CA1195509A - Method of producing metallic nickel - Google Patents

Abstract

Method of Producing Metallic Nickel Abstract A method of producing metallic nickel from a nickel--bearing ode material comprises producing a plasma jet by passing a reducing gas through the zone of electric discharge, heating this material by the plasma jet to the nickel melting temperature. In the course of heating nickel oxides are reduced to metal, and iron and cobalt oxides contained in the nickel-bearing oxide material are partially reduced with the resultant formation of a melt of metallic nickel. The reduction of' nickel oxides to metal is effected in the presence of reducing gas fed in an amount ranging from about 1.2 to 1.75 times that of the reducing gas required in accordance with stoichiometry. In addition, the method includes desulphurization of the resultant melt of metallic nickel and its subsequent refinement by removing therefrom the gases dissolved in the melt and incompletely reduced iron and cobalt oxides.

Description

~E~HOD QF PRODUCI~G ME'~I~IC NICKEL
The prese~t invention rela-tes to plasma metallurgy~
and more particularl~, to a mebhod o~ prod~ci~ metallic nickel~
~ he invention is readily applicable to t~e production o* nickel which is made in the ~orm o~ pellets a~d i~ots ~or use in the iron-a~d-steel making industr~9 as well as to the production of n~w alloys7 such as Mon~ metal, to be used in the manufacture of engines, and ma~netic alloys for the ele¢tronic indus~ry.
In view o~ an ever growing demand for less expe~sive ~rades of metallic nickel, as compared with appreciably ex-pensi~e elec-trolytic and carbonyl nickel~ it is an imFerative ~or the producers o~ nickel to reduce its production cost.
One o~ the mos-t wid~ly used methods o~ producing înex-pensive grades of metallic nickel comprises processing nickel-bearing oxide material by way o~ its reductio~9 which is ef~ected by melting this material i~ a mi~ture with a solid reduci~g age~t through -the usa of elec-tric current.
The above met~od consists i~ that a charge is prepared Prom a ~ickel-bearing oxide ma-terial ? Por example, ~ickel monoxide, and a solid reducing agent; such as petroleum or pitch cokeq whereupon the charge is melted down under the action of electris currentO In the process o~ melting, -the oxygen o~ the ~ickel-bearing oxide material intera¢ts with the solid reducing agent with the resultant -~ormation o~ a metallic niGkel mel-t.
~ 'o effect decarbonization o~ metall~c nlckel, nickel .. ~

monQxide is introduced into the melt o~ the ~o:rmerO There-a~-ter, silicon is added lnto th~ melt o~ metalllc n~ ck~l to ef~ect its deo~idation, ~he melt o~ me~allic nickel is ~ur-ther subjected to desulphuriza-tlon~ which is e~eoted through th~ use of calcium-con-taining materials~ such as lime. The described method is per~ormed b~ means o~ ~ three-phase electrio ~urnace similar to that used in the steel~
making practice. The product o~ reduction contains about 98% o~ metallic nickel (see, ~'or example~ a book '~etal-lurgy o~ Copper~ Nickel a~ Cobalt", vol~ 2~ ppr122~126g Metallurgia Publisher~g ~oscow~ 1977). The yield o~ ~ickel obtained in accordance with the a~oredescribed technology was 99-%~
Howevers the method re~erred to above su~ers ~rom a seriou~ disadvantages~ namely: the production cost o~
metallic nickel is increased due to the necessîty o~ usi~g a solid reducing agent; premixing an initial material with the reducin~ agent; consuming an excessive amount o~ power re~uired for the operations of decarbonization, deoxidation a~d desulphurization; employing slag-forming materials and d~o~idizing age~t.
In addition, the above method is disadvantageous in that the iron and c obalt oxides contained in -the nickel-bearing materlal are completel~ reduced, as a result o~ which iron and oobal-t are transferred into the m~lt o~ metallic nickel and thus bring down the content o~ -the la-tter in the melt.

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The above-mentioned disadvantages of the prior-art process called for the necessity to develop a me-thod of pro¢es-sing a nickel-bearing oxide material ~o be e~fected under the action of a low-temperature plasma.
Thus a new method was developed according -to which car~othermic reduction of a nickel-beari~g oxide material is e~fected with the use o~ plasma~arG heating performed in a plasma furnace equipped with an ingo-t mould / see a book by YuoV4 Tsvetov~ S.A. Pa~filo~, entitled "Low-Tempera~e Plasma';, Nauka Publishers, Moscow, 1980~ p.261/.
According to this met~od 9 a granula-ted charge with a gra~ule size o~ 1-2 cm, composed of nickel monoxide, such as fired converter matte with a particle size of 50 -to 100 ~m, coke ~ines with a particle size o~ 63 to ~0~ ~m9 and a bi~der.
The charge -thu ~ repared is then fed in-to tke reactîon zone of a chamber in an amount o~ 0.1 to 0.2 -times that o~ the total weight of the charge delivered durin~ the first feed.
The chamber is evacua-ted to a pressure of 005 mm Hg, a~d then treated with technical-grade argon. Thereafter~ the charge i5 subjected to heating by means of argon-shielded plasma arc. U~der the action of plasma arc, the charge is melted do~n. In the process of mel-ting, the ox~gen contained in tbe nickel-bearing oxids material reac-ts with -the carbon o~ the solid reducing agerlt to result in the r~-duction o~ nick:el to metal. ~he remainder amount OI the charge mateirial is ~ed at regular int~r~als in small batches into bhe melt o~ metallic nickel. The method in ques-tion is carri-ed out with a pressure in the p:lasma plant being maintained in the order of 1005 k~/cm20 A~-ter an ingot has been produ-ced, the plant is deenergized alld the ingot is held in the atmosphere of argon to permit its cooling~ ~he metallic nickel produced in accordance with this method contains abo~t 2 per cen-t of carbon and sulphur, the amou~t o:E which corresponds to i-ts content in the ini-tial material in the range ~rom 0.24 to 0~45 per cen-t.
~ he practioal value o~ the above process is somewhat lowered by -the necessity to prepare granulated charge and to use low-temperatuxe plasma ~or a si~gle purpose o~
heating r In addition, to produce metallic nickel of a desired quality~ the reduction o~ a nickel-bearing oxide material should be effected with -the use o~ slag~forming, decarbonizing and deoxidizl~g materials added into the mel-t o~ metallic nickel as a solid reducing agent~ In o-ther ~Jords, the melting process in a p~asma furnaGe during reduction o~ a nickel~
-bearing oxide material hardly dif~ers from -the processes run in arc three-phase electric ~urnaces. ~hus 9 the method in question has all the disadvantages i~herent in the processes of reduc-tion melting carried ou~ in electric furnacesv Xt is an object o~ the prese~-t invention to reduce the amoun-t o~ admix-tures in metallic nickel produced in accordance ~:~g~s~

wi-th a pgrometallurgical technique~
Another objec-t of the invention is to reduce -the amount of losses o~ metallic nickel carried awa,y with slags by lowering the am~;~unt o~ the latter.
Still ano-ther object o~ the lnvention is to bring down the time re~uired ~or the produc-tion o~ me~allic nickel by reducing the number o~ slag~formiDg operations and egclu-di~ such operations as de~arbonizatlon and deoxidationO
Yet another object o~ the invention is to prevent pollution o* the atmosphere by eliminating or substantially reducing the amo~nt o~ carbon o~ide i~ the outgoing gases.
These and other obaects o~ the invention are accomplis-hed by the provision o~ a method ~or produci~ metallic ~ickel from a nick~1-based oxide ~aterial, comprising pro-ducing a plasma aet by passing a reducing gas through the zone oP electric discharge; heating the nickel-based oxide material by the plasma ~e-t to the melti~g tempera-ture o~
metallic ~ickel; in the process o~ heati~g, nickel o~ides being reduced ~o metal, and iro~ and cobalt oxides contai~ed in the nickel-bearing material bei~g partially reduced in the presence of a reducing gas ~ed in an amount ranging ~rom about 1.2 to 1~75 times that of the reducing gas required in accordance with stoichiometry, with the re~ul-tant ~ormation of a melt of me-tallic nickel; subaecti~g the m~lt o~ ~e-tallic nickel to desulphurization and then e~fecti~g its :re:t`inement by removing there:~rom incomple-tely reduced iron and cobalt o~ides as well as gases dissolved inthe m~lt.

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~ hus, the me-thod OI -the inventi on permi-t s -the amolLnt o:~ admixtures cont~ined in metallic nickel -to be reduced by eliminati~g the necessity o~ using a solid reduci~g agent, slag :~orming materials and d~o:~idizing aOents. As a result, the amou~t o~ carbon o~de con-tained in the outgoiDg gases i~ brought d~wn9 thereby preventi~g pollution of the atmosphere and improvi~g health conditions at industrial enterpri se s .
Employing a reducing g~s as the plasma-~orming agent would enhance its reacti~ity with the resultant decrease in the time re~uired ~or nickel oxides to be reduced to metal~
If the amount o~ the reduci~g gas used in th~ process is less than 1.2 times ~hat o~ the reducing gas required in accordance with stoichiometry, the metallic nickel -to be produced will contain an excessive amount o~ oxygenO I~
however, the amount of this gas is more than 1.75 times that requ~red in accordance with stoichiometryy -the metallic nickel to b~ produced ~ill contain an e~cessive amou~ of iron and cobalt which are red~lced ~rom the initial nickel--bearing oxid~ materialO ~he sele~ted lower and upper boundaries in.the amount o:e the reduciDg gas required in accordance with stoichiometry, ranging ~rom 1r2 to 1.75 times res-pectively, ensure -the pxoduction o:E metallic ni¢k:el wi-th a minimum co~tent o~ admix~ es, suah as iron and cobalt.
By using a reduc:ing gas in the pxocess9 lt i~ pos~ible to bring down the aontenti o~ aarbon in m~talliG nickel, whereby the quality o:f metal is improved and the process time is sub-sta~-tially shortened b;T eliminating such -technological operations a 5 decarboniza-tion o~ metallic nickel and its subsequent deoxidation. In addit:ion" in the method o~ the i~vention use is made OI hydroge-n of -the reducing gas ~or the desulphurization OI metallic nic:kel, which enters in-to reac~
tio~ with sulphur, contained in the melt~ to Iorm vola-tile compounds therewith~ In -this way sulphur is removed from the melt and its content in the metallic nickel being pro-duced is materially lowered~ As a result9 i-t becomes Ieasible to cut down -the ~umber o~ operations ~ ~or e:~ample, such as the production o:f slags for -the removal o:e sulphur 9 and -thereby -to shorten the time of -the production process and reduce losses OI metal wasted with slags~
'rhe raducir~; gas passed -through the zone of electric discharge is pre~erably substituted by a neutral gas to be used for re:Eining the melt o~ metallic nickel by removing there.ïorm incompletely reduced iron and cobalt oxides as wel~ as gases dissolved in the melt.
'rhis permits the hydrogen of -the reduci~g gas dissolved in the melt o~ metallic cobalt -to be removed thereIrom.
In -the course o:E re:~ining, the tempe~ature OI the melt of me-tallic nickel is pre~erably raised -to about 162i~C
with a view to obtaining quality metal when poured in ingot mould 5 .
~ he invention will be :further lllustrated, by way o~ example o~ly, wi-th re~erenc~ to the accompanying drawing 9 wherein:
FIG. 1 is a longi-tudinal sectional view o~ a plasma ~eltin~ ~urnace with a ceramic crucible and a hearth electro-de ~or carryl~g i~to e~ect the me-thod o~ the inventio~
~or producing metallic nickel.
The method of the i~en~ion is carried ou-t by means o~ a plasma melti~g furnace l, such as sho~ in FI~
which comprises a ceramic crucible 2 closed b~ a refractory -lined cover 3 having a gas outlet pipe 4. Fi-tted i~ the central part of -the cover 3 is an opening 5 provided the-rei~ to receive a plasma ~enerator 6 having its worklng electrode connec~ed to the negative polarity o~ a power source (not show~). The positlve polarit~ o~ the power source is co~ected to an electlode 7 uhich is located in the bottom ~f th~ crucible 2~ Formed in the side wall of ~he crucible 2 is a tap hole 8 with a pouring lip 9.
The method c.~ the inventio~ is carried out as ~ollows.
A nio~el-bearinæ oxide material 10 i9 ~ed into t~e ceramio crucibl~ 2. The material 10 i9 heated by a plasma jet 11 to a nickel melting temperature pro~uced by ~he plasma generator 6. The plasma jet ll i9 produced by passing a reducing gas~ such as hydrogen9 natural raw or conversion gas mixed with a neutral gas, through the ~one o~ electric discharge.
The electric discharge is produced between the working elec-tro-de o:~ the plasma generator 6 and the melt 12. 'rhe reduc-tion 5~9 of nic:kel oxide s to me-tal is eIfec-ted under the actio~
of a reducing gas with an enhanced reactivity~ which is ~ed in an amolmt ranging from about 1.2 to 1075 times -that of the reducing ~as re~uired in accordance with stoiehiometry~
Simultaneousl~ the melt of me-tallic cobalt is subjec-ted to desulphuriza-tion, which is made possible due to the ~ormation Gf hydrqgen sulphide discharged toge-ther with the outgGing gases -through the uu-tle-t pipe 4~ A required -tempera-ture in the range of 140~ to 1520C is maintained throughou-t the reduction process by adausting the power capacity o~
the pla sma generator 6.
A~ter nickel oxides have bee~ reduced to metal and the resultan~ melt s~bjected to desulphurization, the melt of metallic nickel undergoes refiniDg operation i~ the course o~ whlch the hydrogen dissolved in the melt is removed.
For this purpose, the reduci~g gas passed through the zone of electric discharge is subs-tituted b~ a neutral gas~ suoh as argon. During re~inlng, the temperature of the metallic nia~el melt is raised to about 1620C, which is -the me-tal tappi~g temperature~ In -this way i~ becomes possible -to en-sure a hlgh quality of metal a~ter it is poured in ingot moulds.
~ he invention will bs further illustrated by th~
following Examples.
Eæample 1 An initial nickel-bearing oxide material composed of 75.4% Ni~ 0.6~o C0~ 0.5% Fe~ 0~5% Cu, 0.01% S, 1.5% Al~ and up to 1.5% Of oxides of other metals (Si, ~n, Mg, etc.) with a si~e particle o~ up to 300~ m~ was subjected to reduction in a plasma ~ur~ace of the type shown i~ ~IG~ 13 with the power capacity o~ the plasma generator being 60 Kwt. A gas miætu~e o~ argon a~d hydrogen9 ~ed wi-th a ratio o~ 1:1 in a ~lo~
rate o~ 10 nm3/h and in an amour~t o~ 1075 times that o~ the reduci~g gas required in accordance with stoichio-~etry~ was introduced -through the plasma generatorO r~he temperature o~ the melt was maintained within the range of 1400 to 1520C~ 'rhe xeduction process was not accompanied b~ any spattering o~ metal, ~he completion o~ the reduction process was dete~mined by an increase in the contents of hydrogen in the outgoing gases, whereupon tke melt o~ metal-lic cobalt was subjected to refining duri~ which the gases (H2) and non-metallic inclusions (parts of the lining and incompletely reduced o~ides of the initial material~
such as FeO9 MgO, etc.) were removed while a neutral gas~
such as argon, was fed through the plasma generator~
In -the course o~ the refini~g procoss 9 metallic nickel w~s hea-ted to a -tempera~ure o~ 1600 -to 1620a, and then poured into ingot moulds~
~ he resu~tant metal had the ~ollo~ing composition:
99.07% Ni~ 0.35~0 Co, 0.05yo ~e, 0~ 52~o Cu, 0.0015ya S~ and 0.005% C.
ample 2 An initial nickel-bearing material o~ the composition and par-ticle size similar to ~tha~t o~ Example 1 was subjected to reductio~ in a plasma furnace9 such as shown in FIG. l, with the power capacity of the plasma generator being 75 Kwto A gas mixture o~ argon9 carbon oxide and hydro~en (Ar-~CO~H2), ~sd in a ratio of 3:1:29 at a f]ow rate of 10 m3/h a~d -in an amount o~ 1.2 -times that of the reducing Oas required in accordance with stoichiometr~; was introduced -through -the plasma generatox. The tempera-ture of the melt was maintained within the range of 1460 to 1510C. ~he reduction process was no-t accompanied by an~ spattering of me-tal.
~he completion of the reduction process was determined as described in Example 1; whereupon the melt of metallic nickel underwent refining operation duri~g which the gases (H2) and nou-metallic inclusions (parts o~ the linin$ and incompletely reduced oxides of the initial material, such as FeOq CoO, ~gO, e-tc~) were removed from the melt while a neutral gas, such as argon, was fed through the pla~ma ~enerator. In the course o~ r0fining, metallic nickel was heated to a temperature o~ 16~0-1620C, a~ then was poured into ingot moulds~
The resultant metal had the following composition-99~01% ~i~ 0~38Yo cO~ 0005~0 Fe, 0.55% Cu) 00 002~o s~ 0.005% C.
~his inven-tion may be variously otherwise embodied within the scope o~ the appended claims.

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 nickel from a nickel--bearing oxide material, comprising producing a plasma jet by passing a reducing gas through the zone of electric discharge; heating this material by the plasma jet to the temperature of melting of metallic nickel and thereby reducing nickel oxides to metal and effecting partial reduction of iron and cobalt oxides contained in the nickel-bearing oxide material, the reduction being effected in the presence of the reducing gas with the resultant formation of a melt of metallic nickel; the reducing gas being fed in an amount ranging from about 1.2 to about 1.75 times that of the reducing gas required in accordance with stoichiometry;
subjecting the resultant melt of metallic nickel to desulphu-rization and then effecting its refinement by removing therefrom incompletely reduced iron and cobalt oxides and gases dissolved in the melt.

2. A method as claimed in claim 1, wherein the reducing gas passed through the zone of electric discharge is substitu-ted by a neutral gas as the melt of metallic nickel is subjected to refining operation during which incompletely reduced iron and cobalt oxides as well as gases dissolved in the melt are removed therefrom.

3. A method as claimed in claim 1, wherein in the course of refining operation the temperature of the melt of metallic nickel is raised to about 1620°C, the metal tapping temperature.

4. A method as claimed in claim 2, wherein in the course of refining the temperature of the melt of metallic nickel is raised to about 1620°C, the metal tapping temperature.