Adsorption Properties of Ca2+ on N a-kaolinite and I ts Effect on Flocculation Using Polyacry lamides

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Colloids and Surfaces, 32 (1988) 127-138 Elsevier Science Publishers B. V., Amsterdam - Printed in The Netherlands 127. ;,,{. 't!

Columbia University, New York, NY 127 (U.S.A.

1 Colloids and Surfaces, 32 (1988) Elsevier Science Publishers B. V., Amsterdam - Printed in The Netherlands 127. ;,,{. 't! Adsorption Properties of Ca2+ on N a-kaolinite and I ts Effect on Flocculation Using Polyacry lamides G. ATESOK*, P. SOMASUNDARAN and LoIJ. MORGAN Henry Krumb School of Mines. Columbia University, New York, NY 127 (U.S.A.) (Received 2 April 1987; accepted in final Conn 26 October 1987) ABSTRACT Adsorption behavior of calcium ions on Na-kaolinite and the adsorption and flocculation behavior of Na-kaolinite by polyacrylamide in the presence of calcium species in solution have been investigated. Parameters examined in calcium adsorption experiments include ph, conditioning time of the suspension with calcium, and calcium concentration. The effect of calcium on adsorption of polyacrylamide and hydrolyzed polyacrylamide by the kaolinite and on its flocculation is determined. Also the effect of the polymer on calcium adsorption is examined. Adsorption of calcium occurs only under ph conditions where it hydrolyzes to CaOH+ and Ca(OH)2. Calcium adsorption (abstraction) is sensitive to the presence of polymer as well as to stiuing conditions. Interestingly, above ph 8, stirring and addition of polymer (HPAM 33) were found to cause calcium desorption suggesting detachment of precipitate from the kaolinite surface. INTRODUCTION Mineral fines can be flocculated by reducing the electrostatic repulsion between particles, e.g. by using inorganic salts, and by using polymers which are capable of bridging the particles with one another. Polyacrylamides are widely used as a flocculating agent for fine particle suspensions and their adsorption has been generally characterized [ 1-4 ]. Most of these systems can also contain ionic species which may alter the surface physicochemical properties of the particles significantly [5,6]. For example, ions such as Ca2+ and Mg2+ have been reported to change the zeta potentioi-9c-u_artz (7,8] as_llt9ffect its-flocculatiuncnaractefistlr:s:-such-effects can iri turnmastically affect-m:- dustrial selective flocculation processes [6,9]. In the last decade, a number of studies of cation adsorption have been conducted [1,11]. Many of these have shown the important role of ph in controlling cation adsorption on hydrous metal oxides [12]. In some cases,.present address: Department of Mineral Dressing, Mining Faculty of Istanbul Technical University, Tesvikiya, Istanbul, Turkey. m RR.Rn?? IRA./.tn "n 1QRR FIo,,;o,. (';on,.,. 1>"hl;... n u

128 increased uptake of the metal ion occurs in a narrow ph range. This is particularly true for strongly hydrolyzable cations [13,14].

On the other hand, a recent work detailing the effect of conditions in the double layer has shown that in a number of cases, phenomena attributed to adsorption can in fact be explained by surface

However, there is little information on divalent cation selectivity on kaolinite [18,19]. There has also been some work on the adsorption of and flocculation by polymers on kaolinite [1-4,2].

2 128 increased uptake of the metal ion occurs in a narrow ph range. This is particularly true for strongly hydrolyzable cations [13,14]. For these systems, adsorption has been correlated primarily with the hydrolysis characteristics of the adsorbing ion rather than with the charge properties of the mineral. On the other hand, a recent work detailing the effect of conditions in the double layer has shown that in a number of cases, phenomena attributed to adsorption can in fact be explained by surface precipitation [15]. Some work has been done in the past on the adsorption of inorganic ions on kaolinite. For example, the selectivity sequence on kaolinite is found to be Li+ <Na+ <K+ <Cs+ [16,17]. However, there is little information on divalent cation selectivity on kaolinite [18,19]. There has also been some work on the adsorption of and flocculation by polymers on kaolinite [1-4,2]. Both of these processes have been shown to depend significantly on the charge characteristics of the polymer and the mineral as determined by the ph and ionic strength. Indeed, the behavior of these systems is extremely complex when both the inorganic and polymer species are present and almost no information is available for such cases even though both are invariably present in most flocculating systems. In this study, the adsorption. response of calcium on Na-kaolinite and the adsorption and flocculation ofna-kaolinite by polyacrylamides in the presence of calcium in solution have been investigated. Results obtained for adsorption and fl6cculation are discussed with the help of electrokinetic data. EXPERIMENTAL Materials Mineral Na-kaolinite. A well-crystallized sample of Georgia kaolinite of 9.94 m2 g-l surface area was obtained from the clay repository at the University of Missouri. A homoionic sample of sodium kaolinite was prepared from this using an ion-exchange treatment discussed elsewhere [2,21]. ; ---Potymers c- :c-::--=--- ",cccc=-=,,; The 14C-Iabeled nonionic polyacrylamide (PAM) of 5.2XIO6 molecular weight and 33 % hydrolyzed polyacrylamide (HP AM 33) of 6.6 X los molecular weight used here were synthesized and characterized by American Cyanamid Company. *The word adsorption is used somewhat loosely here as it is clear there may also be precipitation in the system. It might be more correct to use "calcium abstraction" to include both the calcium which adsorbs and that which precipitates. However, for simplicity, "adsorption" is used and the likelihood of precipitation is kept in mind.

$:1 29" 1., J norganic reagents ;;, Fisher certified HCI and NaOH were used to adjust the ph of the suspension. \ Amend Drug and Chemical Company reagent grade NaCI (99.96% pure) was.$ L:A ' f' Flocculation procedure For flocculation tests, 5 g samples of Na-kaolinite were pre-conditioned in 15 cm3 salt solution in 25 cm3 Teflon bottles for 2 h using a wrist-action shaker and for

L:A ' f' Flocculation procedure For flocculation tests, 5 g samples of Na-kaolinite were pre-conditioned in 15 cm3 salt solution in 25 cm3 Teflon bottles for 2 h using a wrist-action shaker and for

These conditions were identified as sufficient to achieve equilibrium adsorption (i.e., no additional change measured). Sedimentation tests were carried out in 25 cm3 beakers at 2.

3 :1 29" 1., J norganic reagents ;;, Fisher certified HCI and NaOH were used to adjust the ph of the suspension. \ Amend Drug and Chemical Company reagent grade NaCI (99.96% pure) was. " used to prepare the 3 X 1-2 kmol m -3 salt solution used in all the experiments: to control ionic strength, J. Methods.;i, :J I. L:A ' f' Flocculation procedure For flocculation tests, 5 g samples of Na-kaolinite were pre-conditioned in 15 cm3 salt solution in 25 cm3 Teflon bottles for 2 h using a wrist-action shaker and for an additional 3 min after adding desired amounts of calcium salt. Polymer which is in 4 ml salt solution was then added and the pulp stirred for 1 min using a 1 inch diameter propeller at 12 rpm. These conditions were identified as sufficient to achieve equilibrium adsorption (i.e., no additional change measured). Sedimentation tests were carried out in 25 cm3 beakers at 2.5% (by weight) pulp density. The slurry was allowed to settle for 3 s and then 1 ml of the supernatant was removed using a suction device. The ph of the pulp was measured at the end of each test. ' r Polymer determinations Supernatant samples were centrifuged for 1 min at 1, rpm, using an IEC centrifuge and analyzed for residual polymer using a Beckman Liquid Scintillation Counter (LSC).... :. Cakium determination i Supernatants were analyzed for total calcium, CaT, also using the LSC to ount 45Ca. Ca2+ concentration in some of the samples was also determined by measuring the calcium potential using a Ca2+ selective electrode. The effect of the presence of the hydrolyzed (anionic) polymer on the calcium measurement was also monitored and taken into account in the calibrating system (Fig. 1). There is significant_interference but only above 1 ppm polymer. Evidently the-anionic polymer quenches the calcium to a certain extent or there is some precipitation of calcium with the negatively charged polymer.. Electrokinetic studies Electrokinetic mobility of Na-kaolinite was measured using a Zeta-Meter in mineral supernatants at.1 % solids content..:..

$1.1 > 151 E.14.J «I i 131 121 \ 11 J 1 \1 I: 311-2kmol/m3 NaCI T: 23; 2.C Condo Speed: 12rpm Cond.Time : 1mln Conc. of Co..: 1 ppm (2.5 11O-3M) Polymer: ph: 6.6-6.44 33% Hydrolyzed Polyacrylamide --.$ $8 u7...6 in z.5 \II Q z.4 2- t:.3 «go.2 Q c(.1. -- " ph: 11.13-11.26 "--- 9.53-9.7., '-'-- ; ; 1. 53-1. 6 - I I I I I I I I I 1 2 3 4 6 7 8 9 1 INITIAL CALCtUM CONCENTRATION 1 Co, ppm Fig. 2. Effect of initjaj calcium concentration on adsorption.$

4 1.1 > 151 E.14.J «I i \ 11 J 1 \1 I: 311-2kmol/m3 NaCI T: 23; 2.C Condo Speed: 12rpm Cond.Time : 1mln Conc. of Co..: 1 ppm (2.5 11O-3M) Polymer: ph: % Hydrolyzed Polyacrylamide --.f!:t!..q!.fi.t o--.o :--: = J 1' I - I I I I INITIAL POLYMER CONCrNTRATION, p pm Fig. 1. Effect of polymer on measuring calcium potential by using a Caz+ selective electrode.. ",@.9..: e.8 u7...6 in z.5 \II Q z.4 2- t:.3 «go.2 Q c( " ph: " , '-'-- ; ; I I I I I I I I I INITIAL CALCtUM CONCENTRATION 1 Co, ppm Fig. 2. Effect of initjaj calcium concentration on adsorption. RESULTS AND DISCUSSION " dsorption Results obtained for adsorption of calcium by Na-kaolinite are given in Figs land 3 as a function of calcium concentration and ph, respectively. Calcium Idsorption density increases with concentration and is higher at elevated ph ( Fig. 2). The more interesting feature, however, is the sharp rise in adsorption

5 131 N e.3 c. e -O25 f ā (.).2 >- t:.15 \&J Z.1 i= IL.5 I : 3 x 1-2 kmol/m3 NoCI T: 22'f2.C Condo Time: 3minute, CO'. Do CoT. CoT 1 u 9O_E. 8 Z. -z- 7 o 6 z 5 IAJ.J uo zu) 4 So u+ 3.J + cl u. 2./ -z ct -.,, 1 \. 1 ci,,, ",',', I I '.O« ph Fig. 3. Adsorption of calcium from 1 ppm aqueous solutions by Na-kaolinite., t,r' above ph 1 (Fig. 3). Similar behavior has been observed in the past for calcium adsorption on silica [22]. The sudden increase in adsorption may be attributed to formation of calcium-hydroxide complexes in solution and at the

1.12 +2 +1 > E -1.J.- Z 1&1.- a. 1&1 N -2-3 -4 I: 3Klo-2kmol/m3 NoCI T: 23+28C Condo Time: 3 minutes -5-6 I I I I I I I 2 4 6 8 1 12 CONCENTRATION of CALCIUM os Co++, ppm Fig. 5.

6 > E -1.J.- Z 1&1.- a. 1&1 N I: 3Klo-2kmol/m3 NoCI T: 23+28C Condo Time: 3 minutes -5-6 I I I I I I I CONCENTRATION of CALCIUM os Co++, ppm Fig. 5. Zeta potential values of Na-kaolinite after adsorption of calcium as a function of concentration of -calcium as Ca2+. CII.3 E - E.25..: ụ.2 >- I-.15 1&1 Z.1 Q. Q: CONDITIONING TIME, hours Fig. 6. Effect of conditioning time of the suspension with calcium on adsorption.

!edtodueto adsorption of tile hy<iioxycomplex, CaOH by hydrogen bonding or water forming reactions between the complex and protons on the solid surface [ 13].

7 . s; mineral surface 15,22,23]. " The presence of calcium also causes significant change in zeta potential above ',' ph 9 (Figs 4 and 5). While increasing calcium concentration causes some reduction in negative zeta potential at ph 7.5, the effect is dramatic at ph 11.3 )_.h otential chan!1!!c2p!!edtodueto adsorption of tile hy<iioxycomplex, CaOH by hydrogen bonding or water forming reactions between the complex and protons on the solid surface [ 13]. It has been shown, however, that under these conditions there can be surface precipitation of Ca (OH) 2 [15]. The negative potential in the interfacial region gives rise to an excess of Ca2+ and the solubility product is exceeded then at the interface before the bulk solution attains the critical concentration. The precipitated Ca (OH) 2, which has a point of zero charge above 12 [23], will impart positive potential to the surface which accounts for the observed increase in zeta potential above ph 9. There is another possible explanation for the observed behavior. Carbonate in solution open to atmosphereic CO2 (g) increases dramatically at high ph and can lead to calcium carbonate precipitation [24]. Formation of CaCO3 is thermodynamically favored over Ca(OH)2 and it too has a higher PZC than kaolinite [24]. Presence of either of these species on the kaolin surface will reduce measured zeta potential. The effect of conditioning time of the suspension in calcium salt solution on Ca adsorption by kaolinite at ph 7.4 and 11.4 is shown in Fig. 6. While condie tioning time had no effect on Ca adsorption at ph 7 A, a sudden marked rise in adsorption resulted at ph lla at 2 h followed by a steady decrease thereafter. The reasons for the sharp rise in calcium adsorption are not evident at present. It is suggested that it may be due to onset of precipitation of calcium species at the surface followed by some detachment of crystallites. 133 Flocculation Calcium alone has only a small effect on kaolinite aggregation. When the percent solids settled is compared in the absence and presence of calcium (Fig. 7), there is a small decrease (dispersion) below ph 11 and a measurable increase above ph 11. This latter is evidently due to the decrease in zeta potential caused by the calcium in alkaline solutions. At ph 11, the zeta potential is reduced from - 55 m V to - 2 m V in the presence of 1 ppm calcium. The results in Fig. 7 show the flocculation of the clay by non ionic polyacrylamide in the presence of calcium and as a function of ph. Adsorption of the polymer in these systems was total at the tested level (5 ppm) both in the absence and presence of calcium and was independent of ph. As expected, the polyacrylamide caused considerable flocculation of the kaolinite and, interestingly enough, addition of calcium a further increase in flocculation. Flocculation of kaolinite by anionic polymer, HPAM (33% hydrolyzed), in

13. 5 1&1 -J.- 8 7 1;j 4 II) 3 II) 6a - ::::::=. - - - -, -.:;; -,;.-'-'.---:::=.. :=-. Somple: No-Koolinlte Polymer: PAM, " Without Cdclum and Polymer.

8 &1 -J ;j 4 II) 3 II) 6a - ::::::= , -.:;; -,;.-'-'.---:::=.. :=-. Somple: No-Koolinlte Polymer: PAM, " Without Cdclum and Polymer.2 x 16MW With Polymer without Calcium CI : 5mg/kg D With Calcium and Polymer Conc. of Co'.: 1ppm 4 With Calcium without Polymer I i.3 a: U)w r z 2 L. QI :;.-= 8.2 w)-..j S/L:.25 T : 23i28C i=-- 1 I : 3x1-2kmol/m3 NoCI.1 Cond.tlme Colc ium - 3 minute. g - Polymer -1mlnute. < ph Fig. 7. Effect of PAM on flocculation of Na-kaolinite in the presence of calcium (CaT, total calcium (ithout distinguishing among species); Ci, initial concentration; SIL, solidf1iquid ratio; I, ionic.strength). 5 IIJ..J 4 IIJ II) 8 r-: 7 6 :J 3 II) at 2 1 I Sample: No-KaolinIte S/L:.25 - Polymer: HPAM, 33% T : C (6.6 x ioe MW I I : 3xlO-2 kmal/m3 CI : 5mg/kg NaCI. CalcIum Cone. of Co ++: 1Oppm Condo Time:. Without Colcium or Polymer With Polymer, Without Calcium With Calcium and Polymer - -3mlnutes Polymer -lominutes :;. Ne % e -.3 t= - '4 U) % O % u.1 i i %e UJ UJ»- U [ 5 ' - -«1 III ph Fig. 8. Effect of HPAM on noccujation of Na.kaolinite in the presence of calcium.

' I. 135 1, ;';,,( c. I: 3xlO-2kmd/m' HoCI Conc. of HPAM: 5ppm E T: 23i2.C (33% 6.6.tO5MW) a. Condo time: Calcium - 3mln a. Condo Speed: 12rpm Polymer -1 Omkl ( HPAM).

$.. u Z Polymer (with blank lolutlon) - \II U D Af ter Polymer addition z 8 4.. % De,orptlon of Colcium os totol 'T 4.$

9 ' I , ;';,,( c. I: 3xlO-2kmd/m' HoCI Conc. of HPAM: 5ppm E T: 23i2.C (33% 6.6.tO5MW) a. Condo time: Calcium - 3mln a. Condo Speed: 12rpm Polymer -1 Omkl ( HPAM).: 1. Canc. of Co..: 1 ppm G 8 G Z 8.2 Before Polymer oddition 8 :»... - Effect of stirring on desorption c( a: 6. of calcium before adding 6 c(... u Z Polymer (with blank lolutlon) - \II U D Af ter Polymer addition z % De,orptlon of Colcium os totol 'T 4. Percentage amount of the adsorbed Calcium de,orbed by HPAM e :» 2..-,,' 1 2 g \II In. \II. a: - I I I I I I I I I I I ph Fig. 9. Adsorption of cakium by Na-kaolinite before and afteredding polymer. "

16 the absence and presence of calcium was investigated as a function of ph. Polymer enhances flocculation only at quite low ph and calcium has no additional effect.

It can be seen from this figure that the adsorption of the polymer was increased by the addition of calcium above ph 9.

10 16 the absence and presence of calcium was investigated as a function of ph. Polymer enhances flocculation only at quite low ph and calcium has no additional effect. Solids settled is the same as with calcium addition (no polymer) up to ph 1. Results obtained for polymer adsorption and flocculation are also given in Fig. 8. It can be seen from this figure that the adsorption of the polymer was increased by the addition of calcium above ph 9. However, there was insignificant change in the flocculation as me-asured by the solids settled. = In= om e l'-to--study-thisc' pc }}en me:n:o rffut he -effecf:ofpo lymer-ijf1 sorption by kaolinite was also examined. Adsorption of calcium before and after polymer addition was determined. Results obtained are presented in Fig. 9. As seen from this figure, addition of the hydrolyzed polymer did cause desorption of calcium. To determine the nature of desorption or detachment, control experiments were carried out in the absence of polymer. It can be seen from Fig. 9 that the stirring process itself (without polymer) does produce measureable desorption of calcium from the clay. These results suggest that calcium depletion from solution might be due to surface precipitation of calcium species which can be detached by stirring. It appears that HP AM enhanced the detachment possibly due to increased particle-particle abrasion in the flocculated system. It is also likely that the calcium species form a complex with HPAM and then detach from the surface. In this.:regard, it is interesting that the flocculation of kaolinite by the anionic polyn1er was not affected by the presence of calcium. The zeta potential of kaolinite in the presence of both calcium and HPAM as a function of ph is given in Fig. 1. These results show that polymer alone reduces the magnitude of the zeta potential only slightly. The addition of polymer. with calcium causes complex zeta potential response. However, above ph 1, the negative potential is restored at least partially, suggesting that some of what adsorbed or precipitated on the surface was removed by the polymer. SUMMARY Clay flocculation by calcium, by nonionic and anionic (33% hydrolyzed) polyacrylamide and by mixtures of calcium and polymer has been studied. Calcium adsorption and polymer adsorption have been examined as well. Electrokinetic data support the results. Calcium has its maximum effect at high ph where kaolinite aggregation is slightly enhanced, the magnitude of zeta potential is reduced and calcium adsorption shows a sharp increase. These effects are attributed to the formation and adsorption ofcaoh+. At high ph, surface precipitation of the hydroxide or carbonate can occur but additional stirring is able to cause some subsequent desorption. Nonionic polyacrylamide flocculates the clay and this is enhanced by the

The addition of calcium does not affect these results significantly even though it seems to lead to higher polymer adsorption at high ph. Adsorbed?

11 addition of calcium even though calcium has no effect on polymer adsorption. Calcium may be increasing bridging among particles. The anionic polyacrylamide has no effect on flocculation except at very acidic ph. The addition of calcium does not affect these results significantly even though it seems to lead to higher polymer adsorption at high ph. Adsorbed?1 calcium species may povide additional adsorption site for _e anionic 1x-,J mer:ccoo t.c-due-to=repulslvffegtsfdonor teat1occ-u latwn. zea'l>ofein tjat results at high ph support the hypothesis that the anionic polymer interactst,tl with calcium species, removing them from the surface. ',!I ACKNOWLEDGEMENTS The authors gratefully acknowledge the support of the Multiphase and Interfacial Phenomena program of the National Science Foundation. REFERENCES 1 P. Somasundaran, Principles of Flocculation, Dispersion, and Selective Flocculation. in P. Somasundaran (Ed.), Fine Particle Processing, AIME, New York, Vol. 2,198, p A.F. Hollander, P. Sornasundaran and C.C. Gryte, Adsorption Characteristics of Polyacrylamide and Sulfonate-Containing Polyacrylamide Copolymers on Na- Kaolinite, J. Appl. Polym. Sci., 26 (1981) P. Somasundaran, Y.H. Chia and R. Gorelik, Adsorption of Polyacrylamides on Kaolinite and Its Flocculation and Stabilization, ACS Symp. Ser., 24 (1984) P.J. Dodson and P. Somasundaran, Desorption of Polyacrylamide and Hydrolyzed Polyacrylamide from Kaolinite Surface, J. Colloid Interface Sci., 97 (1984) K.P. Ananthapadmanabhan and P. Sornasundaran, Role of Dissolved Mineral Species in Calcite-Apatite Flotation, Miner. Metall. Process., 1 (1984) R.H. Heerema and I. Iwasaki. Chemical Precipitation of Alkaline Earth Cations and Its Effect on Flocculation and Flotation of Quartz, Trans. Am. Inst. Min. Metall. Eng (198) J.K. Critchley and S.H. Jewitt, The Effect of CU2+ Ions on Zeta Potential of Quartz, lost. Min. Metall. Trans. Sec. C, 88 (1979) S. V. Krishnan, Influence of Surface Precipitation on Separation Process, Presented in the 15th Annual Metting of the Fine Particle Society, Orlando, FL, August R.H. Heerema, R.J. Lipp and I. Iwasaki, Complexation of Calcium Ion in Selective Flocculation of Iron Ore, Presented at the Annual AIME Meeting, New Orleans, G.M. Zhabrova and E. V. Egorov, Sorption and Ion Exchange on Amphoteric Oxides and Hydroxides, Russ. Chem. Rev., 3 (1961) V. Vesely and V. Pekarek, Synthetic Inorganic Ion-Exchanger. I. Hydrous Oxides and Acidic Salts of Multivalent Metals, Talanta, 19 (1972) A. Breeuwsma and J. Lyklema, Physical and Chemical Adsorption of Ions in the Electrical Double Layer on Hematite [a-fe23], J. Colloid Interface Sci., 43 (1973) R.O. James and T.W. Healy, Adsorption of Hydrolyzable Metal Ions at the Oxide-Water Interface, J. Colloid Interface Sci., 4 (1972) V.V. Pushkarev, Adsorption of Radioactive Isotopes on Ferric Hydroxide, Russ. J. Inorg. Chem., 1 (1956)

1:18 l.r; K.P. Ananthapadmanabhan and P. Somasundaran, Surface Precipitation of Inorganic and Surfuct.'1nts and Its Effect on Flotation, Colloids Surfaces, 1:l (1985) 151-167. 16 A.P. Ferris and W.B.

12 1:18 l.r; K.P. Ananthapadmanabhan and P. Somasundaran, Surface Precipitation of Inorganic and Surfuct.'1nts and Its Effect on Flotation, Colloids Surfaces, 1:l (1985) A.P. Ferris and W.B. Jepson, The I-:xchange Capacities of Kaolinite and the Preparation of Homoionic Clays, J. Colloid Interface Sci., 51 (1975) M.D.A. Bolland, A.M. Posner and J.P. Quirk, Surface Charge on Kaolinite, Aust..J. Soil Res., 14 (1976) E.J. Udo, Thermodynamics of Potassium-Calcium and Magnesium-Calcium Exchange Reactions on a Kaolinite Soil Clay, Soil Sci. Soc. m. J., 42 (1978) :l9='; E. B i tt.e I and-.r;.}.m illel-i!:ad;: admiumandcalciumselcctmtyceuefficien t,s{}on to;- morillonite, Illite and Kaolinite, J. Environ. Qual., 3 (1974) A.F. Hollander, P. Somasun.daran and C.C. Gryte, in P.R. Tewari (Ed.), Adsorption from Aqueous Solutions, Plenum, New York, 1981, pp :1 H. Van Olphen, An Introduction to Clay Colloid Chemistry, Wiley, New York, S.W. Clark and S.R.B. Cooke, Trans AIME, 241 (1968) M.C. Fuerstenau and B.R. Palmer, Anionic Flotation of Oxides and Silicates, in M.C. Fuerstenau (Ed.), Flotation, A.M. Gaudin Memorial, Vol. I, AIME, NewYork,1976,pp P. Somasundaran, J. Ofori Amankonah and K.P. Ananthapadmanabhan, Mineral-Solution Equilibria in Sparingly Soluble Mineral Systems, Colloids Surfaces, 15 (1985) i I' f,

Alizarin Red S as a Flotation Modifying Agent in Calcite-Apatite Systems

International Journal of Mineral Proce3sing, 18(1986) 287-296 Elsevier Science Publishers B. V., Amsterdam - Printed in The Netherlands 287 Alizarin Red S as a Flotation Modifying Agent in Calcite-Apatite