The potential of electrostatic separation in the upgrading of South African fine coal prior to utilization a review

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1 The potentil of electosttic seption in the upgding of South Aficn fine col pio to utiliztion eview by S.O. Bd*, R.M.S. Flcon*, nd L.M. Flcon* J o u n l Synopsis Col is complex mixtue of ognic nd minel constituents nd is the most bundnt esouce of fossil enegy in the wold. In ecent yes, significnt esech into dy col beneficition hs gined much ttention, pimily due to the need to impove gdes nd educe the envionmentl contminnts in col without the use of wte, nd to chieve this in s cost-effective mnne s possible, eltive to wet beneficition pocesses. This ppe seeks to eview the ppliction of vious electosttic septos with thei pocess pinciples, to dw compisons between diffeent dy beneficition techniques with specific emphsis on the tiboelectosttic seption method, nd finlly to epot the esults of tiboelectosttic seption conducted on vious South Aficn cols. Pevious esech conducted on Indin, Euopen nd Ameicn cols hs indicted tht this technique is likely to led to significnt economic benefit though the eduction of sh content, NO x nd moe specificlly SO x by septing out the libeted Fe-S-being minels pio to utiliztion. The emovl of the ltte suite of minels is lso likely to significntly educe o eliminte the emissions of ssocited tce elements, including mecuy nd senic. The esech esults epoted in this ppe indicte tht the oty tiboelectosttic pocess hs the potentil fo significnt upgding of high sh pulveized South Aficn col. The impct of vious opetionl pmetes ws investigted nd key fctos estblished fo the optimum ecovey of low sh nd low sulphu fine col. Keywods Col, dy beneficition, electosttic technique, oty tiboelectosttic septo, high-gdient mgnetic seption. Intoduction Col epesents the single most bundnt souce of fossil-bsed enegy vilble in most counties ound the wold. The Republic of South Afic (RSA) is the fouth lgest colpoducing county nd the thid lgest expote of col, behind USA nd Austli (Budge, 2000). The South Aficn cols deposits wee fomed duing the Pemin peiod in Gondwnlnd, the supe-continent tht included Afic, Austli, Indi nd South Ameicn. Now found pedominntly in continents in the southen hemisphee, these cols e known s the Gondwn cols. They e chcteized by possessing lowe popotions of vitinite nd liptinite, nd considebly highe sh contents thn those fomed duing the Cbonifeous peiod in the nothen hemisphee. Col is highly heteogeneous, with wide viety of minels nd ognic components, ll occuing in widely vying popotions fom one sem to nothe nd between diffeent colfields. The minels exhibit diffeent degees of integowth in the ognic mtices, esulting in vious levels of libetion nd theefoe potentils fo seption nd beneficition of the host col. This ptilly explins the difficulty in dopting pticul wshing technique fom the numeous techniques vilble in the mket (Dieudonne, 2001). The totl estimted eseves of col in South Afic e ppoximtely 34 billion tons, nd t the pesent consumption te, it hs been estimted tht mee 7 billion tons might emin by 2040 (Mbedi, 2004). Futhemoe, most of the high gde clene cols hve ledy been, o e fst being, mined out pimily fo expot puposes, theeby leving the lowe gde, high sh cols fo extction nd use in the futue. In ddition, moe stingent envionmentl contols in tems of pticulte, gseous nd tce element emissions e being imposed on the uses of col, with specific emphsis on SO x fom sulphu-elted minels, NO x nd CO 2. Fo these esons, nd in ode to ensue the continued use of col fo powe genetion, hydocbon poduction nd industil het nd powe, thee is n ugent need to conduct detiled esech into the upgding of South Aficn col leding to clene nd moe efficient use in the futue. * School of Chemicl nd Metllugicl Engineeing, Fculty of Engineeing nd the Built Envionment, Univesity of the Witwtesnd, Johnnesbug, South Afic. The Southen Aficn Institute of Mining nd Metllugy, SA ISSN X/ This ppe ws fist pesented t the, Indb Col, Cbon nd Enegy Confeence, Mch 2009, Glen Hove Confeencing Cente, Melose, Johnnesbug. P p e The Jounl of The Southen Aficn Institute of Mining nd Metllugy VOLUME 110 NOVEMBER

2 The potentil of electosttic seption in the upgding of South Aficn fine col The pinciple of using dy beneficition techniques the thn the conventionl wet techniques fo the beneficition of South Aficn cols ises fo sevel esons, Fist, South Afic is wte-poo county nd this sitution imposes sevee limittion on ll pocesses equiing wte s medium to succeed. Secondly, the beneficition of ult fine fctions of col (-600 µm) using wte-bsed techniques such s foth flottion is costly nd difficult in tems of dewteing the finl poduct, nd hndling nd stoge. In tems of the bigge sized fctions, the lge quntities of wte used nd lost duing conventionl col peption, s well s the high cost of mnging nd teting the lge quntities of queous sluies geneted duing the wet pocessing techniques, seve s futhe motivtions fo the intoduction of dy beneficition techniques. Futhemoe, most col beneficition pocesses cuently employed in South Afic e bsed on wet techniques nd these poduce lge quntities of potentilly polluted wte. The estimted cost of hndling nd teting these pollutnts constitutes mjo disdvntge to this technique, not only in South Afic but lso woldwide (Lockht, 1984). It hs been stted tht the tetment of sluies, contminted wte nd ecovey poblems in wet beneficition techniques e moe expensive comped to the dust contol nd the disposl of dy tilings, which e esie nd less expensive in the cse of dy beneficition pocesses (Lockht, 1984). The fct tht wte demnds will be mjo poblem fo pesent nd futue developments in mining, beneficition nd in the constuction of new powe plnts in SA, iespective of the technicl nd economic fesibility of the wet techniques, gives ise to futhe motivtion fo the development of n ltentive ppoch to wet-bsed beneficition of col. The dy beneficition of col hs inspied inteest not only becuse of the limittions of wet beneficition techniques listed bove, but lso due to the pocess benefits in downstem utiliztion whee enegy is sved though not being equied to dy the col poduct befoe being sold s souce of fuel. Futhemoe, it is envisged tht the potentil to educe o eliminte Fe nd S-being minels (pyite) to eltively high degee pio to use my lso led, in tun, to the elimintion of SO x nd pevent the need fo flue gs desulphuiztion plnts (FGD) t the bck end of powe plnt. In ecent yes, extensive esech hs been conducted on viety of dy col beneficition pocesses, ll fo the pupose of poducing high pticle seption efficiencies, optimum cost-effectiveness nd miniml moving-pts engineeing leding to educed mintennce issues. These techniques e bsed on diffeences in the chcteistics of the col constituents, including such popeties s specific gvity, gindbility, fibility, shpe, size, mgnetic susceptibility, electicl esistivity nd fictionl coefficient. On the bsis of these diffeences in popeties, equipment such s the fluidized bed, i/dense medium fluidized bed septo, tiboelectosttic septo, octgonl oty tiboelectosttic septo, pneumtic jig, pneumtic tble nd Sotex systems which e pplicble to diffeent pticle sizes, hve been used to beneficite col (Cheng nd Yng, 2003; Weitkämpe nd Wotub, 2004; Biswl et l. 2005; Choung et l., 2006; Dwi nd Ro, 2007; Dwi nd Ro, 2008). The fist ttempts t the dy beneficition of fine pulveized col (-170 micons) in South Afic wee undetken by Bd et l. (2010) using the tiboelectosttic septo. In this eview, numbe of dy beneficiting techniques nd thei fesibilities e eviewed, followed by the pesenttion of esults obtined when testing selected high sh South Aficn cols on oty tiboelectic septo (RTS). Comments egding the emovl of Fe- nd S-being minels such s pyite, sulphu nd sh fom the cols unde investigtion using diffeent opeting conditions e lso included. Dy beneficition s col beneficition pocess Dy beneficition could be egded s ptil eplcement fo wet beneficition techniques o n ltentive ppoch fo ecoveing ejected fine col tht is ceted in conventionl col peption plnts in the fom of undeflow thickenes nd sluies. The dy beneficition of col cn be economiclly competitive nd envionmentlly sfe, nd it my eliminte the need fo flue gs desulphuiztion (FGD) in futue powe plnts in South Afic. In ddition, it could seve s potentil technique fo exploiting cols tht would hve othewise hve been clssified s unecoveble becuse of envionmentl o economicl constints. Dy col beneficition hs lso emeged s n ltentive ppoch to solving the poblem of the sccity of wte in col-poducing counties nd s get benefit in downstem utiliztion. Enegy is not expended in dying wet col unde dy beneficition, theeby llowing full use of col fo mketing puposes (Lockht, 1984). The dy pocess is lso less cpitl intensive thn wet techniques; it does not equie thickenes to settle fines nd it etins the high cloific vlue nd qulity s col being beneficited in wet-pocessing technology (Dwi nd Ro, 2007). This pocess ws lso found to be envionmentlly dvntgeous due to the effective emovl of the now well-libeted sh (minel-ich) pticles, Fe-S pyitic minels nd thei ttendnt hmful tce elements, mecuy nd senic (Higshiym et l., 1998). The dy beneficition technique elies on the diffeences in physicl nd chemicl popeties of the minel (inognic) nd mcel (ognic) components in col nd is lso ffected by such fctos s pticle size, mgnetic susceptibility, electicl conductivity, shpe, nd density. Such popeties contol the effective seption of the ognic components (mcels) fom the inognic components (minels) which, in tun, ffect the wshbility potentil, seption efficiencies nd yields fo cetin qulities (initilly detemined by sh content). Notble dvnces in dy col peption with specific efeence to fluidized bed tiboelectosttic seption of ult fine o pulveized col hve been mde by sevel uthos including Dwi nd Ro (2008). Whees good eductions in sh nd sulphu contents with consequent inceses in gde of poduct hve been found, emphsis in these esech ppoches ws lid moe on eviewing the pinciples of electosttic seption s comped to the othe techniques which e lso discussed below. Hving poved to some extent the efficcy of this technique, esech is now equied to incese the yields nd futhe seption efficiencies of 692 NOVEMBER 2010 VOLUME 110 The Jounl of The Southen Aficn Institute of Mining nd Metllugy

3 The potentil of electosttic seption in the upgding of South Aficn fine col this pocess in ode to mtch the highe efficiencies nd yields encounteed when testing the sme col qulities nd size nges unde conventionl wet beneficition techniques obtined. Given the impotnce of dy col beneficition in South Afic, the pesent sttus of this technique is heein eviewed. This is followed by epot on esults obtined when testing selected smples of high sh South Aficn fine col in scle tiboelectosttic septo. The theoy nd mechnisms of dy electosttic beneficition techniques Theoy of electosttic beneficition techniques The ppliction of electicl conductivity of pticles unde the influence of high potentil diffeence hs eceived significnt ttention in ecent yes. This seption technique depends on the diffeence in the electicl esistivities nd conductivity, nd lso diffeences in the electonic sufce stuctue of the minel fom the ognic phses in col (Kelly nd Spottiswood, 1989). These diffeences in popeties enble the pticles to develop two diffeent chged phses which contibute to the seption of these pticles. Hence, with the ppliction of vious opetion pmetes on the septo, the seption efficiency of vious col pticles fom one nothe cn be impoved. The simplicity of this technique nd ese of opetion, s well s the now poven potentil fo diffeent col pticles to exhibit diffeent electicl popeties, hs led to incesed esech in this diection in ode to seek ltentive ppoches to existing wet technologies fo the upgding nd beneficition of South Aficn col. Electosttic seption is bsed on electophoesis, which involves chged pticles, nd dielectophoesis, which involves unchged pticles. Electophoesis seption of col pticles in n electic field equies high-intensity field, following the pechging of the col though the field. The two electicl seption methods tht hve been used fo the clening of col e the coon electosttic nd the tiboelectosttic pocesses. These hve now been incopoted into vious configutionl systems with fluidized bed nd cylindicl nd octgonl oty chging chmbes (Butche nd Rowson, 1995; Dwi nd Ro, 2008; To, et l. 2009; Bd et l. 2010). The pticles electophysicl popeties detemine the wy in which the pticles cn be endowed with chges. This is chieved eithe by conductive induction o tiboelectifiction o coon-electosttic chging mechnisms. The thee min mechnisms fo chging pticles e ion o coon bombdment, contct o tiboelectifiction nd conductive induction (Knoll nd Tylo, 1984; Kelly nd Spottiswood, 1989). Chging mechnisms Tibochging occus though contct chging nd fiction chging mechnisms nd by utilizing the diffeences in the electonic sufce stuctue of the pticles involved. In both cses, the mechnicl pocesses tht poduce the chging of mteils e sliding, olling o milling, impct, vibtion of the sufce t contct, seption of solid solid, solid liquid, nd liquid liquid sufces nd defomtion leding to chge distibution t stess points (Mzumde et l., 2006). The quntity of tiboelectic chge exchnged between two contcting sufces depends upon thei contcting speed, the eltive wok function nd on the pessue between the sufces in contct. In ddition, s the pessue inceses, thee is the possibility fo n incese in the sufce chge density due to the high sufce e o numbe of contct points between pticles. This mechnism hd been found to be most effective fo chging mteils with little diffeences in conductivities such s col. This ssists the seption of minels nd high sh col pticles fom clen mcel-ich col pticles. Ion bombdment is one of the most efficient chging pocesses nd cn be pplied in consistent mnne to chge both insulting nd conducting pticles nd doplets, eithe positively o negtively, within eltively shot peiod of time (usully less thn 1 second). The pticles e bombded though tmospheic gses geneted fom high-intensity electic field between the oll nd one of sevel electodes connected to high-voltge supply. Once the ion bombdment ceses, the insulting pticles e held o pinned to the sufce of the otting oll electode by the electic imge foce, while the conducting pticle loses its cquied chge to gound vey pidly s thee is no electosttic foce holding it to the conducting sufce (Smuil et l., 2005). Though this ction, both pticles cn be septed. This ppoch is vey efficient duing the seption of two mteils with significnt diffeences in conductivities. Induction chging is the pocess by which sttic field is used in chging pticles. The unchged pticle comes into contct with chged sufce such s plte o sceen in n electic field. Thee it ssumes the sme polity nd potentil of the contcted sufce. This pticle is then consideed to hve become polized, whethe it be conductive o dielectic (Dyenfoth, 1978). Unde this influence, conductive pticle will become n equipotentil sufce by edistibuting the chge lmost instntneously vi the gounded oto. The pticle will cquie chge opposite to tht of the highvoltge electode geneting the electic field (Inculet, 1984). Howeve, dielectic pticle will become polized so tht the side of the pticle wy fom the chged sufce develops the sme polity s the sufce. In ddition the pticle will emin polized due to its inbility to effectively edistibute electons (Dyenfoth, 1978). Fo this eson, non-conducting pticles hve no net chge nd so e neithe ttcted no epelled by the field. Knoll nd Tylo (1984) epoted tht the foces geneted by induction seption e genelly weke thn tht of ion bombdment due to less pticle chging, theeby educing pocess efficiency. Hence, effective seption of the pticles cn be chieved only unde the ion bombdment pocess nd subject to significnt diffeences in the vious pticles conductive popeties. This is the eson why tiboelectosttic seption is pefeed in the cse of col seption. Dy electosttic seption methods Coon electosttic method The utiliztion of electosttic seption techniques hs been lgely developed nd employed in vious field fo minel J o u n l P p e The Jounl of The Southen Aficn Institute of Mining nd Metllugy VOLUME 110 NOVEMBER

4 The potentil of electosttic seption in the upgding of South Aficn fine col beneficition, emovl of the unbuned cbon in fly sh nd fo gicultul ppliction (Tigwell et l., 2003; Butche nd Rowson, 1995; Dwi nd Ro, 2007; Dwi nd Ro, 2009; To et l., 2009). The oto-type techniques, using induction by coon chging, hs been employed in septing w mteils bsed on thei conductivity into conductive nd non-conductive mteils. The coon is pplied in cses whee thee is lge diffeence in the wok function of the mteil involved. Howeve, due to the simility in the popeties nd the closeness in the wok functions of the minels o sh contents found in col fines, the oto-type technique hs not been found to be effective fo the seption of pticles of col with vying quntities of minels (sh) in them. Tiboelectifiction, on the othe hnd, hs been found to be f moe effective s n ltentive technique fo the seption of pticles with little diffeences in conductivity popeties (Higshiym nd Asno, 1998; Soong et l., 2001; Chen nd Wei, 2003; Dwi nd Ro, 2008). The coon electicl septo technique using ion bombdment fo chging nd septing minels is the most common nd stongest method of chging pticles fo electosttic seption (Butche nd Rowson, 1995; Dwi nd Ro, 2007). It hs been employed in ecoveing coppe nd plstic mteils fom powe cble, emovl of stlks fom te leves, seption of metls fom glss, cemics, plstics, nd polymes, nd lso fo emoving contminnts fom gins nd pocessed foods (Mooe, 1973; Hykw et l., 1985; Tylo, 1988; Higshiym nd Asno, 1998). In the minel pocessing industy, the commecil pplictions of coon seption e in the concenttion of hevy minels (utile, zicon, ilmenite, monzite) fom bech snds nd lluvil sediments, nd fo the seption of zicon nd TiO 2 phses duing the pocessing of hevy minel concenttes deived fom hevy minel snds (Yongzhi, 1992 nd Woobiec et l., 2007). The eliest ppliction of the coon technique fo the beneficition of col used the pticle size nge Micons (Muki et l., 1967). A col poduct of pe cent sh content eniched in vitinite ws obtined, with ecoveies of pe cent. A futhe exmple of the eduction in sh content nd mcel seption in col ws shown expeimentlly by Olofinskii et l. (1959). Hee coon-chmbe, tibo-dhesive-dum nd fluidized-bed electic septos wee used fo beneficition, size clssifiction, nd dust ecovey. The esults eveled tht pticle size nd col density wee esponsible fo the seption of the col pticles, with cose nd fine fctions hving diffeent minel nd mcel contents. The Advnced Enegy Dynmics (AED) s epoted by Lockht (1984) conducted n extensive test in beneficiting col pticles down to 37 micon size levels. The esult indicted tht significntly highe quntities of sh (minelich pticles) nd totl sulphu contents could be emoved using electosttic methods thn could be chieved using ny conventionl wet beneficition method. Recoveies wee highe, with the emovl of 65 to 89 pe cent of sh pticles nd ll t ppecibly lowe opeting costs. The electosttic seption of pyite fom col using the coon oll septo ws conducted by Butche nd Rowson (1995) on Moi Pottey col, using vious tmosphees, feed pe-tetments, pticle distibution sizes nd eltive humidities. The uthos estblished tht n sh eduction of pe cent could be chieved unde compessed i tmosphee using micon pticle size fctions eltive to only pe cent sh eduction unde mbient condition on the sme size nge. Results obtined unde the nitogen nd cbon dioxide tmospheic condition wee found to be compble to esults chieved unde stndd i tmospheic conditions. Howeve, cetin limittions in efficient seption of vying minel-ich col pticles wee noted when using the coon electosttic seption fo col beneficition. Thus futhe investigtions wee undetken by othe uthos nd it ws estblished tht tiboelectifiction ws ble to incese the effectiveness of pticle seption due to its bility to septe col pticles with close wok functions little diffeence in conductivities. A futhe limittion ws noted by ely eseches, nmely, tht thee ws limittion in the seption of pticles below sevel hunded micons using the coon technique (Higshiym nd Asno, 1998). This ws futhe investigted using the tiboelectosttic technique s well. Tiboelectosttic method The electicl seption using the tibochging method hs been shown to hve consideble potentil fo col peption in the fine size nges. The tiboelectic seption of col nd its tibochging chcteistics hve been investigted by mny eseches nd ll hve epoted successful seption of minel mtte (high sh foming pticles) fom col (Mukhejee et l., 1987; Nifiku et l., 1989; Bn et l., 1993, 1993b; Higshiym et l., 1998; Tigwell et l. 2003b; Dwi nd Ro, 2008; Dwi nd Ro, 2009). This method, howeve, hs not eched commecil sttus in the col industy s yet, s epoted by Howe et l. (1997), Dwi nd Ro (2007) nd Dwi nd Ro (2008). This electosttic method tkes plce in septo using cyclone, fluidized bed, octgonl oty chmbe, otting cone o chging pipe. The tibochging occus though the impct of pticles with othe pticles eithe by contct o fiction o with thid mteil, usully the wlls of contine o pipe. This is followed by the downwd feefll of the pticles though n electic field tht deflects the pticles ccoding to the mgnitude nd sign of thei chges (Gidspow et l., 1987; Msud et l., 1984; Finseth et l., 1993; Higshiym et l., 1998). The test conducted by Msud et l. (1984) using cyclone chge (Figue 1) illustted tht positively chged col pticles e deflected towds negtive electode nd the negtively chged pticles (usully minel-ich (shfoming) pticles) e deflected towds positive electode. The esult obtined indicted tht the col sh content ws educed fom 15.2 pe cent to 7.1 pe cent with clen col ecovey of 90 pe cent. This finding is suppoted by the investigtions conducted by Lockht (1984) nd Alfno et l. (1988) whee they found tht clen col pticles e genelly chged positively nd minel-ich o high-sh col pticles e chge negtively. Bsed on these esults nd obsevtions, futhe esech ws undetken to estblish the impct of vying opeting pmetes on efficiency of electosttic seption potentils 694 NOVEMBER 2010 VOLUME 110 The Jounl of The Southen Aficn Institute of Mining nd Metllugy

5 The potentil of electosttic seption in the upgding of South Aficn fine col of col. A coppe tibochge pipe opeting unde diffeent conditions such s vying velocity, diffeent concenttions (o lods) of col feed in i nd diffeent septo voltges wee investigted by Finseth et l. (1993). The uthos found tht the tiboelectosttic beneficition method using tibochging pipe (Figue 2), hd efficiently emoved high sh pticles theeby poducing clen col with 2.1 pe cent sh (eltive to the 24.4 pecent sh in the feed col) nd 0.6 pe cent sulphu (with 1.4 pe cent in the feed col) nd chieved cbon ecovey te of 38.8 pe cent. Dwi nd Ro (2006) lso investigted the effect of diffeent tibochges on high sh non-coking Indin theml col using pticle size nges of µm t constnt voltge of 15 kv nd tibochge peiod of 5 minutes. Coppe ws found to hve the best seption efficiency mong the tibochges tested nd it ws concluded tht this ws due to coppe s highe electicl conductivity. The esults obtined by these uthos on the high sh Indin col shows clen col poduct collected in the negtive bin with 18 pe cent sh eltive to 43 pe cent sh content in the feed col. The pllel hevy medi wshbility test conducted on the sme high sh col ws ble to educe the sh content only to 25 pe cent sh, with cbon ecovey yield of 65 pe cent. The emovl of pyitic sulphu fom finely gound col ws conducted by Gidspow et l. (1987) in n electosttic sieve conveyo. The esult obtined showed tht the pyitic sulphu content of 2.4 pe cent in the feed col ws educed to 0.86 pe cent fte five stge sieve conveyo. The eltively high te of efficiency ws ttibuted to the ginding of the col to -40 µm size which esulted in good libetion of the pyite minels fom the ognic col mtix nd hence ese in seption (Figue 3). The pecombustion clening of col by tiboelectic seption of minels ws lso exmined by Tigwell et l. (2003b). These esults indicted tht the tiboelectic seption of minels fom col is vible beneficition method with significnt potentil commecil ppliction. Cle eduction of both sulphu nd sh contents fo Pittsbugh No. 8 nd Illinois No. 6 col smples ws illustted by petogphic nd XRD nlyses undetken on the feed nd septed col smples. Fine ginding of the col smples yielded even clene col, with the Pittsbugh smples showing gete eduction fo both sulphu nd sh s comped to the Illinois feed nd clened col due to bette minel libetion. Similly, Lewowski (1993) studied the electosttic desulphuiztion of polish stem cols nd his esults confimed those of Tigwell et l. (2003b), i.e. tht the tiboelectosttic method of dy beneficition cn clely septe minels nd minel-ich pticles of col fom clen col pticles (Figue 4). Figue 2 Schemtic epesenttion of electosttic seption with tibo-chging pipe Finely gund col Scew feede Feed D.C. High Voltge Pefeted electode Clen col Pyite eniched Figue 3 Schemtic epesenttion of electosttic sieve conveyo (Gidspow et l. 1987) J o u n l P p e Cyclone chge +HV N 2 Gs + Feede E Flow mete Blowe Collecting in Figue 1 Schemtic epesenttion of electosttic cyclone chge fo col clening Figue 4 Tiboelectosttic (Dwi nd Ro, 2006) The Jounl of The Southen Aficn Institute of Mining nd Metllugy VOLUME 110 NOVEMBER

6 The potentil of electosttic seption in the upgding of South Aficn fine col Inculet et l. (1980) used fluidized bed tibochge fo beneficition tests on col. Thei epot indicted tht sh ws successfully educed in the poduct eltive to the feed col while still etining the sme cloific vlue s in the oiginl feed col. In ddition, the sh content obtined on the electostticlly ecoveed poduct ws compble to tht obtined when beneficiting the col smple using wet pocesses. Dwi nd Ro (2008) lso investigted the potentil of fluidized bed tibochge with intenl bffle system (FTB), this time fo the beneficition of non-coking col fom Hingul block of Tlche col field. The effect of pticle size on the seption potentil ws detemined fo two size fctions, -75 mm nd -1 mm. The esult showed eduction in sh fom pe cent in the feed col to 25 pe cent sh fo the -75 mm size fction, nd to 17 pe cent sh fo the -1 mm size fction, the ltte with 85 pe cent yield. It ws concluded tht non-libetion of minels fom col in the -75 mm size nge ws esponsible fo the highe sh content. Expeimentl esult obtined t 15 kv nd t 30 second tibochging times eveled tht it ws possible to chieve 15.6 pe cent sh clen col fom 25 pe cent feed col with 69 pe cent yield. A cylindicl fluidized bed tibchge with intenl bffles mde of coppe metl ws ecently designed nd used by Dwi nd Ro (2009). This ws used fo testing the beneficition potentil of Indin theml cols fom the Rmgundm mines. The uthos estblished tht col pticle size distibution, tibochging time, voltge, gs flow te nd esidence time of fluidiztion ll plyed ole in the seption of clen col fom its ssocited minels. These uthos epoted eduction in sh content fom 43 pe cent in the feed col to 18 pe cent in the septed poduct using -300 micon pticle sized mteil with 30 pe cent yield, t 10 Kv nd 60 second tibochging times. At highe yield of 67 pe cent, n sh content of 33 pe cent ws obtined. Conventionl wet wshbility studies conducted on this smple esulted in the poduction of clen col poduct with 25 pe cent sh nd yield of 65 pe cent. The seption efficiency fo both the tiboelectosttic method nd bench scle fuel oil gglometion technique ws investigted by Howe et l. (1997) nd the esults wee comped with ech othe. The bench scle tiboelectosttic septo ws found to povide moe efficient seption in compison to the bench scle fuel oil gglometion technique when testing the thee esten Kentucky nd two Illinois cols. Petogphic nlyses indicted tht the clen col fction ws eniched in vitinite nd vitinite-eniched micolithotypes while the tilings wee dominted by inetinites, liptinite nd minels. Futhe wok indicted tht simil cols evluted by this technique hve diffeent seption efficiencies due to vying moistue contents. The uthos then poposed tht moistue educes the degee of chging nd lowes the seption efficiency but it is not cle whethe the diest mteils hd the best chging popeties (Mzumde et l., 1995; Kwetus, 1994). Subsequent esech epoted by Mzumde et l. (1995) hs shown tht the esistivity of col pticles will depend getly on the moistue nd sh content of the feed col nd theefoe diffeent types of col e likely to hve diffeent esistivity. Bsed on the obsevtions bove, futhe studies wee undetken on how to modify o lte the sufce enegetic stuctue of fine col in ode to impove its seption efficiency. The incese in col seption efficiency fte chemicl petetment ws fist investigted by Zhou nd V-1 V-4 FTB Cyclone V-2 V-3 RM V-5 Septo A B Voltge souce VS +Ve Ve Chemicl Keithley electomete with 6532 scnne cd S-1 S-2S-3S-4 Nitogen cylinde S-5 S-6 Figue 5 Schemtic epesenttion of fluidized bed tiboelectosttic septo (Dwi nd Ro, 2006) 696 NOVEMBER 2010 VOLUME 110 The Jounl of The Southen Aficn Institute of Mining nd Metllugy

7 The potentil of electosttic seption in the upgding of South Aficn fine col Bown (1988). They utilized the vpous of diffeent ognic chemicls such s methyl cette, cetone, nd cetic cid unde dy nitogen tmosphee in the fluidized-bed tibochging medium in ode to impove the chging cpbility of the col. The sufce tetment pefomed on the col smples with pticle sizes between 75 nd 150 micons showed n impovement of seption to some degee. Tigwell et l. (2003) studied the influence of cetone, mmoni, nd sulphu dioxide vpous on the chge popeties of col exposed to these chemicl. They found beneficition to be slightly enhnced when using cetone whees mmoni ws found to be detimentl to beneficition. SO 2 ws found to be ineffective s conditioning gent. Dwi nd Ro (2009) ecently epoted ongoing esech in which fine col is being teted in the vpou of cidic nd /o bsic ognic solvents in the fluidized bed tibo-chge. The esults, howeve, will be pesented only in futue publictions. Mzumde et l. (1995) suggested tht thee e sevel fundmentl fctos ssocited with tibochging nd seption pocesses which hve been hindeing commecil implementtion to dte. This included (1) the effect of the col sufce composition on wok function nd (2) the composition of diffeent tibochges such s coppe, stinless steel, luminium nd nylon. These spects wee evluted by Tigwell nd Mzumde (2001) using X-y photoelecton spectoscopy nd UV photoelecton spectoscopy. The investigtion showed tht the wok functions fo smples vied considebly s function of the smples sufce composition, which in tun cn diffe due to ltetion in thei sufce composition s esult of exposue to diffeent envionments. This hs led to the undestnding tht electon tnsfe duing fictionl chging is sufcepopeties dependent the thn bulk-popeties nd tht the mgnitude of chge nd polity tnsfeed between two dissimil mteils ws contolled ptly by the sufce chemisty (Ruckdeschel nd Hunte, 1975; Tigwell, 2003; Tigwell et l., 2003; Shm et l., 2004; Mzumde et l., 2006). Peliminy esults of tiboelectosttic seption of South Aficn col On the bsis of the enhnced undestnding glened fom pevious eseches, peliminy tests using the tiboelectic septo wee undetken by Bd (2010 nd in pess) on viety of South Aficn cols. Figue 6 shows the oty tiboelectosttic septo (RTS) used fo the beneficition of South Aficn fine col, with the chcteistic fetues discussed by Bd et l. (2010). The RTS tests conducted by Bd et l. (2010) educed the sh content of the -177 micon col fctions fom 36 nd 31 pe cent in two high sh powe sttion feed smples to 14.9 pe cent nd 12.2 pe cent espectively, with coesponding combustible ecovey vlues of 10.7 pe cent nd 8.9 pe cent. Totl sulphu contents wee educed fom 2.1 pe cent to 0.9 pe cent nd fom 2.8 pe cent to 0.4 pe cent, with coesponding combustible ecovey vlues of 5.7 pe cent nd 8.9 pe cent, espectively. Bd epoted futhe investigtion using two-stge seption pocess on the -177 µm size fction. This indicted tht the RTS educed feed col with 30 pe cent sh to clen poduct of pe cent nd pe cent sh espectively, t combustible ecovey of 9.83 pe cent nd pe cent. The cloific vlue fo the feed col ws incesed fom MJ/Kg to MJ/Kg with combustible ecovey of bout 10 pe cent fte the second stge of seption. The single stge seption lso poduced clen col poduct with 25.7 MJ/Kg, pe cent sh nd pe cent combustible ecovey. A simil seption pefomnce with nothe high sh powe sttion feed col chieved col poduct of ppoximtely 17 pe cent sh with combustible ecovey of 50 pe cent when the seption voltge ws t 20 KV. Bd et l. (2010) then exmined the effect of Co-flow on two sem cols, the Numbe 2 nd 4 Sems in the Witbnk Colfield. The effect ws evluted on the bsis of gde (sh content) nd ecovey of the col poducts geneted. The effect of co-flow te ws ssessed in ode to mximize col clening. Co-flow, lso known s the flow stightening pocess, is povided fo sweeping wy the pticles dwn to the sufce of electodes nd fo educing the tubulent flow by foming smooth co-flow of gs pllel to the feed stem upon enteing the seption zone. The iflow within the seption zone is expected to be lmin so tht the chged pticles e only deflected by the ction of the electic field which is of compble stength to the dg foce. The test on No. 2 nd No. 4 sem cols wee pefomed t constnt injection velocity of 1.9 m/s nd vied outlet velocity of 1100 ft/min, 1300 ft/min nd 1500 ft/min. The effect of co-flow speeds of 2.5 m/s, 3.0 m/s nd 3.5 m/s fo No. 2 sem col e pesented in Figue 7. Vcuum 1. Octogonl oty oto Thin smple distibuto 4. Pticle seption zone 5. Splitte Cyclone Vibtoy feede 2. Cylindicl chging chmbe 3. Vible voltge Co-flow Vible voltge Poduct bins Figue 6 Schemtic epesenttion of n octgonl oty tiboelectosttic septo (Bd et l. 2010) J o u n l P p e The Jounl of The Southen Aficn Institute of Mining nd Metllugy VOLUME 110 NOVEMBER

8 The potentil of electosttic seption in the upgding of South Aficn fine col The highest gde poduct fom No. 2 Sem ws obtined t the lowest co-flow velocity of 2.5 m/s, with poduct sh of 8.9 pe cent nd 9.6 pe cent yield fom feed col of 30.4 Cumultive yield % 2.5 m/sec 3.5 m/sec Cumultive sh % Figue 7 Effect of Co-flow on No. 2 sem col t constnt i velocity: 1.9 m/s; chging nd septing voltge: 0 KV nd 12.5 KV; nd diffeent outlet velocity of 1100 ft/min, 1300 ft/min nd 1500 ft/min Cumultive yield % Ash ejection % m/sec 3.5 m/sec 3.0 m/sec 3.0 m/sec Ash ejection % Cumultive sh % Figue 8 Effect of Co-flow on No. 4 sem col t constnt i velocity: 1.9 m/s; chging nd septing voltge: 0 KV nd 12.5 KV; nd diffeent outlet velocity of 1100 ft/min, 1300 ft/min nd 1500 ft/min pe cent sh. At 3.5 m/s co-flow velocity, col poduct with 9.41 pe cent sh ws obtined unde the sme two stge test. The sme tend ws lso obseved fo No. 4 sem col s illustted in Figue 8 whee the highest gde col poduct ws obtined t 2.5 m/s co-flow velocity. At 2.5 m/s co-flow velocity fo the two cols pesented, the esults show tht the highest qulity col poducts wee obtined t 1100 ft/min outlet velocity. This ws ssumed to be the esult of decese in tubulent flow cused by the smooth stem of i within the seption zone s the outlet velocity deceses. A simil esult ws obseved by To et l. (2009), whee n incese in co-flow velocity unfvoubly ffected the seption cpcity of the cylindicl oty septo. In tems of qulittive diffeences between feed cols nd finl poduct fte tiboelectic beneficition, Bd et l. (2010, in pess) undetook XRD nlyses on the smples unde investigtion. The diffctogms in Figue 9 to 12 illustte the X-y diffction pttens fo five South Aficn cols nd thei poducts. Anlysis evels tht the South Aficn feed cols consist mostly of cystlline minels such s qutz nd kolinite with smooth hump epesenting the ognic fction. The pek intensities of qutz nd kolinite in the feed cols e vey stong eltive to the considebly lowe peks in the clen poducts fom the single pss nd second pss. This eduction in pek intensities is chcteistic of the eduction in minel mtte content fte beneficition, which is typicl in pocessing technology of high sh cols of the southen hemisphee. In contst, lowe ognic hump djcent to the high minel mtte peks in the feed cols followed by much lge hump in the clened poduct coesponds to the highe popotion of ognic mtte nd lowe minel mtte contents in the poducts col, s my be seen in ll the cols tested. The impct of tiboelectosttic seption on commecil pmetes such s cloific vlue, totl sulphu nd sh content is illustted in Tbles I nd II. Fom these it is 800 Kolinite Kolinite Qutz 700 Pyite 600 Lin (Counts) Thet - Scle Figue 9 X y diffction ptten K feed (below), clened single pss poduct (middle) nd clened second pss col poduct (bove) fte tiboseption 698 NOVEMBER 2010 VOLUME 110 The Jounl of The Southen Aficn Institute of Mining nd Metllugy

9 The potentil of electosttic seption in the upgding of South Aficn fine col Kolinite Kolinite Qutz Pyite J o u n l Lin (Counts) Thet - Scle P p e Figue 10 X y diffction ptten M feed (below), clened single pss poduct (middle) nd clened second pss col poduct (bove) fte tiboseption Kolinite Lin (Counts) Kolinite Qutz Pyite Thet - Scle Figue 11 X y diffction ptten of No. 2 sem feed col (below), clened single pss poduct (middle) nd clened second pss poduct (bove) fte tiboseption 400 Kolinite Kolinite Qutz Pyite 300 Lin (Counts) Thet - Scle Figue 12 X y diffction ptten of No. 4 sem feed col (below), clened single pss poduct (middle), nd clened second pss poduct (bove) fte tiboseption The Jounl of The Southen Aficn Institute of Mining nd Metllugy VOLUME 110 NOVEMBER

10 The potentil of electosttic seption in the upgding of South Aficn fine col Tble I Second stge tiboelectosttic test esults Col (-177 µm) Feed sh content (%) Cloific vlue (MJ/Kg) Totl sulphu Second pss (cum. sh) % Cum. Wt % Cloific vlue (MJ/Kg) Totl sulphu L No. 2 sem No. 4 sem M K K Tble II Single stge tiboelectosttic test esults Col (-177 µm) Feed sh content (%) Cloific vlue (MJ/Kg) Totl sulphu Second pss (cum. sh) % Cum. Wt % Cloific vlue (MJ/Kg) Totl sulphu L No. 2 sem No. 4 sem M K K possible to obseve the pocess optimum conditions yielding mximum sh eduction nd poduct ecovey, nd the fctos esponsible fo effective seption using dt fom both single nd two stge pss esults. Fo exmple, in Tble II, col L feed hs n sh content of 31.3% which is educed to 14.6% fte single stge pss. The effectively inceses the cloic vlue fom 21.3 MJ/Kg to 26.8 MJ/Kg nd educes the sulphu content fom 1.7% to 0.5%. The peliminy dt obtined fo both seption stges indicte tht single stge tiboelectic seption is effective in poducing clened cols, but clene, highe gde with lowe totl sulphu content poducts e obtinble unde two stges of seption but t the expense of col cbon ecovey. Conclusions It is evident fom this eview tht col, nd moe specificlly South Aficn col, cn be beneficited though the ppliction of dy clening pocesses. The ppliction of tiboelectosttic seption s n ltentive ppoch to wet beneficition pocesses hs been shown to be pomising step in elizing this gol, nd moe specificlly fo the upgding of fine col. Futhemoe, it does not hve the dwbcks of wet clening, subsequent dying, nd the pocessing of ssocited queous wste. The impotnce of this esech, in tems of its futue ppliction, is tht it could be of potentil benefit to numbe of industies. Poviding lowe sh col could incese the efficiency of ll pulveized fuel fed kilns in the cement industy nd cetin opetions in the pyometllugicl field, such s ion nd steelmking. It could led to highe efficiencies in col utiliztion by educing the unbuned cbon content obtined in fly sh. This in tun would led to low cbon sh poducts which hve high vlue s minel dmixtues fo cement in the mnufctuing of concete. Moe so, the ppliction of RTS to beneficite phosphte fom its host ock concentte could be of benefit to the South Aficn phosphte industy. Such pocess developments e likely to become incesingly impotnt in county such s South Afic due to the fct tht wte is n extemely limited commodity especilly in loctions whee futue mining will tke plce nd becuse millions of tons of ult fine col e being poduced nd stoed in sluy ponds o discded in bndoned mines. Given tht such fine col mteil is compised of minels tht e lgely libeted fom thei host col pticles nd tht significnt popotion of clen col pticles in this fine size nge is theefoe vilble (subject only to successful seption), beneficition of this mteil could led to the poduction of high gde, low sh poducts with potentilly high vlue. Mkets fo such mteils could nge fom feed to powe sttions, cement kilns nd blst funces using pulveized col injection nd fo the eduction of chomite o mngnese oe in the feolloy industy. Cuent esech is lso undewy to utilize ult clen fine col s souce fo nnotechnology. Pehps the getest ppliction of this dy fine col beneficition pocess would be the significnt eduction of Fe-S pyitic minels nd the ssocited tce elements including mecuy nd senic. If successful, this could led to the potentil eduction in the need fo flue gs desulphuiztion plnts nd ssocited technologies in utiliztion of col in futue. Fo these esons, futhe esech is equied to upgde the oty tiboelectosttic technique fo specific ppliction to South (nd southen) Aficn col. In ode to chieve this, viety of pmetic studies is equied in ode to optimize the conditions suitble fo these cols nd to obtin dt fo vlidting this pocess fo scling-up puposes nd fo evluting it eltive to conventionl wet fine col beneficition pocesses. In ddition, the sufce electodes used in this esech would be eplced with gid electodes to mitigte the effect of pticle build-up within the septing zone nd incese the seption efficiency nd ecovey t highe seption voltge. 700 NOVEMBER 2010 VOLUME 110 The Jounl of The Southen Aficn Institute of Mining nd Metllugy

11 The potentil of electosttic seption in the upgding of South Aficn fine col Refeences 1. ALFANO, G., CARBINI, P., CICCU, R., GHIANI, R., nd ZUCCA, A. Pogess in Tiboelectic Seption of Minels, E. Fossbeg (ed.), Poceedings of the XVI IMPC, Stockholm, Sweden. Amstedm, pp BADA, S.O., TAO, D., HONAKER, R.Q., FALCON, L.M., nd FALCON, R.M.S. A Study of Roty Tibo-Electosttic Seption of South Aficn Fine Col. Poceedings of the XVI Intentionl Col Peption Congess, Lexington, Kentucky, USA, pp BADA, S.O., TAO, D., HONAKER, R.Q., FALCON, L.M., nd FALCON, R.M.S. Pmetic study of electosttic seption of South Aficn fine col. Mining Science nd Technology, pp (Aticle in pess). 4. BAN, H., SCHAEFER, J., nd STENCEL, J. Size nd velocity effects on col pticle tiboelectifiction nd seption efficiency. Poceedings of Intentionl Pittsbugh Col Confeence, Pittsbugh. PA, pp BAN, H., YANG, J., SCHAEFER, J., SAITO, K., nd STENCEL, J. Mesuement of chge nd chge distibution on col nd minel mtte duing electosttic dy col clening. Poceedings of Intentionl Confeence on Col Science. Bnf, AB, Cnd, 1, 1993b. pp GIDASPOW, D., GUPTA, R., MUKHERJEE, A., nd WASAN, D. Seption of Pyites fom Illinois Cols Using Electo-fluidized Beds nd Electosttic Sieve Conveyos. Pocessing nd Utiliztion of High Sulfu Cols II, Elsevie HAYAKAWA, S., SAKAGUCHI, E., nd YAMASHITA, R. Conditions of Suited fo seption of te stems by electosttic septo. Jounl of Institution of Agicultue Mchine, vol. 47, pp HIGASHIYAMA, Y. nd ASANO, K. Recent pogess in electosttic seption technology. Pticulte science nd technology, vol. 16, no. 1, pp HOWER, J.C., HANG, B., SCHAEFER, J.L., nd STENCEL, J.M. Mcel/micolithotype ptitioning though tiboelectosttic dy col clening. Intentionl Jounl of Col Geology, vol. 34, pp INCULET, I.I., QUINGLEY, R.M., BERGOUGNOU, M.A., nd BROWN, J.D. Electosttic beneficition of ht ceek col in the fluidized stte. CIM Bulletin, vol. 73, pp INCULET, I.I. Electosttic Minel Seption, Englnd, UK: Resech Study Pess Ltd, pp. J o u n l P p e 6. BISWAL, S.K., DAS, S.P., REDDY, P.S.R., nd MISRA, V.N. Pospect of beneficition of high sh non-coking cols. Engineeing Tends in Minel Pocessing nd Extctive Metllugy, New Delhi, Indi, pp BUDGE, G., BROUGH, J., KNIGHT, J., nd BAKER PROCESS. Review of the Woldwide Sttus of Col Peption Technology, Repot No. Col R199 DTI/Pub URN00/ pp., BUTCHER, D.A. nd ROWSON, N.A. Electosttic seption of pyite fom col. Mgnetic nd Electicl Seption, vol. 6, pp CHENG, Q. nd YANG, Y.F. Development of dy beneficition of col in Chin. Jounl of Col Peption, vol. 23, pp CHEN, Q. nd WEI, L. Col dy beneficition technology in Chin: The stteof the-t Chin. Pticuology, vol. 1, no. 2, pp CHOUNG, J., MAK, C., nd XU, Z. Fine Col Beneficition using n Ai Dense Medium Fluidized Bed. Intentionl Jounl of Col Peption nd utiliztion, vol. 26, no. 1, pp DIEUDONNE, V., HEWITT, S., nd WYK, D.N. Jigging the South-Afic cols new chllenge. Mintek, Rndbug, South Afic, DWARI, R.K. nd RAO, H.K. Tibo-electosttic behviou of high sh non coking Indin theml col. Intentionl Jounl of Minel Pocess, vol. 81, pp DWARI, R.K. nd RAO, H.K. Dy Beneficition of col A eview. Minel Pocessing nd Extctive Metllugy, vol. 28, pp DWARI, R.K. nd RAO, H.K. Chcteising Electon Tnsfe Mechnism in Tibo Electifiction of pyite though Contct Angle Mesuements. The Open Minel Pocessing Jounl, vol. 1, pp DWARI, R.K. nd RAO, H.K. Non-coking col peption by novel tiboelectosttic method. Fuel, (Aticle in pess), DWARI, R.K. nd RAO, H.K. Fine col peption using novel tibo-electosttic septo. Minels Engineeing, vol. 22, no. 2, pp DYRENFORTH, W.P. Electosttic Seption, Minel Pocessing Design. AIME. Mulle nd Bhppu (eds.), 2nd edn, pp FINSETH, D., NEWBY, T., nd ELSTRODT, R. Dy electosttic seption of fine col. Pocessing nd Utiliztion of High Sulfu Cols, V.B.K. Pekh, nd J.G. Goups, (eds.), Amstedm, Elsevie, pp GIDASPOW, D. Seption of pyites fom Illinois cols using electofludized beds nd electosttic sieve conveyos. Poceedings of the Second Intentionl Confeence on the Pocessing nd Utiliztion of High Sulfu Cols II, Cbondle, IL KELLY, E.G. nd SPOTTISWOOD, D.J. The theoy of electosttic septions: A eview. Pt I. Fundmentls. Minels Engineeing, vol. 2, no. 1, pp KNOLL, F.S. nd TAYLOR, J.B. Advnces in Electosttic Seption. SME Pepint, pp KWETUS, B.A. Contct electifiction of col nd minels. Jounl of Electosttics, vol. 32, pp LEWOWSKI, T. Electosttic desulphuistion of Polish stem cols. Col Peption, vol. 13, pp LOCKHART, N.C. Dy Beneficition of Col- Review Ppe. Powde Technology, vol. 40, pp MASUDA, S., TARAGUCHI, M., TAKASHASHI, T., nd HAGA, K. Electosttic Beneficition of Col Using Cyclone-Tibochge. IEEE Tnsctions of Industy Applictions, vol. 1A MAZUMDER, M.K., TENNAL, K.B. nd LINDQUIST, D.A. Tiboelectic seption of col fom minel impuities. Poceedings of the Annul Meeting of the Electosttic Society of Ameic, Mogn Hill, CA, Lplcin, pp MAZUMDER, M.K., SIMS, R.A., BIRIS, A.S., SRIRAMA, P.K., SAINI, D., YURTERI, C.U., TRIGWELL, S. DE, S., nd SHARMA, R. Twenty-fist centuy esech needs in electosttic pocesses pplied to industy nd medicine. Chemicl Engineeing Science, vol. 61, pp MBENDI South Afic Col Mining Oveview (Cited, 22 Febuy 2008). 36. MOORE, A.D. Electosttic nd its ppliction. Wisley Publishe, New Yok, MUKAI, S., ISHIKAWA, T., SHIDA, Y., nd WAKAMATSU, T. Study on the Electosttic Concenttion of low sh col in coon dischge field. Society of Mining Enginees AIME Tnsction, , 205 pp. 38. MUKHERJEE, A., GIDASPOW, D., nd WASAN, D.T. Sufce chge of Illinois col nd pyites fo dy electosttic clening. Ameicn Chemicl Society, Division of Fuel Chemisty, vol. 32, no. 1, pp NIFUKU, M. Sttic electifiction phenomen in pneumtic tnspottion of col. Jounl of Electosttics, vol. 23, pp OLOFINSKII, N.F. Electic coon seption of col fines nd cetin minels. Moscow. Tnslted by Isel Pogm fo Scientific Tnsltions, The Jounl of The Southen Aficn Institute of Mining nd Metllugy VOLUME 110 NOVEMBER

12 The potentil of electosttic seption in the upgding of South Aficn fine col 41. RUCKDESCHEL, F.R. nd HUNTER, L.P. Contct electifiction between insultos: Phenomenologicl spects. Jounl of Applied Physics, vol. 46, no. 10, pp TRIGWELL, S. Coeltion between sufce stuctue nd tibochging of powdes. Doctol dissettion, Univesity of Aknss t Little Rock, USA, SAMUILA, A., URS, A., IUGA, A., MORAR, R., AMAN, F., nd DASCALESCU, L. 49. TRIGWELL, S., GRABLE, N., YURTERI, C.U., SHARMA, R., nd MAZUMDER, M.K. Optimiztion of Coon Electode Position in Roll-Type Electosttic Septos. IEEE Tnsctions on Industy Applictions, vol. 4, pp SHARMA, R., TRIGWELL, S., SIMS, R.A., nd MAZUMDER, M.K. Modifiction of electosttic popeties of polyme powdes using tmospheic plsm ecto. Mittl, K.L. (ed.), Polyme Sufce Modifiction: Relevnce to Adhesion, vol. 3, VSP, AH Zeist, the Nethelnds, pp SOONG, Y., SCHOFFSTALL, M.R., nd LINK, T.A. Tiboelectosttic beneficition of fly sh. Fuel, vol. 80, pp TAO, D., MAO-MING, F., nd JIANG, X. Dy col fly sh clening using oty tiboelectosttic septo. Mining Science nd Technology vol. 19, pp TAYLOR, J.B. Seption of gnul mteils. Confeence ecod IEE 47. TRIGWELL, S. nd MAZUMDER, K.M. Tibochging in electosttic beneficition of cols: Effects of sufce composition on wok function s mesued by X-y photoelecton spectoscopy nd ultviolet photoelecton spectoscopy in i. Jounl of Vcuum Science nd Technology, vol. A, 19, no. 4, pp NOVEMBER TRIGWELL, S., TENNAL, K.B., MAZUMDER, M.K., nd LINDQUIST, D.A. Pecombustion clening of col by tiboelectic seption of minels. Pticulte Science nd Technology, 2003b. vol. 21, no. 4, pp WEITKÄMPER, L. nd WOTRUBA, H. Recent development in the dy clening of col. Poceedings of Minel pocessing Technology, Bhubnesw, Indi, Allied, pp WOROBIEC, A., STEFANIAK, E.A., POTGIETER-VERMAAK, S., SAWLOWICZ, Z., SPOLNIKA, Z., nd VAN GRIEKEN, R. Chcteiztion of concenttes of hevy minel snds by mico-rmn spectomety nd CC-SEM/EDX with HCA. Applied Geochemisty, vol. 22, pp YONGZHI, L. Electosttic seption study nd pctice of fine pticles Annul Meeting, vol. 23, pp Effects of sufce popeties on the tibochging chcteistics of polyme powde s pplied to industil pocesses. IEEE Tnsctions on Industy Applictions, vol. 39, no. 1, pp VOLUME 110 utile. Poceeding, 1st Intentionl Confeence. Moden Pocess Minelogy nd Minel Pocessing, Beijing, pp ZHOU, G. nd BROWN, D. Col sufce conditioning fo electosttic seption. Cndin Jounl of Chemicl Engineeing, vol. 66, pp The Jounl of The Southen Aficn Institute of Mining nd Metllugy