CA1148365A - Vapourmetallurgical process for the recovery of ultrapure cobalt from aqueous solution - Google Patents

Abstract

Abstract of the Disclosure The invention is directed to the separation of nickel and cobalt contained in hydrometallurgical by-products such as hydrates and carbonates occurring in plants adapted to work up nickel, copper and cobalt ores wherein a slurry of the initial oxidized material is reduced by hydrogen under pressure in the presence of cobalt metal. The nickel content of the slurry is removed by pressure carbonylation and the remaining solution, after filtration to remove precipitated impurities, is acidified to produce cobalt hydridocarbonyl which is removed from the reaction mixture by sparging with a reducing gas and is collected.

Description

BAC~GROUND OF T~E IMVE~TION
It is known that cobalt occurs in many nickel ores and other ores as a relatively minor c:onstituent. Because the chemistry of cobalt and nickel are so similar, the cobalt is carried along with the nickel through the mill and smelter.
A tendency exists to separate the cobalt from the main stream of the material going through the refinery after smelting is complete to provide a metallurgical or hydrometallurgical by-product relatively rich in cobalt but with other metals including usually nickel, iron, copper, etc~ being copresent ther~with. The nature of the hydrometallurgical by-products tends to be oxidic with the material being in finely divided hydrous form as a hydrate or a carbonate with considerable quantities of water, possibly with residual ammonia and other compounds. Because of the physical nature of the by-products and the difficulties of separating nickel from cobalt on a quantitative basis, these materials are difficult to treat although the materials and problems associated with their treatment have been recognized in the art. As an example, the COFFIELD U.S. Patent No. 3,728,104 is directed tG the exact problem set forth hereinbefore. The solution suggested by COFFIELD is to convert the nickel content of the material in slurry form by treatment with a carbon monoxide containing gas under conditions whereby the nickel is converted to nickel carbonyl and the cobalt is converted to cobalttetracarbonyl anion which is thereafter extracted from the aqueous phase by means of an organic solvent. The potential for formation ~; of cobalt hydridocarbonyl tHCo(CO)4) is recognixed by COFFIELD but no attempt to utilize this compound as a means ~' ~, ~8~5 for removing cobalt from the mixture is recognized. U.S.
Patents Nos. 4,097,272, 4,148,813, '815 and '816 are directed to a similar process ~o that of COFFIELD with again great attention being paid to the make-up of the organic solvent used to separate cobalt from aqueous mixture. These prior art processes are said to produce nickel of high purity but to produce cobalt of "acceptable" purity. It is pointed out in the art that in order to provide high purity cobalt in accordance with the tetracarbonyl anion extraction procedure that foreign anions such as iron and copper should ~e removed from the reaction mixture upstream of the carbonylation. Canadian Patent No. 986r281 is also known as disclosing the production of metal hydridocarbonyls from solid materials contAining iron, cobalt and nickel.
; 15 S~MMAR~ OF TH~ I~VE~TION
The invention provides a process~for the recovery of nickel and cobalt from oxidic mixtures containing the same so as to effect the separation of the nickel and cobalt and to provide nickel and cobalt products of high purity.
The process involves slurrying the initial material which usually will be a hydrometallurgical by-product in finely divided oxide, hydrate or carbonate form in water, hydrogen reducing the nickel and cobalt contents thereof under pres-sure in the presence of powdered cobalt metal, pressure carbonylating the reduced slurry under basic conditions to volatilize and remove nickel as nickel carbonyl therefrom and to convert cobalt to cobalttetracarbonyl anion, removing precipitated impurities and then acidifying the resulting solution with a strong acid to a pH at least as acid as pH
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1.5 while sparging the solution with a reducing gas to vol-atilize and recover cobalt as cobalt hydridocarbonyl. The volatile cobalt hydridocarbonyl is stripped from the sparge gas and thereafter decomposed to provide a metallic cobalt of high purity.
DESCRIPTIOI~ OF PREFE:RRISD EUBODIM~NTS
The process in accordance with the invention involves treatment of the starting material which will be an oxidic precipitate usually finely divided and may, for example, be a mixed nickel/cobalt carbonate or a nickel/cobalt mixture resulting from the precipitation of cobaltic hydroxide by means of chlorine. The material is slurried in water in a solids concentration of about 3~ to about 30% by weight and pressure reduced with hydrogen at a temperature in a range lS of about 150C to about 250C and a hydrogen partial pressure in a range of about 200 to about 1000 pounds per square inch.
Desirably, finely divided cobalt metal is included in the slurry to act as a catalyst in promoting the reduction of the nickel and cobalt oxidic or carbonate material. The benefits of cobalt powder presence during reduction are par-,j .
ticularly marked when the cobalt and/or the nickel contents of the material to be treated are in the trivalent form.
The cobalt metal can be obtained from other sources or by recycle of some of the reduced metal values prior to carbony-lation. The finely divided cobalt metal improves reaction kinetics in reduction. After reduction, the slurry is made basic with a material which preferably is sodium carbonate and the slurry is then carbonylated with or without the copresence of hydrogen. A mixture of 1 to 1 volume propor-I

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tions of hydrogen and carbon monoxide is beneficial. Car-bonylation i5 continued until essentially all the nickel contained in the slurry is removed as nickel carbonyl.
Concommitantly the reduced cobalt is converted to the form of a cobalttetracarbonyl anion (Co~CO)4-~. At this point the slurry may be filtered to remove precipitated impurities including any copper and iron initially present in the crude by-product material. A liquor containing ~he cobalt as cobalt-tetracarbonyl anion and essentially devoid of other metallic ions results. The solution is then acidified with a strong acid to a pH at least as acid as pH 1.5 and sparged with a reducing gas from the group consisting of hydrogen and CO to remove the cobalt as volatile cobalt hydridocarbonyl.
!: Carbonylation, which may be accomplished using carbon monoxide alone or diluted up to approximately equal volume parts with hydrogen is conducted over the carbon monoxide partial pres-` sure range of about 100 pounds per square inch to about 2000 - pounds per square inch at a temperature in the range of about ~; 50 to 225C. A partial pressure of carbon monoxide on the order of 500 pounds per square inch is advantageousO
It will be appreciated that the pH of the water slurry of material initially to be treated will generally be in the neutral to slightly acid range and that the pH oi the slurry will generally become more acid as hydrogenation pro-ceeds. However, if the nature of the starting material is such that the initial water slurry is on the alkaline side of pH 7 no untoward effect results. Carbonylation, of course, is conducted under basic conditions preferably generated through use of a base such as sodium carbonate. For reasons :
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which are not presently understood, sodium carbonate appears to be a more effective base than does sodium hydroxide.
Carbon monoxide or a mixture of hydrogen and carbon monoxide are passed through the basic mixture at a sufficient rate and for a sufficient time to convert essentially all of the nickel present in the reduced state in the mixture to volatile nickel tetracarbonyl. The nickel tetracarbonyl product is carried from the reaction environment by the stream of car-bonylating gas and is separated therefrom outside the vessel in which carbonylation is taking place. The evolving gas mixture is checked for the presence of nickel and when nickel is no longer detected therein, the carbonylation operation is regarded as being complete. At this point, the reaction mixture is filtered, then acidified to a pH to at least as low as p~l 1.5 with a strong acid which may be for example sulfuric or hydrochloric acid and sparging with a gas from the group consisting of hydrogen and carbon monoxide is started to remove from the reaction mixture cobalt as volatile cobalt hydridocarbonyL IHCo(CO)~]. The sparge gas should be in the amount of at least about 5 milliliters per milliliter of liquor per minute on a carbon monoxide basis. The temperature of the reaction mixture during the evolution of cobalt hydrido-carbonyl should be maintained in the range of about 20 to preferably not more than 55C. The retention time of the mixture during cobalt evolution should preferably be about 1 hour when the pH is about 0.1 up to about 2 hours when the pH is about 1. Desirably, the content of electrolytes such ;
as sodium sulfate should be high for example at least about 20 grams per liter during the evolution of cobalt .
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336~ii hydridocarbonyl as the presence of a large electrolyte content in solu~ion increases the ionic strength of the solution and assists in the removal of the cobalt hydridocarbonyl therefrom.
In this connection, it can be pointed that the cobalt hydrido-carbonyl is not a strongly polar compound and that increasing the polarity of the solution appears to create a salting out effect with respect to cobalt hydridocarbonyl. Sulfates and phosphates are desirable anions for this purpose.
Some examples will now be given. In the examples, reduction and carbonylation were performed batchwise at ele-vated temperature and pressure while evolution of cobalt hydridocarbonyl was performed continuously at atmospheric pressure to avoid formation of Co2(Co)g.
` ~XAMPLE I
' ~ 15 Into a single stage reactor provided with a stirring device, were fed 100 grams of wet cobaltic hydroxide or 44.5g dry cake analyzing about 54.5~ weight percent cobalt, 1%
nickel, 0.03~ copper and 0.15% iron. The crude cobaltic hydroxide material was slurried in 1.1 liters of slurry and 80 grams of crude cobalt metal analyzing in weight percent 97.9% cobalt, 1.8~ nickel, 0.05% copper and 0.27% iron and having a particle size of less than 400 Tyler mesh was also introduced. The reactor was heated to 180C and hydrogen at l a partial pressure of 500 pounds per square inch was fed -~ 25 into the reactor for 13 minutes. At the end of hydrogen reduction, the slurry pH was 6.3. Analysis confirmed that more than 99% of the cobalt from the initial cobaltic hydrox-ide slurry was reported to a crude cobalt meta~. The reaction mixture resultlng from hydrogenation was then treated at 36~;i 150C with a gaseous mixture of equal volume proportions of hydrogen and carbon monoxide at a partial pressure of 1000 pounds per square inch in the pre~ence of 110% stoichoimetric excess of sodium carbonate. A gas containing nickel carbonyl resulted which was evolved from the reactor. After the com-pletion of nickel carbonyl evolution, which occurred after about 240 minutes, the slurry was filtered and washed provid-ing a copper-iron cake and a clear yellow liquor assaying in grams per liter, 38.8 cobalt, 0.012 nickel, O.OQ2 copper and 0.022 iron. A portion of the cobalt carbonylate solution thus produced was diluted to a cobalt content of 28 grams per liter, was acidified at atmospheric pressure and 22C
with 6 normal hydrochloric acid and sparged with 5.33 milli-liters of hydrogen per milliliter of solution per minute.
The cobalt-containing liquor, acid and sparge gas were fed continuously to the bottom of a sealed single stage vessel, with spent liquor and HCo(CO)4 containing gas being taken off the top. Cobalt volatilization from the reaction mixture was checked at pH levels from pH 3 to pH -0.26 with the results set forth in the following Table I~
TABLE I
% CO volatilizedR.T. (min) . .
-.26 95.8 60' 0 97.3 77' 1.0 86.9 149' 3.0 45.6 103' Example II
A further portion of the basic cobalt carbonylate solution having a cobalt content of 28 grams per liter was ; treated at 23C in the manner described in Example I with a 6 normal sulfuric acid solution to provide a pH of 1. A
mixture of hydrogen and CO was sparged through the solution at a rate of 5.33 milliliters per milliliter per minute for various times. It was found that, at 89 minutes, 74.2% of the cobalt was volatilized; at 96 minutes, 84% of the cobalt was volatilized; and at 149 minutes, 86.9~ of the cobalt was volatilized as cobalt hydridocarbonyl.
'` , ~ample YII
`~ A cobalt carbonylate basic solution prepared gen-~ eralIy as in the method set forth in Example I and containing ; 15 80 grams per liter of cobalt was treated at 23~C with 12 normal sulfuric acid to yield a pH of 1. The solution was sparged with 5 milliliters per milliliter per minute of a 1 to 1 mixture of hydrogen and carbon monoxide at a retention time of 83 minutes~ Two tests were conducted, in one of which the solution also contained 154 grams per liter of sodium sulfate and in the other of which no sodium sulfate was present. It was found that, in the retention time employed, the cobalt carbonylate solution containing sodium sulfate yielded a 73.2% cobalt volatilization at 83 minutes whereas the solution containing no sodium sulfate yielded a volatization of only 47.2% of the cobalt in the same timeO
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33~i5 ~ample IV
To illustrate the effect of temperature during the evolution of cobalt hydridocarbonyl from a basic solution containing cobalt carbonylate~ i.e., cobalttetracarbonyl anion, a run was made at a temperature of 90C treating a basic solution containing 70 grams per liter of cobalt with a 12 normal sulfuric acid solution to yield a pH of 2. In 90 minutes of sparging with 5 milliliters per milliliter per minute carbon monoxide, 96% of the cobalt was volatilized but the formation of insoluble black solids (likely tetra-cobalt dodecacarbonyl) occurred.

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Example V
A cobalt carbonylate basic solution containing 25 grams per liter of cobalt was treated in the manner described in Example I with 3 normal sulfuric acid to pH 1~ I'he solu-tion was sparged with carbon monoxide at rates of 2, 5 and lO milliliters per milliliter per minute for 59 minutes residence time at each sparging rate and it was found that, respectively, 51.6%, 64% and 83.7% of cobalt was volatilized.

.
~ample VI
A comparison between the use of carbon monoxide alone and an equal volume of mixture of hydrogen and carbon monoxide was conducted in the treatment of an 80 grams per liter cobalt-containing basic solution treated with 12 normal sulfuric acid to pH 1 using a sparge rate of 10 milllliters per milliliter per minute as in Example I. It was found _9_ I

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that after 92 minutes using carbon monoxide alone 96% of the cobalt was volatilized, and after 83 minutes using the mixture of hydrogen and carbon monoxide, 73.2% of the cobalt was volatilized indicating a superior result for the use of carbon monoxide alone as sparge gas.
Cobalt powder produced by the decomposition of cobalt hydridocarbonyl gas when thermally decomposed in a temperature range of 150 to 300C was found to yield a cobalt powder containing as impurities only 30 parts per million of nickel, 0.4 part per million of iron, and 0~1 parts per million of copper. The process of the invention provides a means for separating nickel and cobalt contained in crude material which heretobefore had been regarded as being diffi-~` cult to handle. In addition, the process of the invention affords the means not only of separating the nickel and cobalt but of providing nickel and cobalt in highly pure form.
Although the present invention has been described in con~unction with preferred embodiments, it is to be under-stood that modifications and variations may be resorted to without departing from the spirit and scope of the inven-tion, as those skilled in the art will readily understand.
Such modifications and variations are considered to be within the purview and scope oi the invention and appended claims.

Claims (9)

WE CLAIM:

1. A process for extracting cobalt from an aqueous basic solution containing cobalt tetracarbonyl anion which comprises acidifying said solution with a strong acid to generate a pH of 1.5 or more acid while sparging said solu-tion with a stream of a gas from the group consisting of carbon monoxide and hydrogen to volatilize cobalt as cobalt hydridocarbonyl and separating said cobalt hydrocarbonyl from said sparge gas stream.

2. A process in accordance with claim 1 wherein said cobalt hydridocarbonyl is decomposed to metallic cobalt by heating at a temperature between 150°C and 300°C.

3. A process in accordance with claim 1 wherein the sparge gas is passed at a rate of at least 5 liters per liter of solution per minute.

4. A process in accordance with claim 1 wherein the solution of pH is at least as acid as pH 1.

5. A process in accordance with claim 1 wherein the sparge gas comprises carbon monoxide and hydrogen in equal parts by volume.

6. A process in accordance with claim 1 wherein said solution, said acid and said sparge gas are fed on a continu-ous basis to a reactor and spent liquor and a gas stream containing cobalt hydridocarboyl are removed on a continuous basis from said reactor.

7. A process for treating a metallurgical by-product containing nickel and cobalt in oxidized form to recover nickel and cobalt separately and to reject impurities such as iron or copper present in said by-product which comprises slurrying said by-product in water, hydrogen reducing the nickel and cobalt contents thereof under pressure, pressure carbonylating said reduced slurry under basic conditions to volatilize and remove nickel as nickel carbonyl therefrom and to convert cobalt to cobalt tetracarbonyl anion, removing solid impurities, acidifying the resulting solution to pH 1.5 or more acid while sparging said solution with a reducing gas to volatilize and recover cobalt as cobalt hydridocarbonyl.

8. A process in accordance with claim 7 wherein said hydrogen reduction is conducted in the presence of finely-divided cobalt metal.

9. A process in accordance with claim 7 wherein said basic conditions are provided by sodium carbonate.