 10-3 mol L -1; pH 9.1-9.5. (From Maltesh C,Somasundaran P and Gruber GA (1996) Fundamentals of oleic acid adsorption on phosphate flotation feed during anionic conditioning.Mineral and Metallurgical Processing 13: 157.) .

In the anionic flotation of phosphate, Ca2 +

affects the grade of phosphate by activating thequartz through formation of calcium-bearing precipi-tates at high pH. This detrimental effect can beprevented by adding sodium silicate, which can inter-act with Ca2 + and form calcium silicate. Since cal-

cium silicate and quartz are negatively charged, de-tachment of calcium silicate from quartz can occurand thus quartz flotation can be depressed.

It ha~ been found that in carbonate/phosphate sys-tems, with fatty acid as collector, apatite is depressedin the acid medium (pH 5.5-6.0) while carbonate isfloated. The depression of phosphate at this pH ispossibly due to the adsorption (or formation) of aque-ous CaHPO4 on its surface, preventing surfactantions from approaching the surface of the phosphateparticles. Free Ca2 + in solution can affect the

formation of aqueous CaHPO4. From thermody-namic considerations it can be predicted that theselective flotation of carbonates from phosphates inacid media can be enhanced by minimizing free Ca2 +in solution and by increasing HPO~ - in the system.This can be done by (1) decreasing free Ca2 + concen-

tration in the system to low values by adding suitablechemical reagents such as sulfuric acid or chelatingagents such as oxalic acid, and (2) adding solublephosphate salts to enhance the depression of thephosphate minerals. Results from experiments with

reagent in the water adsorbs. This will also result ina lower reagent concentration in solution reducingthe precipitation eject. The int~nse agitation in theplant conditioner may also remove some of the boundreagent from the surface.

The adsorption isotherms of oleic acid on fran-colite under laboratory and plant conditions arecompared in Figure 11. Adsorption is markedlyhigher under laboratory conditions than under plantconditions. On the other hand, under plant condi-tions the adsorption is similar in distilled water andplant water. This suggests that the effect of dis-solved species is reduced under plant conditions.

From the above discussion, it can be seen that theadsorption of surfactant on a mineral is a compli-cated process involving interactions such as surfac-tant self-association, mineral dissolution, bulkprecipitation, adsorption and surface precipitation.The interactions are further complicated by the kin-etic effects of the various reactions.

Understanding the effect of the water chem-istry on reagent adsorption offers opportunitiesto manipulate such processes by optimizing the con-tributing factors such as alteration of the surfaceproperties, complexation of ions which cause precipi-tation of the surfactant, prevention or enhancementof collector adsorption and changes in the adsorptionkinetics to achieve the desired selectivity in flotation.

x 10-8

X 10-8

X 10-6

X 10--

X 10-7

1570 II / FLOTATION / Reagent Adsorption on Phosphates

Figure 11 Adsorption isothenns of oleic acid adsorption on francolite in distilled water and plant water under laboratory and plantconditions. Squares, distilled water in laboratory conditions; open circles, distilled water in plant conditions; filled circles, plant water inplant conditions. (From Maltesh C, Somasundaran P and Gruber GA (1996) Fundamentals of oleic acid adsorption on phosphateflotation feed during anionic conditioning. Mineral and Metallurgical Processing 13: 157.)

minerals. Even though Alizarin Red S adsorbsmore on apatite than on calcite, it depresses the flota-tion of apatite using oleate as collector more than thatof calcite (Figure 12). In the absence of the dye, bothcalcite and apatite float with oleate at pH 10.5. Whenthe dye concentration increases to 5 x 10-6 mol m-3,the flotation of calcite is very little affected witha recovery of about 90%, while apatite flotation isdepressed to 5-10%. Calcite flotation is onlyaffected at higher concentrations of dye. AlizarinRed S or its derivatives are hence promising reagentsfor the beneficiation of phosphate with carbonaceousgangues.

SummaryMineral-solution equilibria, surfactant-solutionchemistry, as well as interactions among dissolvedspecies, surfactant and solids, can have a drastic ef-fect on surfactant adsorption and flotation separationof sparing soluble minerals. Studies on the effectsof water chemistry on adsorption of surfactant onphosphate minerals such as apatite and francolite andassociated minerals such as calcite and dolomite showthat these interactions have marked effects onthe reagent adsorption as well as flotation. Sur(actantcan exist in different forms in solution dependingon the solution pH and the surfactant concentration.Minerals can undergo dissolution, with the extent of

natural phosphate ores are in agreement with thetheoretical predictions.

Based on the oleic acid solution chemistry, a two-stage conditioning process for the flotation of dol-omite from apatite has been proposed. The mixedminerals are first conditioned at pH 10 with oleic acidcollector. The system is then reconditioned below pH4.5 where dolomite is floated. The selectivity of dol-omite from apatite is attributed to two factors in thisprocess.

1. High adsorption of oleate on dolomite during thefirst stage at pH 10, which is maintained afterreconditioning "at lower pH.

2. Oleate to oleic acid transformation upon recon-ditioning, reducing its efficiency, and this re-duction being more severe for apatite than fordolomite.

In the high pH range, oleate adsorbs on to apatiteand calcite through specific interactions, while atlow pH, when oleic acid is the major species, theadsorption is through weaker physical interaction.Thus, oleic acid is a poor collector compared tooleate.

Modification of collector adsorption on mineralscan be used to control their flotation response. In onestudy, Alizarin Red 5, a dye that stains calcite,was tested as a modifying agent in calcite-apatitesystem due to its preferential adsorption on these

II/FLOTATION/Reagent Adsorption on Phosphates 1571

t2 3 4 5 6 7Initial alizarin red S concentration (10. x kmol m-1j

810

Figure 12 Aotation of calcite (triangles) and apatite (circles) from their mixture (1 : 1) at pH 10.5 as a function of Alizarin redS concentration. Alizarin red S conditioning time = 1 min; K oleate = 9 x 10-5 kmO! m-'; KCI = 3 x 10-2 krnol m-'; pH = 10.5:t 0.2.(From Fu E and Somasundaran P (1986) International Journal of Mineral Processing 18: 287. with permission from Elsevier Science.)

Further Readingdissolution depending upon solution conditions suchas pH, ionic strength and concentration of constitu-ent ions. The dissolved mineral species can furtherinteract with mineral solids, leading to surface con-version of the minerals. They can also interact withsurfactant, leading to surface and bulk precipitation.All these processes can significantly affect theadsorption of surfactant on minerals. A full under-standing of the various interactions in surfactant-solid-solution system is essential for developingefficient separation schemes. Indeed, desired se-lectivity can be achieved by using appropriate addi-tives to control dissolved species or modifyingcollector adsorption and by optimizing solution con-ditions as well as the kinetics involved.

Amankonah JO, Somasundaran P and Ananthapadma-nabhan KP (1985) Effects of dissolved mineral spe-cies on the dissolution/precipitation characteristics ofcalcite and apatite. Colloids and Surfaces 15: 295.

Amankonah JO, Somasundaran P and Ananthapadrna-nabhan KP (1985) Effects of dissolved mineralspecies on the electrokinetic behavior of calcite andapatite. Colloids and Surfaces 15: 335.

Ananthapadmanabhan KP and Somasundaran P (1980)Oleate chemistry and hematite flotation. In: Yarar Band Spottiswood DJ (eds) Interfacial Phenomena inMineral Processing, p. 207, New York: EngineeringFoundation.

Ananthapadmanabhan KP and Somasundaran P (1984)The role of dissolved mineral species in calcite-apatite flotation. Mineral and Metallurgical Processing1: 36.

Ananthapadmanabhan KP and Somasundaran P (1985)Surface precipitation of inorganics and surfactantsand its role in adsorption and flotation. Colloids andSurfaces 13: 151.

AcknowledgementThe authors acknowledge financial support of

the National Science Foundation (CTS-9622781 and

EEC-94-02~89)

1572 II / ION EXCHANGE / Catalysis: Organic Ion Exchangers

methods. International Journal of Mineral Processing18: 139.

Moudgil BM and Chanchani R (1985) Selective flotation ofdolomite from francolite using two-stage conditioning.Mineral and Metallurgical Processing 2: 19-25.

Somasundaran P (1969) Adsorption of starch andoleate and interaction between them on calcite inaqueous solutions. Journal of Colloid Interface Science31: 557.

Somasundaran P and Ananthapadmanabhan KP (1986)Solution chemistry of flotation. In: Somasundaran P.(Ed.), Advances in Mineral Processing, p. 426. NewYork: AIME.

Somasundaran P, Amankonah JO and Ananthapadma-nabhan KP (1985) Mineral-solution equilibria in spar-ingly soluble mineral systems. Colloids and Surfaces 15:309.

Somasundaran P, Xiao L and Wang D (1991) Solutionchemistry of flotation of sparingly soluble minerals.Mineral and Metallurgical Processing 8: 115-121.

Ananthapadmanabhan KP and Somasundaran P (1988)Acid-soap formation in aqueous oleate solutions. Jour-nal of Colloid Interface Science 122: 104.

Dho H and Iwasaki I (1990) Role of sodium silicate inphosphate flotation. Mineral and Metallurgical Process-ing 7: 215.

Elgillani DA and Abouzeid A-ZM (1993) Flotation of car-bonates from phosphate ores in acidic media. Interna-tional Journal of Mineral Processing 38: 235.

Fu E, Somasundaran P (1986) Alizarin red S as a flotationmodifying agent in calcite-apatite systems. InternationalJournal of Mineral Processing 18: 287.

Leja j (1982) Surface Chemistry of Froth Flotation. NewYork: Plenum Press.

Maltesh C, Somasundaran P and Gruber GA (1996) Funda-mentals of oleic acid adsorption on phosphate flotationfeed during anionic conditioning. Mineral and Metallur-gical Processing 13: 157.

Morgan Lj, Ananthapadmanabhan KP and SomasundaranP (1986) Oleate adsorption on hematite: problem and

most otten recyclable from one run to the next with-out any added treatment. Potentially, they sufferone major disadvantage over homogeneous catalysts.Intimate contact between reactants and the catalyticsite is not achieved simply by mixing the heterogen-eous catalyst with the reactants. In a stirred reactor,intimate contact between reactants and the homo-geneous catalyst is very easily achieved and masstransport of reactants to catalyst is very rapid andalmost never rate-limiting. With heterogeneous cata-lysis, mass transport of reactants to the catalytic sitemay btten be the rate-limiting element, especially ifthe activation energy for the reaction is small and thechemical reaction is rapid. There are excellent textsand monographs on the issues surrounding hetero-geneous catalysis, and the reader is referred to thesefor the development of a fuller understanding(see Further Reading).

Catalysis: Organic IonExchangers

R. L. Albright, Albright Consulting,Southampton, PA, USA

Copyright @ 2000 Academic Press

Nature of Organic Ion ExchangePolymers

IntroductionThe ion exchange polymers most otten used in cataly-sis are insoluble materials that can be constructedfrom inorganic or organic monomer units. Thisarticle will present only catalysis performed by theorganic ion exchangers that are insoluble solids.There are commercial ion exchangers that are liquids,but to date they have been used very little incatalysis and, therefore, will not be included in thisdiscussion.

Insoluble ion exchangers carry out their catalyticwork in a heterogeneous rather than a homogeneousfashion and are, therefore, part of the group calledheterogeneous catalysts. Heterogeneous catalystshave three very significant advantages over homo-geneous catalysts: first, they are not corrosive; sec-ond, they are very readily separated from the reactionmixture by a simple filtration; and third, they are

Chemical Composition

Organic ion exchangers are made by p<:>lymerizationof organic monomers into large molecules which aremade insoluble by crosslinking with a p<:>lyfunctionalmonomer. The nature and the level (concentration) of