P. Somasundaran Columbia University U.S.A. Synopsis

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Proceedinqs of the International Conference on Mineral Science and Technology, Mintek 50, Vol 1. Hauqhton, L.F., ed., Council for Mineral Technology, S.A., 1985, pp. 279--285. by P.

have been considered to be responsible for the problems Involved in the processing of fine particles.

interactions between surface layers resulting from precipitation or coating that can be a major force responsible for the behavwr of fines are discussed.

Chemical and hydrodynamic interactions between organic layers or polymer-surfactant layers can play an important role in such processes as carrier flotation and flocc-flotation.

INTRODUCTION The beneficiation of mineral fines and ultrafines is not achieved efficiently in several cases and yet has become a necessity in the processing of many finely dispersed ores.

1 Proceedinqs of the International Conference on Mineral Science and Technology, Mintek 50, Vol 1. Hauqhton, L.F., ed., Council for Mineral Technology, S.A., 1985, pp by P. Somasundaran Columbia University U.S.A. Synopsis Many factors, such as a decrease in mass and an increase in surface area. have been considered to be responsible for the problems Involved in the processing of fine particles. In this paper, the role of alterations in morphology, mineralogy, and surface chemical composition in the fine and ultrafine size range is considered. Particularly. interactions between surface layers resulting from precipitation or coating that can be a major force responsible for the behavwr of fines are discussed. Significant surface chemical alterations can result from surface precipitation of inorganics. organics. and polymers. depending upon solution properties such as ph. Chemical and hydrodynamic interactions between organic layers or polymer-surfactant layers can play an important role in such processes as carrier flotation and flocc-flotation. These interactions are discussed in terms of the solution chemistry of minerals, surfactants, and polymers in the system. INTRODUCTION The beneficiation of mineral fines and ultrafines is not achieved efficiently in several cases and yet has become a necessity in the processing of many finely dispersed ores. A significant portion of the mincral values is lost during the processing of these ores because of the poor performance of the mineralprocessing techniques in the subsieve size range 0 Yet it is to be noted that the understanding of the problems in this size range remains largely speculation. The influence of many factors, such as increases in surface energy and surface area and a decrease in particle mass, on such processes as flotation have been consideredj.2. However, these factors cannot be considered as the fundamental ones for the failure of the processes in the ultrafine size range since even ionic entities that are sevcral orders of magnitude smaller can be selectively separat(.-d, even though not very efficiendy. Also, data given by Trahar and Warren for the size range of various sulphide mincrals for maximum recovcry do not show any correlation between the specific gravities of these minerals and their optimum notation sizes]. B<:sidcs, there arc in fact many sulphioto ort's that can bc rccovered efficiently in the subsi<.'vt' sizt, range. Clearly, other factors specific to the ores and to the pro<:essing schemes used must be rcsponsiblto for the poor performance, particularly with respect to the selectivity of thc opcration. In this pal>cr, specifically our observations on the possible role of alterations in morphology, mineralogy, and mifart' chemical composition in the fine 'and ultrafine size range on their processing will be considered. MORPHOLOGICAL EFFECTS Morphology, or the roughness of particles, can be expected to be important in detennining the adhesion of particles to bubbles during collision for a variety of reasons. Alterations in angularity will affect both their attachment and detachment to bubbles. More important, however, is the effect of roughn<:ss on the wettability of particles. Measurements of contact angle have shown that a hydrophobic material can be made totally hydrophilic by making it rough.. Recent work has shown that significant variations in the morphology of fines can result upon fracture, depending on the grain size distribution and crystal structure of the ore particles. There can also be differences in the roughness of coarse and fine particles if different grinding mechanisms are operative in these size ranges. The scanning electron micrographs of the washed and unwashed hematite coarse and tht:; slimes given in Figure 1 clcarly show that the morphology or fines can be different from that of the coarse particles. Slime particles are more angular in this case than the coarse. With purer samples, significant morphological dilterenc('s havc often IxTn recorded even though no mineralogical differences could be observed". Measurable decreases in density with fineness also were observed for quartz (Figure 2). 279

$MINTEK 50 Morphology of coarse and fine hematite \ -..... y,.,.;.: Unwashed p.$ considered as clear evidence of the amorphous nature of these fines. Morphology can also depend upon the grinding mechanism used.

considered as clear evidence of the amorphous nature of these fines. Morphology can also depend upon the grinding mechanism used.

pared by abrasion exhibited grooves suggestive of erosion in comparison with quartz particles from an impact tester (Figure 3).

chemical composition of the mineral particles7.

4). Indeed, if the fines have undergone a more severe treatment in the grinding mill than the coarse, sufficient differences can

280 MINERALOGICAL AND SURFACE CHEMICAL ALTERATIONS A major characteristic of ultrafines that gives rise to problems in their

While COarse phosphate is mosdy apatite, phosphate in slimes is present not only in the form of apatite but also in the form of

2 MINTEK 50 Morphology of coarse and fine hematite \ y,.,.;.: Unwashed p.m Washed Washings Figure 1 Scanning electron micrographs oj unwashed and washed hematite and the slimes4 This decrease can be considered as clear evidence of the amorphous nature of these fines. Morphology can also depend upon the grinding mechanism used. For example, fines of quartz pre;. pared by abrasion exhibited grooves suggestive of erosion in comparison with quartz particles from an impact tester (Figure 3). It is important to note that the presence of grooves on the surface can cause drastic alterations in the wettabilitr and therefore flotation. Prolonged grinding of minerals has been observed to alter not only the surface morphology but even the polymorphism and the chemical composition of the mineral particles7. Calcite particles, for example, showed a measurable change in the crystal structure with grinding owing to such effects (Figure 4). Indeed, if the fines have undergone a more severe treatment in the grinding mill than the coarse, sufficient differences can be expected between their surface properties and hence between their flotation characteristics. 280 MINERALOGICAL AND SURFACE CHEMICAL ALTERATIONS A major characteristic of ultrafines that gives rise to problems in their beneficiation is the mineralogical alterations in this size range. The effect of such alterations is best seen with phosphates. While COarse phosphate is mosdy apatite, phosphate in slimes is present not only in the form of apatite but also in the form of wavellite, which responds poorly to beneficiation by flotation. A more serious problem arises from possible changes in the surface chemical composition due to the oxidation of the surface, interactions in the surface region leading to precipitation or coating of the surface by precipitates or slimes. For example, fines of sulphides are found to be more oxidized than the coarse particles. Although some amount of oxidation might be beneficial for the flotation of sulphides, fines that are heavily oxidized 3fe not floated with

$size.. \' ".,"$ "",..,..,;J < 100> 150

$'t... A, \.l. 1 p.$ m Impact Abrasion Figure

$frac/ion smaller /han$ 400 mesh prepared (a)

3 Morphological effect of size.. \' ".,""",..,..,;J < 100> 150 mesh 10 p.m < 400 mesh Quartz Figure 2. Scanning electron micrographs of COtlTse and fine quartz prepared by impilct4 Morphological effect of grinding mechanism: fine quartz -. 't... A, \.l. 1 p.m Impact Abrasion Figure 3. Scilnning electron micrographs of quar/z frac/ion smaller /han 400 mesh prepared (a) wi/h an impac/ les/er and (b) by abrasion with a ptst/e and mor/arl 281

$M(:'\TF:K 30 'J'!fI I y _, t 2 1 t-.! } *-, I - II ++. II,". III j " j ---: I,_.... 1 """ Ti FIgure 4.$ that of pure aragonite') h in the zeta potential of calcite when it is contactcd with apatite. The point of zero charge of calcite is found to move toward!; that of apatite. Com:!

that of pure aragonite') h in the zeta potential of calcite when it is contactcd with apatite. The point of zero charge of calcite is found to move toward!; that of apatite. Com:!

The notation of apatite with oleate is similarly affected by the presence of dissolved species of calcite.

4 M(:'\TF:K 30 'J'!fI I y _, t 2 1 t-.! } *-, I - II ++. II,". III j " j ---: I,_ """ Ti FIgure 4. 11re det:omposition temperature of ground calcite samples and the fraction of aragonite fanned as afunction of the grinding time (A indicates the decomposition temperature of pure calcite, and B, that of pure aragonite') h in the zeta potential of calcite when it is contactcd with apatite. The point of zero charge of calcite is found to move toward!; that of apatite. Com:!lponding changes in the flutation ochaviour of calcite with oleate are illustrated" in Figure 6. The notation of apatite with oleate is similarly affected by the presence of dissolved species of calcite. It is clear that, under these conditions, a flotation separation scheme devised on the basis of the surface properties or notation characteristics of the single minerals is not likely to perform salisfacwrily. Indccd, in it system containing calcite, apatite, and oleate, there are many complicating reactions that will take place, depending particularly on phil). In these cases, in addition to the precipitation of one mineral on another, One can also get either precipitation of calcium oleate in bulk, in which case the flotation will be depressed because of the collector depletion, or surface precipitation of oleate, in which case the flotation will be enhanced. conventional reagents. With non-sulphides, precipitation of inorganic and even organic compounds on the surface can occur, resulting in surface chemical alterations. Particularly in the case of sparingly soluble minerals, such as calcite and apatite, sum swface precipitation can be the controlling factor in determining the feasibility of their separation by such processes as flotation and flocculation that are dependent on the surface properties of the particles. The drastic nature of the alterations that can occur in these systems is best illustrated by the changes in the zeta potential of calcite and apatite when they are contacted with dissolved species of each othelob. Figure 5, for example, shows the shift F,prt ph 6. Effect of apatite supernatant on the flotation of calcite with oleate Figure 5. Effect oj apatite supernalant on the zeta poten tiai of &akite 282 INTERACTIONS IN THE SURFACE LAYERS When a collector is precipitated or adsorbed on the mineral particles, there can be interactions between the surface layers on different particles, which can playa governing role in separation processes. The effect of such interactions has been examined for carrier Ootationl'.12 and flocc-ootation'3.'4 (selective flocculation plus flotation). It was observed that moods for interactions between particles and particles, and particles and bubbles, based on only electrostatic and dispersive forces cannot explain the behaviour of carrier flotation.and flocc-flotation systems. In carrier flotation, where anatase impurity is floated from clay and coarse calcite is used as carrier particles, the mechanism responsible for the process is enhanced aggregation between anatase and calcite with negligible aggregation between clay and calcite. This mechanism was suggested by the results of scanning electron microscope and microprobe

FINE-PARTICLE FLOTATION (a) (a) (b) Figure 7. Scanning electron micrographs (a) untreated 20 to 381J.

as a function of the size and amount of the carrier.

cohesive interaction between oleate laycrs on thc particlcs.

aggregates arc not n..dispcrscd undcr the intense agitation conditions u.'icd in this process.

(a) Scanning electron micrograph, and (b) X- ray image of a float sample of TiO212.

Intense agitation will also enhance the chemisorption of the oleate on the anatase and the calcite since there is a measurable increase in the temperature of the

5 FINE-PARTICLE FLOTATION (a) (a) (b) Figure 7. Scanning electron micrographs (a) untreated 20 to 381J.m calcite, and (b) flotation sample showing coaling oj fine particles on the cakitel2 analysis of floated products (Figures 7 and 8) and the flotation results obtained as a function of the size and amount of the carrier. Interestingly, all the materials (calcite, anatase, and kaolinite) are very negatively charged in the flotation pulp; nevertheless, aggregation takes place owing to the cohesive interaction between oleate laycrs on thc particlcs. The interaction energy was calculated to be appreciable for calcite-anatase aggregates compared with the relative kinctic encrgy of thc particlcs, so that the aggregates arc not n..dispcrscd undcr the intense agitation conditions u.'icd in this process. Thc agitation is considered to help the process by retarding the aggregation of kaolinite itself with calcite, (b) Figure 8. (a) Scanning electron micrograph, and (b) X- ray image of a float sample of TiO212. Magnification 1500 x on account of possible preferential detachment of any weakly adsorbed oleate from the kaolinite surface. Intense agitation will also enhance the chemisorption of the oleate on the anatase and the calcite since there is a measurable increase in the temperature of the flotation pulp owing to the agitation. Clearly the fonnation of the couector layers on the particle surfaces and inleractions between them can contribute towards selective aggregation in fine-particle processing systems. Selective aggregation is achieved with polymers also, and in this case there are many interactions h<'lween surface lavt"rs that can be of extreme significance. Thus lymers can affect flotation by causing activation or depression, depending upon the system. In the case of depressants, they are normally considered to act by preventing thc adsorplion of collectors on the mineral particles. A study of the syslern quartz-dodccylamine-cationic polyacrylamidc. however. showed the polymer in this 28:i

MINTEK 50, -', Flpre Polymr ronrnlr"'mm, mk-kk 9. Depression oj amine flotation of quartz by a cationic polymer. Adsorption oj amine in the presence and absence oj polymer is shown in the inset13.

Zeta-potential" measurements showed that, whenever the polymer adsorbed, whether or not there was amine adsorption, it was the zeta potential of the polymer that was always recorded.

6 MINTEK 50, -', Flpre Polymr ronrnlr"'mm, mk-kk 9. Depression oj amine flotation of quartz by a cationic polymer. Adsorption oj amine in the presence and absence oj polymer is shown in the inset13.14 case to depress flotation without any effect on the adsorption of the collector (Figure 9). Zeta-potential" measurements showed that, whenever the polymer adsorbed, whether or not there was amine adsorption, it was the zeta potential of the polymer that was always recorded. This suggested a model for the interfacial layer with the adsorbed polymer species masking the amine leaving the particle exterior essentially hydrophilic (Figure 10). This model predicts the flotation of quartz with an anionic surfactant in the presence of a cationic polymer even though normally such a surfactant will not float quartz (Figure lob). Such activation was actually $33$$5,,, - - (b) Figure 10. A schematic representation of flotation, (a) depression, and (b) activation by poljmers Quart z/sul pho nate/p ama sulphonate, kmol. m3 6. 6,0 x ,2 X 10-4 ph - 6,5 60 tj o! IQ 1 10 / Effect Polymer concentration, mg' kg of polymer on sulphonate adsorption (Cj= 2 x 10-3 kmol- m3 mer, mg-kg bonate, p.m - g 100 Figure 11. Activation of flotation of quartz with dodecylsulphonate by a cationic poiymd# I

FINE-PARTICLE FLOTATION observed for the system quartz-dodecylsulphonatecationic polyacrylamide (Figure 11).

a full understanding of the behaviour of mineral fines and ultrafines during their processing is being developed.

Both the amount adsorbed and the state (chemical state and configuration) in which various species adsorb and interact are critical in determining the performance of most interfacial processes, such

In turn, the state of the species adsorbed or precipitated on the surface will be influenced by interactions in the bulk and on the surface involving dissolved mineral species.

7 FINE-PARTICLE FLOTATION observed for the system quartz-dodecylsulphonatecationic polyacrylamide (Figure 11). CONCLUDING REMARKS Evidently there are many interactions between adsorbed layers, governed by their properties, such as strength of binding and configuration, that have to be taken into account while a full understanding of the behaviour of mineral fines and ultrafines during their processing is being developed. In this regard, first and foremost there is a dire need for the developing of techniques that can be used for monitoring in situ the above properties of adsorbed layers. Both the amount adsorbed and the state (chemical state and configuration) in which various species adsorb and interact are critical in determining the performance of most interfacial processes, such as flotation and flocculation. In turn, the state of the species adsorbed or precipitated on the surface will be influenced by interactions in the bulk and on the surface involving dissolved mineral species. Mineral-solution equilibria become a major factor particularly when one is dealing with sparingly soluble minerals, such as calcite. Other factors deserving of consideration because they can have a significant influence on the performance of flotation operations in the sub sieve size range are the morphology and rugosity of the particles. There is sufficient evidence to suggest that there can be significant alterations in morphology with particle size and that such alterations can have an effect on the wettability of the particles. There can also be chemical and mineralogical alterations in the subsieve size range, which will indeed affect the adsorption properties and therefore the flotation and flocculation characteristics of fmes. Identification of the precise role of the factors in determining the performance of major mineral-processing operations is pivotal in developing solutions for the fine-particle processing problems. ACKNOWLEDGEMENT The author wishes to acknowledge the minerals and primary materials programme (CPE ) of the National Science Foundation for partial support of this work. REFERENCES SOMASUNDARAN, P. Fine particles treatment. RESEARCH NEEDS IN MINERAL PRO- CESSING. SomasundlDian, P., and Fuerstenau, D. W (eds.). New York, Columbia University, pp FUERSTENAU, D.W., CHANDER, S., and ABOUZEID, A.M. The recovery of fme particles by physical separation methods. BENEFI- CIA TION OF MINERAL FINES. Somasundaran P., and Arbiter, N. (eds.). New York, AIME', pp TRAHAR, W.J., and WARREN, L.J. The floatability of very fme particles-a review. Int. J. Miner. Process., vol pp OLIVER, J.F., HUH, C., and MASON, S.G. An experimental study of some effects of solid s:urface roughness on wetting. Colloidr Surf, vol pp ROUSSEV, R., and SOMASUNDARAN, P. Morphology of mineral fines produced under different grinding conditions. (To be published.) 6. LIN, I.J., and SOMASUNDARAN, P. Alterations in properties of samples during their preparation by grinding. Powder Technol., vol pp KULKARNI, R.D., and SOMASUNDA- RAN, P. Mineralogical heterogeneity of ore particles and its effects on their interfacial characteristics. Powder Technol., vol pp AMANKONAH, J.O., and SOMASUN- DARAN, P. (Unpublished results.) 9. VAMAN RAO, D., NARAYANAN, M.K., NAYAK, U.B., ANANTHAPADMANA- BHAN, K.P., and SOMASUNDARAN, P. Flotation of low grade Mussorie phosphate ore. (To be published in Int. J. Miner. Process.) 10. ANANTHAPADMANABHAN, K.P., and SOMASUNDARAN, P. The role of dissolved mineral species in calcite-apatite flotation. (Accepted for publication in Minerals and Metallurgical Processing.) 11. WANG, Y.H.C., and SOMASUNDARAN, P. A theoretical approach to flocculation in carrier flotation for beneficiation of clay. (To be published in Colloidr Surf) 12. CHIA, Y.H., and SOMASUNDARAN, P. Carrier flotation of anatase from clay and its physicochemical mechanisms. UL TRAFINE GRINDING AND SEPARA TION OF IN- DUSTRIALMINERALS. Malghan, S.G. (ed.). New York, AIME, pp SOMASUNDARAN, P., and LEE, L.T. Polymer-surfactant interactions in flotation of quartz. Sep. Sci. Technol., vol pp SOMASUNDARAN, P., and CLEVER- DON. J. A study of polymer/surfactant interaction at the mineral/solution interface. Paper presented at the American Chemical Society Meeting, Washington, D.C. Aug (To be published in Colloidr Suif) 285

FLOTATION OF QUARTZ AND HEMATITE: ADSORPTION MECHANISM OF MIXED CATIONIC/ANIONIC COLLECTOR SYSTEMS

Paper No. 548 FLOTATION OF QUARTZ AND HEMATITE: ADSORPTION MECHANISM OF MIXED CATIONIC/ANIONIC COLLECTOR SYSTEMS A Vidyadhar 1, *, Neha Kumari 2 and R P Bhagat 3 ABSTRACT Using pure quartz and hematite