Invited opening lecture - reprinted from:Mineral Processing at Crossroads, Wills, B.A.and Barley, R.W. eds., Nijhoff publishers, 1986.

AN OVERVIEW OF THE ULTaAFINE PROBLEM

P. SomasundaranHenry Krumb School of Mines, Columbia University, New York

ABSTRACTProcessing of fines poses many problems mainly because

traditional techniques do not work efficiently. In thispaper, problems in fine grinding, concentration of fines andultrafines and dewatering of slimes are revie~ed along withthe fundamental reasons involved. Effects of chemicaladditives on grinding and interference by dissolved mineralspecies in selective separation are examined in detail.Promising techniques considered for the beneficiation of finesinclude selective flocculation and agglomeration, oil anddissolved air flotation, column flotation, and magnetic,electrostatic and electrophoretic techniques. Subsidencebehaviour of slimes utilized in the formulation ofphenomenological models is discussed. Finally, importantresearch opportunities in fine particle processing areas arenoted.

INTRODUCTIONTreatment of fines and ultrafines in mineral processing

involves resolving severe problems. Increasing amounts ofultrafines are generated during mining and milling of largetonnages of low quality ores. Ores mined today in many partsof the world are of very low liberation size, and a directconsequence. of this is an increase in the need for finegrinding and in the need for technology to beneficiate thefines. Also, slimes and sludges generated during milling areoften not amenable to normal waste treatment techniques.Mineral fines discarded are actually of incredible proportionsin many cases. And, finally, as much as twenty to fiftypercent of mineral value is lost during the processing of manyores (see Table 1).

TABLE 1 Examples of mineral values lost as slime

One-third of the phosphate mined in Florida.

One-half of the tin mined in Bolivia.

One-fifth of the world's tungsten

Also Cu, U, fluorspar, barite, zinc, iron, etc

The amounts thus discarded likely to increase in theare

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future owing to increased mining of lower quality ores. Thenature of the problem is clear and solutions are appearing onthe horizon even though the fundamental reasons for theexistence of the problem are not as evident. Factorsconsidered in the past to be responsible for the fineparticles processing pLobleuo'" are list,"," in rig. 1. . It is

important to recoqnise that, since in the case of ultrafinesand colloids, surface forces will begin to dominate all otherforces, alterations in surface chemical or .ineraloqicalcomposition can playa major role in causing difficulties intheir separation.

In this paper, some of the major problems and the basicreasons involved in grinding, beneficiation and dewatering inthe ultrafine size range are reviewed. This review is anabridged compilation of ~ome of our previous work in this area(1-4).

Problematic properties of finesFig- 1

FINE GRINDINGConuninution is known to be the energy consuming8Oat

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operation in mineral processing. A 1934 estimate shows theenergy consumed in grinding alone to be as much as 70' of thatfor the whole beneficiation process (5). Correspondingfigures for today are .likely to be only higher. It is to benoted in this regard that the actual energy needed forc_~~..-~ " C L-1 u ~--" I ~,.r"' I ' '~ s ~ t 1. ... :. ,'",- -~ - -, ,.. . -~ Uu ~'" ,.-. ~u- k~~'" u!.t::d ~.:.."," ..u . y ~~

the total energy input to the grinding mill. A greatproportion of the energy input is lost as heat, owing tofriction and elastic and plastic deformation. Consideringthat some amount of plastic deformation is necessary for theactual breakage of any mineral matter, the energy required forit might be included in the calculatien of the efficiencywhich now becomes 20-50' (6). It is clear that even then theenergy utilization can be improved by reducing the abovelosses.

A real problem in ultrafine grinding is the existence of apractical grind limit which often results from a physicalequilibrium between the process of size reduction andreagglomeration of fines. Importantly, under these ~onditionsthe fluidity of the pulp can often deteriorate dramaticallyleading both to poor pulp movemement in the mill and excessivecoating of the mill walls and the grinding medium by theground mass. Evidently, use of means to reduce agglomerationand thereby grind limit should prove fruitful.

Grinding ~Grinding aids such as ethylene glycol, propylene glycol and

butylene glycol reportedly have been used in vapour form inseveral countries for improved cement grinding (7-10).Grinding aids used in the past include polysiloxane in thegrinding of ultraporcelain and talc; silicones in thedrop-weight crushing of limestone and quartz; glycols, amines,organosilicones, organic acetates, carbon blacks, and woolgrease in the grinding of cement; silicones in the ballmilling of quartz; acetones in nitromethane, benzene, carbontetrachloride and hexane in vibratory milling of ground glass,marble and quartz; and wool grease in the milling of gypsum,limestone and quartz. Some of these reagents are reported toact by preventing ball coating that can affect grindingefficiency. Use of grinding aids and the mechanisms by whichthey act have been discussed in our recent reviews (11-13).

Water. Grinding in water is usually more efficient thandry grinding (14-16). This effect of water has been ascribedto a reversible reaction between unsatisfied surface bonds andwater molecules (17). For this reason, humidity can also beexpected to affect the grinding process. The grinding rate ofsoda lime glass is higher in humid air than in vacuum (18).Increased efficiency of wet grinding can also be due tophysical reasons. Detrimental effects of cushioning by fineswill be less during wet grinding than during dry grinding,since the fines in the water can remain suspended. Inaddition, effects of viscosity and specific gravity of themedium can also be significant (19,20).

Orqanic liquids. Grinding in organic liquids can often bemore efficient than that in water. As much as a 12-foldincrease in production of surface area has been obtained by

.

4

grinding in organic liquids, such as isoamyl alcohol (21).Higher grinding rates have been reported also in carbontetrachloride and methylcyclohexane than in nitrogen (17)~Interestingly, grinding efficiency was the same as that inwater when a small amount of water was present in t.he orqAnic-J.l.quids.

Surface-active aqents. Surfactants have been reported bymany workers to produce significant effects on grinding. Asan example, Fig. 2 shows that as much as a 100\ increase inspecific surface area could be obtained in wet ball milling ofquartz and limestone by additions of up to 0.3\ of FlotigramP, a flotation agent. Higher additions caused a decrease inspecific surface area. In contrast, addition of Armac T tothe grinding of quartz in a ball mill (23) has been shown tobe detrimental under all concentrations. These detrimentaleffects can well be due to experimental artifacts introducedby the aggregation of fines or the result of changes ininterfacial properties due to surfactant adsorption onparticles. Flocs in the mill could consume durin~qrindinqsome of the impact energy for deflocculation. In addition,hydrophobization of particles by the adsorbed surfactant canresult in a lowerinq of the qrindinq efficiency.

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CONCENTRATION OF FLOTIGAM PI kmol/m3

Fig. 2 Effect of Flotigram P on grinding of quartzite andlimestone in a rod mill (8)

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5 IRecently, El Shall et al (25) have obtained finer products

in the neutral and alkaline pH range on adding dodecylammoniumchloride during quartz grinding in a stainless steel ballmill. Detrimental effects were obtained in the acidicsolutions, as shown in Fig. 3. The authors correlated their..."",.,1t-- ..i th +-,,~ -l"'_L ~ f ~ ("". 0 .L',. '-- .Ld.L' (" o r'~ LC.LeS ' ot- "'v, ,.. ~ ~,.~"~ "..,-c..J.~'-' ...~...~quartz (zeta potential and flocculation characteristics) undersimulated chemical conditions.

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El-Shall et al (25) also saw significant coating of themill wall by the ground product under certain conditions.Somasundaran and Atli (26) in fact observed poor grinding inamine solutions under conditions of thick coating of millwalls and balls (see Fig. 4). Obviously, flocculation leadsto coating of mill walls and balls and thereby to reducedgrinding. Addition of polymers or dispersants also can beexpected to affect the colloidal state of the pulp and therebythe performance of a grinding mill (27-33).

6

Fig. 4 a

b

Coating of mill walls by pulp in 5x10-3 kmol/lamine at pH 10.5 (poor grinding conditions)For comparison purposes, coating was scraped offfrom all around inside the mill except the reqionbetween two lifters

Inorqanics. The effect of inorganic electrolytes ongrinding has been investigated by several workers (22, 34,35). Although results reported in the literature are oftencontradictory, grinding has in general been found to be moreefficient in the presence of inorganic electrolytes. It hasbeen reported by various workers that multivalent ions doaffect the grinding efficiency of minerals. For example,Frangiskos and Smith (36) have reported an increase of as muchas 50\ and 15\ in surface area of ground quartz due toaddition of 2.0 kmol/l A1Cl and CuSO4 ' respectively.

Somasundaran and El-ShAll (33) also have observed A1Cl]to improve grinding of quartz (Fig. 5), while CaCl iAobserved to be detrimental (Fig. 6). Sodium silicati andsulphate also produced reduced grinding, at least under thetested conditions. The extent of the effect of these reagentswas particularly sensitive to pH of the slurry (Fig. 7).Importantly, it was shown through this study that chemicalscan affect a number of basic properties of the grinding

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Fi9- 6 Effect of different additions of CaC13 on wet ballmilling of quartz at pH 5.9-6.1 (33)

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system, such as pulp fluidity, flocculation, fractureinitiation and propaqation and it is the cumulative effect ofthe chanqes in all these properties that will determine thenet efficiency of the. qrindinq process. Both enhanced andreduced qrindinq can be obtained dependinq upon thepredol!'; """',..0 ,,1' ,,;ori nl'~ eff~,..t-.. '.,C'c. t:'i,.. p'- ~ . J

IONIC STRENGTH. 3a'62kmOI/m3 NoCI0

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Diagram illustrating change in differentproperties30f quartz suspensions due to10 kmol/m A1Cl) addition as a functionof pH (33)

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Diaqram illustratinq chanqe in differentproperties30f quartz suspensions due to10 kmol/m amine addition as a functionof pH (33)

Opportunities!.Q!:. enhanced qrindinqIt is clear that opportunities do exist to make use of

flocculants and dispersants, introduced specifically into thegrinding circuit, or elsewhere for other purposes, to modifypulp properties and thereby to achieve enhanced grinding,particularly in the ultrafine size range. In addition,aggregation can be retarded using a number of othertechniques. It can be minimized by removing the finestparticles continuously using closed-circuit grinding. It isconsidered advisable to successively reduce the size of thegrinding medium as the grinding proceeds into fine andultrafine regions, since the ratio of the size of the grindingmedium (balls, pebbles, etc.) to the size of the particlesshould be kept within certain limits for maximum grindingefficiency. Also, cooling the machines by improvingventilation or by external or internal watersprays canminimize agglomeration due to rising temperatures (37).

It has been suggested that improved ultrafine grinding canbe obtained by generating additional flaws, for example, byapplying thermal shocks, since depletion of flaws duringgrinding is considered to increase the stress for initiatingfracture. In addition to all the above factors. it is

11

important to recall that liberation is the aim of grinding inmineral processing; in this regard every effort has to bedirected primarily to devise methods by which intergranular,rather than transgranular, fracture can be produced. And forthis, basic studies are needed to identify means by whichapplied force can be ff"":!1spn f'~to t-~~ grain h()"~d~'!:~~s wherethe force is needed. In turn, this requires an understandingof the mechanisms by which forces are tr~nsmitted to the cracktip and dissipated there in polycrystalline and polymineralspecimens.

CHARACTERIZATION OF FINESOf course, once particles are produced, one has to classify

and characterize them. The main problem here is that in theultrafine and colloidal size range, there is oftenconsiderable inconsistency between results obtained usingdifferent measuring techniques. Also, it is important torecognise that for ultrafines and colloids, in addition toproperties such as size and porosity, surface forces willstart to predominate all the other forces, tWbs it isessential to determine surface chemical composition andsurface mineralogical heterogeneity if one is to do meaningfulresearch with such fines.

Surface properties of minerals can be strongly influencedby surface heterogeneities arising from natural variations inmineralogy or crystal structure as well as from samplepreparation (38). In this regard it is important to recognizethat large discrepancies can result from different samplepreparation techniques employed by investigators and fromcontamination by impurities present in the liquid or gas phasewith which the mineral particles are contacted. Clearly, itis important to avoid the artifacts introduced by samplepreparation techniques.

BENEFICIATION OF ULTRAFINESThe most important step in the mineral processing flowsheet

is indeed the beneficiation itself. Most conventional mineralprocessing techniques do not work adequately in the sub-sievesize range (Fig. 9). For example, -150 mesh size phosphatesare not floated efficiently even though these fractionscontain one third to one fourth of the phosphate. Equallyserious problems exist in the processing of cassiterite,taconite and pentlandite ores. Clearly, it should provefruitful to understand the reasons for the existence of thelower size limit. It does not appear that we are nearintrinsic limits in these separation processes since even ionscan be floated selectively although under different aerationand agitation conditions. The reasons for the currentpractical limits are not yet established.

In the case of gravity separation, it has been suggestedthat in the fine size range, particles can begin to lose theiridentity and thus act as fluids. Under such conditions,separation on the basis of specific gravity difference alonebecomes nearly impossible. Another major reason for the sizelimit might be the interference between transport andseparation functions in a separator. Then, the key for

12

extending the gravity techniques to lower size limit might bethe design of devices which will produce minimum interferencebetween separation and transportation. It will be useful todetermine what other forces, such as centrifugal force, canproduce differences in positions taken up bv njfferentparticles and thus extend the operating range of thesetechniques. It could also prove beneficial to identify thefluid properties which control drag forces and therebyinfluence separation.

SORTING

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GRAVITY METt«>DS

lORY MAGNETIC MET~9P~~

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10 100 1,000 10,000 100,000

Fig. 9 Effective size range of application of conventionalmineral beneficiation processes (2)

In the case of flotation, flocculation and such techniques,the problem results from a number of contributing factors thatare not always mutually exclusive. They include factors suchas surface area, low mass and, in addition, mineralogical andchemical alterations, such as oxida~ion that is particularlyserious for sulphide fines. Also changes in rugosity or shapeof particles with size can significantly influence adhesionduring collision.

Morphological differences can result from differences infracture mechanisms in various size ranges or variations inthe mineralogical composition as a function of particle size.Morphology of fines has, in fact, been found to be differentfrom that of coarse particles. For example, increasedangularity of particles in the slimes range has been observedin the case of washings of coarse hematite particles (39). Inanother study, quartz fines prepared by abrasion appeared to

13

have undergone more erosion in comparison to quartz particlesfrom an impact tester (40). Also, prolonged grinding ofminerals can produce amorphousness, polymorphic transitionsand even solid state reactions (41).

Differences in morphology can have a siqnificant effect. oni.ioLdtiull. l'nere 1.S suJ.l..l.cient evidence in literature for thestrong influence of roughness on the wettability of particles.Contact angle measurements have shown that a hydrophobicmaterial can be made hydrophilic by roughening it (42).

A major characteristic of the fines which can give rise todifficulties in separation is the mineralogical alterations inthis size range. For example, while coarse phosphate is~ostly apatite, phosphate in slimes is present not only in theform of apatite but also in the form of wavellite, which willrespond poorly to separation by flotation. A more seriousproblem arises from possible changes in surface chemicalcomposition due to oxidation of the surface, surfaceprecipitation, or coating of the surface by precipitates orslimes. Surface chemical alterations can result frominteractions in the surface region leading to precipitation ofinorganic compounds. Results obtained for the calcite-apatitesystem clearly illustrate the effect of such surface chemicalalterations (43,44). Conditions predicted for the separationof calcite from apatite on the basis of single mineral testsrarely work with mixed mineral systems. Zeta potentialresults for apatite fines in water and in calcite supernatantand that for calcite fines in water and in apatite supernatantshow that the point of zero charge of these mineralsinterchange in the supernatant of one another (Figs. 10 and11). Such results can be considered to be the result of manycomplex surface processes. Using available thermodynamicdata, we have recently shown from theoretical considerationsthat, depending on the solution conditions, apatite surfacecan be converted to calcite and vice versa through surfacereaction or bulk precipitation of the more stable phase (44).Similar surface conversions have also been observed in thecase of mixed sulphides (45).

Obviously, even more complicated situations can be expectedin the case of flotation with the introduction of collector.In addition to the surface reactions discussed above, thereare also mineral species-collector interactions leading tobulk precipitation, for example, of calcium oleate in whichcase the flotation can be depressed, or surface precipitationof oleate on the particles in which case the flotation can beenhanced. The conditions for surface precipitation and itseffect on various mineral-surfactant systems have recentlybeen examined in detail by Ananthapadmanabhan and Somasundaran( 46 ) .

When collector adsorbs or precipitates on the surface ofminerals, there are specific surface forces which becomeprimarily responsible for the separation processes. This isparticularly true in the case of modified flotation processessuch as carrier flotation and flotation processes usingpolymers. Models for interactions between particles andparticles based only on electrostatic and dispersive forcescannot explain the behaviour of these systems. In carrier

14

flotation, where anatase impurity is floated from clay usingcoarse calcite as carrier particles and oleate as collector,the mechanism responsible for the process is enhancedaggregation between anatase and calcite and almost noaggregation between clay and calcite (47). A detailed..., ly",i., Uk Li,t! ~}""-,,,,;. "'I.uwed t.h~ illt~Lal:tion o~l:ween aasoroedoleate layers to be responsible for the aggregation in thissystem (48). Selective aggregation of anatase with calcitewas considered to be due to weaker attachment of oleate to theclay surface, compared to that of oleate to the anatasesurface, such that the clay-calcite aggregates formed are not$table at the high agitation intensities used in carrierflotation (49).

-,,'-... .oj

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Fig- 10 Effects of calcite supernatant on the zetapotential of apatite (43)

In floc-flotation, polymers can affect flotation bydepressing it when they are added to flotation systems.Normally, a chemical that depresses flotation is considered toact by preventing adsorption of collectors. However, a recentstudy of quartz-dodecylamine-cationic polyacrylamide systemshowed the polymer to depress flotation without any effect onthe adsorption of surfactant itself (50). Zeta potentialresults showed that whenever the polymer adsorbs, irrespectiveof whether the amine adsorbs, it is the zeta potential of thepolymer that is always recorded. This suggested that the

15

adsorbed amine is masked by the massive polymer speciesleavinq the surface of the particle essentially cationic andthereby hydrophilic. Accordinq to this model anionicsurfactant can be expected to float quartz in the presence ofa cationic polymer even thouqh normally such a surfactantwould not float it. This was indeed observed for the;.:.:.:.'.::: "':=:;:::j'lsulp~:::-:::.':-:. -_.:::'v;-.';':: pol:r"2:::~:':..~=-:;;:. syste..:.Evidently, therefore, there are many interactions betweenadsorbed layers, qoverned by their properties such as strenqthof bindinq and confiquration, which have to be taken intoaccount while developinq a full understandinq of fine particleflotation and flocculation.

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FiC;. 11 Effects of apatite supernatant on the zetapotential of calcite (43)

~~Qtial ~~I:1QQ$ for concent~atjOPMany techniques have been discussed in the recent past for

the beneficiation of fines. These are intended either torestore the selectivity that is often lost in the fine sizerange or to enhance probabilities for collision and adhesionof particles to air bubbles.

Modified flotation. Conventional froth flotation can beextended to lower size ranges possibly by three means:

1. Use of variables such as temperature as a processparameter.

2. Use of techniques which permit refluxin9 e.9. column

16

flotation.3. Use of flotation aqents which adsorb specifically, e.q.

use of oximes in the flotation of oxidized lead andzinc ores.

Improved flotation of iron ore fines ~as been obtained byCleveland Cliffs Iron Company by conditioning the pulp witht-h~ ~~.".~_L_- ~.. ,.,,~. '-1 L. . Even ' r l '- ~ - ~ ~"""'-"'-~~"'-"-"'- "-"V"';1" ~1~",technique has been used also for the beneficiation of a fewother ores such as fluorite, temperature has larqely beeniqnored as a factor used to control flotation. Also,mechanisms involved in determininq the effects of temperaturedurinq conditioninq are mostly unknown. It has been clearlyshown that hot-conditioninq of hematite with oleate isbeneficial, at least on a l~~oratory Jcale, but only below anionic strenqth of 2 x 10 kmol/m; above this, it isdetrimental (51). The reasons involved are yet to bedetermined.

In column flotation, the countercurrent flow of bubbles andmineral slurry causes better particle-bubble contact, theresultant mineralized bubble beinq continuously cleaned 9Y thecountercurrent flow of water. It has been reported to qiveresults that are superior to conventional flotation forun-deslimed uranium ore, fine qraphite containinq clay, and-100 mesh copper ore. It qave poorer results for the copperore in upper size ranges. Also, use of columns that aretaller than 28 feet has been reported to cause seriousproblems.

Attempts to develop flotation aqents which specificallyadsorb, might involve synthesis of reagents that chemisorbmore strongly and selectively. Reagents that adsorb byhydrogen bondinq or even by electrostatic bonding can probablybe ruled out for use as collectors for the above purpose.Reaqents with chelatinq functional qroups have receivedincreased attention in recent years, beinq known to exhibitexcellent metal selectivity in analytical separations. Manychelatinq agents have been tried as collectors for variousmineral systems and excellent s~parations have been obtainedin certain cases. For example, oxidized copper ores have beenbeneficiated recently by the use of reagents with oximefunctional groups that chelate with copper (52-55). Theflotation responses of chrysocolla and cuprite usinq LIX65N

(2-hydroxy-S-nonyl-benzophenone oxime) are shown in Fiq. 12 asa function of pH. LIX6SN is an efficient collector for theabove minerals which do not normally float using conventionalreaqents. Solubility of cuprite(copper leached from 1 gram in10 minutes) is also given in this figure. Interestingly, acorrelation between flotation and dissolved copper wasobtained. The flotation decrease with copper solubility wasattributed to the depletion of oxime by the dissolved copperto form a Cu-oxime chelate in the bulk solution which had no

collectinq property.Collector action of these type of reaqents appears to

result from their chelation with species on the surface ofminerals. The mechanisms which control their collectingaction are not, however, adequately established. Inparticular, differences in their mode of action at the mineral

17

Flotation of chrysocol~a and cuprite, compared withconcentration of copper leached fro. cuprite, as afunction of pH

Fig. 12

surface versus that in the bulk are not fully recognized and,as a result, the development of collectors based on their usein analytical separations is not achieved easily. It is to benoted in this regard that chelating collectors are seldom8etal-specific or mineral-specific and the properties of boththe chelating agents and the mineral are important indetermining their collecting action. The donor atoms on thechelating agents, as well as those associated with the mineralspecies, playa governing role in their interactions on thesurface. The application of chelating agents in mineralprocessing systems has been reviewed recently on the basis ofthe donor properties of the chelating groups and the metalspecies (56). The number of chelating agents which have beentested successfully (at least on a laboratory scale) ascollectors, depressants and flocculants for various mineralsystems, is large. Use of these types of reagents in mineralprocessing is likely to undergo a significant increase in thefuture.

Floc-flotation. If the decrease in efficiency ofseparation is due to such factors as lower collision and

18

adhesion rate of fines, the obvious solution is preaggregationof the fines before flotation. Selective flocculation hasbeen successfully used during recent years on a co.mercialscale for the beneficiation of low grade iron ore by theCleveland-Cliffs Iron Company. This process uses reagentswhich flocculate the hematite leaving the quartz and silicatesdi!;l"'~r~~~ orh... cn"1!"-:-c-i;::l -.::::-;" ~~~.:.'"' !:cchno~v,,) ~'" ..\Jwevt::L,

currently limited to the beneficiation of the Tilden iron oreand to that of potash in a Cominco plant in Saskatchewan. Theprocess of selective flocculation holds tremendous potentialwhen it is accompanied by flotation, elutriation etc. However,various problems existing both at the basic and applied levelswill have to be solved before this potential can be fullyrealized. A Major proble. in this regard is that most of thecurrently available long chain polymers are bulk flocculantsand lack the desired specificity. Specificity can be inducedby incorporating active groups into the polymers. Past workon selective flocculation using such modified polyaers dealsmostly with binary mineral systems. Reports of separation byselective flocculation of multi-component natura~. ores arescant. In addition to the two c~ercial app"lications.entioned above, one noteworthy attempt is that of Carta et al(57) for the beneficiation of ultrafine fluorite from latium.For most systems, however, selective flocculation is noteasily achieved even under conditions when excellentselectivity is expected. This fact becomes easily evidentupon examinin9, for example, the results obtained by Usoni etal (58) durin9 their investigation of the selective propertiesof anionic, cationic and non-ionic polymers as flocculants forseveral minerals individually and then in combination witheach other.

In this reqard, it is thou9ht that a discussion of thequestions that arose durinq an analysis of the role of variousreagents and solution conditions selected by U.S. Bureau ofMines for the selective flocculation of taconite ore mighthelp towards developing similar schemes for the beneficiationof other problem ores, characterized by fine dispersion ofvalues in the matrix (59, 60): How exactly do the dispersantswork? Why is a particular dispersant, or, as in this case, amixture of dispersants, chosen? What is the interactionbetween the dispersant and the flocculation reaqent that issubsequently added? What is the basis for the pH selection?Also, it would be fruitful to see whether the conditionschosen for selective flocculation are in accord with thepresent theoretical concepts of flocculation and dispersion.It is qenerally considered that if the ma9nitude of the zetapotential of particles is less than 10 to 20 mY, they canaqgreqate, provided, of course, that there are no otherinterferin9 factors such as steric stabilization bymacromolecules adsorbed on the particles. Selectivecoaqulation of hematite from its mixture with quartz ispossible then if the zeta potential of hematite is say, -10 to-15 mY, and that of quartz is -30 to -40 .V. On the basis otthe reported pzc values for hematite (pH 8.0) and quartz (pHbelow 3.0), it should be possible to achieve selectivecoa9ulation by operatinq at a pH of 9 or so in the absence of

.19a flocculant (39,61). So why was it necessary to increase thepH to 10.5-11 in this process (62)1 Why was it necessary toadd sodium silicate and sodium tripolyphosphate? Does thelatter also act as a dispersant or only as a sequesterinqagent to minimize the effect of ions such as calcium that arepresent? Indeed, one clear possibility is that it is the,",clectivc ctusurption or ::;carcci on nematite particles which isresponsible for their selective flocculation and that otherconditions were so chosen in this process so as to minimizeadsorption of starch on quartz particles. Is it then possiblethat the zeta potential of the adsorbed starch layer onhematite (which may not be undesirably hiqh) is responsiblefor producinq selective flocculation?

Another major point that needs clarification is the lack offlocculation of quartz by starch even when hematite orgoethite is disseminated in this quartz. Is it likely thatstarch adsorbed on iron oxide reqions of the quartz particlesprovides incomplete coveraqe leadinq to exposure of the hiqhlycharged quartz reqions and thereby possible electrostaticrepulsions between them? On the other hand, is it ~ikely thatthe iron oxide was selectively removed from the surfaceregions during agitation of the pulp? Using Auqerspectroscopic studies, we have observed that excessivesegregation of quartz is possible on the surface of naturalhematite particles (39). Very little research has been doneon the role of composition and heteroqeneity of surface layerswhich playa controllinq role in adsorption, flocculation, andflotation. Recent development of such techniques as electronspectroscopy for chemical analysis (ESCA) and secondary ionmass spectrometry (SIMS) does make it possible now to obtaininformation on the surface composition of the minerals withwhich one is workinq.

Selective flocculation or dispersion of natural ores isoften made difficult owinq to interference from dissolvedspecies. This is often considered to be the result ofadsorption or surface precipitation of such species on one ormore minerals in the system. Recent flocculation andelectrophoretic studies conducted with chalcopyrite andpentlandite support the above consideration (45).Flocculation tests showed pentlandite to depress chalcopyriteflocculation below pH 4 and to enhance it above that pH, whilethe chalcopyrite supernatant activated the pentlanditeflocculation in the complete pH ranqe studied (see Fiq. 13 aand b). Zeta potential of chalcopyrite and pentlandite werefound to be markedly reduced, apparently due to the adsorptionor surface precipitation of dissolved ions and their hydroxyspecies on the mineral surfaces. Additives that can complexwith such dissolved ions or adsorb on mineral particlesselectively to modify them can be used to enhance selectivityin these cases. Polyphosphates and polysilicates are widelyused as bulk dispersants. Such dispersants are particularlyeffective when excessive slimes are present in the systemsince these colloidal particles do have a tendency to coat themineral particles and thereby reduce the selectivity of aflocculation operation (65).

An interesting approach to activation has been recently

'i

20

aUJ-Jt-t-'"'(I)

(I)Q:i0(I)

at

pH

13(a) Chalcopyrite flocculation as a function of P~2in pe~dlandite supernatant containinq J x 10kmol/m HaCl (45)

..

~j13(b) Pentlandite flocculation as a function of pH i2

chalco~yrite supernatant containing 3 x 10-kmol/m HaCl (45)

~~

21

developed to induce selectivity in flocculation (66).Selective flocculation was obtained in this case using"hydrophobic polymers" on minerals which are preconditionedwith surfactants to produce a hydrophobic surface.

Another problem of major importance on wh~ch almost nobasic work has been reported, is the effect of addition ofrea9~nr.s such as fl~cculants on subsequent operations such asflotation, filtration, and possibly even pelletizing. We haveshown that polymers can enhance or depress flotation dependingon the nature and concentration of the polymer. For example,a cationic polymer activated quartz for flotation using ananionic surfactant, while it completely depressed itsflotation using dodecylamine, see Fig. 14 (67). With regardto effect of flocculants on filtration, major setbacks canresult if the yield strength of the flocculated product is notmaintained at a level that can prevent deterioration ofpermeability during filtration.

Carrier-flotation. Oleate flotation of ultrafine anataseimpurity from clay using an auxiliary material such as calciteis an example of carrier flotation or ultraflotation. Theauxiliary mineral used as a carrier for the fine particles arecoarser than the material to be floated. It is speculatedthat the fines form a coating on the carrier mineral and arethen floated along with the coarser carrier particles.Recently Wang and Somasundaran (47) have obtained evidencethat anatase can be floated also without the carrier eventhough to a lesser degree than in the presence of the calcitecarrier. The typical effect of carrier addition is shown inTable 2. Addition of 40 grams of -44 micron calcite particlesdecreased the retention ratio (, TiO2 in cleaned clay I ,TiO in the feed) from 0.72 to 0.39 and increased the clayyield from 44 to 92'. A low TiO2 retention ratio correspondsto good separation; thus, the use of the calcite carrier hasin this case enhanced the removal of the anatase. Carriercalcite particles activate the process apparently both due tothe action of dissolved calcium and due to the enhancedsize-dependent aggregation between the calcite and the anataseparticles.

TABLE 2 Comparison of carrier flotation with conventionalflotation (47)

'!'l

22

Even though this technique has been used on a commercialscale for clay for almost 25 years, it has not beensuccessfully used, to my knowledge, for beneficiating anyother ore on a commercial scale. Work with phosphatic slimegave limited success in some cases and practically nobeneficiation in some other cases. The reasons for thefa~:;' ::; vi: thib pcu-::es~ J.II Lite case 01 phosphat1.c slime or foreven its success in the case of clay are not understood.

,,

Fig. 14(a) Diagram illustrating the effect of the cationicpolymer, PAMD, on the flotation of quartzusing sodium dodecylsulphonate (67)

:~~;.:...~*~'.

Fig- 4(b) Diagram illustrating the effect of the cationicpolymer, PAMD, on the flotation of quartz usingdodecylamine hydrochloride (67)

,

23

S~herical-aaalomeration. Agglomeration with the help ofoil has been used by Puddington et al (68,69) for graphite,chalk, zinc sulphide, coal, iron ore and tin ore in aqueoussolutions. Fines are tumbled in this case in an aqueoussolution containing an immiscible liquid which forms capillarybridges between reagent coated particles and causes their-;C;::c;::tion. :.:,." ",iiililat- fJlucess, Warren o:.fJJ.J.ng Laboratoryis reported to have obtained good separation for a lead/zincore (701 owing to hydrophobic bonding between reagentizedslime particles. Here a slime fraction of the ore wasdispersed by a combination of sodium silicate, sodiumcarbonate and a polyacrylite and subsequently conditioned withcopper sulphate, and then potassium amyl xanthate was added.Formation of flocs was attributed to similar reasons that gaveGaudin and Malozemoff (71) selective aggregation of galenaslimes in the presence of xanthates. The major problem withthis process is the cost of the oil or other reagents requiredfor the capillary bridging. Understanding of the basic roleof the intensity and type of agitation and chemicalinteractions at the oil-solid interface might prove useful forfurther development of this process. *

Fine-bubble and oil-flotation. Another potentialaggregation process-that needs to be looked into is emulsionflotation (1,3). It has been pointed out by several workersthat fines can be collected more easily by oil droplets andfiner bubbles. Techniques that can yield fine bubbles includedissolved air (vacuum depressurization) flotation andelectroflotation (1,3). Again, none of the above techniqueshas been used so far, to my knowledge, on a commercial scalefor the processing of mineral fines. Also there are a numberof fundamental questions to be answered here. For example,why are smaller bubbles more effective in floating fines andwhat is the role of increased capillary pressure in thesmaller bubbles? How does the shape of particles affect theattachment to fine bubbles under turbulent conditions? Whatis the relationship of particle and bubble size to the scaleof turbulence normally encountered? How can cell geometry becontrolled for optimum turbulence? What causes the strongflocculation observed in agglomeration flotation? Is oil infact more efficient at capturing fine particles selectivelythan air? And if . so, why? Investigation of problems mayassist in solving practical problems encountered in flotationin general.

Maqnetic. electrostatic !!!9. electrophoretic separations.Use of differences in magnetic, electrostatic andelectrophoretic properties has been attempted by variousworkers for beneficiation purposes (1,3,72-74). There hasbeen considerable work recently in the area of high gradientmagnetic separation. A schematic diagram of such a separatoris given in Fig. 15 (3). The high intensity used in theseseparators, along with high gradients, affords separation ofvery fine paramagnetic particles. Both low and high intensitywet magnetic separators have been used for separation in thesub-sieve size range, the former for treating -325 meshmagnetic taconites and the latter mainly for purification of-2 micron kaolin and for removal of pyrite and ash from fine

...OJ

24

coal-in-water slurry. Commer~ial application of high gradientmagnetic separation has been limited so far, to my knowledge,to the beneficiation of kaolin. Use of extraneous agents totreat the ore to generate areas of higher magneticsusceptibility might possibly extend the application of this'1..~"

Il. ' qu ' ',-' - ('-'~ I " ~ r ~~ f'~- "'~ .L' Opll1 ~ I ' ',-.,. ',. t '11""~~.,. "'. ,...~~.._~ .-u..~ "--~~ ~ --'" -~. '-"".~ ~ ,~ ..~-'" ~~ ~

use of super-conducting magnets. Problems exist due to thenecessity of washing the matrix intermittently without havingto switch the magnet off.

Use of air instead of water as the fluid medium has beensuggested in order that the problem in the fine size range ofthe fluid-drag forces exceeding magnetic forces can beminimized (75). In this case, there is also the added.advantage that introduction of water, which is oftendeleterious to the system, can be avoided.

Water is avoided in electrostatic separators also.Possibility exists here for its application in the fine sizerange with the help of pulsed corona discharge, high rotorspeed and external electric field.

Electrophoresis and electropermeation (electrodiai~sisusing charged mesh in place of membranes) suffer fromdifficulties in scaling-up these processes for any significantcapacity while maintaining the required quiescent hydrodynamicconditions.

TAILINGSOUT

Fig- 15 A schematic of the carousel continuous HGMseparator. By rotating the carousel throughcollection, cleaning and discharging stages,continuous operation is achieved (3).~

DEWATERING OF SLIMES AND SLUDGESDewatering of mineral slimes and sludges is another serious

problem facing the mining industry in various parts of theworld. For example, filtration of the product obtained afterselective flocculation was the major technical problem facedduring the recent commercial development of this process forbeneficiating taconites. The dewatering problem is

,

25

particularly acute whenever certain clay minerals are presentin waste products. A prime example of this is the phosphaticslime that is generated during the mining and processing ofthe phosphate rocks. This slime is currently being held inlakes covering thousands of acres of land, and since it isslow-settling, the land that it covers remains unused and:.':'::ions ::.: ::id.i..i.Vll~ 0:: wate::: to.a:: 1.t. coi.tains L-"'illainimmobilized. Other examples of slow settling suspensionsinclude red mud, acid mine drainage sludge, and coal slimes.Large amounts of these slimes are generated annually (Table 3)with loss of a large quantity of mineral values. It wouldprove fruitful in this regard to have a proper understandingof the fundamentals of the dewatering or the subsidencebehaviour of these slurries. However, while sedimentationtheories have been adequately developed to cover the twoextremes of slurry concentrations, very little is known aboutthe basic aspects of sedimentation of slurries in theintermediate concentration range. Thus, while we havetheories for very dilute suspensions based on Stoke's law andfor consolidated beds based on models develo~ for flowthrough porous media, sedimentation or dewatering behaviour ofconcentrated suspensions or slurries has not been adequatelylIodelled.

J

TABLE 3 Examples of industrial slimes generated annually

Waste Million tons per year

Phosphatic slime 40-50

Red mud 8-10

Acid sludge 0.5

Coal slime 10.0

Others: Potash, Clay fines, Uranium tailings, drilling mudwaste, paper and pulp effluent, TiO2

A phenomenological ~odel has b~en devel.~p9d by us recentlyfor phosphate slime samples, by closely observing thebehaviour of the slurry during dewatering (76-79). Asystematic attempt was also made to identify thecharacteristics of the minerals responsible for the slowsubsidence behaviour of such slurries. This has been reviewedby us (80-82) and is summarized below.

PhenomenolOQical modelThe observed behaviour of the slurry during dewatering is

schematically shqwn in Fig. 16. Four stages are exhibited bythe slurry during this time:1. Within a few seconds after mixing is stopped, allrotational movements inside the slurry terminate.2. In a few minutes, tears are created by coarser sizeparticles and small air bubbles are trapped in the solidifiedslurry. Water seeps up through these tears and forms lenses

...~~

26

of water.3. Additional tears develop leading to channels connectingvarious lenses, and finally opening up at the slurry-waterinterface to permit water to exit. The slurry/supernatantinterface now subsides rapidly and water, along with entrainedparticles, can be seen sprouting through the interface.4. Continuous compression of the slurr'J ~'!~i~~ ~hi~':""~dCeLl.119 pLocess tl.na.l..l.y causes the channels to contract andthereby to retard additional dewaterin9.

D""

t(~..

35min 2 hr 4hr

Diagrammatic illustration of subsidence of atypical 2.6' phosphatic slime sample

Fiq 16

~~:?]&""" 0'_1

,,'.' 1,",_0:

Accordinq to this, dewaterinq is dependent essentially uponthe availability of seepaqe paths and in the present systemsuch paths are proposed to be essentially the result of theheteroqeneity of the system. This hypothesis was tested bydetermininq the effect of the addition of coarser particles tothe slurry and the qeneration of .icrobubbles in it. If thehypothesis is valid, such procedures should enhance thedewaterinq of the slurry. The addition of coarse particles(>50 .icrons) to the phosphatic slimes did in fact reducetheir stability siqnificantly~ the subsidence rate increasedalmost 50 times. Movement of .icrobubbles throuqh the slurrysimilarly enhanced the sedimentation. A phen08enoloqical

1

~.~~ ~""" -:.~.;;:.~,

27

equation was derived considering the fact that a slurry withan internal structure subsides according to the action of twotntp;r-r"l~t~~ p!:ocesses., n.-~~l~, :c~..:i:::'.~iG:1al e:':pu::'zi:::: ;)~water from the slurry, which depends upon the amount and thetype (interaggregate, interfloc and intrafloc) of forces, andthe amount of water which has already passed through theinterface. The phenomenological model has been tested bydetermining various rate parameters and comparing theresultant curves with the experimental curves. Even thoughthe model fitted the experimental results satisfactorily, itwill be important to identify the major physical and chemicalfactors that determine these parameters.

The microscopic mechanism, responsible for the stability,.of phosphatic slime was investigated by formulating modelsystems, made from the major constituents of the phosphaticslime (80). Of the various combinations of kaolinite,montmorillonite, attapulgite, quartz, chrysatile, andamphibole tested, the montmorillonite-attapulgite-kaolinternary and the montmorillonite-attapulgite-kaolin-quartzquarternary systems behaved very similarly to the phosphaticslime. The minerals, montmorillonite and attapulgite, withtheir characteristic shape and properties of swelling, surfacecharge and viscosity, were identified to be mainly responsiblefor the unique subsidence behaviour of phosphatic claysuspensions. In addition to the electrokinetic properties,morphology, swelling properties, and the ion-exchangecapacities of the mineral constituents are responsible for thesubsidence characteristics of the phosphatic slimes while thesupernatant clarity is determined mostly by the electrokineticproperties.

Problems similar to that of the phosphatic slimes alsoexist with coal slimes, red muds and steel mill sludges.There is a definite need here to determine the causes for thepertinacious behaviour of slime-sized particles in suspensionsand for developing economical processes for dewatering theslimes. Fundamental studies are also needed on thepermeability properties of capillary systems made up ofmineral fibres and fines so that capability can be developedfor controlling the fluid flow in sedimentation and filtrationsystems. Also the effects of chemical additives as dryingagents and physical parameters such as temperature on fluidflow should be understood for producing any significantdevelopment in this area.

CONCLUDING REMARKSThe treatment of mineral fines is a critical problem of

increasing magnitude and is being so recognized. Problems inbeneficiating fines were discussed in detail and the researchneeds in different areas were identified during a 1979workshop (83). A summary of this is given below.

FlocculationResearch needs in flocculation were classified into three

groups: water chemistry, dewatering, and flocculation theory.Water chemistry. Flocculation and dispersion phenomena

are in general very sensitive to water chemistry. However

'to.~

28

theory does not accommodate realistically complex waters andsuspensions. First of all. it is necessary in this reqard todevelop criteria for characterization of water in terms of pH.total dissolved solids. ionic strenqth. hardness. temperature.suspended solids. etc. Secondly. the effect of orqanicsolutes present in feed waters and recycled mill waters has to'-p e ..,L-I.-'~"'~"' d ~',' '1" -' ml.' ght }' e l. n'--~r' L ;.~ ~ tudy1'- ~~"',)---, '-"~--'- '" ~ '..p",, ~-"

statistical and seasonal variations in water chemistry.Calcium variations in mill waters from winter to summer arewell known.

Dewaterinq. Problems which normally exist in dewaterinqare slow settlinq of the slurries and hiqh filter cakemoisture. It will be useful. first of all. to qenerateinformation on the chemical. thermal and mechanical enerqyrequired to achieve dewaterinq usinq various techniques.Major advances in this area will probably result fromdeveloping capability to control floc structure by chemical.mechanical or hydraulic means.

Flocculation theory. The challenqe here is to developunderstandinq of flocculation processes in terms ot thestructure and its bindinq mechanisms and the rat6s ofnucleation. qrowth and disinteqration of flocs. It isnecessary to understand also fundamental chemical and physicalprocesses that control selective flocculation. as well asselective dispersion and adsorption dependence on the chemicalstructure of flocculants and dispersants, so that efficientreaqents can be synthesized for specific purposes.Flocculation/dispersion models have to be expanded toaccommodate relevant variables such as temperature. dissolvedelectrolytes and orqanic solutes. They should also beexpanded to applications to problems involvinq solid/air.solid/oil. oil/oil and oil/air flocculation.

FlotationSolutions to problems of low recovery, low selectivity and

high reagent consumption in the flotation of fines arerecognized to reside in controlled agglomeration of particlesinto larger units, use of smaller bubbles and use of oil inplace of air. In this regard it is important also to developimproved methods of dispersing ultrafines and of generatingfine bubbles for flotation and in general to develop machinesespecially suited to flotation in the ultrafine size range.It may also prove useful to understand the reasons for theadvantages of both oil over air as a collecting medium andfine bubbles over coarser bubbles. More work is also neededto scale-up such techniques as electroflotation and columnflotation.

LeachincrIn the area of in-situ leaching, it is important to know

how the liquid flow through capillaries inside porous beds canbe controlled and to know ways by which fines can bestabilized so that their movement will not cause plugging-Research needs here are an economic creation of fines, andcontrol of their surface properties, both to enhance leachingand to prevent coating that may impede dissolution, scale-up

.,

29

of mixer-settlers, identification of critical variablesdevelopment of means to aeasure and control them.

and

Maqnetic techniQuesIt will be useful to optimize the aaqneticseparation

techniques to minimize the entrapment of fin~~ "..,1 tol"\ j...~r~~$~th~ throu9~.p'.lt. .1I1S:) technique:. sh;:)..lj be developed ,-uenhance differences in magnetic properties of fines, in somecases, by surface modifications.

Most i.portant1y, all the above techniques can make aajoradvances only if the fundamental reasons for the size 1i.itsof their efficient performance are understood. Once suchreasons are understood, current processes could be modified asrequired, or appropriate new techniques could be more easilydeveloped. It is clear that even thouqh there are manytechniques on the horizon for processinq mineral fines, manyi8portant practical problems remain to be solved before theycan be used on a 1arqe scale. It is also clear that solutionsto these problems will best be achieved when the manyfundamental problems related to the behaviour of - .inera1sfines in concentration systems are better understood.-

ACKNOWLEDGEMENTThe author wishes to acknowledge the support of

National Science Foundation (CPE-83-18163, CPE-83-04059).the

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2. Somasundaran, P., "Processing Mineral Fines", Enqineerinq~ Mininq Journal, Dec. 1979, pp. 46-67.

3. Fuerstenau, D.N., Chander, S., and Abouzeid, A.M., "TheRecovery of Fine Particles by Physical Separation Methods", in~neficiation of Mineral Fines, Somasundaran, P. amd Arbiter,N., AlME, 1979,pp. 3-59.

4. Somasundaran, P., "Role of Surface Phenomena in thehneficiation of Fine Particles", Mininq Enqineerinq, Vol. 36,1984, pp. 1177-1186.

S. Gow., A.M., Guqqenheim, M. and COg'hill, W.H., "Review ofFine Grindinq in Ore Concentrators", U.S. Bureau of Mines, IC,5757, January 1934.

6. Orr, C. Jr., Particulate1966, pp. 44-86.

TechnolOClY, Macmillan, New York,

7. Locher, F.W. and Seebach, H.M.V., "Influence of Adsorptionon Industrial Grinding", Industrial ~ Enqineerinq ChemistryProcess ~~, Vol. 11, 1972, pp. 190-197.

'tj

30

8. Korac, v., "UseProduction", TehnikaAbstr. 77, 922609.

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Auxiliary Agents in Cement27, 1972, 649-653, Chem.

9. Popov!~,.. .\~ In,,Pcr,

76, 14444

"Effects of Grindinq~ :Z.Jc;=~~, 15. 14-

Aids7,1971

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on

10. Furukawa, T., Anan, A., and Yamasaki, K., "U.e of GrindingAgents in Closed Circuit Grinding System for Cement Clinker",Semento Gi1utsu NemPO, 25, 69-75, 1971, Chem. Abstr., Vol. 77,143409.

Engineering Ch..istry, Process ~ ~~, Vol.1f~ 1972,pp.321-331.

13. Somasundaran, P. "Theories of Grindinq"P~2cessing before GrindinQ, Onoda, G.Y., Jr., andW~ley, 1978, pp. 105-123.

in CeramicHench, L.,

14. Bond, F,C., "Wet versus Dry Grindinq", MininQVol. 43, 1957, pp. 38-40.

Conqr. ~,

15. Coghill, N.H., and Devaney, F.D., "Ball Mill Grinding",U.S. Bureau of Mines, Tech. Paper No. 581, 1937.

17. Lin, I.J., and Mitzmager, A., "The Influence of theEnvironment on the Comminution on Quartz", Trans. AIME, Vol.

241,1968, pp. 412-418

18. Locher, F.W., Eichartz, W., von Seebach, H.M. and Sprung,S., "Environmental Effects in Grinding", Extended Abstracts,163rd National Meeting of the American Chemical Society,Boston, 1972, p.81.

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Comminution". ~ ~ ~ ~, Vol. 43, 1965,1S. kapur,of Fluids Jonpp. 119-124. - -- --

20. Hockinqs, W.A., Volin, H.E., and Mular, A.L., "Effect ofSuspendinq Fluid Viscosity on Batch Mill Grindinq", Trans.~, vol. 232, 1965, pp. 59-62.

21. Kiesskalt, S.Z., ~ ~ ~ Vol. 91, 1949, pp. 313-315.

'toJ

. K.~,~

9 p.

11. El-Shall, H., and So.asundaran, P., "Physico-ChemicalAspects of Grinding: A Review of Use of Additives", PowderTechnoloav, Vol. 38, 1984, pp. 275-293.

12. Somasundaran, P., and Lin, I.J. "Effect of the Nature ofEnvironment on Comminution Processes", Industrial and

22. Van Szantho, E., "Der Einglux Van OberflachenaktivenStoffen Seider Feinzerkleinerung", ErzberqbauMetallhubettenwes, Vol.2, 1949, pp. 353-360.

23. Gilbert, L.A., and Hughes, T.H., "Some Experiments inAdditive Grindinq", Symposium Zerkleinern, Verlaq Chern.,nl'~~ldorf, (:~!:"!!'~":. 1962, PF "::;-193.

24. °poczky, L., Epitoanzaq, Vol. 19, 1967, 121-125.

25. El-Shall, H.E., Gorken, A., and Somasundaran, P., "Effectsof Chemical Additives on Wet Grinding of Iron Ore Minerals" inMinera~ Processinq, Laskowski, J., ed., Elsevier, Vol. 2.,Part A, 1981, pp. 695-726 and 738-755.

26. Somasundaran, P., and Atli, A., "Effect of ChemicalAdditives on the Pulp Fluidity and Grinding in Wet BatchMilling", World Congress on Particle Technology, Nuremberg,April 1986. .

27. El-Shall, H.E., "Effect ofGrinding", D.E.Sc. Thesis, Columbia1980.

Chemical Additives onUniversity, New York,

and Velamakanni,the Dynamics ofin Ball Mills",

15. 1985, pp.

28. Fuerstenau, C.W., Venkataraman, K.S.,8. V., "Effect of Chemical Additives onGrinding Media in Wet Batch GrindingInternational ~ Mineral Processinq, Vol.251-267.

29. Klimpel, R., and Manfroy, W., "Development of ChemicalGrinding Aids and their Effect on Selection-for-Breakage andBreakage Distribution Parameters in the Wet-Grinding of Ores",paper presented at ~ ~ ~ Proc. Conq., Sao Paulo,Brazil (1977).

30. I<limpel, R.R., and Manfroy, W., "Chemical Grinding Aidsfor increasing throughput in the Wet Grinding of Ores", ~~ Chern. Process ~~, Vol. 17, 1978, pp.518-S23.

31. I<limpel, R.R., "The Engineering Analysis of DispersionEffects in Selected Mineral Processing Operations", in ~Particles Processinq, Somasundaran, P., ed., AIME, New York,1980, pp. 1129-1152.

32. Klimpel, R.R., Powder Technol., Vol. 32,1982, p. 267.

33. Somasundaran, P., and El-Shall, H., "MechanochemicalEffects in Ultrafine Grindinq" in Yltrafj,!}e. Grindinq .!.!lQ.Separation 2.!. Industrial Minerals, Malqham, S.G., ed., AIME,New York, 1983, pp. 21- 7-

14 Brown, J.H., M.l.T. Progress Report, N.Y.O. 7172, 955.

32

36. Frangiskos, A.W.Z., and Smith, H.G., Trans.DressinQ ConQr., Stockholm, Sweden 1957, pp. 67-84.

37. Becke, B., Principles Qi Co.minution, Akademiai Kiado,Budapest, 1964.

Miner.

38. Somasundaran, P., and Moudqil, 8.M., "Preparation andCharacterization of Clean Mineral Surfaces" in SurfaceContamination, Vol. 1, Mlttal, X.L., ed., Plenum, 1979, pp:457-475.

39. Kulkarni, R.D., and Somasundaran, P., "MineraloqicalHeteroqeneity of Ore Particles and its effects on theirInterfacial Properties", Powde£ Technol., Vol. 14, 1976, pp.279-285.

41. Lin, I.J., and Somasundaran, P., "Alterations in

Properties of Samples during their Preparation by Grinding",Powder Tech., Vol. 6, 1972, pp. 171-180.

42. Oliver, J.F., Huh, C., and Mason, S.G., "An ExperimentalStudy of some effects of Solid Surface on Wetting, ColloidSurfaces, Vol. 1, 1980, pp. 79-104.

43. Somasundaran, P., Amankonah, J.O., and Ananthapadmanabhan,K.P., "Calcite-Apatite Interactions and their effects inSelective Flotation using Oleate" in ~ !~ternationalMineral ProcessinQ ConQress, Vol. 11, 1985, pp. 244-254.

44.(a) Somasundaran,p.,Amankonah,J.O.,and Anathapadmanabhan,K."Mineral-Solution Equilibria in Sparingly Soluble MineralSystems", Colloids ~ Surfaces, pp. 309-333; (b) Amankonah,J.O., Somasundaran, P., and Ananthapadmanabhan, K., "Effectsof Dissolved Mineral Species on the Dissolution/Precipitation

Characteristics of Calcite and Apatite", Colloids ~Surfaces, pp. 295-307; (c) Amankonah, J.O., and Somasundaran,P., "Effects of Dissolved Mineral Species on theElectrokinetic Behaviour of Calcite and Apatite", Colloids and

Surfaces, pp. 335-353. vol. 15 45. (a) Acar, S., and Somasundaran, P., "Effect of Dissolved

Mineral Species on Flocculation of Sulphides", Minerals and

~~~~llu~Qicfl! ProCessi~Q, Vol. 2, 1985, pp. 231-235; mAcar, S., Interactions between Polymer, Complexing Reagentand Dissolved Mineral Species in Selective FlocculationSystem", D.E.Sc., Columbia University, New York, 1985.

33

46. Ananthapadmanabhan, K.P. and Somasundaran, P., "SurfacePrecipitation of Inorganics and Surfactants and its role inAdsorption and Flotation", Colloids and Surfaces, Vol. 13,1985, pp. 151-167. ---

47 Chi~; Y ~., ~nd SO;;-:~~u..'::";'a.,. l'., "Carrier Pl/:'t-ation-ofAI'Q..a5~ from Clay and its Physicochemical Mechanisms", inUltrafine Grindinq.!!!9. Separation, Malgham, S.G., ed., AIME,1983, pp. 117-131.

48. Chia, Y.H., and Somasundaran, P., "A Theoretical Approachto Flocculation in Carrier Flotation for Beneficiation ofClay", Colloids .!!!9. Surfaces, Vol. 8, 1983, pp. 187-202.

49. Chia, Y.H., and Somasundaran, P., "Role of Agitation inElectrokinetics and Carrier Flotation of Clay using Calciteand Oleate", Transactions §g, Vol. 272, 1983, pp. 1970-1973.

50. Somasundaran, P., and Cleverdon, J., "A .Study ofPolY8er/Surfactant Interaction at the Mineral/SolutionInterface", Colloids ~ Surfaces, Vol. 13, 1985, pp. 73-85.

51.Kulkarni,R.D., and Somasundaran,P.,"Effects of ReagentizingTemperature and Ionic Strength and their Interactions inHematite Flotation", Trans. §g, 202, 1977, pp. 120-125.

52. Nagaraj, S.R. and Somasundaran, P., "Copper, Flotationwith Anti-5-Nonyl-2-Hydroxy Benzophenone Oxime", U.S. Patent 4130 415, 1979.

53. Nagaraj, C.R., and Somasundaran, P.,Extractants as Collectors: Flotationusing 'LIX' Reagents", Trans. Am. Inst.

266, 197?, pp. 1892-7

"Commercial Chelatinqof Copper Minerals~ Enqrs., Vol.

54. Nagaraj, D.R. and Somasundaran, P. "Chelating Agents asFlotaids: LIX-Copper Minerals Syste." in Recent Developments~ Separation Science, Li, N. et al, eds., CRC Press, Yol 5,1979, pp. 81-93.

55. Naqaraj, C.R., and Somasundaran, P., "Chelatinq Aqents asCollectors in Flotation: Oximes-Copper Minerals Systems",Mininq Enqineerinq, Vol. 33, 1981, pp. 1351-7.

56. Somasundaran, P., and .-. D.R., "Chemistry andApplications of Chelatinq J in Flotation andFlocculation", in Reaqents in Minerals Industry, IMM(London) 1983, pp. 209-219.

Nagaraj,Aqents~

57. Carta, M., et al, "Investigations on Beneficiation ofUltrafine Fluorite from Latium", XIth International MineralProcessinq Conqress, Cagliari, 1975;-paper 41.

34

1968, paper 0-13

61. Iwasaki, I., Cooke, S.R.B., and Colombo, A.F. Report ofInvesti9ations~ No. 5593, u.s. Bureau of Mines, 1960.

~~:j,-:.~~,~1

62. Colombo, A.F., "Selective Flocculation - Flotation ofOxidised Taconites", in Theory, Practice and ProcessPrinciples !9.£ Physical Separations, Freeman,~.P.;. andFitzpatrick, J.A., eds., Engineering Foundation, N.Y., 1981,pp.221-225.

63. Read, A.D., "The Use of High Molecular WeightPolyacrylamides in the Selective Flocculation Separation of aMineral Mixture", Brit. Polym.~, Vol. 4, 1972, p. 253.

64. Attia, Y.A., and Kitchener, J.A., "Development ofComplexing Polymers for the Selective Flocculation of CopperMinerals", Proc. ~ ~ ~ Proc. Conqr., Cagliari, 1975,p.1233.

65. Read, A.D., and Hollick,Techniques for Recovery ofVol. 8, 1976, p. 202.

66. Rubio, J., and Kitchener, J.A., "New Basis for SelectiveFlocculation of Mineral Slimes", Trans. ~ (London), Vol. 86,1977, p. C97.

67. Somasundaran, P., and Lee, L.T.,Interaction on Flotation of Quartz",Tech., Vol. 16, 1981, pp. 1475-1490.

"Polymer-SurfactantSeparation g.!.,- ~

68. Sirianni, A.F., Capes, C.E., and Puddinq, I.E., "RecentExperience with the Spherical Aqqlomeration Process", Canadian~ 2K Chemical Enqineerinq, Vol. 39, 1969, p. 166.

69. Farnand, J.R., Smith, H.M., and Puddinqton, I.E.,"Spherical Aqqlomeration of Solids in Liquid Suspension",Canadian ~ 2K Chemical Enqineerinq, Vol. 39, 1961, p. 94.

70. Read, A.D. and Hollick, C.T., "Selective FlocculationTechniques for Recovery of Fine Particles", Minerals ScienceEnqineerinq, Vol. 8, 1976, p. 202.

Lation~,

3S

71. Gaudin, A.M., and Maloze80ff, P., "Recovery by Flotationof Mineral Particles of Colloidal Size", ~ PhysicalChemistrv, Vol. 37, 1933, p. 579.

72. Iannicelll, J., "Hlqh Intensity, Biqh Gradient MaqneticSep.aration" in Beneficiation of Mineral Fines: C:':""~~'.l!'.~aran,p-, d/ld Arbitel:, N., ed., ;..:ME, '~'979, Vp. 363-37~.

73. (a) Oberteuffer, J.A., and Wechslet, I., "Recent Advancesin High Gradient Magnetic Separation", pp. 1178-1216; (b)Hopstock, D.M., and Colombo, A.F., "Processing Finely GroundTaconite by Wet High Intensity Magnetic Separation", pp.1241-1260; (c) Petrakis, L., Ahner, P.E. and Kiviat, F.E.,."High Gradient Magnetic Separations of Fine Particles fromIndustrial Streams", pp. 1261-1286; (d) Corrans, I.J., "ADevelopment in the Application of Wet High Intensity MagneticSeparation", pp. 1294-1309, in ~ Particle Processinq,Somasundaran, P., ed., AIME, 1980.

E.A. "Fundam.ntals ofParticles", in ibid, pp.

74. Revnivtsev, V.I., andTribioelectric Separations1325-1341.

Khopunov,of Fine

75. Hopstock, D.M., "Electric and Magnetic Separation", Morey,8., Discussion .!!! Research Needs .!!! Mineral Processinq,So.asundaran, P. and Fuerstenau, D.W., eds., ColumbiaUniversity, 1976, pp. 88-102.

76. Somasundaran, P., and Sresty, G.C., "Dewatering ofSlow-Settlinq Sludges", Second Handbook Volume .2!!.Particle-Fluid Separation Technoloqy, lIT Research Institute,Chicaqo, 1977.

77. Somasundaran, P., Smith, E.L., Jr., and Harris, C.C.,"Dewaterin9 of Phosphate Slimes usin9 Coarse Additives", ~!!!h Minerl. Proc. Conqr. Proceedinqs, Instituto de ArteMinerai e Preparazione dei Minerali, Universita de Ca9liar1,1975, pp. 1301-1322.

78. Somasandaran, P., Smith, E.L., Jr., and Barris, C.C.,"Effect of Coarser Particles on the Settlin9 Characterisiticsof Phosphatic Slimes", Proc. ~ Conte ~ ParticleTechnoloqy, Chica90, lIT Research Institute, 1973, pp.144-150.

79. Harris, C.C., Somasundaran, P., and Jenson, R.R.,"Sedimentation of Compressible Materials: Analysis of BatchSedimentation Curves", powder!!£h, Vol.11, 1975, pp. 74-84.

80. Nagaraj, D.R., McAllister, L., and Somasundaran, P.,"Subsidence of Suspension of Phosphate Slime and its MajorConstituents", .!nh ~ ~ Proc., Vol. 4, 1977, pp. 111-129.

81. Somadundaran, P., "Thickening or Dewatering of SlowSettling Mineral Suspensions", XIIIth International MineralProcess. Conqr. Proceedings, Elsevier, 1982, pp. 233-262.

36

82. Somasundaran, P., "Fundamentals of Dewatering FineParticulate Slurries" in Proqress!!!. ~ Dewaterinq .2.!. ~Particles Conference, USBM and U. Alabama, 1981, p. 35.

v..J. r'drKs, G., Ui..:~~, M., iinkelste:"o, N.P., l'iOrey, B., andSomasundaran, P., "Summary of Problems and Research Needs", inBeneficiation.2.!. Mineral Fines, Somasundaran, P., and Arbiter,N., eds., AlME, 1979, pp. 391-398.

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