CA1196502A - Method of producing metallic cobalt from oxide cobalt- based material - Google Patents

Abstract

Method of Producing Metallic Cobalt from Oxide Cobalt-Based Material ABSTRACT

A method of producing metallic cobalt from an oxide co-balt-based material which comprises producing a plasma jet by passing a reducing gas through the zone of electric dis-charge, heating the oxide material by the plasma jet to a temperature of about 1450°C to about 1580°C, at which metal-lic cobalt is melted down and cobalt oxides are reduced to metal. The reduction of cobalt oxides to metal is effected in the presence of the reducing gas fed in an amount rang-ing from about 1.15 to about 1.5 times that of the reducing gas required in accordance with stoichiometry. In addition, the method comprises desulphurization of the molten metallic cobalt and its refinement effected by removing gases dis-solved therein.

Description

METHOD OI~l Pl~ODUCING ~IETA1~IC COBA~T

The present invention relates to pla~ma metall~rgy, and more in particular~ to a method of' producing metallic cobalt.
The invention can be especially useful in pyronetallur-gy for the reduction of' metal o~ides when s1lbjected to the action o~ a lo~ temperature plasmaO
~ he demand in metallic cobalt increases with every yearO
More and more cobalt producing plants are coming in-to serviceO
Cobalt is finding an ever greater application in such bran-ches of indus-try as s-teelmaking, elec-tronics, electrical erl-gineering, atomic induutry~ etc.
There are known three pyrometallurgical methods of pro-ducing metallic cobalt, namely:
- reducing a cobalt-containing oxide material by means o~' a solid reducing agenS at a temperature of' up to '1200C;
- reduclng a cobaLt-bearing oxide material in a flow of a reducirlg ga~1 such as hydrogen, followed by melting o~
cobalt po~lder in an induction f'urnace;
- reducing a cobalt-bearing oxide rnaterial in an elec-tric furnace in the process of' melting with a solid redu-cing agent whereby molten cobalt i~ obtained The l'irst o~' the above-Tner1tioned method~ l`ai:L~ to px~o-duce high-~uallty metn:l 'becau~e o~' the ~'act tha-t uulph~
~nd other adml~:t~e~ pre~cnt in ~mal.l. amo~ in the cobal-t-cor1t~r~ln~; o~lc1~ materia:l are tr~n~e.rred into rnetal and thu~ ~ower th~ cont~r1t o:~' cobalt ther~in.
rr1le ~eaorlcl E)x~:~or-~x~t method i~ u~e(l ~'or the productlor a~

o~' hard cobalt-bearing alloys. A di~advantage o~' this method i~ a long d~atlon of the reduc-tion cycle which proceed~ at relatively low tempera-t~es.
The mo~t f'requently u~ed is the third method according to which a cobalt bearing oxide material i~ reduced in the proce~s of melting e~'fected in electric f'urnaces ~ith the aid of a ~olid reducing agent. This methocl i~ carried ou~
as follow~. An electric furnace is charged with an oxidized cobalt-bearing material intermixed with a solid reducing material. What i8 importan-t to attain in the reduction mel-t~ng of this material is a complete reduction o~ the cobalt oxidized compounds, removal of admixture~ ~'rom~ and desul-phurization of', metal. Pe-troleum coke or g~raphite powder are normally used as the reducing agent ln the reduction melting, The mel-ting iR u~ually carried out in resistance fur-nace~ equipped with carbon hea-ting elements or in electric furnace~ with an arc burning between the electrodes.
The reduction melting of a cobalt-bearing oxide mate-rial i~ eff'ected in a ~tepwise manner in ~ix stages t com-prising:
- preparatlon and char~irlg, ol' arl initial material, mel~lg--down ~nd x~e(lu~tion;
- decarbol~lza tio~;
- deox~datlt~
- de~ulphluriza-tiorl;
- -tappin~o~' metal.
~oporldi~ ; on tho ~ype o~ rnnce, th~ heat time may ?%

rc~nge from 6 to 8 hourciO The ma-terial charged into the fur~r nace is compo~ed of r~5 to 88(7V of cobalt-'bearing rnaterials, uch a~i cobalto-cobal-tic oxide and secondar~ raw material~
(scrap, magnetic frac-tio~ of' slag, rejec-ted metal) and o~
'l2 to 2~% of a reducing agent, ~uch as petrole~n coke, coke ~'ines, broken graphite and powder.
Silicon or aluminium are u~ed, separately or together, a~ the deoxidizing agent.
Decarbonization o' metal iB ~ffected with the aid o~' cobalt mix~d oxide added therein-to.
De~ulphuriza~ion of metal is e~ected by producing f'rom 'I to 5 lime slag~, wi-th chalk or lime and calcium flu-oride or ~oda being charged into the f'urnace.
The recovery o~ ~lag constitutes 10 per cent of the ~'ini~hed metal (commercial cobalt), with up to 20 per cent of cobal-t contained therein.
On completion o~' melting, the metal is poured into ingot mould~ and then delivered a~i ingots to a tumbler barrel to be cleaned o~ lag.
The prior art technology permit~i the recovery of co~
balt to be in the range of 98~7 to 997v by weight:
- the content o~' commercial metal rarlging ~rom 95 to '~7,'o;
- the corlterlt o~' du~t r~ng~in~ rom ~ to 'I~,5%;
thr3 conterlt o' ~l~g r~n~-rirlg l'xom ~I.o to ~.5',~"
Xrrever~ible lo~e~ ol' me-~al amoun~ tro 'l~O - 'I.j%~
~ nb~ve-~d~cribed method and apparntu~ ~u~'l'er ~'ro~
th~ l`o;llowlng clL~3nclv~n~a~ , r~lmcl~:

- long duration o:~` the hea-t cycle;
- fre~uent replacement o~ electrodes~
- poor heat reEJi~3tance of the refrac tory lining and of itc3 c3eparate part~3;
- un~3table power ~upply conldi-tion~ during operation;
- exce~3E~ive amount~ of fwne~3 and ~reat losse~3 o:f metal carried away with duat;
- excec3sive noise (for furnacec3 with independent arc) - a E3ubst~tial consumption ol secondary material~;
- multiple production of ~31agB required for the rem val of' E3ulphur, - a conE3iderable waE3~e OI metal loE3t wi-th lining and f31ag~3;
- enormouE3 liberation o~` E3moke.
The above diE3advantages of the prior-art melting pro-Cef3E3, aF3 well a~ itE3 low ef:f`iciency, called for the neces l3ity to develop a new method which would be f3uitable for uE3e in the proceE3sing of an oxide cobalt-bearing material b~r way of itB reductlon to be e:E:fec ted under -the action of a low-tempera ture pla~3ma.
Attempt~3 to find ~olution to thiF3 problem led to a method of' carbothermic reduc tion o:~' an ox Lde cobalt-bear-in~,~ material whloh i~3 3ub~ec ted to p:l.aEJma-ax c heating in a pln~ma :f`urrlace e~luipped with nn ~~ o t mould ( ~3ee a book by ~u. V. r~`~3-vel;lco~r Qnd ~ 0 Panl'llo~, enli Lt:led 'I:tow-Tempera-tur~ Pln~3mn ~ l~educ t:Lon Proce~3e~ auka Publi~3her3, ~,lo~cow, IC3~3~ ) ~ccordlrl~ to th~ m~thod~ a ~;ranulated charge with gra~ule ~izes of l to 2 cm, compo~ed of cobalto~cobal-tic oxide, coke ~ine~ and a binder 9 i.S fed into a crucible (20% of the total weight of the charge) which is placed wi-thin a chamber. The latter i8 evacuated to a pressure of up -to 0.5 mm ~g, and then i~ treated wi-th technical-grade ~rgon. ~hen9 a plasma generator i~ brought in operation.
Its power capacity and the flow rate o~ the pla~ma-gene~a-ting ga~ are adjusted as required~ The charge in the cru-cible i~ melted do~n by means of a plasma ~rc, and the re~
mainder of the charge material i~ fed at regular inter~als in ~mall batches onto the surface of molten metal. Apart from being vigorou~, the reduction proce~ accompanied by the production of ~oot carbon which i~ depo~ited on the wall~ of -the chamber accomodating the crucible. During melting, Co~ e and Cu comple-tely pa~s into metal .
The proce~ critical as regards the carbon/oxygen ra-tio, and carbonization o~ metal is po~ible.
The practical value o~ the above proce~ is somewhat lowered by the nece~ity to prepare the granulated charge and to use the low-temperature plasma for a single purpose of heatinP
In addition, the reduction of the oxide cobalt-bearing materlQ~ with tha u~e o~` a ~olid reducing agent make~ lt nece~ary ~or the pl~mn f`urnace to be charged with ~la~
iormlng, dac~rbonlæing ~nd d~ox~dlæing~ materiala. In oth~r word~ tho meltlng proc~ ln a pla~ma ~`urnace during re-du~lon o~ -th~ cobalt~be~rirlg oxide mator~al with the ~olid reducing agen-t hardly di~'~erf~ :E.rom the proces~es run in -the electric Yurnaces of indirect heating ~a resif3tance f'urnace Or a furnace with independent arc). ~heref'ore, this me-thocl suf~er.~ ~rom all tne di~advantagles inherent in the af'orede-scribed method o~' reduction melting~ e~cept of production capacity.
It is an object o~ the presen-t invention to reduce the amount o~ admi~tures in metallic cobal-t.
Another object of the invention is to reduce the losses of metallic cobalt carried away with slQgs by lowering the amo~t of the latter.
Still another object of the invention i~ to bring down the time of operating cycle during which metallic cobalt iB produced, by reducing -the n~nber o~ slag-forming opera-tions.
Yet another objec-t of' the invention is to preve~t pol-lution of the atmosphere by elimi~ating or f3ubstantially reducing the amount o' carbon oxide in the outgolng gases~
r~hese and other objectfs of the invention are accomp-lifshed by the provifsion of a method f'or production of' me-tallic cobalt ~'~om a cobalt-based oxide ~a-terial by heat-ing this material with plafsma je-t to the cobalt melting temperature, reducin~ cobalt oxide~ to metal in the pre-~ence of' a redllc~ng gaf~, uubjecting the re~ult~lt rnolter metal ~o de~ulph~ ation, nnd re'~nlng the latter by r~
mov~n~ the ga~3~ dlf~olv~d there~l, wh~re~l, according -to tho :In~entlon, the pln~ma jet iu produced by pa~f~ ; the ~o~ucln~ ~'Q~ 'O~Ig'h 't~ on~ o~' electrlc dl~chargre~ the _ f~ _ oY.ide material :i~ heated -to a temperature ranging f'rom about '1450oc t~ about '1580C, and the reducirlg gas requir~d ~'or the reduction oi` cobal-t oxide~ i.s fed in an amo~-t ranging f~rom about '1.15 -to about '1.5 time~ that of the reducing gas re~uired in accordance with stoi.chiometry.
~ hua, the method of -the inve~tion permit~ the a~ount of admix-tures conta~ned in metallic cobalt to be reduced by eliminating the nece~sity of' u~i.ng a solid reduc,ing agent in the proce~.
~ g a re~ult, the amount of carbon oxide contained in the off-ga~es i~ brought down, thereby prev~nting pollution of the atmo~phere and impro~ing health condi~tion~ at ~n-du~trial enterprises.
Emplo~ing a reducing ga~ a~ the pla~ma-forming agent would enhance it~ reactivity with the resultant decrease in the time re-luired for the reduction o~' cobalt oxides to metal.
If the amount oY the reducing ga~ u~ed in the method i~ lee~ than '1.'15 time~ that of the reducin~ ga3 re~luired according to ~toichiometry, the metallic cobalt produced will contain an exces~ive amo~mt o~' oxy~en. If, however~
the amourlt of thi~ ~a~ i~ more than '1,5 ti1ne~ that -requi-red by ~toichiometry, the metQllic coba.lt thu~ produced will contain ~1 exce~ive ~mount of'.ixon reduccd ~'rom the cob~lt-bearin~ oxid~ mat~r:la:l.
Tho ~elec-1;e('l lower and uppe:r boundo:~ie~ in tho amo~t~
o.l' roducin~ ~a~ , r~~ ln~,1 l'rom ~bout 1~'15 to about 5 tlm~ -thnt o~' 1;he .~.~oducln~ a~ ro(lu:Lred in accor(l~lce with ~toichiome-try9 en~ure the production o~ metallic cob~lt with a minimum content o~ admixtures, for example, iron.
~ he temperature limits ~1 t:he proce~s9 r~nging from ab-out 1450C to about l580C, are :respectively ~elected in accordance ~Jith the cobalt melting temperature and tha ope-rating conditions oi the refractory lini:ng o~ the ceramic crucible and the roof of the furnace with a ~iew to pro longing its service li~e.
~ Ioreover, in the method of the invention u~e is made of hydrogen of the reducing gas for the desulphurization of metallic cobalt, which enter~ into reac-tion wi-th ~ulphur, contained in the melt, to form volatile compounds. This make~ i-t po9~ible to remove sulphur from the melt and thus to lower the contents of ~u~phur in the produced metallic cobalt. As a re~ult, it become~ fea~ible to reduce -the number of technological operation~, ~or example, ~uch as the production o~ ~lag~ ~or the removal o~ eulphur, and~
conse~uently, to bring down the time of the production proces~ and the losse~ o~ metal wa~ted with slags.
Utilizing a reducing ga~ would permit the content~
of~ carbon in metallic cobalt to be lowered with the re~ul-tant improvement in the quality o~ metal ancl ~horter dura-tion of thc process due to ellmination o~ ~uch technolo-~ical operQtio~ a~ ~lecarbonlzatlon oi m0tallic cobalt and it~ ~u`~oCluent clooxldatlon.
q'he reduci~n~ ga~ pa~d thxough the zo~ of burn~ng of ~ elect~-ic Idl~char~o iu pre~erab:Ly ~ub~titutcd by a n~ut,r~ to bo u~od lo~ r~iln:ln~l; the m~lt form~d o~ me-~) _ ~g~

-tallic cobalt, whereby it becomes possible to remove the h~droO~en o~ a reducing ~a~ ~rom the molten me~alllc cobal-t.
In the course oP refirling, -the temperature of -the mol-ten metallic cobal-t i9 preferably raised to -the metal tappin~
temperatuxe, which is about 'l650~', whereby high quality metal i8 obtained when poured into ingot mould~.
The invention will ~e ~`urther illustrated~ by way o example only, with reference -to -the accompanying drawing, whereino ~ IG. 1 is a schematic view of plasma melting furnace ~ith a ceramic crucible and a hearth electrode for carrying into effect the method of the in~ention for producing me-tallic cobalt.
The method of the invention i~ carried out in a plasma melting furnace 1, ~uch as shown in E`IG. 1, which compri~es a ceramlc cruclble 2 closed by a refractory-lined cover havin~ a gas outlet pipe 4. The central part of the cover ha~ an ope~ing 5 which receives a plasma ~enerator 6 whose workin~ elec-trode 18 connected to -the negative polari-ty of a power ~ource (not ~hown). 'rhe po~l-tive polarity of the power source i~ connected to an electrode 7 which is loca-ted at the bottom of the crucible 2. ~i`oxmed in -the side w~ll of th~ crucible 2 1~ ~ tap hole ~ wlth Q pouring llp 9.
'rhe methocl of the irlvent:Lon i~ o~rrl~d out a~ -follow~.
~ cob~ boMrlrl~ ox:Lde matorlal 'lO is l'ed into the c~r~mic cruc:L`ble ~. ~rhe m~tex~ l 10 i~ hcated by a pla~ma I O

d jet 11 to a temperature ranging from about 1450C to about i5800C. The plasma je-t 11 is generated by pas~ing a reducing gas7 such as hydrogen, natural raw or conversion gas mixed with a neu-tral gas, -through the zone of electric dischargeO
The electric discharge glows betweerl the working elec-trode of the pla~ma generator 6 and thle melt 12.
The reduction of` cobalt oxi~des to metal i~ effected ~der the action of a reducing gas with an enhanced reacti~
vity, fed in an amou~t of` about lo15 to 1~5 times that of the reducing ga~ required in accordance with stoichiometry Simultaneously, the molten metallic cobalt is subjected -to desulphuxization ~hich is made pos~ible due to the forma-tion of hydrogen sulphide discharged -toge-ther with the out-going ga~es throu~h the outlet pipe 4.
A required temperature, rangin~ from 1'~50 to 1580C, iB maintained throughout the reduction process by adjus-t~ng the power capacity of the plasma generatox 6.
~ fter cobal-t oxides have been reduced to metal and the desulphurlza-tion o~ the re~ultant melt completed, the lat-ter ie then subjected to re~ining, -the operation aimed at re-movin~ hydrogen di~solved in the melt. ~or thi~ purpo~e, the r-educing ga~, pacsed through the æone o~ electric di~-charge, i~ ~ubatitu-ted by a neu-trR~ Q~ ~uch as ar~on. In the cour~e o~ re~inln~;l the temperature o~ the molterl co-balt i~ r~ d to about ~1680C, which is the metal tappirlg `tempqratUra t on~urln{, a hi~h quallty oi rnet~l on be~lg oured lnto ingot moulcl~.
'l'h~ lnv~n~ion wl:ll b~ iu~-ther lllu~trated by the lollow-ing exar,1ple.
~xample Initial cobalt~bearing oxide material, composed o~ 71%Co, 0~25% Ni, 0.28~ E~e, 0.02% Cu, 0O07% Mn, 0.01~% C and 0.2~o S~ with the particle ~ize~ o~ up to 3 mm, was æubjected to reduction of the pla~ma furnace, ~uch a~ ~hown in FIG. '1, with the power capacity of the pla~ma generator being r~o Kwt.
A hydrogen-con-taining gas ( ~ ) or a synthetic ga~ (Co ~
was introduced through the plasma generator in an amount o~' 1.4 time~ that of -the gas required in accordance with stoi-c~iometry. The temperature of the melt was maintained with-in the range o~ 1480 to 1520Co The reduction proce~ wa~ not attended by any spatter~
ing of molten me~al;
~ he completion of -the reduction proce~s wa~ determined by an increase in the content~ of` hydrogen ~L the outgoing ga~e~, whereupon the molten metallic cobalt wa~ ~u~jected to ref'ining during which -the ga3e~ ( ~ ) and non-metallic inclusions (par-ts o~ the lining) ~ere removed therefrom while a neutral gas, ~uch a~ argon, wa~ ~ed -through the plaRma ge.nerator 6.
In the cour~e of refining operation, ~etallic cobalt ~wne heated to a temperature o~`'162~ to 1~50C, ~ld then po~ed into lngot mould~.
'~he ~'in:l~hed metal wa~ compo~ed o~ 99.5~0 Co, 0.~ Ni, 0,09,~ 'e~ 0.0~% Cu, ~ol~yv ~, 0~ t a~ ~ ~
~ h~ method. o~` producin~ metalllc cobalt according to 1;he ~llverl~ion m~y bc car:~ied :into e~:tect by mean~ o:f' a '12 ~6~i~Z

pla~ma :Eurnace wi-th a ceramic crucible, ~uch a~ disclosed in U . S . Pat . No 4, 002 9 4 66 .

~ 13 _

Claims (4)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:-

1. A method of producing metallic cobalt from a cobalt-based oxide material, comprising producing a plasma jet by passing a reducing gas through the zone of electric discharge;
heating said material by the plasma jet to a temperature ranging from about 1450°C to about 1580°C at which metallic cobalt is melted down and cobalt oxides are reduced to metal;
the reduction of cobalt oxides to metal being effected in the presence of the reducing gas fed in an amount ranging from about 1.15 to about 1.5 times that of the reducing gas required in accordance with stoichiometry; subjecting the resultant melt of metallic cobalt to desulphurization and effecting its refinement by removing gases dissolved in the melt.

2. A method of producing metallic cobalt as claimed in claim 1, wherein the molten metallic cobalt is refined by a neutral gas used instead of the reducing gas passed through the electric discharge zone.

3. A method of producing metallic cobalt as claimed in claim 1, wherein in the course of refining operation the temperature of the metallic cobalt melt is raised to the tapping temperature of cobalt 1680°C.

4. A method of producing metallic cobalt as claimed in claim 2, wherein in the course of refining operation the temperature of the metallic cobalt melt is raised to the tapping temperature of about 1650°C.