Note: Descriptions are shown in the official language in which they were submitted.
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 _
