Increasing the capacity of existing and new exothermic autoclave circuits

Transcription

1 11-18:Templte Jounl 6/25/09 11:52 AM Pge 329 Incesing the cpcity of existing nd new exothemic utoclve cicuits by G.M. Dunn* J o u n l Synopsis Pessue lech utoclve cicuits e employed in the leching of oes, concenttes, mttes, lloys nd intemedites fo the ecovey of metls into solution. Once the metls e extcted into solution, the vlue metls cn be ecoveed by hydometllugicl mens such s by puifiction followed by electowinning, hydogen eduction, pyohydolysis, cystlliztion nd othe unit opetions. In mny of these integted flowsheets the pessue lech step is pivotl to the ecovey of the vlue metls fom the host mteil. Futhemoe, the utoclve cicuit invibly is high cpitl cost component of the plnt nd n e tht is cefully scutinized when debottlenecking nd cpcity inceses e being consideed. This ppe identifies unique poven wy of incesing the cpcity of existing o new exothemic pessue oxidtive lech utoclve cicuits by s much s two o thee times. Intoduction Pessue lech utoclve cicuits e employed in the leching of oes, concenttes, mttes, lloys nd intemedites fo the ecovey of metls into solution. Once the metls e extcted into solution, the vlue metls cn be ecoveed by hydometllugicl mens such s by puifiction followed by electowinning, hydogen eduction, pyohydolysis, cystlliztion nd othe unit opetions. In mny of these integted flowsheets (efe Figue 1) the pessue lech step is pivotl to the ecovey of the vlue metls fom the host mteil. The exothemic leching pocess The leching of sulphide concenttes nd intemedites s well s lloys is often ccompnied by the elese of enegy, which hs to be emoved fom the utoclve sluies in ode to void the sluy tempetues within the vessel exceeding the design opeting vlues. Fo exmple, in the pessue lech of chlcopyite the ection could be epesented by the following eltionship: The enegy elese, s clculted fom hets of fomtion (25 C), is ppoximtely kilojoules pe gm mole. This exothemic het elese cn limit the cpcity of n utoclve to 1.1 to 1.3 tonnes of concentte pe ctive cubic mete pe dy whee etention time of ppoximtely 1.2 hous hs been pescibed. Thee e chlcopyite concentte utoclve cicuits tht hve been subjected to fesibility studies nd designed to opete in this cpcity nge (ppoximtely 8 12% (w/w) feed solids). At highe feed concenttions the enegy elese is such tht the utoclve tempetue will exceed the C typicl opeting nge being consideed fo POX utoclves teting chlcopyite. This condition tigges the need to emove enegy fom the utoclve in ode to mintin tempetue contol nd the desied oxygen ptil pessue in the vessel. Thee e viety of het emovl pocesses tht e vilble to the utoclve designe, nd these will be exmined individully. Quenching The quenching pocesses ppe to be fvoued by most enginees involved in utoclve design. The genel concept is cptued in Figue 2. It is simple to configue nd hs eltively simple contol fetues. Quench liquo, in the leching of coppe concenttes, cn be solvent extction ffinte o spent electolyte. The CCD 2 liquo cn be consideed fo the quench in cses whee thee is countecuent decnttion solid-liquid seption cicuit. The cool queous liquo is nomlly fed to the utoclve comptments on tempetue contol. In cses whee thee e little solids pesent in the * Hydomet (Pty) Ltd, South Afic, hydomet@hydomet.co.z, hydomet@mweb.co.z. The Southen Aficn Institute of Mining nd Metllugy, SA ISSN X/ This ppe ws fist published t the SAIMM Confeence, Hydometllugy 2009, Febuy P p e The Jounl of The Southen Aficn Institute of Mining nd Metllugy VOLUME 109 NON-REFEREED PAPER JUNE

2 11-18:Templte Jounl 6/25/09 11:52 AM Pge 330 Incesing the cpcity of existing nd new exothemic utoclve cicuits Figue 1 Exmple of hydometllugicl flowsheet fo the ecovey of coppe fom flottion concentte quench fluid, multistge centifugl pumps cn be employed nd, whee this is not the cse, n ppopite positive displcement pump my be suitble. The quench cicuit of Figue 2 is lso employed in the leching of nickel nd nickelifeous sulphides nd mixed nickel nd coppe sulphides. The use of quench liquo does equie n incese in the utoclve ctive volume nd cn esult in dilution of the pegnnt lech solution (PLS) if wte o some diluted liquo is employed in this duty. Intenl cooling coils In some utoclves, intenl cooling coils hve been fitted into the comptments to bstct het. These cooling coils e often fixed to the dividing wlls of the utoclve nd e seviced by cooling wte o othe pocess fluids. Thee e numeous limittions ssocited with the use of coils, which include: Difficulties in fixing the coils to the vessels intenls Designing the coils nd thei suppots fo the theml stesses Depivtion of ecto volume by the coils A low degee of flexibility in being ble to ccommodte n incese in ection extent nd its concommitnt impct on whee the het is geneted within the utoclve, nd Scling of het tnsfe sufces by pecipittes o gngue fom the feed mteils. Cooling coils e employed in the mixed minel milleite, chlcocite nd covelite lech utoclves of Southen Afic1 nd the USA. They e lso used extensively in the Noilsk pyhotite-pentlndite lech utoclves2. Figue 3 povides the cooling system concept employed in some Southen Aficn utoclves. Extenl cooles An enhncement of the intenl cooling coil concept is to be found in the use of extenl cooles. The sluy is emoved fom the utoclve nd pumped though het exchnge befoe being etuned to the sme comptment of the utoclve. Some of the disdvntges of the intenl cooling coils e ddessed in the use of these extenl het exchnges, howeve: Scling of the het tnsfe sufces cn still occu, lbeit to lesse extent. This educed scle popensity is s consequence of the highe tube side velocities tht cn be chieved within the het exchnge The pumps equied to ciculte the utoclve contents though the extenl het exchnges hve cetin tempetue nd pessue limittions, esulting in this concept being limited to low nd medium pessue utoclve cicuits, nd Significnt we to isoltion vlves cn be expeienced on the pump suction nd het exchnge dischge lines. One cceptble fetue of extenl pumped cooles is tht dditionl cooling sufce cn be dded, theeby impoving thei flexibility with espect to vying o unpedictble ection extents duing the opetion phse. Figue 4 povides simple flowsheet of the extenl coole employed in coppe-coblt lech utoclve in Zmbi3. Figue 2 Flowsheet of utoclve with quench cooling Figue 3 Flowsheet of utoclve with intenl cooling coils 330 JUNE 2009 VOLUME 109 NON-REFEREED PAPER The Jounl of The Southen Aficn Institute of Mining nd Metllugy

3 11-18:Templte Jounl 6/25/09 11:52 AM Pge 331 Incesing the cpcity of existing nd new exothemic utoclve cicuits Figue 4 Flowsheet of utoclve with extenl cooles Flsh-ecycle In most exothemic utoclve cicuits mjoity of the enegy is libeted in the fist comptment, with only smlle quntities being geneted in the downstem comptments. An ltente ppoch to the emovl of het fom exothemic utoclves ws intoduced in South Afic in the mid 1980s in pessue lech step fo blend of chlcocite, covelite nd smll quntities of milleite. Since then it hs been instlled in two othe opetions in South Afic1, one in Zimbbwe4, the USA5 nd Austli. The flowsheet fo some Southen Aficn opetions is given in Figue 5. Any enegy elese in the fist comptment tht will esult in the sluy exceeding the design tempetue is bstcted by emoving sluy fom the fist comptment to the feed tnk vi flshing pocess nd etuning it to the utoclve. The feed tnk becomes n extension to the fist comptment in this cicuit nd while ecycle loop is estblished between this tnk nd the utoclve, the ovell etention time of the utoclve is elted to the net new feed te enteing the cicuit fom the concentte tnk nd is not influenced by the ecycle loop flow tes. Thee e sevel contol methods vilble to the utoclve enginee fo the flsh-ecycle cicuit nd these seve, in well designed system, to mintin the tempetue in the fist comptment t the set point with tolence of +3 C. This tempetue contol is nomlly cceptble fo most bick lined, lloy o lloy cld utoclves. Some of the dvntges of this system comped to the thee options bove e tht it povides: Fo optiml utiliztion of the instlled ecto volume Fo enhnced wte blnce contol The bility to concentte the ecto contents, if equied, though the evpotion of wte flshed s stem The potentil to use the flshed stem s n enegy souce elsewhee in the opetion, nd Fo n oppotunity to intoduce fist comptment egent ddition into the feed tnk. The flshed sluy ecycle loop cn povide lowe cost vehicle fo egent dditions to the fist comptment of n utoclve. The flsh ecycle (FR) cicuit cn be etofitted to utoclves employing ny of the ltente het emovl systems listed bove. Invibly, ny exothemic het cied ove into the second nd ensuing comptments cn be emoved, fo exmple, by the use of coils s this nomlly constitutes smll potion of the ovell exothemic het lod. When the bove het emovl inteventions e consideed holisticlly only the FR cicuit povides the utoclve designe with the mximum degees of feedom. A disdvntge, fo exmple, of the quench pocess is tht the fluid intoduced into the fist comptment fo tempetue contol cn often contin the poducts of the utoclve dischge, which my distub the desied equilibium conditions in tht fist comptment. It could lso, fo exmple, s in some mtte lech cicuits, be spent electolyte, which intoduces n cidic liquo into the fist comptment. The cid concenttion in this nd ensuing comptments is theefoe influenced by the theml quench nd my esult in condition whee the opeto is not ble to contol this pmete. He my in fct equie diffeent cid concenttion fo the optiml lech conditions ove tht which is deliveed by the quench tempetue contol. A futhe disdvntge in the cse of the intenl nd extenl coole system is tht ny feed density fluctutions bove the set point my esult in the intoduction of lge feed mss, fo exmple, of the sluy to the utoclve. The tempetue ise in the utoclve fist comptment my be excessive nd the enegy elese gete thn wht the cooles cn hndle. In continuous opetions the ection extent in the fist comptment could be educed nd consequently the second nd ensuing comptments het J o u n l P p e Figue 5 Flsh-ecycle flowsheet The Jounl of The Southen Aficn Institute of Mining nd Metllugy VOLUME 109 NON-REFEREED PAPER JUNE

4 11-18:Templte Jounl 6/25/09 11:52 AM Pge 332 Incesing the cpcity of existing nd new exothemic utoclve cicuits emovl cicuits my not be ble to bstct the ext het lod thust on them by the feed density fluctution in this cse. Unless design flexibility is povided, the tempetues cn un wy nd n incomplete leched poduct cn be dischged fom the utoclve. Howeve, in the flsh-ecycle cicuit: Tempetue contol is chieved without distubing o chnging the pocess vibles within the fist comptment by the etun of nothe pocess fluid The lechte cn be concentted, if equied, by not eplcing ll the wte tht is flshed s stem in the flsh step If the feed mss is highe to the utoclve s consequence, fo exmple, of poo density contol then the utomtic level djustment of the feed tnk cn be invoked to ensue the design ection extent is chieved in the fist comptment, theeby peventing conditions developing in which unected poduct is dischged fom the utoclve, nd The men utoclve etention time is the highest of ll the known methods of bstcting het fom the utoclve, theeby incesing the utoclve poductivity (tonnes pe dy pe cubic mete of utoclve volume). Autoclves in mtte lech cicuits tody hve been incesed in cpcity by in excess of 45 pe cent employing the flsh ecycle system whees othes hve been deted in pessue nd tempetue without ffecting the oiginl tetment te. In utoclves opeting t tempetues close to the tmospheic boiling point of the queous fction, Noilsk hve poposed thei ptented vcuum flsh. This cicuit ws in opetion t its Tti Nickel demonsttion plnt in Botswn6. The fist comptment flsh vessel is opeting t ptil vcuum, which llows the flsh undeflow sluy to be educed in tempetue below the tmospheic boiling point. This genetes highe sensible het loss thn would othewise occu in flsh-down to n tmospheic boiling condition. Additionl mechnicl equipment in the fom of condenses, vcuum pumps nd seling fluid cooling cicuits, etc. e equied in this vint of the flsh-ecycle cicuit. Flsh-thickene-ecycle (FTR) cicuit An extension of the flsh-ecycle cicuit is to be found in the incopotion of solid-liquid seption step fte the flsh. This solid-liquid seption step cn be on the fist comptment flsh but it cn lso be on the flsh fom ny comptment of the utoclve. This solid-liquid seption is often best chieved with thickene but it cn be effected with othe equipment such s clssifie o filttion step. This flow sheet modifiction will be efeed to s the flshthickene-ecycle o FTR cicuit. The FTR cicuit povides mens of incesing the etention time of the solids fction within the utoclve ove tht of the liquid fction. A futhe embellishment of the flowsheet concept of Figue 5 incopotes thickene in the flsh-ecycle loop. In cicumstnces whee thee is mss eduction of the feed concentte in the lech, the incopotion of thickene in the flsh cooling cicuit pemits the emovl of fction of the lechte. The ptilly leched solids e etuned fom the thickene to the utoclve vi the feed tnk. The thickene thus povides mens of incesing the solids etention time in the utoclve ove tht of the liquid phse. Altentely, fo fixed etention time, the cpcity of n utoclve cn be incesed subject to the impelles deliveing sufficient oxygen mss tnsfe. Figue 6 depicts this concept of the FTR cicuit. The FTR cicuit not only pemits the bstction of lechte fom the fist comptment, but lso povides mens of estoing some wte to the feed tnk to dive the equilibium in fvou of the lech extction. Altentely, in the bsence of wte ddition, slt hydolysis cn occu if this is desied. In the design of o modifiction of n existing utoclve, the fist comptment is sized to chieve in excess of 50 pe cent but typiclly 85 to 95 pe cent of the ovell ection extent. This cn nd often esults in the thickene oveflow being vey simil in composition to the utoclve dischge stem fte flsh. The men mss flow te in the fist nd ensuing comptments of the utoclve is: In the FTR cicuit the net feed te (5) though the utoclve cn be djusted to suit the equied mss flow nd extction simply by djusting the volumetic flow t stem Figue 6 Flsh-thickene-ecycle flowsheet 332 JUNE 2009 VOLUME 109 NON-REFEREED PAPER The Jounl of The Southen Aficn Institute of Mining nd Metllugy

5 11-18:Templte Jounl 6/25/09 11:52 AM Pge 333 Incesing the cpcity of existing nd new exothemic utoclve cicuits J o u n l Figue 7 Covellite-chlcocite POX lech P p e (4) subject to thickene undeflow viscosity nd density constints. By diveting the thickene oveflow to the dischge tnk it hs been possible to incese the etention time by s much s 200 pe cent befoe the utoclve sluy density inceses to point whee it is not economicl to incese it ny futhe. Othe fctos such s oxygen mss tnsfe t the utoclve impelles my become te limiting. The flsh-thickene-ecycle (FTR) concept hs been ptented by Hydomet7. The lowe coppe extction in the FTR cicuit is ttibuted to the te limiting fetues of the gittion systems, which ws unchnged in both cses. Chlcopyite lech The pessue oxidtive lech of chlcopyite is stongly exothemic pocess. The clssicl ppoch with quench Applictions Covellite-chlcocite pox lech The flowsheet of Figue 7 hs been consideed nd tested by n opetion pocessing nickel-coppe sulphide mttes. The utoclve ws opeted s bulk lech to povide n ppoximtely 90% mss eduction in the feed. It ws followed by polishing lech utoclve cicuit. This modifiction ws mde to n existing thee comptment utoclve nd: Incesed the etention time of the solids fction fom 3.0 hous to n excess of 7.5 hous, nd Incesed the cpcity of the utoclve fom 0.71 to 1.32 tonnes of feed pe cubic mete (ctive volume) pe dy t n opeting tempetue of 150 C. The impelles in the utoclve wee not upsized fo the FTR duty. These gittos becme te limiting in thei oxygen tnsfe te nd wee esponsible fo cpcity incese significntly below wht would hve been expected fo the dditionl etention time tht ws chieved with this modifiction. The extction of coppe nd oxidtion of sulphide sulphu t the highe cpcity in the FTR cicuit is given in Figue 8 nd Figue 9. It needs to be noted tht this ws thee comptment utoclve possessing the noml deficiencies of such vessel. In this cse the ovell ection extent in the fist comptment ws in excess of 80%. When the cicuit ws opeted s stndd flsh ecycle cooling cicuit (without the thickene in sevice) nd with men solids etention time of 3 hous, the coppe extction pofile ws typiclly tht shown in Figue 8 with fist comptment coppe extction of 97%. Figue 8 Extction of coppe in the FTR cicuit fo covellitechlcocite lech Figue 9 Oxidtion of sulphide sulphu in the FTR cicuit fo covellite-chlcocite lech The Jounl of The Southen Aficn Institute of Mining nd Metllugy VOLUME 109 NON-REFEREED PAPER JUNE

6 11-18:Templte Jounl 6/25/09 11:52 AM Pge 334 Incesing the cpcity of existing nd new exothemic utoclve cicuits cooling cn esult in the feed density being educed to between 8 nd 12% feed solids equivlent on weight bsis. In Zmbi, Knsnshi Mining plc ( compny 80% owned by Fist Quntum Minels Limited) instlled chlcopyite pessue oxidtion (POX) pocess to the flowsheet in Figue 10. An tmospheic lech of oxidized coppe oe is being undetken on the pesent site nd the pln is to integte the sulphide POX lech into the tmospheic lech cicuit to povide sulphuic cid, enegy nd some feic ion s lixivint fo some secondy sulphides in the oxide oe. The PLS fom the tmospheic lech CCD cicuit is fed to coppe SX cicuit. The ffinte fom this SX cicuit is etuned, in pt, to the POX cicuit fo the epulp of concentte nd the quench. The POX cicuit hs been designed to opete: At 210 C nd ppoximtely 3.0 MP(g) With fist comptment men solids esidence time of just unde one hou nd n ovell esidence time of ppoximtely 1.7 hous, nd With two utoclves fo concentte tetment te of 105 kt/nnum. Knsnshi Mining e consideing the FTR cicuit on single POX utoclve employing the flowsheet of Figue 11. The FTR cicuit will: Opete t 210 C nd ppoximtely 3.0 MP(g), i.e. t identicl conditions s those in the quench concept With the sme men solids etention time distibution s the quench cicuit, nd With one utoclve designed to tet ppoximtely kt/nnum. The specific pocess fctos of the cicuit e summized in Tble I. In the FTR cicuit, in excess 75% of the leched coppe in the utoclve will be emoved in the thickene oveflow nd diveted diectly to the dischge tnk. This is ppoximtely 80% of the totl coppe leched in the fist comptment. The emining leched coppe is in the sluy oveflowing fom the fist comptment to the second nd ensuing comptments of the utoclve. The leching of nickel sulphides Nickel sulphides mttes hve been leched in Southen Aficn mtte POX cicuits fo ove 35 yes8,9. The leching of nickelifeous sulphide concenttes hs been pctised t Outokumpu using the Hitu concentte10 nd is cuently pctised t Noilsk on pyhhotite-ich concenttes. Inco e consideing pessue lech cicuit fo its Voisey By concentte. The flowsheet in Figue 12 hs meits whee thee is significnt mss loss fom the feed concentte in the lech. It is, fo exmple, suited to the cid pessue oxidtive leching of mixed nickel nd coblt sulphides geneted fom hydogen sulphide pecipittion pocess of lteite lechte. The utoclve cpcity cn be educed by ove 200% of tht employed in the clssicl quench cooling pocess. Kineticlly diffeent lech systems The pltinum goup metls e known to espond moe slowly thn the bse metls in the cid lech of mix of bse metl sulphides nd PGM sulphides, selenides, telluides, senides, bismuthides, etc. Figue 10 Knsnshi Mining s chlcopyite POX cicuit with quench cooling Figue 11 Knsnshi Mining s chlcopyite POX cicuit with FTR 334 JUNE 2009 VOLUME 109 NON-REFEREED PAPER The Jounl of The Southen Aficn Institute of Mining nd Metllugy

7 11-18:Templte Jounl 6/25/09 11:52 AM Pge 335 Incesing the cpcity of existing nd new exothemic utoclve cicuits Tble I Pocess fctos of the cicuit Quench concept FTR concept Specific utoclve feedte t 1.7 hous (t.concentte/dy m3) Ovell etention time (t.cu/dy m3) (t.s=/dy m3) Sulphuic cid equiements (t/tonne concentte) 0.43 ~nil Fist comptment men solids etention time (h) Fist comptment sluy feed te (m3/h) Fist comptment dilution feed te (m3/h) Fist comptment oxygen tnsfe te (kg/m3h) J o u n l P p e Figue 12 Pessue oxidtion of nickelifeous sulphides with FTR Figue 13 FTR cicuit fo minels displying diffeent lech kinetics Whee it is the intent to dissolve both the bse metls nd the pecious metls, it my be ppopite to septe mjoity of the bse metl lechte in fist comptment FTR cicuit. The extction of the pecious metls cn then be mde in the downstem comptments of the utoclve in considebly smlle utoclve volume. The cicuit of the type shown in Figue 13 hs some meits in tht: A lge pt of the bse metls is emoved in the lechte oveflow fom the FTR thickene Any PGE tht do dissolve in the fist comptment e pecipitted on the concentte, which is blended with the fist comptment lech sluy pio to thickening. The thickene oveflow will theefoe be low in pecious metls concenttion The lixivint tht is employed fo PGE dissolution e.g. chloide ions in the Pltsol pocess my need to be dded only into the second comptment of the utoclve. This could educe the mteil nd mintennce costs of the utoclve significntly, nd The volume of lechte contining PGE is much smlle, s is the utoclve itself. The Jounl of The Southen Aficn Institute of Mining nd Metllugy VOLUME 109 NON-REFEREED PAPER JUNE

8 11-18:Templte Jounl 6/25/09 11:52 AM Pge 336 Incesing the cpcity of existing nd new exothemic utoclve cicuits Conclusions The intoduction of the thickene in the flsh font end cooling cicuit inceses the etention time of the solids fction ove tht of the queous stem. The FTR cicuit cn be etofitted to existing POX cicuits to incese the cpcity of these cicuits t miniml cpitl nd opeting cost. The FTR concept cn be designed into new POX cicuits to educe the size of the utoclve o educe the opeting complement of utoclves whee pllel units e being consideed fo plnt. Refeences 1. STEENEKAMP, N. nd DUNN, G.M. Opetions of nd Impovements to the Lonho Pltinum Bse Metl Refiney, EPD Congess, 1999, pp BORBAT, V.F. nd VORONOV, A.B. Autoclve Technology fo Pocessing of Nickel-Pyhotite Concenttes, Metllugy, Moscow, 1980, p MUNNIK, E., SINGH, H., UYS, T., BELLINO, M., DU PLESSIS, J., FRASER, K., nd HARRIS, G.B. Development nd Implementtion of Novel Pessue Lech Pocess fo the Recovey of Coblt nd Coppe t Chmbishi, Zmbi, The Jounl of the South Aficn Institute of Mining nd Metllugy, Jn. Feb MONTGOMERY, G.W.G. nd HOLOHAN, T.N. Development nd Design of the Htley Pltinum Bse Metl Refiney Flow sheet, South Aficn Institute of Mining nd Metllugy, Apil NEWMAN, L. nd WYRICK, R. Modifiction of the Stillwte Bse Metl Refiney Pocess Pessue, Hydometllugy, 2004, pp SWARTS, A. HOLLIDAY, H. DONEGAN, S., nd NEL, G.J.G. The Tti Activox Demonsttion Plnt: Chnging the Futue of Nickel Poduction in Southen Afic, Cpe Confeence, South Afic, DUNN, G.M. Exothemic Pessue Lech Autoclve Cicuits, PCT/ZA 2005/ PLASKET, R.P. nd ROMANCHUK, S. Recovey of Nickel nd Coppe fom High-Gde Mtte t Impl Pltinum by the Sheitt Pocess, Hydometllugy, 1978, pp PLASKET, R.P. nd DUNN, G.M. Commissioning Expeiences in the Coblt plnt t Impl Pltinum Ltd, Minels nd Metllugicl Pocessing, 1986, Feb Issue. 10. NYMAN, B., AALTONEN, A., HULTHHOLM, S.E., nd KARPALE, K. Appliction of new hydometllugicl developments in the Outokumpu HIKO pocess, Hydometllugy, 1992, pp JUNE 2009 VOLUME 109 NON-REFEREED PAPER The Jounl of The Southen Aficn Institute of Mining nd Metllugy