Coal rank and surface properties of oil agglomerates

Coal rank and surface properties of oil agglomerates K.DARCOVICH, T.J. SMYTH andC.E.CAPES Institute National Research Council Chemistry, ofCanada, forEnvironmental KIA OR6 Process Ontario, Canada, Section, Ottawa, Technology 5August 1992 Received forAPT 15February 1992; accepted Abstract-The wettabilities ofagglomerates made from coals ofseveral different ranks were measured Oillevels from 0to10% were used. Aswas itwas found bytheadhesion technique. byweight expected, thathigher-rank coals aremore oil-wetted and that the surface of the easily propertiesagglomerates correlate with andashremoval data. recovery agglomeration 1.INTRODUCTION finepowders intolarger masses inorderto processes bring together Agglomeration Inconventional coalmining, muchofthefinecoal improve powder properties. isrejected withtailings asitisimpractical torecover. Dueto (typically -100 mesh) nature ofcoal,smaller tendtobeeither theheterogeneous particles individually richer inashorcarbonaceous matter withtheoverall ofthe compared composition facilitates effective Thetailings arehandled in coal.Thisdiscretization separation. water formandinanagglomeration/separation treatment animmiscible oil slurry isadded underhigh-shear conditions toenhance surface phase mixing properties. Theoilselectively adheres tothecarbonaceous surfaces andalsoactsasa bridging toconsolidate several oiledcoalparticles intoanenlarged The liquid agglomerate. andisseparated ashisexcluded viascreening orbyselective bubble flotation. Many andillustrated authors haveresearched thisprocess. Theagglomerate flotation [1-3] hasbeenknown since theturnofthecentury asshown byFroment technique [4]; to date,thereisa considerable thefundamentals however, gapinunderstanding Workby Brown thatproperties involved. inherent to coal-oil [5]hasshown arefavorable ofthisstudyto forflotation. Thus,itistheobjective agglomerates thesurface formed withcoalsofdifferent determine ofagglomerates properties data.Thiscanprovide ameans ranksandtocompare these results withrecovery to surface inrelevant assess theeffectofthenature oftheagglomerate processing situations. 2.EXPERIMENTAL . 2. 1Sample . preparation inverylarge Fivedifferent coals were usedinthisstudy. Some ofthesamples arrived Toapproximate thestateofparticulates inwaste fines thefollowtreatment, pieces. wasusedtoprepare thesamples. Thecoalchunks werereduced to ingprocedure millimeter sizebysuccessively themthrough a rollmill,thena Wiley Mill passing NRCC No.34229.

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117 were thenwetground witha 1mmscreen. Thesamples heatandoxidation) (toavoid inanattrition millforapproximately 30 min. Theparticle sizedistributions were 2600 thenmeasured witha Malvern laserdiffraction instrument. Their as-received aresummarized inTable1.Analysis ofthecoals'composition wasdone properties ona LecoMac400instrument. Eachcoalwasagglomerated atoillevels hexadecane of 0,1,5 and10 wt070 using wereprepared at a 10%pulpdensity. Agglomerates p = 0.773 g/ml). (n-C16H34, Thecoalwasmixed withdistilled water andstirred under vacuum forabout 90min to remove Afterdeairing, therequired volume of anyair fromthesystem. hexadecane wasintroduced, andthecoal-oil-water wasfurther stirred with system amagnetic barunder vacuum inabaffled flaskforatleast30mintoachieve air-free andoil)allows fora less (coal agglomeration. Having onlytwo-phase agglomerates material forthestudy ofthesurface complex properties. Normally, agglomerations carried outinhigh-shear vessels asblenders) willintroduce substantial (such mixing amounts ofairintothesystem fromthevortices created aswellasby bythestirring cavitation inthewater fromthemixing blades atextremely At moving highspeeds. hasaddressed thetopicofagglomerates formed asa present, verylittleresearch material. ApaperbyDryzmala etal.[6]discussed the (coal-oil-air) three-phase ofairinagglomerated presence systems. 2.2.Surface tension measurements Theadhesion the technique developed byAbsolom [7,8]wasusedtocharacterize surface ofthecoal-oil Thistechnique hasbeen properties agglomerates. successfully etal.[7]tomeasure surface tensions ofcoalparticles, aswell employed byAbsolom asbyDarcovich etal.[8]forcoal-oil Itwasoriginally to agglomerates. developed measure surface ofsolidmaterials thatoccur properties onlyinparticulate form, inblood, suchaserythrocytes asshown etal.[9].Theadhesion method byAbsolom involves theextent ofparticulate adhesion onvarious substrates asa measuring function ofthecomposition ofthesuspending (surface tension) liquid. Thefreeenergy ofadhesion, isexpressed as, where theparticle-substrate, and are,respectively, ypsYPL , andYSL particle-liquid interfacial tensions. substrate-liquid Ifthesurface tension ofthesuspending isgreater thantheparticle surface liquid tension > ypv),equation thattheextentof adhesion should (1)suggests (yLV decrease withincreasing substrate surface tension Theopposite trendis (ysv). = Ypv, when < ypv.When neither theparticle northeliquid will expected yLv YLV beenergetically favored toformaninterface withthesubstrate andtheextent of adhesion should beindependent ofysv.Theterms 'surface tension' and (dyne/cm) 'surface freeenergy' canbeusedtorepresent thesame Thelatter (erg/cm2) quantity. withinterfacial isofusetoassociate thermodynamic systems. properties teflon blocks 12.7 cmthickwith1cmdiameter holes were usedtocontain Virgin ofthismaterial theparticulate Thelowsurface minimized interaction slurry. energy of theparticulates andsuspending Thepolymer film liquidwiththecellwalls. substrates were cleaned cuttothesizeoftheteflon andaffixed totheblocks blocks, withan inertmedical the gradesilastic (DowCorning MDX4-4210), leaving intheteflon surface totheopening block. substrate exposed

118 Table 2. film substrate Polymer properties

Fourdifferent filmsubstrates wereusedto spanthepossible surface polymer tensions ofthecoal-oil These aredetailed inTable 2.Beisthe system. polymers contact formed withwater inair.These values were measured withanoptical angle match values etal.[7],calculated goniometer. They closely reported byAbsolom by Neumann's surface tension of state.Thisequation is fullydetailed in equation Absolom etal.'spaper[7].Solid surfaces tensions inTable 2 areforthesolid-air interface. After theattritor themoisture inthecoal-water mixture wasdetermined grinding, withtoluene. Thecoal-water mixtures were toprevent byextraction keptwellsealed ofwater. evaporation Particulate ineachoffivewater-methanol slurries were prepared compositions. These coalslurries contained a solids fraction of0.01.Equal were weight aliquots were thensealed ontopwitha silastic bonded filmto putineachcellwhich plastic of theliquid. Twocellswereprepared foreachcase.The prevent evaporation water-methanol aresummarized inTable 3below. suspending liquid compositions Thewater-methanol wasselected, since asshown andStephen system byStephen is essentially immiscible across theirentirebinary [10],hexadecane composition structure wasnotinterfered with.Thisdatafor range.Thustheagglomerate water-methanol solution surface tensions air at 20°Cwasgivenby against Weast [11]. Theparticles were allowed tosettle andadhere tothesubstrates for3days. Ithas beenshown theextent ofadhesion stabilizes byAbsolomal.et[7]that,bythistime, toa plateau value. Table 3. and surface tension Suspending liquid composition

119 andgently fromtheblocks Thepolymer substrate filmswerecarefully peeled Thesamples weredrybefore settled butnon-adhering rinsed toremove particles. andcentered on a microscopic Thefilmswerethenmounted stage viewing. wastaken. anda video ofeachsample SZH) image (Olympus Theimage ofadhering fromeachcellwasinputtoanimage analysis particles a grey-level cut-off wasdetermined to where (Kontron Image Analyzer) program Pixelregions as discriminate fromthebackground. designated adhering particles areaadhesion. wereintegrated togivea percent particles areaadhesion asa Foreachsample, a linear fitwasdetermined forthepercent tension foreachdifferent function ofsubstrate surface suspending liquid composioil.The 1shows sucha plot,thisdatafromtheHighvale coalat0wtolo tion.Figure thenplotted asa function ofthesuspending oftheseregressions were liquid slopes surface withaninterpolated curve tension, puttothedata(i.e.Fig.2,alsoforHighwasconsidered thiscurve crossed thex-axis valecoalat0wt?lo oil).Thepointwhere ofthisprocedure tobetheparticulate surface tension. Amoredetailed description isgiven etal.[12]. byDarcovich 2.3.Agglomeration tests oilusing wererunoneachof thecoalsat 1, 5 and10 wto7o Agglomerations waterin a Waring with500mlof distilled hexadecane. Coal(50g)wasmixed Thecoalwasthusagglomerated Blendor withtheappropriate amount ofoiladded. for30s andlow-shear at1007o pulpdensity, undergoing high-shear mixing mixing flotation cellwasused.The for1min.Fortheflotation tests,a Denver laboratory in1500 mlofwater. Theskimmed was 1007o wasfloated product pulpdensity sample inthesamecell.This washed in 500 ml ofwaterfor2minandthenre-floated

007o surface tension 1.Percentage area adhesion versus substrate (Highvale oil). Figure

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0%0 surface tension 2.Slope versus oil). (Highvale suspending liquid Figure wasdriedinan fromthefirstandsecond withthetailings floating, along product, oftheproducts andthetailings were Themasses oven at300°C recorded, overnight. asabove Thesame forashcontent. andthenthese were procedure analyzed samples oil. outwithNo.4 fuel wasalsocarried 3.RESULTS tensions 3. 1Agglomerate . surface asdetailed the measurements thedatafromtheareaofadhesion above, Interpreting across therange ofoillevels tested areshown oftheagglomerates surface properties The formed withhexadecane. inFig.3.Thisdatapertains onlytoagglomerates inagreecoals fallintherange of54.0-64.0 tensions oftheunoiled surface erg/cm2, et al. [13]andSablik of Varga-Butler mentwiththeprevious [14].At findings coals tensions ofthebituminous andsub-bituminous 10wtvo closely oil,thesurface show a more Thetwolignite thatofpurehexadecane. gradual samples approximate ahexadecane andasurface, which even at10wtolo curve oil,doesnotexhibit wetting character. andashremoval 3.2.Agglomerate recovery dataareshown inFigs4and andashrejection Theagglomerate flotation recovery as(([07o ashinfeed] [°7o 5.Thepercentage ashrejection isdefined - ashincleaned Twooilswere usedinthiswork, i.e.hexadecane x 100/[07o ashinfeed]j. product]) therecovery toshow andNo.4 fuel oil.Thefueloilwasusedprimarily properties didnotagglomerate toberecovered ofthelignite sufficiently samples. They simply was illustrative of theirwettability, withhexadecane; somerecovery, however, and moreviscous, No.4 fuel oil.Asreported withtheheavier, achieved byCapes

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3.Agglomerate surface free versus wt% oil. Figure energy

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5.Percentage ashrejection versus wt% oil. Figure Germain oilscontain someinorganic suchas polarspecies [15],morecomplex agreater oilwettability andsulfur. These functional nitrogen, oxygen groups impart coalsurface suchaslignite. toa lower rank,morehydrophilic 4.DISCUSSION ThedatainFig.3show howtheamount ofoilusedtoformcoal-oil agglomerates Aswasdiscussed a netsurface freeenergy forthatagglomerate. produces by Darcovich al.et freeenergies atintermediate oillevels 0to [16],thesurface (from 1wt%oil)reflect a heterogeneous surface ofbothcoalandoilcompocomposed nents. These intermediate surface freeenergy values canbeattributed toimperfect ofthesurface fromsurface surface and wetting arising heterogeneities, roughness in whichthe discretized of theoil through theaqueous medium dispersion thewetting witha non-zero takesplace.Further, occurs contact agglomeration willnotbespontaneous andcomplete, andspreading angle,sothatthewetting in patches andspread as it canlocally. A rathertheoilwillcoatthesurface ofoilonthecoalwould ifthesurface wasvery monolayer coverage onlybeachieved smooth andtheoilwasperfectly intheaqueous Themonolayer dispersed phase. ismorerelated tomodel rather thanwithimpure, real coverage systems, irregular surfaces. ItcanbeseenthatfortheDevco, andMontgomery coals(subHighvale inrank), thesurface freeenergy atlowoil bituminous andhigher verysharply drops toa value nearthesurface freeenergy ofpurehexadecane. Thusthesurface levels, oftheseagglomerates hasessentially anoilcharacter atlowoillevels. At10wt 07o coalshows asurface freeenergy lessthan oil,thedatafortheHighvale thatofhexadecane. Thisdifference isslight andshould beunderstood tobewithin

123 errorforthismeasurement. Theadhesion method is therangeof experimental oferror.Theprescence ofashintheadhesion cellswith toseveral sources subject withthesettling andadhesion. Itwasassumed theagglomerates mayhaveinterfered mineral theashisofsufficiently thatbecause oftheirinorganic, nature, highsurface toadhere tothepolymer substrate freeenergy thatitwasunlikely surfaces. Further, thesurface tensions ofthewater-methanol mixtures werevery suspending liquid sensitive to composition. ofevaporation or evensmallvolumetric Anyamount intheirpreparation couldmakesubstantial errors.Greatcarewas inaccuracies takenintheexperimental worktoensure sound andreasonable data. InthecaseoftheBienFaitandCostello thesurface freeenergy lignite samples, doesnotdecrease withoillevel hasa value atleast and,evenat 10 wtolo, sharply 10erg/cm2 have a highmoisture thanthatofhexadecane. Typically, lignites greater content andcontain thatinhibit oilwetting. Thishasbeen manypolargroups results andlongcontact confirmed al.[17] time,as byJin et showing poorflotation wellasbyNakaandNishida to bemuchmorewater [18],whoshowed lignites Rosenbaum andFuerstenau wettable thanothercoalranks.Similarly, [19]noted thatcoalsurfaces contain anincreasing amount ofhydrophilic functional as groups rankislowered. Acomparison between thetwolignites canalsoreveal mechanistic reasons forthe wasfound tobemorewettable observed results. TheCostello sample byhexadecane thantheBienFaitsample, asshown bythedatainFig.3. Themostmarked thetwolignites isthattheBien Faitsample contains difference between composition to hydrophilic behavior oil 50%moreash,contributing suppressing relatively wetting. It hasbeenreported Good etal.[21]andothers, thatthe byWojcikal. et[20], ofrank. surface freeenergies aresimilar fora widevariety ofcoals, independent forthe Thisisconfirmed ofsurface freeenergy values obtained bythesmall range inthisstudy, inFig.3forthecaseof0wt%oil.However, fivecoalsamples shown basedonsurface areveryrank it is wellknown thatrecovery processes wetting dependent. 4shows dataandFig.5shows theashrejection theflotation data recovery Figure Theoil-wettable sub-bituminous forthesub-bituminous andthelignite samples. recovered thanthelignite Theflotation tests arefarmoreeasily samples. samples astheagglomerating oilshow donewithhexadecane results; however, poorrecovery withincreased oilwettability. thetrendof increased theydouphold recovery Hexadecane hasbeenfound byJariczukal.et[22]tohavea weak bonding ability in dynamic andairbubbles it is not between coalparticles systems. However, forcommercial it issimply intended tousehexadecane rather, recovery processes; a wellcharacterized suitable forthiswettability study.Asa purehydrocarbon ismuch lessviscous thanNo. 4fueloil,soit ismore practical point,hexadecane flaskagglomeration vacuum amenable towetting thecoalinthelow-shear procedure.Theagglomeration inthecaseoftheflotation measurements wasdoneina heavier oils. ofmorethoroughly blender, dispersing high-shear capable oilwasalsousedtoconduct flotation tests.Therecovery of No.4 fuel recovery withthehexadecane thesub-bituminous coalswasmarkedly compared improved results a smallamount of recovery wasachieved withthelignite and,further, thistothepresence ofaromatics inthe samples. Tampyal. et[23]haveattributed interact morefavorably withthecoalsurface toformsome fueloilwhich hydrogen

124 Thisphenomenon in turn,willholdtheoil-bubble bondswithpolargroups. ina flotation situation. Thisconcept isconfirmed moresecurely interface bythe ofpolar datashowing thelignite which havea much higher composition samples tothefueloilasanagglomeration/flotation agent, favorably groups, responding oil.If hexadecane while toberecovered bythepurely dispersive essentially failing it would forthehexadecane-lignite sizedatawereavailable likely agglomerates, toenhance theprobability which would bea process show littleornoenlargement, ofsuccessful flotation. were60.5erg/cmZ fortheBien oftheunoiled Thesurface freeenergies lignites and57.3erg/cmz fortheCostello Across theentire ofoil Faitsample sample. range maintained a lowersurface free theCostello levels tested, sample agglomerates different Ifweconsider tobenosubstantially oil,thereappears energy. dyPV/dwto7o coals. Inthissense, force topromote theoilwetting ofthese thermodynamic driving tobeslightly canbe therecovery show theBienFaitsample data,which superior, extent ofwetting The thattheabsolute bysuggesting maybethesame. explained moisture content of lower volatile content andthelower (hydrophilic) (lyophobic) foritsslightly between the Faitsample could thenaccount theBien greater recovery havea morefavorable interaction withthe twolignites, inthesense thatitwould surface freeenergy model forheterogeneous surfaces No.4 fuel oil.Amacroscopic isthemacroItisstated asyH= Ec,y; where hasbeenproposed , YH byCassie [24]. oftheheterogeneous solid andyiisthesurface freeenergy surface freeenergy scopic In thefraction which of theithcomponent comprises eioftheentiresurface. ashcontent willcontribute toa higher surface freeenergy, while volatiles general, isassumed tohave it.Ifthevolatile fraction andfixed carbon would tendtoreduce of a surface freeenergy value similar tothatofhydrocarbon oils,thentheaddition attracted tothecarbonaceous would bepreferentially suchoilsasa wetting agent issignificantly morehydrophilic thanthe ofthecoalsince theashcontent portion ofanoiloveranalready oil-like restofthesurface, andthewetting (volatiles) Thuswithfixed carbon favorable. contents surface isnotverythermodynamically fortheBien FaitandCostello theextent and39.79070, of38.59 samples, respectively, beconsidered tobeverysimilar. ofwetting oil)could (dypv/dwtO7o It isofinterest to compare thedifferences inagglomeration/flotation recovery inview andMontgomery sub-bituminous shown inFig.4fortheHighvale samples, oftheirapparently similar Consider thesurface freeenergy values for wettability. was64.2erg/cm?, the TheMontgomery result while theirunoiled surfaces. sample canbeconsidered recovercoalvalue was54.6erg/cmWhile . bothcoals Highvale theMontgomery showed a ablebytheagglomeration/flotation method, sample withtheNo.4 fueloil,and recovery (seeFig.4),especially markedly superior TheMontgomery hada withtheNo.4 fueloilat lowoillevels. sample notably oftheMontgomery withhexadecane aswell. Thelower ashcontent recovery higher withitshigher unoiled surface freeenergy, could indicate moreof sample, coupled which lenditselftoa morecomplete a fixedcarbon fraction atthesurface would wetted state.Thatis,ifthesurface freeenergy ofa solid ishigher, butnotashigh thethermodynamic force foroil assaytheashfraction sotobehydrophilic, driving willbegreater. ifalarger fraction ofthesurface isoilwettable, this Further, wetting flotation. Ifthe andthesubsequent willenhance ofbothagglomeration probabilities exceeds the theMontgomery sample oil)is considered, quantity (dypv/dwtvo that wt%oil.Thisisanother Highvale sample byabout10erg/CM2 wayofsaying

125 forthesameamount of oilpresent, thesurface character of theMontgomery thatimproves its hasbeensubject to farmoremodification bywetting sample Ifitcanbesupposed thatwithasmaller area agglomeration/flotation performance. ofoilonits available forwetting, theHighvale sample mayhavea thicker covering wettable Ithasbeenshown thatthedetachment force byJariczukal.et[22] regions. islower when theoillayeristhicker. This forairbubbles onoiledcoalsurfaces isthusconsistent withtheideaofa restricted areaandhence a wetting finding Athigher oillevels, when thewetting becomes lessselective, thicker wetting layer. islesspronounced bothinterms ofthequantity thiseffect (dypv/dwtolo oil)aswell intheagglomeration/flotation obtained. asthedifference recovery 5shows theashrejection asa function of agglomerate oillevel.The Figure isrecovered intoa greater isatthesame timeless coal,which degree, Montgomery ThiswasthecasewiththeNo.4 fueloil.Thelower unoiled deashed. efficiently oftheHighvale coalwould makethewetting moreselective surface freeenergy ata particle sizemuch smaller thantheMontgomery coal,thereisa and,further, tohavea cleared discretization between ashandcarbonaceous higher probability matter. inthisdiscussion Onepointwhich hasnotbeengiven toomuch consideration is thatofthemean size. TheHighvale hadamean sizeof9.4 pm, while particle sample theMontgomery coalwaslarger, witha meansizeof20.3,um. ThedatainFig.3 thattheoilcharacter totheagglomerate surface isroughly thesame suggest given atoillevels from1to10wt°7o. Even at1wt?7o oil,thereisstillmorethansufficient oilpresent tofully wettheentire surface areaofbothsamples ofcoal.Ifparticle size itwould beat anoillevel suchas (orsurface area)weretohaveaneffect, likely 0.50 wt% orbelow, where thelarger coalwould beexpected toshow a comparacharacter. Where thisfactordoesmake a difference is moreoil-like surface tively withtheagglomeration/flotation data.Itwasshown recovery byDarcovichal.et thatexcess oilonacoalsurface contributes toimproved bonds for [16] inter-particle theformation ofagglomerates. Wellwetted, would larger agglomerates improve flotation aslarger offermoreinertia tocounter recovery, particles hydrodynamic resistance inthebubble-particle collisions forattachment. Thusfora less necessary ofagglomerating oilwetted thechoice oil coal,suchastheHighvale easily sample, becomes morecrucial forachieving goodrecovery. the sub-bituminous and Thedatain Fig.3 showthe difference between oilwetted, andthelignites which donotreadily bituminous coalsthatareeasily Theoil-wetted coals havea sharp anoilcharacter totheirsurfaces. acquire dropin andhavea surface character ofthe surface freeenergy atlowoillevels essentially Thischaracteristic ofthecurve indicates thatit oilitselfathigher oillevels. wetting andupgrading of thecoalbythe isreasonable to expect successful recovery butit doesnotreallypredict whatextent of agglomeration/flotation procedure, canbeexpected. Thesuccess ofrecovery onthecomponents ofthe recovery depends coalmatrix itselfandhowthesecomponents interact withwhatever agglomerating oilisselected tobindthem. Inview oftheabove consider a definition ofhydrophobicity index discussion, h, fortheas-received as: coal,formulated

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handoillevel. 6.Agglomerate surface tension versus Figure hisessentially theratiooftheamount ofthecoal Thisparameter ofthecomponents andoilwettable andvolatiles), totheamount thatwillbehydrophobic of (carbon thatarecomparatively muchmorehydrophilic. components (ashandmoisture) 6 shows a three-dimensional surface wherethesurface tension of the Figure is mapped outas a function of theoillevelusedin making the agglomerate andthevalueofh determined forthefivecoalsamples used.The agglomerate surface wasgenerated fromthedatawitha two-variable constrained quadratic routine. In Fig.6, it canbe seenthatif thecoalis notoverly interpolation amount ofoilisrequired tomake anagglomerate hydrophobic (h z2),onlyasmall withasurface thatcanbeconsidered tobethesame asthatoftheagglomerating oil. inthedata. Theridges onthesurface canbeattributed tothescatter canberecovered withhigh Witha properly chosen oilforflotation, agglomerates atoillevels 2wtO7o. Thelowoilrequirement isanattractive feature of below yields theagglomeration/flotation process. 5.CONCLUSIONS From theworkcarried correlation between out,itcanbesaidthatthereisa direct inaqueous themeasured surface freeenergy ofcoal-oil media andthe agglomerates andbituminous results. Coals ofsub-bituminous agglomeration/flotation recovery

127 rankwillacquire anoil-like surface at oillevels aslowas1wt%.Lower ranked show a decrease insurface freeenergy astheoillevel isincreased, buttheir lignites tobeagglomerated andfloated islimited. Forthetwosub-bituminous ability coals, similar theagglomeration/flotation was curves, despite showing wetting recovery different andthisdifference hasbeenattributed tohowtheircomposition markedly contributes to theirmacroscopic surface behavior. Coalshighin asharemore onthesurface andthisin turndepresses the likelyto haverestricted wetting smaller andsmaller agglomeration/flotation recovery. Further, particles agglomerateswillencounter morehydrodynamic resistance tosuccessful andeven flotation, collisions toagglomeration andwetting. leading Ashrejection thecoals tested washigh,nomatter whatoillevel used.It among wasfoundto be mostselective at lowoillevels where thehydrophobic and of microscopic onthecoalsurface aremoreprohydrophilic properties regions nounced. Inthiscase,thereisnotanexcessive amount ofoilpresent towetless favored suchasash,when thefuelbearing have thermodynamically regions portions beenoilwetted. Provided thatthehydrophobicity index h isgreater than already about2,small amounts ofoilarerequired togivetheagglomerate surface anoil which andrecovery. character, promotes agglomeration donotshowgoodrecovery andagglomeration atlowoillevels. Lignites They would some sortofsurface conditioner tomodify sites require polarandhydrophilic toallow lowoillevel andflotation. agglomeration REFERENCES 1.C.E.Capes andK.Jonasson, ofoil-water ofcoals inbeneficiation. In: Application wetting Phenomena inCoal G.D.Botsaris andY.M.Glazman New York: Interfacial Technology. (eds.). Marcel Dekker Inc., 1989, pp.115-155. 2.T.Hirajima, E.Chan, S.Whiteway, M.Stefanski andI.Stewart, Beneficiation ofchar, from a eastern Canadian flotation. Coal 1987. coal, pyrolyzed byaggregative Prep. 5,85-108, 3.W.Wójcik andA.M.AlTaweel, Beneficiation ofcoal fines flotation. Powder byaggregative Technol. 1984. 40,179-185, 4.A.Froment, to the concentration of ores. UK No. June Improvements relating Patent, 12,778, 4, 1902. 5.D.J.Brown, Particle collision andattachment infroth flotation. In:Aerodynamic trajectories, E.G.Richardson London: Capture of Particles, (ed.). Pergamon Press, 1960, pp.35-43. 6.J.Dryzmala, R.Markuszewski andT.D.Wheelock, Influence ofaironoilagglomeration of inaqueous carbonaceous solids Int.J.Miner. Process. 1986. suspension. 18, 277-286, 7.D.R.Absolom, K.Eom, E.I. Vargha-Butler, H.A.Hamza andA.W.Neumann, Surface ofcoal inaqueous media. II.Adhesion ofcoal topolymeric substrates. properties particles particles Coll. 1986. Surf. 17,143-157, 8.K.Darcovich, C.E.Capes andF.D.F.Talbot, Surface ofcoal-oil inthe properties agglomerates floc 196th ACS Natl. 1988. regime. Preprints Meeting 33, 765-776, 9.D.R.Absolom, W.Zingg, C.Thomson, Z.Policova, C.J.Van OssandA.W.Neumann, adhesion topolymer surfaces. J.Coll. Sci. 1985. Erythrocyte Interface 104, 51-59, 10.H.Stephen and T.Stephen, Solubilities andOrganic Vol. 2:Ternary and ofInorganic Compounds, New York: Part 1740. Multicomponent Systems. Pergamon Press, 1964, 2,No. 5160, 11.R.C.Weast CRC Handbook and Boca FL: CRC Press (ed.), ofChemistry Physics.Raton, Inc., 1987. 12.K.Darcovich, L.S.Kotlyar, W.C.Tse, J.A.Ripmeester, C.E.Capes and B.D.Sparks, Wettability oforganic-rich solids from Athabasca oilsands. and Fuels study 1989. separated Energy 3, 386-391, 13.E.I. Vargha-Butler, M.Kashi, H.A.Hamza andA.W.Neumann, Direct contact angle measurements onpolished 1986. sections ofcoal. Coal 3,53-75, Prep. 14.J.Sablik, Free surface ofcoals ofhighest Pol. J.Chem. 1985. energy hydrophobicity. 59,433-438,

128 infine 15.C.E.Capes andR.J.Germain, Selective oilagglomeration coal beneficiation. In:Physical Y.A.Liu(ed.). New York: Marcel Dekker Inc., 1982, Cleaning ofCoal, pp.293-352. 16.K.Darcovich, C.E.Capes andF.D.F.Talbot, Surface characteristics ofcoal-oil in agglomerates thefloc andFuels 1989. 3, 64-70, regime. Energy 17.R.Jin,Y.Ye, J.D.Miller andJ.S.Hu,Characterization ofcoal hydrophobicity bycontact angle, bubble attachment andFTIR In:116th AIME Annual no. time, spectroscopy. Meeting. Preprint 1987. 87-146, pp.Denver, 19 CO, 18.N.Naka andY.Nishida, Water wettabilities offoreign coals. 1984. 33, 80-87, Yukagaku 19.M.Rosenbaum Onthevariation ofcontact andD.W.Fuerstenau, with coal rank. Int.J. angles Miner. Process. 1984. 12,313-316, 20.W.Wójcik, T.Bialopiotrowicz and B.Jaczuk, surface tension ofPolish The critical coals and their surface free Fuel 1988. 67,688-692, energy components. 21.R.J.Good, N.R.Srivasta, M.Islam, H.T.L.Huang andC.J.Van oftheacid-base Oss, Theory contact and thehysteresis ofwetting: tocoal and interactions, hydrogen bonding angles, application Sci. Technol. 1990. surfaces. J.Adhesion graphite 4, 607-617, 22.B.Jaczuk, W.Wójcik andT.Bialopiotrowicz, Studies oncontact and work of adhesion in angle film-air thesystem coal/n-alkane bubble-water. Powder Technol. 1990. 61,211-216, 23.G.K.Tampy, M.E.Prudish, R.L.Savage andR.R.Williams, Free andhydrogen energy changes inthewetting ofcoal. 1988. andFuels 2, 787-793, bonding Energy 24.A.B.D.Cassie, Contact Discuss. Soc. 1948. 3,11-16, angles. Faraday