Flotation cell technology and circuit design an Anglo Platinum perspective

Transcription

1 SAIMM_Oct_11-18:Templte Jounl 11/5/07 8:02 AM Pge 615 Flottion cell technology nd cicuit design n Anglo Pltinum pespective by C.M. Rule* nd A.K. Anyimdu* J o u n l Synopsis Foth flottion is the pimy minel pocessing seption step employed in the beneficition of PGM oe bodies. Anglo Pltinum opetes significnt potion of the totl instlled flottion cpcity in the PGM industy, which is instlled t 20 opeting plnts coss the Bushveld. PGM flottion hs undegone consideble evolution in both the cpcity of flottion cells employed s well s in the cicuit design configution ove the pst 30 yes. Cetin of Anglo Pltinum s flottion cicuits hve been in opetion fo eltively long time (in some opetions instlled equipment dtes fom the 1960s), nd this llows comptive opeting pefomnce between vious equipment types nd cicuits to be evluted. This ppe summizes some spects of this expeience. Resech tends in flottion e continuously monitoed so tht ppopite findings cn be incopote into existing nd futue cicuit designs. Continuous evlution nd monitoing of flottion pefomnce is undetken to identify oppotunities fo incesing flottion efficiencies. Minelogicl nd fctionl nlyses of plnt composites nd suvey smples e nlysed to inteogte specition nd ssocition dt. This nlysis hs enbled bette undestnding of pioities nd oppotunities fo impoved metllugicl pefomnce. These oppotunities e divided into thee impovement es: stbility, libetion, nd fines flottion. The ppe discusses these, s well s the cicuit design impovements equied to tke full dvntge of the oppotunities identified Intoduction Most compnies tht extct PGMs fom bse metl sulphide deposits cuently use flottion s pimy extction pocess. Fo the foeseeble futue, comminution followed by foth flottion will continue to be the mjo focus es in the PGM minel beneficition pocess. Continuous effot is being mde to impove the technicl nd opetionl efficiency of flottion. Anglo Pltinum hs 20 opeting concenttos sited ound the Esten, Nothen nd Westen limbs of the Bushveld complex, s illustted in Figue 1. The concenttos tet minly Meensky nd UG-2 oes, with Potgietesust (PPL, Sndsloot) nd PPRust Noth being the only two plnts designed to tet the Plteef oe. Since the ely 1990s, n incesing popotion of UG2 oe hs been pocessed. This hs incesed dmticlly in ecent yes, eching level of 54% of ll oe teted in FY 2006 (excluding WLTR, the Rustenbug tilings etetment opetion). The cpcities of individul concenttos nge fom smll plnts hndling 50 thousnd tons pe month (ktpm) plnts to lge opetions teting in excess of 600ktpm. A tionliztion of concentto opetions whee much of the old equipment nd plnts e being eplced nd modenized is cuently in pogess. This hs esulted in eduction in the numbe nd n incese in the unit size of instlled flottion cells. Anglo Pltinummnged opetions cuently tet ove 4 million tons of oe pe month though hundeds of flottion cells of vying cpcities, nd poduce bout 90 thousnd tons of flottion concentte. Exmples of the wide viety of instlled cpcity of flottion units in Anglo pltinum e given in Tble I. The figues illustte the tnsition to fewe, lge cells, which e shown in ed, s comped with the olde genetion plnts Fnk nd Klipfontein, built in the 1960s. The best exmple is shown in the Rustenbug opetions figues the new Wtevl complex, UG2 nd Retofit, commissioned in 2002 nd Recent histoy, evolution nd cuent sitution The evolution of Foth Flottion in Anglo Pltinum cn be simplisticlly summized into thee diffeent concentto es s follows: * Concenttos, Anglo Pltinum. The Southen Aficn Institute of Mining nd Metllugy, SA ISSN X/ This ppe ws fist published t the SAIMM Confeence, Flotton Cell Technology in the 21st Centuy, 20 June P p e The Jounl of The Southen Aficn Institute of Mining nd Metllugy VOLUME 107 NON-REFEREED PAPER OCTOBER

2 SAIMM_Oct_11-18:Templte Jounl 11/5/07 8:02 AM Pge 616 Flottion cell technology nd cicuit design n Anglo Pltinum pespective Union Smelte Stedy-stte opetion PGM pojects Anglo Pltinum joint ventues Rmp-up opetion PTM JV RUSTENBURG PSA1 + 2 NORTHAM Anglo Pltinum Concentto Opetions on the Bushveld complex PPRust PROJECT RPM: AMANDELBULT BOIKGANTSHO JV (ANOORAQ) POTGIETERSRUST PLATINUMS LIMITED LIMPOPO BELA BELA RPM: UNION NORTH WEST BAFOKENG/RASIMONE RPM: RUSTENBURG GAUTENG Wtevl PANDORA JV Smelte PRETORIA POLOKWANE POLOKWANE SMELTER MOKOPANE LEBOWA PLATINUM MINES GA PHASHA JV TWICKENHAM SHEBAʼS RIDGE JV DER BROCHEN BOOYSENDAL JV MODIKWA MPUMALANGA WITBANK Kilometes BURGERSFORT MOTOTOLO JV LYDENBURG Figue 1 Anglo Pltinum concentto opetions Tble I Summy of instlled flottion equipment in Anglo Pltinum (s t end 2007) Opetion Oe type pocessed Plnts Cpcity ktpm No. of cells m 3 instlled Roughes Clenes Roughes Clenes BRPM Meensky Wtevl concenttos Meensky/UG Klipfontein/Fnk Meensky/UG WLTR Tilings Union Motime UG Union Ivn UG2/tilings Amndebult Meensky Meensky Amndebult UG2 UG PPL Plteef PPRust Plteef Lebow Meensky/UG Modikw UG Mototolo UG Wtevl slg Convete nd funce slg Pe 1980s Minel extction cicuits wee chcteized by multiple smll flottion mchines (typiclly 1m3) with shot esidence times, employing single mill-flot configution. Typiclly thee-stge cushing, closed cicuit bll mill comminution cicuit ws used to pepe feed fo flottion. These cicuits teted Meensky oe only. 1980s 1990s Individul flottion mchine cpcities incesed to up to 30m3. MF2 cicuits, which hd evolved fom oughe tilings egind wok done in mid 1980s, wee employed. Typiclly 60 minutes minstem esidence time ws instlled. Induced i oughe cells nd foced i clening cells wee the nom. The 3kW/m3 mnt evolved, oiginlly diven by gind-psd suspension equiements, pinciplly fo pimy FAG opetion nd UG2 oes. 2000s Lge tnk cells, with cpcities up to 130 m3, wee instlled. Longe esidence times wee utilized, especilly in concentte clening. The 3kW/m3 doctine ws discded, pticully on the lge cells. R&D nd opetionl impovements effots focused on minimizing flottion losses, dvnced pocess contol nd cicuit stbility. Cicuits teting UG2 becme moe pedominnt. Flottion impovement pioity es In pusuing oppotunities fo optimiztion, Anglo Pltinum constntly evlutes flottion opetions within the goup. Technologicl dvnces in minelogicl nlysis hve llowed ccute mesuement nd quntifiction of the loss pofiles coss ll eef types nd opeting plnts within the Anglo Pltinum goup. A typicl PGM distibution pofile fo selected stems in UG2 opetion is shown in Figue 2. Appoximtely 80% of the PGM minels in the feed e eithe individully libeted, o e ttched to o ssocited with bse metl sulphides (BMS). The eminde e locked o middlings pticles. The concentte consists of libeted nd BMS ssocited/enclosed pticles, with much smlle popotion of locks nd middlings. 616 OCTOBER 2007 VOLUME 107 NON-REFEREED PAPER The Jounl of The Southen Aficn Institute of Mining nd Metllugy

3 SAIMM_Oct_11-18:Templte Jounl 11/5/07 8:02 AM Pge 617 Flottion cell technology nd cicuit design n Anglo Pltinum pespective 100% 80% 60% 40% J o u n l 20% Figue 2 Typicl UG2 PGM ssocition pofile monthly composite 0% Feed Concentte Tiling Libeted PGM/BMS ssocited Enclosed in oxide Enclosed in BMS Enclosed in silicte Attched to oxide Attched to BMS Attched to silicte Gin boundy P p e 40 Recovey (fom tils stem) % Recovey M M M Ap Ap Ap My My My Jun Jun Jun Jul Jul Jul Aug Aug Aug Aug Sep Sep Sep Oct Oct Oct Nov Nov Nov Befoe Gind Afte Gind Figue 3 Additionl hot flot nd egind hot flot flottion potentil fo n opeting UG-2 plnt The tilings disply ppecible popotions of libeted. BMS ssocited nd locked/middlings pticles, but it is impetive to note the distibution of these losses between the vious size clsses. In this pticul cse the totl tilings mounted to ~ 0.5 g/t 4E, (Pt, Pd, Rh & Au). Of this, 0.35 g/t occus s locked PGM pticles nd 0.15 g/t s libeted/bms ssocited PGMs. The depotment in size clsses shows the mjoity of fines losses occu in the -10 micon fction. Fo simplicity, the cuses of these losses e loosely gouped into thee ctegoies: Inefficient flottion pedominntly fine libeted PGM (nd BMS) losses Incomplete o non-libeted vlues composites with gngue Plnt instbility sub-optiml pocess contol nd plnt stops/stt-ups; poo opetion. The second nd thid ctegoies of loss hve lmost obvious solutions impoved ginding (esulting in incesed libetion) nd impoved plnt opetion nd especilly stbility. Thee pioity es hve been identified fo optimiztion: stbility, libetion, nd fine pticle flottion. These thee fctos e inteelted, but will be discussed septely in this ppe. Stbility Fo the puposes of this discussion, ll pocess inefficiencies e collected unde the definition of plnt instbility. This would include the non-ecovey of dequtely libeted (but not fine which cn be bitily defined s <10 μm) flotble vlue minels. Selectivity issues, gngue competition, sufce coting coveed by, nd inhibited flottion e ll included in this definition, which includes ll the pticles tht should hve been ecoveed in the flot, but wee not. Opetionl instbility includes, mong othes, suboptiml pocess contol, plnt stops nd stts, nd suboptiml cicuit configution (such s insufficient esidence time nd inppopite egent egimes). The extent of ext flottion potentil in this ctegoy of losses cn be guged by pefoming tilings e-flots, o the so-clled hot flots tht e outinely pefomed on the vious opetions. These eflots genelly poduce oughly 10% ecovey (of the tils stem) fo moe stble opetions, but up to 25% ecovey (of the tils stem) fo less stble plnts. These hot flots e done on s is mteil nd fte dditionl eginding. A typicl exmple of hot flot esults fo UG-2 opetion is shown in Figue 3. The Jounl of The Southen Aficn Institute of Mining nd Metllugy VOLUME 107 NON-REFEREED PAPER OCTOBER

4 SAIMM_Oct_11-18:Templte Jounl 11/5/07 8:02 AM Pge 618 Flottion cell technology nd cicuit design n Anglo Pltinum pespective The biggest oppotunity fo ecovey impovement is clely linked to impoved libetion. The minelogicl nlyses nd ssy wok on sized composite smples fom the plnts indicte tht the mjoity of PGM losses in plnt finl tils e due to eithe un-libeted o ptilly libeted minels composites o locked pticles. The popotion vies between plnts nd between oe types. Once plnt stbility hs been consistently chieved, the lgest oppotunities tht emin fo flottion impovement e fine ginding of flottion feed, nd impovement in the flottion of the fines thus geneted. The need to gind moe finely The economics of cquiing dditionl cpitl equipment nd the ssocited opeting costs in pusuit of optimum libetion nd hence ecovey of metls needs to be justified by n ctul business ppliction. Ginding moe finely hs limittions with espect to flottion pefomnce, nd lso in es such s filttion of concenttes nd the thickening nd deposition of tilings. All of these must be consideed in the ovell poposl. Howeve, numeicl evlution of the dt cetinly shows the potentil of fine ginding ssuming tht flottion cn ecove fine PGMs. In summy the dt show: Feeds clely this is eltively good UG2 oe. The mjoity of PGMs e eithe libeted o ssocited with sulphides, sy 83% in these clsses Concenttes clely demonsttes tht ecovey of PGMs is pedominntly of libeted o sulphide ssocited PGMs, sy 97% in these clsses Tilings s mentioned elie, the losses e split between libeted nd ptilly libeted pticles, fines losses in the -10 micon fction pedominntly nd ptilly o not libeted losses in the cose fctions. The following tilings MLA-souced photomicogphs indicte the difficulty of PGM libetion cse of needles in hystcks. In summy, Tble II nd Figue 4 illustte the following: The PGMs in the cose fction (+53 micon) of the tils e not sufficiently libeted PGM Ni Sulphides Fe Sulphides Cu Sulphides Chomite Pyoxene Feldsp Alteed Silictes Qutz 150 μm Figue 4 MLA output fo PGM losses in the flottion tils typicl smple Tble II UG2 Plnt Typicl PGM ssocition tble fo feeds, concenttes nd tilings Feed Concentte Tilings Tilings-10 Tilings+10 Tilings+53 Libeted Enclosed in BMS Attched to BMS PGM/BMS ssocited Enclosed in silicte Attched to silicte Enclosed in oxide Attched to oxide Gin boundy Totl No. of pticles OCTOBER 2007 VOLUME 107 NON-REFEREED PAPER The Jounl of The Southen Aficn Institute of Mining nd Metllugy

5 SAIMM_Oct_11-18:Templte Jounl 11/5/07 8:02 AM Pge 619 Flottion cell technology nd cicuit design n Anglo Pltinum pespective Recovey Libeted Fines: High sufce e Need high collecto nd low depessnt Intemedite: fst floting Lowe collecto need, Composites need depessnt Cose Pticles Low libetion J o u n l Figue 5 Typicl flottion size/ecovey cuve Size (micons) P p e Figue 6 Flottion ecovey vesus size fo diffeent minels 100 Pt Recovey pe size, nd % of totl lost Pt fom size clss Pt Recovey (%) Sceen size (micon) % lost Pt Recovey pe size Figue 7 Pticle size vesus flottion ecovey; nd % of lost PGM fom diffeent pticle size clsses in n Anglo Pltinum UG2 plnt 2 The PGMs contined in the ult-fines fction (-10 micon) of the tils e well libeted. This is not supising infomtion given tht in typicl UG2 oe, PGMs e typiclly less thn 10 micons in size. In fct, it cn be sid tht the typicl industy-wide definition of poo o good metllugiclly chcteized oe types e simply shows eltivity with espect to the degee of sulphide minel ssocition with totl PGMs: poo oe hs highe PGM pticle ssocition with silictes. Hving gound moe finely, cn we flot fines? Clssiclly, flottion ecovey pe size clsses is known to hve flttened n shpe s indicted in Figue 5, which lso povides some explntions fo the dop-off in ult-fines nd vey cose pticles. Even though the genel shpe emins fo most minels, the bsolute numbes of the theshold (fo dopoffs etc) vy fo diffeent minels nd flottion systems, s indicted in Figue 6, n except fom ppe by Pofesso Jmeson tht illusttes typicl eltionships. Fo typicl UG2 oes, fo exmple, the fine ntul PGM gin size in the in situ oe nd the eltive pefomnce of PGM flottion plnts indicte tht the wteshed size whee flottion dops off significntly must be eltively fine. This is indicted in Figue 7, whee dt collected fom UG2 The Jounl of The Southen Aficn Institute of Mining nd Metllugy VOLUME 107 NON-REFEREED PAPER OCTOBER

6 SAIMM_Oct_11-18:Templte Jounl 11/5/07 8:02 AM Pge 620 Flottion cell technology nd cicuit design n Anglo Pltinum pespective concentto illustte the eltive ecovey by size fction in the minstem oughes nd scvenges. The supising fetue is the vey good fines flottion nd steep dop-off in cose fction PGM ecovey. This shows tht fine pticles hve bette chnce of ecovey thn cose (> 53 micon) pticles. Moe evidence fo the bility to flot fines is given fo Zn-Cu systems (Mt. Is) s well s PGMs (Anglo Pltinum) in the sections tht follow. Lessons fom Pb/Zn, McAthu Rive nd Mt Is mines The oe minelogy equied tht ult-fine flottion ws needed in the opeting egime to poduce sleble concentte poduct. The only option ws theefoe to develop n ult-fine ginding technology, nd design the ppopite cicuit to flot the fines geneted. McAthu Rive nd Geoge Fishe, Mt Is plnts theefoe implemented flottion cicuit pefomnce nd optimiztion though ult-fine ginding (UFG), s illustted in Figue 8. IsMill technology ws developed by scling up fom existing ginding technology specificlly to enble these pticle size distibutions to be chieved. The technology is ecognized s the eson tht both plnts e in opetion tody. The enhnced fines flottion fom the Mt. Is Mine, Geoge Fishe plnt, cn be seen in Figue 9, which shows ecovey pe size clss esults. The successful use of IsMilling fo poduction of fine pticle size distibutions pesents useful lessons pplicble to in the PGM industy. Fines flottion t Anglo Pltinum Typicl size-by-size nlysis of flottion feed poducts nd tils coss full scle flottion plnt poduces the cuves shown in Figue 10. The dt in Figue 10 show tht fines hve much bette chnce of flottion. This tend is in geement with the nlysis of UG2 monthly composites of feed tils nd concenttes (n exmple of which is shown in Figue 7). Even with the pesent flottion equipment, sub 10 micon pticles e floting esonbly well. Wok is cuently ongoing to identify bette wys of impoving ult-fine (less thn 5 micon) flottion. It is the uthos opinion tht diffeent flottion technology will solve this poblem eventully. It is unlikely to be chieved by the intoduction of moe nd moe powe into conventionlly vilble mechnicl cells. In this incesingly enegy-we wold, the use of enegy foinefficient flottion systems in inheently wong! Cicuit considetions A typicl Anglo Pltinum UG-2 cicuit is s shown in Figue 11. Figue 8 Mount Is led zinc concentto flow sheet 620 OCTOBER 2007 VOLUME 107 NON-REFEREED PAPER The Jounl of The Southen Aficn Institute of Mining nd Metllugy

7 SAIMM_Oct_11-18:Templte Jounl 11/5/07 8:02 AM Pge 621 Flottion cell technology nd cicuit design n Anglo Pltinum pespective Zinc ecovey in size fction % 100.0% 90.0% 80.0% 70.0% 60.0% 50.0% 40.0% 30.0% 20.0% 10.0% 0.0% Recovey by size in the zinc cicuit wt oughe con Zinc distibution in feed Zn ecovey by size C7 C6 C5/C4 C3-C1 38/53 75 size fction 50.0% 45.0% 40.0% 35.0% 30.0% 25.0% 20.0% 15.0% 10.0% 5.0% 0.0% Zinc distibution in feed % J o u n l P p e Figue 9 Recovey by size clss in the zinc cicuit E + Au gde (g/t) μm μm unsized E + Au ecovey (%) Figue 10 PGM gde-ecovey pofile down oughe bnk fo diffeent pticle size fctions 2 Figue 11 Flowsheet oveview of UG-2 opetion t Anglo Pltinum The Jounl of The Southen Aficn Institute of Mining nd Metllugy VOLUME 107 NON-REFEREED PAPER OCTOBER

8 SAIMM_Oct_11-18:Templte Jounl 11/5/07 8:02 AM Pge 622 Flottion cell technology nd cicuit design n Anglo Pltinum pespective Resech into impotnt fctos consideed fo flottion cicuit design e monitoed nd incopoted into Anglo Pltinum s designs whee ppopite. Much of this wok is done with extenl inititives nd ptnes, e.g. AMIRA. Fctos include pmetes such s: Minelogicl nlysis Residence time nd cicuit configution size, numbe nd ngement of cells Fundmentl flottion cell design Flotbility mtching o kinetic mtching philosophy Mchine type, cell size, lunde nd foth tnspot, nd gde contol. The need fo ult-fine flottion (especilly fo UG2 oes nd lteed oes genelly) pesents chllenges tht must be met in cuent nd futue flottion cicuit designs. In ode to chieve metls ecoveies in excess of 90% fo ll UG2 oes, fo exmple, these poblems nd issues must be successfully ddessed. Issues tht e cuent es of focus include the following: Thee is physicl constint on fines flottion due to the enegy equiement fo vey smll pticle to ttch to bubble. How is this to be ovecome? Recovey deceses becuse viscous nd electosttic foces hve stong influence on ult-fine pticle ttchment. With ult-fines, incesed sufce e flux is equied to cy given mss of solids. Will new flottion cell technology in design diffeent fom the cuently vilble cells evolve fo widesped commecil use? Scling up flottion pefomnce designs fom the lbotoy to the pilot stge nd then full commecil ppliction ises questions bout, Is putting moe nd moe powe into conventionl cell designs solution? Does the incesed tubulence esulting hve negtive impct? Dive designs nd ssocited cost fo lge cpcity cells e el constint on cost effectiveness. Is this n enegy-efficient oute? Futue cicuit considetions nd conclusions Cetin fctos will hve to be consideed in the flottion cicuits of the futue, in ode to tke dvntge of esech findings fo enhnced PGM flottion. These include, but e not limited to: The mige of vilble nd new technology flottion mchines in hybid cicuits fo optiml flottion cicuit design could esily involve conventionl cells, contct cells nd column cells, nged optimlly in one flottion cicuit The use of mechnicl cells of sizes to mtch equied esidence time nd configution, with high powe cells esticted to potions of the minstem is likely. Clssic cell configutions could be developed with espect to by pssing diving instlled cells pe bnk; othe fctos tht influence ovell esidence time nd cell sizes e foth lunde lip length to cell volume tio nd duty A combintion of mechnicl nd column cells should be used fo UG2 ovell gde-c 2 O 3 optimiztion dives lso tking into ccount, flexibility fom flotbility mtching, cell size, lip length tios nd open cicuit ngementsd Foth ecovey nd lunde lip length e impotnt issues fo optimizing minstem ecovey. In pticul the ecovey of difficult nd slow floting species cn be ffected by egents nd moe significntly by intemedite concentte eginding Pocess contol nd cicuit ssessment will dive open cicuit opetion in conjunction with UFG (ult-fine ginding) of intemedite concentte stems. Open cicuit opetion hs numeous dvntges, not the lest of which is being of which is ble to monito pefomnce in el time New flottion technology will be equied to impove ult-fine flottion i.e. sub 5 micon pticles. This my well be n extenl bubble geneto, possibly in hybid design Flottion in size clsses is desible The flottion cicuit of the futue could be multistem plnt tgeting specific size fctions with specific equipment employed to mximize the ecovey chcteistics of the pticul stem Acknowledgments Executive Mngement of Anglo Pltinum fo pemission to publish the content of this ppe. Xstt Technology (XT), fo pemission to use excepts fom published XT infomtion. Refeences Intenl epot: Motime UG2 Tilings Re-flots. By Vusumuzi Mhlngu. Decembe Intenl epot: The Effect of Cicuit Design on UG2 flottion compison of the two Amndelbult UG2 Concenttos, (210 ktpm nd 75 ktpm). By A.K. Anyimdu, M. Smith nd S. Nik. Novembe, Intenl Anglo Pltinum minelogicl epots Anglo Resech, Minelogy Section. Excepts fom vious ppes nd pivte communictions fom Xstt Technology, published infomtion elted to the development of the IsMill technology nd the impct on the McAthu Rive nd Mt Is- Geoge Fishe Concenttos. Vious epots conducted in the Ami pogmme. Anlyses of numeous studies t plnt, pilot nd bench scle conducted ove the yes within Anglo Pltinum. 622 OCTOBER 2007 VOLUME 107 NON-REFEREED PAPER The Jounl of The Southen Aficn Institute of Mining nd Metllugy