CA1151881A - Cobalt metal powder by hydrogen reduction - Google Patents

Abstract

Abstract of the Disclosure Cobalt powder is produced by the elevated temperature and pressure hydrogen reduction of cobaltous sulfate solution wherein sodium hydroxide solution is introduced at a rate which does not exceed the rate of sulfuric acid generation. The powder after a number of densifications is of high density, has a good appearance and may be handled in air without difficulty.

Description

P~ 20/CAN 115~8~

Field of the Invention -The invention pertains to the field of producing cobalt metal powder by hydrogen reduction from a cobalt con-taining solution.

Background of the Invention . .
Hydrogen reduced elemental cobalt powder is an article of commerce. One presently available commercial product is known to be produced by hydrogen reduction of aqueous cobalt ammine ammonium sulfate solutions usIng a catalyst such as a sodium sulfite-sodium cyanide c~talyst.
The nucleation of cobalt powder in t~is system is ~rre~ular, resulting in production of powder having an apparent density of 0.6 to 1 gm/cubic centimeter. In order to prov~de a denser commercial product, repeated densification cycles are employed which deposit further co~alt upon the initially formed powder from fresh cob~lt-containin~ solution. In this manner the particle size is increased suc~ that poss~bly about 60% of the product will have a greater particle size than 200 mesh on a Tyler screen scale (75 microns~, and t~e apparent density of the product increases to approx~matel~
3.~ gm/cubic centimeter. The cobalt bite per reduct~on cycle is on the order of about 40 gm/l and ~bout 30~ of the cobalt metal is recycled and redissolved in the reduct~n of cobaltic ion to cobaltous ion in the feed cobaltic amnine ammonium sulfate solution. The average hydro~en reduction cycle is reported to require about 30 minutes. The final cobalt powder particles have an irregular shape with a rough pebbly surface. In many instances the powder is a d~rk grey to black in colo.r. The product produced must ~e handled carefully and exposure to air is avoided until the powder product is cool. Drying of the washed cobalt powder ~s usually conducted in an atmosphere of hydrogen or nitrogen.
It would be desirable to provide a cobalt powder of uniform coarse particle size having a higher apparent density than the produst presently available.

Prior Art Th~ prior art is exemplified by the nickel prefer-ential reduction scheme which is set forth in a paper ~y Schaufelberger and Roy entitled "Separation of Copper, Nickel and Cobalt by Selective Reductions from A~ueous Solution", Transactions of the Institute of Mining and Metallurgy, London, Vol. 64, 1954-1955, pages 375-3~3 and in U S. Patents 2,694,005 and 2,694,006. The soluble cobaltic ammine scheme i~ disclosed in U.S. Patents 2,767,055 and 2,767,054. Another hydrogen reduction process wherein the leach solution is made alkaline with ammonia, is described in a paper by Mitchell entitled "Cobalt Pressure ~eaching and Reduction at ~arfield", which appeared in Jourhal of Metals, March 1~57 on pages 343-345.
Direct gaseous reduction of cobaltous oxide or hydroxide aqueous slurries to cobalt metal has been reported in the literature, for example, Schaufelber~er U.S. Patent 2,805,149 and papers by R. Soubirous et al which appeared in C. R. Acid. Sc., Paris, t. 270, pages 1595-1597 and by Dobrokhoto~ et al which appeared in C~e-tn. Metally, 35, 1962, page 44, In ~ .
many of the processes the starting material is cobaltic hydroxide which must be converted to the co~altous for~.
The dissolution of cobaltic hydroxide with an organic reductant such as methanol has been disclosed in U.S. Patent 4,151,258 11531 88~

and in an article by L. Syper entitled "Oxidation of Some Organ-ic Compounds by Cobalt (III) Hydroxide", Roczniki Chemii, Vol. 47, No. 1, pages 43-48, (1973). The use of nucleating ayents in hydrogen reduction processes is disclosed in U.S. Patents Nos.

2,767,081, 2,767,082 and 2,767,083.
Summary of the Invention The process of the invention may generally be defined as a process for producing dense cobalt powder of coarse, relatively uniform particle size which comprises subjecting a portion of a cobaltous sulfate solution to hydrogen reduction at a hydrogen ' partial pressure of at least one megapascal and a temperature of at least about 180C in the presence of a reaction initiator while introducing sodium hydroxide solution at a rate not sub-stantially exceeding the rate of sulfuric acid production due to hydrogen reduction. The hydrogen reduction is continued to reduce substantially all the cobalt content of said portion with production of end reduction solution and cobalt powder. The hydrogen reduction is repeated cyclically with fresh successive portions of cobaltous sulfate solution and with each successive reduction being performed in the presence of substantially all the cobalt powder formed in the previous cycle to provide a densified cobalt powder product.
The invention includes the product of the process ~ust des-cribed, namely a cobalt powder of coarse/ relatively uniform particle size, having a smooth surface and a density in the range of about 4.5 to about 5.5 grams per cubic centimeter with at least 98% of the particles exceeding 75 microns in size.
Description of the Drawing Figure 1 is a photomicrograph taken at 200 diameters of a fine, commercial cobalt powder of a kind useful as seed particles 1 -, .. ~

~53~8131 in accordance with the invention;
Figure 2 is a photomicrograph taken at 200 diameters of a product powder after 2 densifications using the seed powder of Figure l;
Figure 3 is a photomicrograph taken at 200 diameters of a product powder in accordance with the invention after 4 densifications starting initially from the seed powder of Figure l;

-3(a) ~l15~

Figure 4 is a photomicrograph taken at 200 diameters of a product powder in accordance with the invention a~ter 6 densifications starting initially with the seed powder of Figure l;
Figure 5 is a photomicrograph taken at 200 diameters of a cobalt powder obtained as a result of self-nucleation; and Figure 6 is a photomicrograph taken at 200 diameters of a product powder obtained after 6 densifications using as seed powder the powder of Figure 5.

Detailed Description of the Invention The invention is directed to a method for producing dense elemental cobalt powder of coarse relatively uniform particle size and to the product resulting from the method.
The method comprises hydrogen reduction at elevated temperature and pressure of cobaltous sulfate aqueous solutions. The steps employed involve heating a feed cobalt sulfate solution which contains about 50 to ~bout 100 grams per liter of cobalt in a sealed autoclave to a temperature of at least about 180C and in the presence of cobalt metal powder which functions as a seed or initiator, introducing hydrogen into the autoclave at a partial pressure of at least 1 megapascal, i.e., at least 150 psi, thereafter introducing a sodium hydroxide solution into the vessel at a controlled rate which does not substantially exceed the rate of formation of sulfuric acid due to the hydrogen reduction of cobal~ sulfate.
This is achieved by maintaining the pH of the solution during cobalt reduction below about pH 4. The addition of sodium hydroxide is stopped when about 80% to 95~ of the ~l15~88~

cobalt in solution has been reduced. Thereafter, the end reduction solution from the autoclave is withdrawn and is replaced with fresh feed cobalt sulfate solution. The aforementioned steps are then repeated to densify the cobalt metal powder and until cobalt powder of the desired particle size is obtained. The seed cobalt powder employed to initiate the precipitation of cobalt during hydrogen reduction may be finely divided cobalt powder produced from other sources or produced by a reaction similar to the foregoing~ For example, extra fine cobalt powder having a particle size in the range of 1 to 20 microns, known in the trade as "Afrimet" powder, may be employed. Alternatively, cobalt powder produced by the thermal decomposition of cobalt oxalate as for example by heating cobalt oxalate at 500C under nitrogen for 15 minutes may be employed. Seed powder may be generated by nucleation using sodium cyanide and sodium sulfide as nucleating agents in the first hydrogen pressuri~ed batch.
Finally, self-nucleated cobalt powder from the first reduc~
tion liquor may be employed. The respective types of seed ~ cobalt powders have different physical shapes and surface area per unit weight. The very small needle shape particles and large surface area which charac-terize the Afrimet cobalt powder renders it a preferred starting material. Thermally decomposed cobalt o~alate also produces fine needle shaped particles. [but not as fine as the Afrimet product] Powder produced by nucleation with sodium cyanide and sodium sulfide as catalysts is irregularly shaped and of large particle size. Self-nucleated cobalt powder is in the form o~ large porous powders. The finely divided needle-shaped initiating powders permit densification by growth of individual particles 8~3~

or aggregates of particles during reduction. With the porous types of cobalt powder seed there is a tendency for the hydrogen reduced cobalt to deposit in the void space of the large cobalt seed particles resulting in loss of available surface area. Such products have lower apparent density than do products seeded with fine, discrete cobalt powder.
The use of the fine, discrete seed powder having a particle size of about 1 to 5 microns on the average, e.g., not exceeding about 2 microns on the average, is thus preferred.
It will be appreciated that one mole of sulfuric acid is formed for each mole of cobalt sulfate that is reduced. It is important that the rate of addition of sodium hydroxide be such that the addition of sodium hydroxide to neutralize the sulfuric acid formed with the production of sodium sulfate and water not exceed the rate of formation of sulfuric acid. If the addition rate of sodium hydroxide exceeds the rate of formation of sulfuric acid, cobaltous hydroxide can form which has a tendency to provide self-nucleated cobalt powder and which interferes with densification of the cobalt powder already present. A saturated NaOH solu-tion is used to avoid dilution.
It will be appreciated that in starting with fine, discrete cobalt powder particles upon which the newly reduced cobalt is precipitated t hat successive operations whereby the cobalt powder remains in the autoclave for the treatment of successive batches of cobalt sulfate solution provide larger cobalt particles having smooth surfaces and having a density in the range of about 4.5 to 5.5 grams/cc. At this density, the cobal~ powder is found to be densified such that 98% or more of the particles exceed 2Q0 mesh Tyler ~5~8~

screen scale. The particles have a uniform spherical shape and appear bright to the eye. The product can be washed and dried in the presence of air. The cobalt bite per reduction cycle can be as high as 90 grams/liter. The end reduction liquor contains no ammonium sulfate and the residual dissolved cobalt can be recovered by simple hydrolysis. The average reduction cycle duxation can be as low as 30 minutes.
The source of the cobalt sulfate feed solution treated in accordance with the invention is immaterial.
Desirably the feed solution should be substantially free of impurities which co-reduce or co-precipitate with cobalt during hydrogen reduction. Thus the contents of nickel, copper, iron and lead should be as low as possible. In addition, species such as chloride ion should be very low, e.g., less than 100 gpm, since such ions tend to be corrosive toward the autoclave. In addition~ unsaturated sul~ur species, i.e., all sulfur compounds except sulfate ~h~ch can lead to sulfur contamination of the cobalt product, e,g., dithionate ion should be removed.
The invention advantageously is applied to the recovery of cobalt from cobaltic ox~de hydrate obtaIned by oxidation-precipitation of cobalt from process le~ch solu-tions using sodium hypochlorite and a ~ase. Treatment o~
cobaltic hydrate to provide cobalt sulfate feed solution suitable or recovery of a cobalt as cobalt pow~e~ according to the invention may comprise the following steps:

3~

~15~8~31 l) treat Co(OH) 3 with H2SO4 and water at 60C
for 30 minutes, with suitable agitatian and aeration to eliminate the soluble Cl as Cl2 according to the xeaction: ~' 2Co(OH) 3 ~ 6H + 2Cl ~ 2Co ~ C12 * 6H
(The r~action is only favoxable at pH
1.5, preferably pH 0.5-l.O.~

2) add methanol to the dechlorinated slurry in the presence of suf~'icient ~I2SO4.~ ea~y ad~d in step 1~ to solubilize the'Co as Co at 60C, according to the react~on;
6Co~OH)3 ~ 6H2SO4 + CH30H ~ 6CoS04 ~ CO2 ~ 17H
(This reaction however, does not ~o to completion unless lar~e excesses of ~2SO4 and CH30H are added. In the presence of the stoichiometric amount ~f ~2S.04 and 1.2 times the ~toichiometric amount of CH30H, 85 to 90% of the Co is d~.ssolved (i.e., at least about 80%1 in one'~our at 60C with a final pH reading of 1.5 to 2Ø

3) add a small amount of H202 to the leach slurry to complete t~e dissolution of Co(OH)3 according to the'reaction 2Co(OH) 3 ~ 2H2SO4 ~ H202 ~ 2CoS04 ~ 6H20 ~ 02 Complete dissolution of the CotOH~ 3 iS
obtained by keeping the pH below about 2.5.

4) add 0.5 to 1.0 g/l of BaCOg for precip~-tation of Pb, at 60~C and pH ~2.5.

5) neutralize the excess H2S04 with'CoCO3 or Na2CO3 to pH 5.5. In thi:s step Fe and Cll are precipitated as t~eir hydroxides.

6~ separate the leach liquor fxom th.e leach residue, containing Pb, Fe ~nd Cu, by filtration.

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7) treat the leach solution through a Cu, Ni selective ion exchange resin (such as XF-4195--by Dow Chemical Company) to remove the residual Cu and the required amount of Ni.

8) recover Co in the elemental form from the purified leach solution by the process of the invention.

Some examples will now be given.
Example I
6.3 kg of wet Co(OH) 3 cake analyæing in weight percent Co 27.6, Ni 0.48, Fe 0.06, Cu 0.Q03, Zn 0.001 and Cl 0.2, were slurried with water and 3 kg of concentrated H2SO4 to a volume of 15 Q. The slurry was heated to 60C and stirred while air was sparged through it for 30 minutes to remove the chloride ion content as gaseous chlorine. At this point the slurry pH was at 0.1 and less than 5~ of the cobalt in the cake was dissolved.
2G The dechlorinated slurry was then subjected tQ a reductive leach ~y introducing a pure methanol solut~on into it at a rate of 600 ml/h for 15 minutes. The prosress of the leach was followed by monitoring the pX which lncreased from 0.1 to 1.5 in one hour. ~t p~ 1.5 about 85% of the feed Co(OH) 3 had been dissolved and further dissolution o~ Co(OH~ 3 was very slow due to lack of ~2S4 and methanol. Complete reaction with methanol would require not only excess of methanol, but a large excess of H2SO4 ~p~ ~ 1 in t~e Pnd dissolution liquor) which ~ust be neu~xalized with ~ase. T~s operation would be costly.
Methanol was therefoxe substituted by ~2O2 whi~ch reacts with Co(OH) 3 as a reducing agent belo~ p~ 4. A 30% H202 solution was added into the leach slurry at a rate of 75 ml~h - 1.15~

for 140 minutes. At this point completion of the leach was evidenced by a sharp change in color from black to pink.
During the completion of the leach the pH was kept at 1.5 with H2SO4 when required. This pH is preferred for the subsequent Pb removal operation. Lead was removed from solution by the addition of 0.5 g of BaCO3 per liter of solution. Ater 30 minutes at 60C, the solution was neutralized to pH 5.5 using a 100 g/l Co containing CoC03 slurry. After filtration the liquor was passed through a Ni selective IX resin for Ni removal. The final purified solution assayed 96 g/l Co and 0.038 g/l Ni, and in mg/l Cu l, Pb ~ 0.3, Fe 1, Zn 5 and Cl 30.
Leach solution prepared in the aforedescribed manner but assaying 92.2 g/l Co, 1.3 g/l Ni, 0.3 mg/1 Cu, 0.3 mg/l Pb and 0.6 mg/l Fe was treated for cobalt recovery in the elemental powder form as follows: 0.8 Q of leach solution and 10 g of fine, discrete Co powder having an apparent density of 0.6 gm/cc were placed and sealed in a 2 Q capacity Parr all Ti autoclave provided with a twin pxopellor a~itator which was rotated in all runs at 1000 rpm. The suspension was heated to 200C and H2 was admitted to the autoclave at a partial pressure of 1.3 MPa (total pressure of 3 MPa or 450 psig). A 9.4 N NaOH solution was then pu~ped into the autoclave at a rate of 150 ml/h for 90 minutes, representin~
an NaOH addition rate of l.l mole per mole of cobalt per hour. The pH of the solution during NaOH addition ~as between 2.0 and 3Ø The reduction was continued after NaOH
addition for 20 minutes to ensure complete elimination of Co(OH) 2 . The end reduction solution was cooled to 80~C and withdrawn from the autoclave through a carbon f~lter, leaving -- 10 ~-~s~

the Co powder inside the autoclave. ~bout 100 ml of end reduction liquor was left in the autoclave.
0.8 Q of fresh feed CoS04 leach solution was pumped into the autoclave and the H2 reduction cycle was repeated as above. After 6 cycles (or densifications), the total amount of Co powder was washed and dried in air at ~-room temperature. The final powder contained 97~ cobalt, 2%
nickel, and in ppm ~15 copper, <40 ixon, 14 zinc, 170 sulfur and 590 carbon. Table I illustrates the densification achieved during the 6 cycles.

TABLE I

Cobalt Powder ,. ~ .
Reduction % Apparent Co ~reduced Cycle S Density Reduced Cseed ` (g/cm3~ (g~ tg/g~
1 0.058 2.0 56 5.6 2 0.024 4.1 104 10.~
4 0.019 5.~ 20~ 20.9 6 ~.017 5.5 300 30.0 The stxucture of the ~inely-divided cobalt seed powder employed in t~is Example is shown in F;~gure 1 and o~
the product powder after 2, 4 and 6 densifications is shown in Figures 2, 3 and 4 all at 200 diameters. The correlation between density and particle cize is marked.

Example II
The H2 reduction pxocedure used in Ex~mple I was repeated but using feed leach salution ~ssayLng 85.5 gjl Co, 1 ~5~

0.13 g/l Ni, 0.2 mg/l Cu, 0.3 mg/l Pb and 0O9 mg/l Fe.
After 8 reduction cycles the cobalt powder was washed and dried in air. The cobalt powder product contained 99% by weight cobalt, 0.32% nickel and, in ppm, 7 copper, 20 iron, < 10 lead, < 5 zinc, 280 sulfur and 630 carbon. Table II
illustrates the densification achieved during the 8 cycles.

TABLE II

Cobalt Powder Reduction % Apparent Co Creduced 10Cycle S Specific Reduced Cseed Gravity (g/cm3) (g) (g/g) 2 0.024 2.35 77.9 7.8 4 0.025 4.59 156.1 15.6 6 0.027 5.48 218.0 21.8 8 0.028 5.50 273.5 27.4 Example III
Leach solution assaying 96 g/l Co, 0.038 g/1 Ni, 0.3 mg/l Cu, 0.2 mg/l Pb, 1.3 mg/l Fe and 5 mg/l Zn was treated for Co recovery in the elemental powder for~ as follows: 0.8 Q o leach solution and 40 g of fine, d~screte cobalt powder (Afrimet) were placed in a 2 ~ capac~ty Parr Ti autoclave. The suspension was heated wit~ stixr~ng to 200C and H2 was introduced into the vessel at a partial pressuxe of lo 2 MPa (total pressure of 3 MPa~. ~ 9.4 N NaOH
solution was pumped into the autocla~e at a rate of 780 ml~h (5.5 moles NaOH per mole of cobalt per hour~ for 18 ~inut~s ll~lB~3~

and 20 seconds. The pH of the solution during NaOH addition was between 2 and 3. The reduction was continued thereafter for another 11 minutes and 40 seconds. (Total time 30 minutes). The end reduction liquor was cooled and withdrawn from the autoclave through a Ti inlet tube equipped with a carbon filter. About 100 ml of end reduction liquor and the reduced Co powder were left in the autoclave.
0.8 Q of fresh feed CoS04 leach solution were pumped in the autoclave and the H2 reduction cycle ~as repeated under the conditions mentioned above. After 11 such cycles, the total amount of Co powder ~as withdrawn, washed and dried in air at room temperature.` T~e powder contained 99% cobalt and 0.042% nickel, by we~ght, and, in ppm, 5 copper, 33 iron, 2 lead, 2 zinc and 210 sulfur.
Results are shown in Table III. Again the S
content was decreased and the apparent density of the Co powder was increased with increasing number of c~cles.

~ABLE III

Co~alt Powder Co -20 Reduction %~pparent Co re-duced Cycle - 5Density Reduced Cseed ~ ---1 0.083 0.8 51 1.3 3 0.040 1.9 160 4.

6 0.018 3.8 310 7.8 8 0.026 4.3 420 10.5 11 0.021 ~.7 5~0 14.0 ~.~IS~8~L

E~ample IV
Feed CoS04 leach solution prepared by the method described in Example I and assaying 92 g/l Co, 0.035 g/l Ni, ~ 0.1 mg/l Cu, 1.1 mg/l Fe, < 0.25 mg/l Pb, and 2 mg/l Zn was treated for Co recovery by ~2 reduction in the following manner: 0.8 Q of CoSO 4 leach solution and 30 g of Co powder, made by decomposition of cobalt oxalate crystals at 500C
under N2 atmosphere for 15 minutes, were placed in a 2 Q
capacity Parr Ti autoclave. The suspension was heated to ~ 200C and H2 was introduced into the autoclave at a partial pressure of 1.3 MPa (total pressure of 3 MPa¦. ~ 9.95 N
NaOH solution was then pumped into the autaclave at a Xate of 150 ml/h or 90 minutes. The pH of the solution during NaOH addition was between 2.5 and 3.5. The reduction was carried out thereafter for another 30-minutes during which the pH of the solution decreased to 2.5. The end xeduction liquor was cooled to 80C and wit~drawn from the autoclave through a Ti inlet tube equipped with a carbon filter. Q.8 Q of fresh CoS04 solution was fed to the autoclave and the H2 reduction cycle was repeated as above 11 times. ~t the end of 11 cycles, the Co powder was washed and dried in air.
The cobalt powder contained, by weight, ~ cobalt and 0.083% nickel and, in ppm, 12 copper, 32 ~ron, 9 le~dJ 4 zinc and 518 sulfur.
The satisfactory densificat~on ~chieved i5 ~llus-trated in Table IV.

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TABLE IV

Cobalt Powder Reduction % Apparent Co Creduced Cycle S Density Reduced ~seed (g/cm3) (g) (y/g) 3 - 3.3 155 5.2 6 - 4.3 271 9.0 ll 0.~5 4.7 518 17.3 In order to illustrate the unsatisfactory results obtained when sodium hydroxide is introduced during ~eduction at a rate substantially exceeding the rate of sulfuric acid production, the following is given:
Example A
Feed CoS04 leach solution assaying 86 g~l Co, 0.046 g/l Ni, 0.3 mg/l Cu, 0.4 mg/l Pb and 2 ~g/l Fe was treated for Co recovery by H2 reduction in the following manner: 0.7 Q of CoS04 leach solution and 10 ~ of AfriInet Co powder were placed in a 2 Q capacity Parr Ti autoclave.
The suspension was heated to 2Q0C and H2 was introduced into the vessel at a partial pressure of 1.3 Mpa ttot~l pressure of 3 MPa~. A 10 N NaOH solution was then pu~ped into the autoclave at a ra.te of 1.44 Q~h ~12 ~oles NaOH pe~
mole of cobalt per hour~ for 7 minutes and 3Q se~onds~ T~e pH of the solution during NaOH addit~on incre~sed from 2.0 to 7Ø The reduction was carried on thereafter until the pH in the solution was below about 3. This took about 110 minutes. The end reduction liquor was cooled to 80C and withdrawn from the autoclave through a Ti inlet tube e~uipped ~:~5~Lt3~31 with a carb~n filter. 0.7 Q of fresh CoS04 solution was fed into the autoclave and the H2 reduction cycle was repeated as above 8 times. At the end of 8 cycles, the produced Co powder was washed and dried in air. The Co powder was light and porous. About 3% of the Co was plastered onto the autoclave internals. The powder contained 99% co~alt and 0.05~ nickel and, in ppm, 5 copper, 30 iron, < 5 lead, 6 zinc, 1,000 sulfur and 500 carbon.
Results are shown in Table A. Evidently with a fast NaOH addition rate and only 10 g of Afrimet seed powder, the apparent density of the Co powder was much lower than in the tests descrihed in the preceding examples.

TABLE A
Cobalt Powder Reduction ~ Apparent Co Creduced Cycle S DensityReduced Cseed ~g/cm3)- (gl (g/g~ _ -8 0.10 1.7 413 41.3 Two attempts were made to produc~ a hydrogen-reduced cobalt powder using self-nucleated seed powder with unsatisfactory results as set forth in the following Examples B and C.

Example B
Leach solution assaying 96 g~l Co, 0.038 g/l Ni, < 0.3 mg/l Cu, < 0.3 mg/l Pb, 1.3 mg/l Fe and 5 mg/l Zn was treated for cobalt powder recovery as follows: 0.7 Q of 8~

leach solution was sealed in a 2 Q Ti autoclave and heated to 200C. A lo 3 MPa partial pressure of H2 was admitted to the autoclave and 0.1 Q of solution containing 20 g/l NaCN
and 2 g/l Na2S was pumped in. This was followed by the addition of a 9.4 N NaOH solution at a rate of 780 ml~h for 18 minutes and 36 seconds. The reduction was continued after NaOH addition for about 12 minutes. The autocla-~e contents were cooled to 80C and the solution was withdrawn from the vessel through a Ti inlet tube e~uipped with a carbon filter.
0.7 Q of fresh feed CoS04 leach soluti~n Was pumped in the autoclave, heated to 200~C and pressurized with H2 to a total pressure of 3 MPa ~450 psig~. ~ 9.4 N
NaOH solution was pumped in a rate of 780 ml~h for 16 ~inutes and the reduction was carried out ~or a total time of 30 minutes. After cooling and solution withdra~al, t~e reduction cycle was repeated 5 times. The pH of the solution during NaOH addition was be~ween 2.5 and 3O0. After 5 cycles, the Co powder was washed and dried in air. The powder conta~ned 99% cobalt and 0.05% nickel, by weight, and in ppm, 4 copper, 150 iron, c 10 lead, ~ 10 zinc and 450 sul~ur.
Densification results are shown in Table ~.

TAB~ B

Cobalt Powder Reduction % ~pparent Co Creduced Cycle S DensityReduced Cnucleat~d ~g~cm ) (g) ~g/g~
0 (nucleation) - - 63 0 2 0.152 1.15 155 2.46 0.045 2O50 274 4.35 Example C
Leach solution assaying 92 g/l Co, 0.032 g/l Ni, ~ 0.1 mg/l Cu, 1 mg/l Fe, < 0.25 mg/1 Pb and 2 mg/l Zn was treated for cobalt powder recovery as follows: 0.8 Q of CoSO~ leach solution was heated in autoclave to 200C and H2 was admitted at 1.3 MPa partial pressure. A 9.4 N NaOH
solution was pumped in at a rate of 1.2 Q/h for 15 minutes (equivalent to 99% of the Co as Co(OH) 2 ) and the reduGtion was continued thereafter for another 35 minutes. ~fter cooling the end reduction liquor was pumped out ~nd 0.8 Q of fresh feed CoS04 solution was pumped in. After heat~ng to 200C, H2 was admitted at 1.3 MPa partial pressure (3 ~Pa total pressure) and a 9.4 N NaOH solution was pumped in at 0.7 Q/h for 17 minutes. The reduction was continued thereafter for 23 minutes. During NaOH addition, the pH of the reduct;on liquor varied between 2.7 and 3.9. The end reduction liquor was cooled and removed through a Ti inlet equipped with carbon filter. After adding 0.8 Q of fresh feed CoS04 solution the reduction cycle was repeated under the same ;
conditions. After 6 cycles, the Co powdex was xemoved, washed and dried in air. The powder contained 99% cobalt, 0.09% nickel, by weight, and, in ppm, 240 copper, 240 iron, <10 lead, < 10 zinc, 1000 sulfur.
Densification results are ~iven in Ta~le C.

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TABLE C

CobalJc Powder Reduction % Apparent Co Creduced Cycle S Specific Reduced Cnucleated Gravity (~/cm3) (g) (g/g) 0 (nucleation) - - 72 0 3 0.04~ 3.6 220 3.0 6 0.100 3.6 350 5.0 The structure of the seed powder at 200 diameters is shown in Figure 5. A large amount of void space is evident.
The powder structure obtained after 6 dens~ficat;ons ~s shown in Figure 6. The powder is still porous and the tendency to deposit reduced cobalt in t~e void space`of the seed ~articles is illustrated. The density of the product is notabl~ low.
However, when the porous seed powder of Figure 5 ~s su~ected to a light grind, as in a ball mill, fine discrete powder particles are produced which are satisfactory as seed powder for the production of a dense cobalt powder product after a number of densifications.
Althou~h the present invention has been described in conjunction with preferred embodiments, it is to be under~
stood that modifications and variatiOnsmay ~e xesoxted to without departing from t~e spirit and scope ~f the ~nvention t as those skilled in the art will readily understand. ~ch modifications and variations are considered to ~e within t~e purview and scope of the invention and appended cla~ms.

Claims (7)

WE CLAIM:

1. A process for producing dense cobalt powder of coarse, relatively uniform particle size which comprises subjecting a portion of a cobaltous sulfate solution to hydrogen reduction at a hydrogen partial pressure of at least one megapascal and a temperature of at least about 180°C in the presence of a reaction initiator while introducing sodium hydroxide solution at a rate not substantially exceeding the rate of sulfuric acid production due to hydrogen reduction, continuing the hydrogen reduction to reduce substantially all the cobalt content of said portion with production of end reduction solution and cobalt powder, repeating said hydrogen reduction cyclically with fresh successive portions of cobaltous sulfate solution with each successive reduction being performed in the presence of substantially all the cobalt powder formed in the previous cycle to provide a densified cobalt powder product.

2. A process in accordance with claim 1 wherein said reduction initiator is fine, discrete cobalt powder having a particle size not exceeding about 20 microns.

3. A process in accordance with claim 1 wherein said cobaltous sulfate solution contains about 50 to about 100 grams per liter of cobalt.

4. A process in accordance with claim 1 wherein the pH of the reaction mixture is at least as acid as about pH
4 during reduction.

5. A process in accordance with claim 2 wherein said cobalt powder has an average particle size in the range of about 1 to about 5 microns.

6. Cobalt powder of coarse relatively uniform particle size, having a smooth surface, a density in the range of about 4.5 to about 5.5 grams per cubic centimeter, with at least 98% of the particles exceeding 75 microns in size.

7. A process in accordance with claim 1 wherein the cobaltous sulfate solution is prepared from an impure cobaltic hydroxide precipitate by the steps comprising a. addition of sulfuric acid to provide a pH less than 1 and aeration to lower the chloride level to less than 100 ppm b. addition of methanol to solubilize in excess of 80% of the cobalt and then addition of hydrogen peroxide to essentially complete the dissolution of cobalt c. addition of base to raise the pH to about 5.5 to precipitate iron d. filtering to obtain a cobaltous sulfate solution which is further purified by contacting with a copper-nickel selective ion exchange resin.