Innovations in precious metal recovery

Transcription

1 Innovtion in peciou metl ecovey by C. vn Tonde* nd M.J. Sole Ppe witten on poject wok cied out in ptil fulfilment of B Tech (Engineeing Metllugy) degee J o u n l Synopi Thi invetigtion elte to multi-pupoe electolytic ytem. It pimy pupoe i to electowin gold fom high o low concenttion gold cynide olution nd/o fom gold ludge, nd to convet the ecoveed gold into gold (lloy) electofom o electode t the gold mine itelf. Thee opetion e cied out equentilly nd in itu in the me electolytic cell. Electoefining of the gold ecoveed my lo be done in the cell. The ytem pplie to ilve well, nd my be dptble to be nd pltinum goup metl. It could lo be ued in envionmentl ppliction, to emove undeible metl peent in queou olution t vey low concenttion. The wok to be dicued fom pt of ecently filed ptent ppliction. Subequent nd futue development of the ytem e biefly outlined. Thi ppe, in pt o in full, h been publihed by the Metllugicl Mine Mnge Aocition (MMMA), with pemiion fom the utho. Intoduction In lge-cle gold mining opetion the finely cuhed oe i leched in odium cynide olution to yield lech olution contining ~6 ppm gold. Thi olution i then teted with ctivted cbon to dob the gold. The loded cbon i ceened off nd the dobed gold i then eluted with hot cutic olution to yield gold elute contining ~600 ppm gold. The cbon i heted peiodiclly to egenete it fo eue lte. The elute then pe though electowinning cell whee the gold i depoited on to cthode of knitted tinle teel wool. The loded cthode e emoved fom the electowinning cell nd mnully whed uing high-peue wte jet to dilodge gold ludge. Thi i filteed, fte which the filte cke i melted nd ct into impue* gold b. Thee b e ent to efiney, genelly t emote loction, fo futhe puifiction. In ecent time the *The min impuity in South Aficn gold oe i ilve, with mll mount of coppe lo peent. electowinning h lo been cied out in oclled ludge ecto 1, which llow the electowinning nd dilodgment tep to be cied out in itu nd utomticlly. The poduct emin gold ludge tht i filteed nd melted befoe. Thee i thu n incentive, not only to convet the elute nd/o the ludge to vlue-dded poduct, diectly t the mine itelf, but lo to exploe the poibilitie of eliminting the cbon ctivtion tep. If degee of gold efining could be chieved t the me time, thi would be n dded bonu. In mll-cle gold mining opetion the poduct i often gold gvity concentte, which my be teted with mecuy to ecove the gold uing mlgmtion nd mecuy voltiliztion. In ny event, the vlue of the poduct tht cn be old i genelly vey low. Agin, thee i n incentive to dd vlue to the poduct nd poibly to efine it well. The im of the peent invetigtion w theefoe to develop pptu nd pocedue to ty to meet the equiement outlined bove. Ptent2,3 hve been gnted coveing the wok epoted hee. Expeimentl Equipment A flow digm nd the genel ngement of the equipment ued e hown in Figue 1. The pimy electowinning (EW) tnk nd the electowinning/electofoming (EWEF) cell, togethe with the electomgnetic pump nd elevnt pipe-wok compie the pimy electowinning cicuit fo gold elute olution fom two South Aficn gold mine. Thee * Univeity of Johnnebug Zenzele Technology Demonttion Cente, Rndbug, South Afic. The South Aficn Intitute of Mining nd Metllugy, SA ISSN X/ Ppe eceived Feb. 2006; evied ppe eceived M P p e The Jounl of The South Aficn Intitute of Mining nd Metllugy VOLUME 106 NON-REFEREED PAPER APRIL

2 Innovtion in peciou metl ecovey HEATER PRIMARY EW TANK POLISHED ST/STEEL CYLINDER ST/STEEL PIPE RUBBER SCRAPER EF SOLN. TANK HEATER PRIMARY EW CELL BEARING VALVE EWEF CELL PUMP TO DRAINS Figue 1 Flow digm nd genel ngement of equipment ued to electowin nd electofom gold metl fom gold elute nd gold ludge elute typiclly contin >600 ppm gold. Inide the pimy tnk i locted one o moe pimy cylindicl EW cell (only one i hown), which plug into ecepto dichge cone(), hown in Figue 1. Viou deign of intechngeble EW cell hve been invetigted, but fo thi invetigtion the implet one w choen, the min conidetion being to genete gold ludge eily nd to tnfe it to the EWEF cell. A themotticlly contolled hete povide fo tempetue contol of the ciculting olution. The pimy EW cell eentilly conit of two coxil tinle teel cylinde, whee the oute one i the node nd the polihed inne one i the cthode. The ltte my be otted peiodiclly o tht electodepoited gold pticle, which e looely dheent to the cthode ufce, e cped off by men of fixed ubbe cpe, nd dop downwd unde gvity. The ction of elute cicultion cue them to be futhe tnpoted down into the EWEF cell. Hee they e cught up on the high ufce e (HSA) cthode of tht cell, which ct filte (ee Figue 2 nd 3). Thu, the gold pticle e in electicl contct with tht electode. Since econdy electowinning my lo be cied out imultneouly in tht cell, the gold fom both ouce i effectively combined t the cthode. Howeve, initilly the EWEF cell w ued on it own to electowin gold fom oiginl nd diluted elute olution. Thee olution wee contined in the mlle electofoming (EF) olution tnk (pio to filling the tnk with the electofoming olution equied fo the electofoming tet). By ppopite vlve mnipultion, the olution could be eciculted though tht ytem uing the me mgnetic dive pump befoe (ee Figue 1). A themotticlly contolled hete enble the tempetue of the ciculting olution to be kept t the equied tempetue. The EWEF cell i hown in moe detil in Figue 2. It i contucted of polypopylene nd fitted with lge inlet pot fo gold elute nd/o ludge, nd mlle one fo gold elute (o electofoming) olution. It contin thee electode. The xil one A i polihed, tpeed, tinle teel o titnium od, which ct mndel duing electofoming opetion. It i fitted with jck-cew, hown, o tht fte emovl fom the cell, the gold electofom my be emoved mechniclly. Clely, othe mndel deign nd mteil could lo be ued. Duing electowinning opetion mndel A my be mde nodic o left unchged. Suounding the mndel i cylindicl coxil HSA electode B. A hown in Figue 3, thi compie poou polypopylene tube ound which i wound, in the fom of Swi oll, combintion of oxide-coted titnium o tinle teel wie-cloth nd gphite felt. Two oxide-coted titnium o tinle teel tip povide the cuent connection, nd cble tie eve to hold the ytem tightly togethe. Duing electowinning thi electode i mde cthodic nd duing electofoming (o electoplting) it i mde nodic. Suounding electode A nd B i thid 298 APRIL 2006 VOLUME 106 NON-REFEREED PAPER The Jounl of The South Aficn Intitute of Mining nd Metllugy

3 Innovtion in peciou metl ecovey Ti MANDREL O-RING SEALS POLYPRO COVER PLATE POLYPRO TOP PLATE POLYPRO CELL EF SOLN INLET POROUS POLYPRO TUBE Ti WIRE CLOTH/GRAPHITE FELT SWISS ROLL POLYPRO BOTTOM PLATE A B C JACK SCREWS ST/STEEL DISC. Ti THREADED RODS POLYPRO PLUG ST/STEEL INSERT WELD EW SOLN./SLUDGE INLET POLISHED ST/STEEL CONE GOLD ELECTROFORM EXPANDED Ti MESH WELD J o u n l P p e Ti STRIP CONNECTORS RECIRCULATION/DRAIN OUTLET Figue 2 Schemtic digm of the EWEF Mk I Cell ued to electowin nd electofom gold/ilve lloy in itu CABLE TIES GRAPHITE FELT POROUS POLYPRO TUBE COATED Ti WIRE CLOTH Ti CONNECTORS Figue 3 Detil co-ection of the high ufce e (HSA) electode ued in the EWEF Mk I cell electode C, which ct n node duing electowinning nd i unchged duing electofoming opetion. It i coxil cylinde of expnded oxide-coted titnium o tinle teel meh. A indicted bove, the EF tnk my be ued fo both elute olution duing electowinning, o fo n electofoming olution duing electofoming. It i dined, of coue between thee opetion. The electofoming olution ued contined, typiclly, potium cynide (5 50g/l), potium hydoxide (5 20 g/l), di-potium hydogen phophte (5 20 g/l), nd ometime bightening gent. A 10 volt, 50 mp DC powe upply w ued duing electowinning, nd 30 volt, 3 mp (ve.) pule powe upply fo the electofoming opetion. Pocedue Undiluted gold elute/ludge The (200 l) pimy EW tnk nd the (2, 5 l) EWEF cell wee filled with gold elute olution, which w then eciculted though the ytem. The pimy hete w witched on nd the olution tempetue w contolled t the deied The Jounl of The South Aficn Intitute of Mining nd Metllugy VOLUME 106 NON-REFEREED PAPER APRIL

4 Innovtion in peciou metl ecovey tempetue. DC powe w upplied to both the pimy EW cell nd to the econdy EWEF cell, t cthode cuent denitie of typiclly mp/que decimete, fo peiod of up to ix hou. Duing thi time olution mple wee tken function of time nd thee wee ubequently nlyed fo gold content. At the end of the electowinning opetion, the cuent nd hete wee witched off, nd, with the olution till being ciculted, the pimy EW cthode w mnully otted, uch tht the gold dheing to it ufce w cped off by the ttiony ubbe cpe. The gold ludge poduced w then whed downwd to be cught up on the oute ufce of the HSA electode. The EWEF cell w iolted nd the ben olution in it w dined nd etuned to the pimy EW tnk. The EF tnk nd the EWEF cell wee then filled with electofoming olution. Uing the me pump, thi olution could be eciculted nd heted fo thi econd-tge electofoming opetion, in the me mnne decibed bove. Solution cicultion w continued t tempetue fo while, to llow ome of the finely divided gold on the HSA electode to diolve in the high cynide olution. (In ome ce gold olution w dded to bing the gold content of the ovell electofoming olution up to bout 0.5 g/l). The DC o puled cuent w then witched on, with electode B now nodic, electode C unchged, nd the centl mndel A cthodic. Electofoming w continued fo up to thee dy, tking olution mple fo nlyi, befoe. At uch low gold concenttion electofoming kinetic i neceily low, but, will be dicued lte, it i believed tht thi poblem cn be ovecome in lge-cle (continuou) opetion. At the concluion of electofoming the EWEF cell w dined, the mndel A w emoved fom the cell, nd the gold (lloy) electofom epted fom the mndel. The metllugicl chcteitic of thi electofom vied, depending upon the electodepoition pmete ued, but integl tpeed cylinde o thimble could be poduced unde optimum condition. Oiginl nd diluted elute olution Impotnt objective in thi ce wee to etblih whethe o not vey dilute gold olution, uch thoe obtining in gold lech olution (i.e. pio to the ctivted cbon gold concenttion tep) could, in pinciple, be teted diectly, uing EWEF cell of thi type, well to compe the kinetic of gold extction unde diffeent condition. Elute olution, t viou dilution, wee teted in the mlle volume econdy ytem lone, uing pocedue nlogou to thoe dicued bove. Both electowinning nd electofoming of gold wee found to be poible in the EWEF Mk I cell. Gold electoefining Viou ppoche wee tied to ee whethe the ilve, the min impuity, could lo be emoved in itu, o tht the min end poduct, gold metl, would be eltively pue. The implet nd bet ppoch w to plte out the ilve fit, uing diect cuent nd vey low cthode cuent denity. In cynide olution ilve (nd coppe), hving lowe electodepoition potentil thn gold, e the moe noble metl nd will plte out pefeentilly. Thu, thee impuitie could be depoited on the mndel A initilly. When thi poce w complete, the mndel could be emoved fom the cell nd the ilve emoved fom it, befoe eplcing it in the cell. The electodepoition pmete would then be optimized fo gold electofoming. An ltentive ppoch would be fit to electoplte the gold lloy on to titnium od, which would lte be ued n node in conventionl gold (chloide) electoefining cell. Reult nd dicuion Electowinning of gold elute The eult of uing the EWEF Mk I cell to extct gold fom viou gold elute fom two South Aficn gold mine (A nd B) e given in Tble I. The volume of olution ued in ech un w 18 lite. Thee eult e lo plotted gphiclly in Figue 4 nd 5. Six ucceive un wee cied out, the fit fou (A) fom elute olution fom gold mine A, nd the lt two (B) fom elute olution fom gold mine B. Thu, the initil gold concenttion vied fom c. 100 ppm to c. 900 ppm. Viou othe pmete wee vied, including tempetue, flow te, nd the cthode cuent denity (expeed in tem of the geometic e of the HSA cthode, which w c. 5 dm2.) Refeing to Tble I nd Figue 4, it i evident tht in ll ce gold extction i vey effective, the eidul gold concenttion being educed to le thn 1 ppm, i.e. gold extction of >99%, in time nging fom 1.5 to 4 hou. In Figue 5 the logithm of the eidul gold concenttion i plotted function of time. It i cle tht in the egion down to bout 1 ppm gold line eltionhip pplie. The time equied to ech thi vlue of gold concenttion unde the diffeent condition e edily defined by the inteection of the gph with the bci. Some othe tend wee obeved: comping un 1 nd 2, highe opetionl tempetue impoved the kinetic of gold extction nd lo ment lowe voltge equiement comping un 3 nd 4, highe cthode cuent denity impoved the kinetic of gold extction, but with highe voltge equiement, lthough the lowe flow te nd tempetue of un 4 would lo hve hd ome effect comping un 2,6,nd 5, it i evident tht t the me tempetue (c. 44 C), flow-te (32 l/min) nd cthode cuent denity (2A/dm2), the time to educe the gold concenttion to c. 1 ppm gold e fily imil, iepective of the initil gold concenttion in ome ce (Run 4 nd 5) vey long extction time eulted in mll mount of gold going bck into olution it my lo be noted tht the lope of the gph in Figue 5 e dependent upon the kinetic; the teepe the gdient, the fte the kinetic. 300 APRIL 2006 VOLUME 106 NON-REFEREED PAPER The Jounl of The South Aficn Intitute of Mining nd Metllugy

5 Innovtion in peciou metl ecovey Tble I Gold extction fom gold elute fom two South Aficn gold mine uing the EWEF Mk I cell Run Elped time (min) Reidul gold (ppm) Ave. temp. deg. C Voltge (volt) Cuent denity (A/dm2) Flow Rte (l/min) 1 A A A A B B <0.01 J o u n l P p e RESIDUAL GOLD CONCENTRATION (PPM) (0/895) RUN 5 : 45 C. 2A/dm2, 321/min RUN 4 : 34 C. 2A/dm2, 161/min RUN 3 : 43 C. 4A/dm2, 321/min RUN 6 : 45 C. 2A/dm2, 321/min RUN 2 : 43 C. 2A/dm2, 321/min RUN 1 : 21 C. 2A/dm2, 321/min ELAPSED TIME (MINUTES) Figue 4 Gph howing gold extction fom viou elute olution function of time, uing the EWEF Mk I cell fo electowinning In lte tetwok, when uing the lge 10 lite EWEF Mk III cell of imil deign, the eult hown in Figue 4, wee confimed, i illutted in Figue 6. Thee eult how quite dmticlly tht gold olution nging in concenttion fom ove ppm, down to 20 ppm gold, cn be teted in EWEF-type electowinning cell. It i evident, theefoe, tht high ufce e gphite felt, which my hve typicl pecific ufce e of > 260 m2/kg 4, i extemely effective in extcting gold fom elute olution. Futhemoe, ccoding to Stvt et l. 4, 2000 kg of gold pe m3 of felt cn be loded t 400 A/m2 fom dilute gold olution (30 mg/l Au), with clic Fdy yield of 6 12%. Thu, the potentil fo employing uch electode in gold hydometllugy i vey ignificnt. In ddition to the bove, electowinning tet un wee cied out in the pimy electowinning cicuit (ee Figue 1), whee the intention w pimily to poduce gold ludge. Thee w tnpent ection in the dichge pipe leding to the EWEF Mk I cell, nd o when the goldloded pimy EW cthode w otted, decibed bove, the gold ludge could be een to be flling into the cell. Thi ludge would lte be conveted into gold electofom (ee below). The Jounl of The South Aficn Intitute of Mining nd Metllugy VOLUME 106 NON-REFEREED PAPER APRIL

6 Innovtion in peciou metl ecovey LOG (GOLD CONCENTRATION IN ppm) RUN 5 34 C RUN 4 RUN 6 RUN 3 45 C RUN 1 44 C 43 C 43 C RUN 2 ELAPSED TIME (MINUTES) EG. #1 EG. #4 EG. #2 EG. #5 21 C EG. #3 EG. # Figue 5 Plot of log (eidul gold concenttion) function of time, which povide n indiction of gold extction kinetic Figue 6 Gph howing gold extction fom viou olution function of time, uing the EWEF Mk III cell fo electowinning Electofoming Following the completion of the ix electowinning un, clcultion howed tht thee hould hve been bout 30 gmme of gold on the HSA electode. To thi w dded 2 gmme of pticulte gold metl by entining it in the eciculting olution, o tht it would be tpped, decibed bove. A mentioned bove, the im w now to tip ll the gold fom electode B, by mking it nodic with epect to electode A in Figue 2. Becue of the limited mount of gold peent, only pt of electode A w ued to poduce electofom. Idelly, the type of electofoming olution tht hould be ued would contin high concenttion of gold (typiclly 8 40 g/l), nd might contin popiety dditive to chieve good integl fine-gined electodepoit t eltively ft depoition te. Becue of the impcticbility of uing uch olution in the peence of uch mll mount of electowon gold ny effect would be wmped the electofoming olution ued w 18 lite of gold elute olution fom mine B. At the tt thi contined c. 200 ppm gold. To thi olution w dded odium cynide (10 g/l), dipotium hydogen phophte (5 g/l), odium hydoxide (5 g/l) nd popiety bightene (5 ml/l). Electofoming w cied out t C, initilly t c A/dm2, nd lte thi w deceed to 0.1 A/dm2. Finlly, the cuent w chnged fom DC to puled output, till t 0.1 A/dm2. Thee chnge wee mde in n effot to impove the qulity of the electofom poduced. Thi initilly hd ppeed dk nd ough, nd poibly unuitble to be emoved fom the mndel n integl electofom. A the gold concenttion of the electofoming olution w vey low nd vey low cuent wee needed, thi implied vey long depoition time, nd elly good depoit w hdly to be expected. Nevethele, good electofom w obtined t n vege cuent denity of 0.3 A/dm2 unde good pule condition. The gold lloy electofom poduced i hown in Figue 7. Finlly, when nely ll the gold hd been emoved fom the totl of 50 lite of gold elute teted, it w found tht the m of gold ecoveed in the fom of electofomed tpeed tube epeented gold ecovey of c. 95%. In commecil pctice, whee gold i continully being extcted, nd gold m of kilogm, o moe, i peent on the HSA electode, thee would be no poblem bout hving high gold concenttion electofoming electolyte in 302 APRIL 2006 VOLUME 106 NON-REFEREED PAPER The Jounl of The South Aficn Intitute of Mining nd Metllugy

7 Innovtion in peciou metl ecovey Figue 7 Electofomed tpeed tube of gold/ilve lloy poduced in the EWEF Mk I cell cicultion. In tht ce the cot of the ciculting lod of gold in the electofoming olution would not be pohibitive in eltion to the vlue of the gold ecoveed. Eentilly, duing the electofoming opetion gold on the node would diolve, while gold in olution would not be conumed nd would meely eve high-peed tnpot medium. Recent development The expeiment epoted bove wee conducted in lbotoy-cle btch unit. Thi h ubequently been upcled to become mll pilot plnt, hving two EWEF (now deignted EWEREF) cell of diffeing deign, nd with volume of 50 nd 100 lite, epectively (ee Figue 8). Initil tet in the lbotoy demontted tht epte ilve nd gold electofom could be poduced in the EWEREF Mk IV cell. Thee e hown in Figue 9. Howeve, befoe ll the intended tet could be completed, the oppotunity oe to intll thi plnt on lge gold mine. Hee gold elute (nd ludge) would be edily vilble, initilly on btch bi, but eventully on continuou bi, nd thee would be the oppotunity to build up expeience unde elitic plnt condition. Tet wok t the Kloof gold plnt of Gold Field Limited i cuently in poge, nd, eult, impoved cell nd ytem deign, fo which ptent potection5 h been ought, e in the developmentl tge. In ddition, cetin lbotoy tet hve hown tht the kinetic of gold electofoming cn be inceed by n ode of mgnitude, o moe, J o u n l P p e Figue 8 Smll-cle gold ecovey pilot plnt, howing the 400 l eevoi nd the EWEREF Mk IV nd Mk VI cell The Jounl of The South Aficn Intitute of Mining nd Metllugy VOLUME 106 NON-REFEREED PAPER APRIL

8 Innovtion in peciou metl ecovey Figue 9 Gold, ilve nd gold/ilve lloy electofom poduced in the EWEF Mk IV cell yet till yielding good integl electofom of hd gold. Thee unuul ynegitic technique hve lo been incopoted into the ltet cell deign, nd ptent ppliction. It i the intention to deign cthode mndel, uch tht viou up-gded pue gold (~99.5%) poduct cn be poduced fom gold elute/ludge in itu nd t the mine loction. Thee poduct might include gold plte, gold foil6 nd hd (~140 VPN) gold jewelley7. It i pehp too ely to peculte, but we believe tht it will eventully be poible to do the me, uing gold lech olution (~6 ppm gold) the tting mteil. If thi pove to be vible, it could evolutionize the gold mining induty. Concluion The following concluion my be dwn fom the invetigtion epoted hee: Gold, ilve, nd gold/ilve lloy electofom cn be poduced in itu in pecilly deigned electochemicl cell, diectly fom gold cynide elute nd gold ludge oiginting fom South Aficn (nd othe) gold mine. Thee i the futhe poibility of doing the me with the coeponding low concenttion gold cynide lech olution The potentil exit to utilize thi type of in itu electofoming to mnufctue vlue-dded peciou metl poduct in the fom of plte, tube, foil, jewelley, etc. t the mine itelf, eithe niche opetion on lge gold mine, o complete ytem on mll gold mine Electoefining of gold nd ilve cn be included in the opetionl equence t the mine, theeby eliminting filttion of ludge, melting, nd gold efining elewhee If the poce fetue outlined cn be fully commecilized, it will be poible to eliminte numbe of tep in the poduction chin fom gold oe to endpoduct, theeby educing cot nd enhncing pofitbility In pinciple, opetion could be fully utomted in ode to minimize the poibility of gold theft. Acknowledgement Thi wok w cied out unde the upice of Zenzele Technology Demonttion Cente, nd the utho wih to thnk mot inceely the cente mnge, D Colin Logn, without whoe enthuitic uppot thi poject would not hve been poible. Thnk e lo due to AngloGold Ahnti fo poviding gold elute olution, nd to Allen Philip, conulting metllugit to Gold Field, who not only nged fo the upply of imil olution, but lo mde poible the intlltion of ou pilot plnt t thei Kloof gold plnt. The helpful coopetion of tff t the Kloof plnt i lo gtefully cknowledged. Phil Voke of C. I. Engineeing mde vluble contibution equipment deign, mnufctue nd mintennce, nd hi evice e mot ppecited. Thi ppe w fit publihed in Cicul No. 2, Novembe 2005, Mine Metllugicl Mnge Aocition. Pemiion w gnted fo thi ppe to be publihed in thi edition of the Jounl. About the utho Michel J. Sole, C.E.F., h been membe of the Ameicn Electoplte nd Sufce Finihe Society (AESF) fo ove 25 ye, nd h pecilied in the electofoming of gold nd be metl. He hold mte degee in Phyicl Chemity fom Rhode Univeity, Ghmtown, South Afic, nd Ph.D. in Chemicl Phyic fom the Univeity of Cmbidge, Cmbidge, Englnd, whee he lo held n Intentionl Atomic Enegy Agency Fellowhip. He i the utho of numeou cientific ppe nd evel ptent. He w the keynote peke t the AESF Sympoium on Electofoming, L Veg, USA, nd guet peke t the Wold Gold Council 1t Sympoium on Gold Jewelley Technology in Vicenz, Itly. He i emi-etied nd wok electochemicl conultnt t Zenzele Technology Demonttion Cente, in Rndbug, South Afic. Cl vn Tonde hold diplom in Phyicl Metllugy fom the Petoi Technikon, South Afic, nd i cuently woking towd bchelo degee in Phyicl Metllugy t the Univeity of Johnnebug. Hi peviou expeience include gold jewelley electofoming unde D Sole t Huddy Dimond, nd poce development in peciou metl t Rnd Refiney nd t Johnon Mtthey in Johnnebug. He i cuently employed technicin t Zenzele Technology Demonttion Cente. Refeence 1. CARTNER, W.N. South Aficn Ptent Appliction No , Electowinning Cell, lodged 22 Decembe SOLE, M.J. South Aficn Ptent No. 2002/6170, Removl of Metl fom Solution, gnted 31 Decembe SOLE, M.J. South Aficn Ptent No. 2005/0298, Metl Recovey Sytem EMD Mk III, filed 12 Jnuy STAVART, A., LEROY, C., nd VAN LIERDE, A. Potentil Ue of Cbon Felt in Gold Hydometllugy. Minel Engineeing, vol. 12, no. 5, pp SOLE, M.J. South Aficn Ptent Appliction No. 2005/02020 ElectoWinning, ElectoRefining nd ElectoFoming Sytem fo Gold Recovey, filed 10 Mch SOLE, M.J. South Aficn Ptent Appliction No. 2004/3697, Gold Foil Mnufctue, filed 14 My SOLE, M.J. South Aficn Ptent No. 2005/01154, Electo Depoition filed 9 Febuy u 304 APRIL 2006 VOLUME 106 NON-REFEREED PAPER The Jounl of The South Aficn Intitute of Mining nd Metllugy