Sulphating roasting of copper-cobalt concentrates

Transcription

1 Sulphting osting of coppe-coblt concenttes by J. Güntne* nd J. Hmmeschmidt* J o u n l Synopsis Most coppe/coblt oes fom the Centl Aficn Coppebelt contin sulphidic compounds, which e not extctble in diect leching. Rosting povides the possibility to tnsfe the vluble components into lechble compounds. In n opetion window defined by tempetue nd off-gs composition it is possible to selectively oxidize ion sulphides to hemtite nd coppe/coblt sulphides to sulphtes. Selective sulphting of the vluble minels is n impotnt condition fo the subsequent leching stge. The dissolved coppe nd coblt e ecoveed by solvent extction nd electowinning. This technology hs been pt of n estblished pocess fo mny decdes. The concenttes fom ecent pojects on the Coppebelt hve lowe sulphu contents, nd fequently highe coppe contents, thn those fom olde pojects. The ppe shows the consequences of this tend fo plnt opetion nd explins useful counte ctions by mens of cse studies. Autotheml combustion is ensued even t vey low sulphu contents. Off-gs tetment hs so f been bsed on SO 2 emovl though sulphuic cid poduction. The geneted cid is used to mke up cid losses in the hydometllugicl plnt section. This well-poven pocess combintion is still the pefeed oute if the feed sulphu content is high enough; howeve, some cses my equie diffeent off-gs clening concepts without compomising on clen i qulity. Rosting in fluid-bed funce emins the coe of the technology. Fluid-bed ostes e esy to opete nd povide n excellent contol of the clcine qulity. Diffeent feeding nd hetecovey systems e used to povide tilo-mde solution fo ech poject. Outotec built it fist sulphtizing oste in Zmbi bout 30 yes go. At tht time, the osting of metl sulphides ws ledy one of the min technologies in the compny. Outotec hs developed osting solutions fo coppe, gold, zinc, led, molybdenum, nd pyite oes. The continuously expnded nd upgded esech fcilities povide n excellent bsis fo developing sustinble, enegy-efficient, nd economic solutions fo coppe nd coblt poduction in Afic. Keywods sulphting osting, coppe concentte, coppe-coblt concentte, coppe sulphte, coppe-coblt sulphte, chlcosite, chlcopyite, Coppebelt. Intoduction Sulphting osting is unit opetion in the poduction pocess fo coppe nd coblt fom sulphidic oes. The simplified block digm in Figue 1 shows tht osting is the fist stge in the pocess flow sheet. The objective of osting is selective sulphtion of coppe nd coblt, while feous minels nd components e oxidized to hemtite. The sulphtes e dissolved in the leching stge. Clcine leching is often cied out with spent cid to impove leching kinetics nd to ecove lso the smll potion of coppe oxides tht e unvoidbly geneted duing osting nd tht would othewise be lost. Unde these conditions ion emins pcticlly insoluble nd cn be septed with the tilings fom the coppe- nd cobltcontining liquo. Extction of coppe nd coblt is cied out by solvent extction with subsequent electowinning (SX-EW). The osting off-gs is used fo sulphuic cid poduction. This poduction pocess hs been in opetion fo sevel decdes. It is pticully suitble fo coblt-contining coppe oes. Pocess contol is uncomplicted nd opetion is pofitble t low cpcities. Rections The sulphtion ection occus in thee min steps. In the fist step the metl sulphides e oxidized to metl oxides. Me denotes minly Cu, Co, nd Fe but lso Ni, C, nd Mg. * Outotec, Gemny. The Southen Aficn Institute of Mining nd Metllugy, SA ISSN X/ This ppe ws fist pesented t the, Industil Fluidiztion South Afic Confeence, Novembe 2011, Cdle of Humnkind, South Afic. P p e The Jounl of The Southen Aficn Institute of Mining nd Metllugy VOLUME 112 JUNE

2 Sulphting osting of coppe-coblt concenttes Effluent Ai Off-gs Sulfuic Acid Sluy feeding Clcine Coppe, Coblt Tilings Figue 1 Simplified block-flow digm fo coppe-coblt poduction In the second step, sulphu dioxide is oxidized to sulphu tioxide. This ection is suppoted by coppe nd ion cting s ctlysts. [5] Finlly, the metl oxides ect with sulphu tioxide to fom sulphtes nd bsic sulphtes. [6] [1] [2] [3] [4] [7] 720 C this popotion dops below 50 pe cent. Coblt is less sensitive. Even t 720 C moe thn 90 pe cent emins in the sulphte fom. Moe thn 95 pe cent of the ion sulphtes e decomposed t 680 C. A elible tempetue contol nd s smll sped of tempetue s possible in the funce e essentil fo high coppe ecovey. Rosting pocess Rosting is cied out in bubbling fluid bed. Figue 3 shows the elements of the osting e. The funce consists of cylindicl bottom section tht contins the fluidized bed, conicl tnsition section, nd n expnded feebod. The feed mteil is injected s sluy by mens of compessed i though sluy lnces into the fluidized bed. In ode to void mteil build-up t the funce wlls s well s bsion of the funce efctoy lining, the injected sluy should not impinge on the funce wlls. Lnce position, diection, nd injection pessue e designed nd djusted ccodingly. The sluy is tomized when it contcts the fluidized bed to ensue homogeneous mteil distibution ove the full funce e. The osting pocess is utotheml. The sulphides in the feed seve s fuel nd s egent to fom sulphtes. The osting tempetue is kept within now nge of ± 10 C. log pso2g) 10 Cu-O-S Phse Stbility Digm t C CuS Cu2S CuSO4 CuO*CuSO4-4 Cu2O -6-8 Cu CuO File: C:\HSC7\Lpp\CuOS680.ips log po2(g) High-sulphu concentte Low-sulphu concentte The diect sulphtion of metl sulphides is lso possible. Oxygen excess is impotnt fo ll sulphtion ections. [8] Figue 2 shows the pedominnce phse digm fo the Cu-O-S system. The off-gs contins typiclly 5-8 vol.% of oxygen in ode to shift the ection to the fomtion of coppe sulphte. High SO 2 contents e lso fvouble fo the ection; howeve, the SO 2 level depends on the sulphu content of the feed mteil. It is possible to intensify the sulphtion ection by ddition of NSO 4 s it ws pctised in the pst2. The typicl tempetue nge is C. Testwok in Outotec s R&D cente confimed tht bove 650 C, Fe 2 O 3 is the pedominnt stble ion compound. Pe-existing ion sulphtes decompose to hemtite, while substntil decomposition of coppe sulphtes stts only t 700 C. At 680 C, 93 pe cent of the coppe exists s sulphte, while t Figue 2 Phse digm AIR BLOWER Figue 3 Rosting pocess FLUID BED FEED SLURRY QUENCH TANK OFF-GAS TO GAS CLEANING AND SULPHURIC ACID PLANT CYCLONE DUST RECIRCULATION SPENT ACID TO LEACHING 456 JUNE 2012 VOLUME 112 The Jounl of The Southen Aficn Institute of Mining nd Metllugy

3 Sulphting osting of coppe-coblt concenttes As explined in the pevious section, the tempetue window is C. The sluy density is djusted to slightly highe thn tht equied fo utotheml opetion. Fine tuning of the tempetue is chieved by wte o liquo ddition into the sluy t the inlet to the sluy lnces. Rosting i entes the funce though the nozzle gte. The height of the fluidized bed is 1 to 1.5 m, coesponding to windbox pessue of mb. The clcine is dischged vi n oveflow wei. Entined dust pticles leve the funce with the off-gs nd e septed in cyclone stge. The smll dust pticles contin moe sulphte-compounds thn the funce bed mteil, due to the diffeent pocess conditions in the feebod. This fct pplies fo coppe, coblt, nd unfotuntely lso fo ion. In ode to limit the content of ion sulphtes, the dust is theefoe septed in the cyclone stge nd etuned to the funce. Owing to its high sulphte content, the dust is sticky nd its flow behviou is poblemtic. A boile is stndd in some othe osting pplictions to ecove het fom the off-gs. Howeve, it is not used in sulphting osting becuse of the low off-gs tempetue nd the stickiness of the dust. The off-gs tempetue is educed with wte in one o two quench stges. Sluy feeding nd wte quenching of the off-gs genetes the high volumes of off-gs. The contined wte vpou hs to be emoved by condenstion in gs cooling stge. A sulphuic cid plnt is stndd fo the finl off-gs tetment. The mjoity of the clcine is emoved fom the oste vi height-djustble bed oveflow nd is dischged to the clcine quench tnk. In othe osting pplictions the clcine is cooled by indiect het tnsfe in wte-cooled fluid-bed coole. Indiect clcine cooling is usully pplied if the clcine is to be conveyed nd stoed dy o if wte is shot. In endothemic pocesses, clcine cooling is souce of het ecovey to educe the fuel consumption. Gold oe ostes tht tet the whole oe insted of concentte e endothemic owing to the low sulphu contents of 2 5 pe cent. moe thn 90 pe cent to CuSO 4 nd CuO.CuSO 4. The tio between the sulphte nd the bsic sulphte is usully ound 2:1. The clcine contins to smll extent CuO nd tces of CuS. Moe thn 95 pe cent of the ion is in the oxide fom. The est ppes minly s sulphte. The ion sulphtes e soluble in the leching stge. Up to 5 pe cent of the ion is usully dissolved; the est emins in solid fom. Moe thn 95 pe cent of the coblt is sulphtized; the est is oxide. The selected exmple is bsed on feed te of 15 t/h (dy bsis). Sluy feeding t wt% solids is usul. The equied osting i flow is Nm³/h. The offgs flow te fte the oste is Nm³/h. It inceses to moe thn Nm³/h in the off-gs quench stges nd is educed to Nm³/h fte wet gs cooling. The SO 2 content of the off-gs is 5 pe cent,, which mkes it suitble fo sulphuic cid poduction. The exmple eflects the bse cse fo sulphting osting. Coppe nd coblt ecoveies e usully bove 90 pe cent. Adpttion to diffeent feed mteils The sulphu distibution between clcine nd off-gs is detemined minly by the tempetue, which in tun should be between 650 nd 700 C to pomote fomtion of ion oxides nd of coppe/coblt sulphtes. The tio of Cu+Co/S is typiclly 1.2 to 1.3 fo concentte A types. This tio is detemined by the minelogy of the oe. High chlcocite content cuses lowe Cu/S tios. Concenttes of type B hve Tble I Chemicl nlyses of typicl concenttes Concentte A, wt% Concentte B, wt% Cu Fe 18 3 Co S 3 3 J o u n l P p e Conventionl sulphtizing osting Feedstock exmples e shown in Tble I. Concentte A is typicl fo most elized pojects so f. The coppe content is usully less thn the sulphu content. The ion content vies between 15 nd 25 pe cent. Coblt is lwys pesent in the low pecentge nge. Concenttes of type B wee the typicl in the pst; howeve, they hve been ppeing in some ecent pojects. The coppe contents e much highe nd the sulphu contents much lowe comped with concentte A. Coppe is between 30 nd 40 pe cent nd sulphu is well below 20 pe cent. Ion contents cn be s low s 5 pe cent. Concentte A contins minly chlcopyite with low potion of chlcocite whees in concentte B chlcocite pedomintes ove chlopyite. This vition ffects the het blnce, the clcine composition, nd the offgs tetment. The dt in Tble II epesents the osting opetion with type A concentte. Coppe sulphide is conveted by Tble II Cse A Design vibles fo conventionl sulfting ost Input Output Feed o clcine Mss flow kg/h Cu % Fe % Co % 3 3 S % 25 9 Moistue % Pocess conditions: Feed = Concentte A Rosting i C t 50 C Nm³/h Roste offgs Nm³/h Gs flow to cid plnt Nm³/h SO 2 (dy) 5 Vol% The Jounl of The Southen Aficn Institute of Mining nd Metllugy VOLUME 112 JUNE

4 Sulphting osting of coppe-coblt concenttes mostly Cu+Co/S-tios below 1. The consequence is tht the clcine contins highe potion of coppe nd coblt oxides nd tht the SO 2 content in the off-gs dops well below the limit fo utotheml sulphuic cid poduction. The phse digm in Figue 2 shows tht the opeting point is shifted towds the stbility fields of bsic sulphtes nd, even, of coppe oxides. The diffeent clcine composition ffects the conditions nd the sulphu blnce in the leching nd SX-EW pocess stges. Het-blnce clcultions show tht utotheml osting is not sustinble t sluy solid content of 65 pe cent. The following possibilities exist to ensue utotheml osting t low sulphu contents: Highe sluy solid content Solid feeding insted of sluy feeding Peheting of osting i Use of oxygen-eniched osting i. A highe sluy solid content is possibility if the sulphu deficit fo utotheml osting is only smll. The physicl limits of thickening nd sluy pumping hve to be consideed. Solid contents bove 70 pe cent e sometimes difficult to chieve in conventionl thickening, nd sluy tnspot becomes citicl t high solid contents. Moeove it is obseved tht tomiztion of the sluy t such high solid contents is difficult. Solid feeding equies filttion of the sluy. The feeding system hs to be chnged. Figue 4 shows feeding with slinge belts, which hve been common pctice in Outotec zinc nd pyite ostes fo long time. The mteil is fed diectly onto the fluid bed. Dust entinment is theefoe limited. The feed mteil cn be moistened with spy wte on the feeding belt conveyo. This helps to contol the tempetue in the funce. Consideble expeience hs been gined in zinc oe nd pyite osting. The mteil entes the funce though feed pots nd is homogeneously distibuted in the funce. The funce hs to be unde slight negtive pessue to void escpe of osting gses though the feed pots. In the event tht plnt opetion is distubed, utomtic gtes shut the feed pots nd feeding is stopped. Slinge belt feeding is used even fo vey fine concenttes with 80 pe cent below 45 µm. If equied, micognultion stge cn be incopoted in the feeding system e in ode to tckle the poblem of supefines. Peheting of the osting i is common fo endothemic pocesses such s clcintion of luminium hydte. In ode to ensue utotheml osting, the het contined in the clcine is tnsfeed in clcine cooling to the osting i. Figue 5 shows typicl fluid-bed coole solution s used in AIR BLOWER FEED FLUID BED QUENCH TANK CYCLONE DUST RECIRCULATION Figue 4 Feeding system fo solid feeding slinge belts OFF-GAS TO GAS CLEANING AND SULPHURIC ACID PLANT SPENT ACID TO LEACHING Roste Feed Bin Ciculting Fluid Bed System Fluid Bed Ai Pehete Clcine Coole Clcine Quench Tnk Gs Clening Oe Fuel Peheted Sec. Ai Ai Het ecovey solution pplied in gold oe osting Peheted Ai to Dy Ginding Wte Sec. Ai Lecing Figue 5 Het ecovey in clcine coole 458 JUNE 2012 VOLUME 112 The Jounl of The Southen Aficn Institute of Mining nd Metllugy

5 Sulphting osting of coppe-coblt concenttes Outotec s fluid-bed pocesses fo sevel decdes. To dte such instlltions e uncommon in osting pplictions s osting is lwys exothemic. Fo endothemic pocesses such s luminum hydte clcintion o decomposition of sulphtes they e common. The exmple in Figue 5 is fom gold osting plnt in the USA. As whole-oe osting ws pplied the pocess ws endothemic. The sulphu contents whole-oe osting e typiclly below 5 pe cent, which is not sufficient fo utotheml osting. Figue 6 shows futhe exmple of fluid-bed coole with het ecovey fo osting ppliction. The fluidizing i is de-dusted in cyclone nd the dust is diected togethe with the coole dischge to the clcine quench tnk. Peheting up to 400 C is common. Pocess clcultions fo osting of concentte B show tht the osting i needs to be peheted to 330 C to ensue utotheml osting with sluy feeding t wt% solids. The clcine is cooled to 250 C. Futhe clcine cooling is possible; howeve, owing to the wek het tnsfe t low tempetues it is moe economicl to quench the clcine once its tempetue dops below 200 C nd to use the contined het in clcine leching. The fluid-bed coole contins i bundles though which the osting i is diected countecuent to the clcine flow. The coole is sttiony; it contins no mechnicl pts, which keeps mintennce t minimum. A fn is equied with cpcity ound 2000 Nm³/h fo fluidizing the clcine. This i stem is heted in the coole nd is intoduced into the funce s secondy i t the conicl funce section. Tble III shows tht the osting i equiement is substntilly lowe thn fo cse A. The offgs volumes e lso less. The SO 2 content is 1-2 vol.%, howeve, which is not sufficient fo sulphuic cid poduction. The SO 2 content should not be less thn 4 vol. % fo economic cid poduction. At SO 2 contents below 1 vol.% simple scubbe solutions cn be pplied. And in the SO 2 - nge of 2 4 vol. %, specil solutions e equied tht e costly eithe in tems of enegy o chemicls. We hve investigted oxygen enichment s it is used in numbe of osting plnts. The dt is shown in Tble III. At n oxygen enichment of 30 pe cent the i needs to be peheted to 280 C fo utotheml osting. No benefit is deived s the expense fo the clcine coole emins unchnged. The SO 2 content inceses to 2 3 vol.%, which is still insufficient fo sulphuic cid poduction o, moe pecisely, fo cid poduction without dditionl sulphu combustion. The off-gs volume deceses considebly to only Nm³/h. Tking ll of the foementioned possibilities into considetion, we find tht peheting of the osting i seems to be the most pofitble solution fo sulphting osting of concenttes with high coppe nd low sulphu contents. The equied equipment is well known nd is in opetion in numeous Outotec fluid-bed plnts. Roste opetion is pcticlly unchnged with sluy feeding t common solid contents. The off-gs volume is low; howeve, it equies scubbe solution fo SO 2 emovl. The high wte content t sluy feeding is supposed to pomote the fomtion of coppe sulphtes. Feeding of solid filte cke t 8 pe cent moistue nd tempetue contol by wte ddition would povide pocess off-gs with lowe wte content; howeve, the offgs composition is nywy quite simil to n opetion with sluy feeding. In numeous pilot tests we could not discen cle tend, whethe sluy feeding suppots the fomtion of metl sulphtes comped to feeding of filte cke. J o u n l P p e Clcine fom toste Coole Secondy i to oste Tble III Cse B Design vibles fo modified sulfting ost Input Feed o clcine Output Ai bundles Secondy i fo clcine fluidiztion Quench tnk Figue 6 Clcine coole fo osting ppliction Mss flow kg/h Cu % Fe % 3 2 Co % 3 2 S % Moistue % Pocess conditions: Feed = Concentte B Opetion with i Rosting i t 330 C Nm3/h Roste off-gs Nm³/h Gs flow to cid plnt Nm3/h SO 2 (dy) 1 2 Vol-% Opetion with oxygen-eniched i Rosting i t 280 C with 30% oxygen Nm3/h Roste offgs Nm³/h Gs flow to cid plnt Nm3/h SO 2 (dy) 2 3 Vol-% The Jounl of The Southen Aficn Institute of Mining nd Metllugy VOLUME 112 JUNE

6 Sulphting osting of coppe-coblt concenttes Figue 7 Pilot plnt fo continuous osting tests Test wok nd plnt design Fo exct plnt design, osting tests e necessy. Outotec opetes numbe of fluid-bed test units in thei R&D cente in Fnkfut. Pilot tests in continuous units pemit detiled plnt design povision of pefomnce guntees. Figue 7 shows the pilot plnt tht ws used in designing numbe of Outotec ostes. All Outotec gold ostes (Cotez nd Clin in the USA, Klgoolie in Austli, Minhs in Indonesi, nd Sym in Mli), s well s numbe of coppe nd pyite ostes, hve been designed following tests conducted in this plnt. The pilot plnt llows one to extct infomtion bout poduct qulity nd off-gs composition. Leching tests cn eithe be cied out t ou R&D cente o by the poject owne. Fo the moe common zinc nd pyite osting pplictions, testwok is mostly not equied s ou dtbse built up ove the yes pemits us to design plnt without tests. Othe pplictions, such s gold nd coppe osting, e diffeent. The numbe of built plnts is fewe nd the vition in feedstock mteils is wide. Outotec hs built osting funces with nozzle get es fom 15 to 138 m². The numbe of plnts fo sulphting osting is low. Most hve funce e of bout 50 m². Outotec hs built ostes below 50 m², mostly fo specific duties; howeve, these e no longe in opetion. Outotec build sevel modulized osting funces in the ely yes of thei development. Fo specific pojects it might be bette choosing smll funce. It is impotnt theefoe to keep the bility not only to design nd build bigge plnts, but lso to develop tilo-mde solutions fo economic opetion on smll scle. Refeences 1. PAWLEK, F. Metllhüttenkunde. Wlte de Guyte, Belin, New Yok, PALPERI, M. nd AALTONEN, O. Sulphtizing osting nd leching of coblt oes t Outokumpu Oy. Jounl of Metls, vol. 34, pp JUNE 2012 VOLUME 112 The Jounl of The Southen Aficn Institute of Mining nd Metllugy