JPH0351764B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a cobalt metal powder and a method for producing said cobalt metal powder from a cobalt-containing solution by hydrogen reduction. Hydrogen reduced elemental cobalt powder is a commercial product. It is known that one currently available commercial product is produced by hydrogen reduction of an aqueous cobalt, amine, ammonium, sulfate solution using a catalyst such as a sodium sulfite-sodium cyanide catalyst. There is. The nucleation of cobalt powder in this system is irregular, resulting in
A powder with an apparent density of 0.6 to 1 g/cm ² is produced. To create denser commercial products, repeated densification cycles are used to deposit additional cobalt from a fresh cobalt-containing solution onto the initially formed powder. In this way, the particle size is increased to such an extent that approximately 60% of the product has a particle size greater than 200 meshes (75 microns) on the Tyler screen scale, and the apparent density of the product is up to approximately 3.2 g/ ^cm2. increase Approximately 40 cobalt bytes per reduction cycle
g/g/g, and approximately 30% of the cobalt metal is recycled and redissolved in the cobalt ion reduction reaction from secondary cobalt ions to primary cobalt ions in the secondary cobalt amine ammonium sulfate solution feed. The average hydrogen reduction cycle is approximately
It is said that it will take 30 minutes. The final cobalt powder particles have an irregular shape with a rough pebble-like surface. The powder is often dark gray to black in color. Manufactured products must be handled with care, powder products must be handled with care, and exposure to air must be avoided until the powder product has cooled. Drying of the washed cobalt powder is usually carried out in an atmosphere of hydrogen or nitrogen. It would be desirable to provide a uniform coarse particle size cobalt powder with a higher apparent density than currently available products. Paper by Schjoferberger and Roy, “Separation of copper, nickel, and cobalt by selective reduction from aqueous solutions,” Bulletin of the Mining and Metallurgical Society, London, Vol. 64,
1954-1955, pp. 375-393, and U.S. Pat.
The prior art is exemplified by the nickel preferential reduction process described in Nos. 2,694,005 and 2,694,006. U.S. Patent Nos. 2767055 and 2767054
The issue is disclosed in the soluble second cobalt amine method. Another hydrogen reduction process, in which the leachate is made alkaline with ammonia, is described in Mitschiel's article, “Cobalt Pressure Leaching and Reduction in Garfield,” Journal of Metals, March 1957, Vol.
It is described on pages 343-345. Direct gas reduction of cobaltous oxides or hydroxides to cobalt metal is described, for example, in US Pat. , Paris, t.270, no.
pp. 1595-1597, and the Doprokhotov paper, Cvetn.
Metally. 35, 1962, p. 44. In many processes, the starting material is cobaltous hydroxide, which must be converted to the cobaltous form. Dissolution of cobalt hydroxide using an organic reducing agent such as methanol is disclosed in U.S. Patent No.
No. 4151258 and Syper's paper “Oxidation of Certain Organic Compounds by Cobalt Hydroxide”,
Roczniki Chemii, Vol. 47, No. 1, pp. 43-48 (1973). The use of nucleating agents in the hydrogen reduction process is described in U.S. Patent No. 2,767,081, no.
No. 2767082 and No. 2767083. The present invention provides hydroxylation at a controlled rate to neutralize the sulfuric acid formed during the reaction such that the pH of the solution phase during cobalt reduction is maintained below 4, preferably in the presence of fine, loose cobalt metal powder. A method is directed to carrying out pressurized hydrogen reduction of a cobalt sulfate solution while introducing sodium. This process continues until a product of desired particle size and density is produced.
A number of cycles are repeated in the presence of the cobalt powder product obtained in the first reduction step. The present invention relates to a method for producing dense elemental cobalt powder of coarse, relatively uniform particle size, and to the products obtained from this method. The method involves high temperature, high pressure hydrogen reduction of an aqueous solution of cobaltous sulfate. The steps used include placing a cobalt sulfate solution charge containing about 50 to about 100 grams of cobalt per liter in a sealed autoclave;
heating hydrogen in the presence of a cobalt metal powder acting as a nuclide or initiator to a temperature of at least about 180°C;
at least 1 megapascal, i.e. at least
introducing the sodium hydroxide solution into the autoclave at a controlled rate that does not substantially exceed the rate of sulfuric acid formation by hydrogen reduction of cobalt sulfate. This is accomplished by keeping the pH of the solution below about 4 during cobalt reduction. Addition of sodium hydroxide is stopped when approximately 80% to 95% of the cobalt in the solution has been reduced. The end reducing solution is then extracted from the autoclave and
Replaced with new cobalt sulfate solution feed. The above steps are then repeated to densify the cobalt metal powder until a cobalt powder of the desired particle size is obtained. The nuclide cobalt powder used to initiate cobalt precipitation during hydrogen reduction may be a finely ground cobalt powder obtained from other sources or by a reaction similar to that described above. For example, ultrafine cobalt powder with a particle size in the range of 1 to 20 microns, known in the industry as "Afrimet" powder, can be used. Thermal decomposition of cobalt oxalate, e.g. cobalt oxalate 500
It is also possible to heat the cobalt powder obtained by heating under nitrogen at °C for 15 minutes. A nuclide powder can be produced by nucleation using sodium cyanide and sodium sulfide as nucleating agents in the first hydrogen pressure batch. Finally, it is also possible to use the self-nucleated cobalt powder obtained from the first reduction solution. Each type of nuclide cobalt powder has a different physical shape and a different surface area per unit weight. The very small acicular particles and large surface area characteristic of Afrimet cobalt powder make it a preferred starting material. Thermal decomposition of cobalt oxalate also forms fine needle-like particles (but not as fine as Afrimet products). Powders produced by nucleation using sodium cyanide and sodium sulfide as catalysts have irregular shapes and large particle sizes. The self-nucleating cobalt powder is in the form of a large diameter porous powder. The finely divided acicular initiator powder allows densification by growth of each particle or particle agglomerate during reduction. In the case of porous cobalt powder nuclides, hydrogen-reduced cobalt tends to be deposited within the voids of the large-diameter cobalt nuclide particles, resulting in a reduction in effective surface area.
The product then has a lower apparent density than the product using fine, loose cobalt powder nuclides. For this reason, it is preferred to use a finely divided nuclide powder having a particle size on average of about 1 to 5 microns, such as a particle size not exceeding about 2 microns on average. It can be seen that for every mole of cobalt sulphate reduced, one mole of sulfuric acid is formed. It is important that the amount of sodium hydroxide added to neutralize the sulfuric acid formed to produce sodium sulfate and water does not exceed the production rate of sulfuric acid. If the rate of sodium hydroxide addition exceeds the rate of sulfuric acid formation, cobaltous hydroxide is produced, which tends to produce self-nucleating cobalt powder and interferes with the densification of the cobalt powder already present. Use saturated NaOH solution to prevent dilution. Starting from fine loose cobalt powder particles to which freshly reduced cobalt is deposited, if the reduction operation is repeated with this cobalt powder left in the autoclave for treatment of each batch of cobalt sulfate solution, Approximately 4.5 to 5.5 with a smooth surface
Large cobalt particles are obtained with an apparent density in the range of g/cc. At this density, the cobalt powder was found to be densified to such an extent that 98% or more of its particles exceeded the 200 mesh Tyler screen scale. These particles have a uniform spherical shape and a bright color. Thus, in the present invention, powder particles are considered to have a smooth surface when they are round, bright, and have a metallic appearance. The product is washed and dried in air. Cobalt bite per reduction cycle is as high as 90g/. The final reductant does not contain ammonium sulfate and residual dissolved cobalt can be recovered simply by hydrolysis. Average redemption cycle time is 30
It will be as short as 1 minute. The source of the cobalt sulfate feed solution treated by the present invention is not critical. Desirably, the feed liquid is substantially free of impurities that co-reduce or co-precipitate with cobalt during hydrogen reduction. That is, the content of nickel, iron, copper and lead should be as low as possible. Furthermore, species such as chlorine ions are very low, for example 100gpm.
Must be less than or equal to This is because ions of this type tend to be corrosive to autoclaves. Also, unsaturated sulfur species, ie all sulfur compounds other than sulfate leading to sulfur contamination of the cobalt product, such as dithionate ions, must be removed. The present invention is preferably applied to the recovery of cobalt from hydrated cobalt oxide obtained by oxidative precipitation of cobalt from a process leach solution using sodium hypochlorite and a base. A process for processing hydrated cobalt oxide to produce a cobalt sulfate feed solution suitable for recovering cobalt as a cobalt powder according to the present invention may include the following steps. (1) By the following reaction, 2Co(OH) ₃ +6H ⁺ +2Cl ^- →2Co ⁺⁺ +Cl ₂ +6H ₂ O (This reaction is performed at PH1.5, preferably PH0.5-1.0
(2) treatment of Co(OH) ₃ with H ₂ SO ₄ and water for 30 min at 60 °C with appropriate stirring and aeration to remove Cl ^- as Cl ₂ ; By reaction, 6Co(OH) ₃ +6H ₂ SO ₄ +CH ₃ OH →6CoSO ₄ +CO ₂ +17H ₂ O To solubilize Co ⁺⁺⁺ as Co ⁺⁺ at 60℃,
In the presence of sufficient amounts of H ₂ SO ₄ (already the first
step), adding methanol to the dechlorinated slurry. (However, this reaction requires an excess of H ₂ SO ₄
It will not reach completion unless CH ₃ OH is added. In the presence of stoichiometric amounts of H ₂ SO ₄ and 1.2 times the stoichiometric amount of CH ₃ OH, 85 of Co
~90% (ie, at least about 80%) dissolves in 1 hour at 60°C, resulting in a final pH of 1.5-2.0. ) (3) Add a small amount of H 2 to the soaking slurry to complete the dissolution of 2Co(OH) ₃ +2H ₂ SO ₄ +H ₄ O ₂ →2CoSO ₄ +6H ₂ O+O ₂ Co(OH) ₃ by the following reaction _. Add _O2 . By keeping the pH below about 2.5, Co
Complete dissolution of (OH) ₃ is obtained. (4) Due to Pb precipitation, at 60℃, PH ~ 2.5, 0.5 ~
Add 1.0g/ _BaCO3 . (5) Neutralize excess H ₂ SO ₄ with CoCO ₃ or Na ₂ CO ₃ until PH5.5. At this stage, Fe
and Cu are precipitated as their hydroxides. (6) From leached sediment containing Pb, Fe, and Cu,
Separate the leachate by filtration. (7) To remove residual Cu and the required amount of Ni, Cu,
Ni selective ion exchange resin (manufactured by Dow Chemical Company,
XF-4195, etc.) to treat the leachate. (8) Recovering elemental Co from the purified leaching solution by the method of the present invention. A few embodiments will be described below. Example: Co27.6%, Ni0.48%, Fe0.06% by weight,
Wet Co with Cu0.003%, Zn0.001% and Cl0.2%
6.3 Kg of (OH) ₃ cake was slurried to a volume of 15 with water and 3 Kg concentrated H ₂ SO ₄ . 60% of this slurry
℃ and stirred for 30 minutes while purging to remove the chlorine ion content as chlorine gas. At this point, the pH of the slurry was 0.1 and less than 5% of the cobalt in the cake had dissolved. Reductive leaching was performed on this dechlorinated slurry by introducing pure methanol solution at a rate of 600 ml/h for 15 minutes. The PH was monitored as the leaching progressed and the PH increased from 0.1 to 1.5 in 1 hour. At PH1.5, incoming Co(OH) ₃
Approximately 85% of Co(OH) ₃ is dissolved and no more
The dissolution of was very slow due to the lack of H ₂ SO ₄ and methanol. Not only is an excess of methanol required for complete reaction with methanol;
A large excess of H ₂ SO ₄ will be required (PH 1 in the final lysate), but this must be neutralized with base. This operation would be expensive. Therefore, H ₂ O ₂ is used instead of methanol and this
H ₂ O ₂ reacts with Co(OH) ₃ as a reducing agent at pH below 4. _Add 30% _H2O2 solution into the leaching slurry, 75
Add at a rate of ml/h for 140 minutes. At this point, completion of leaching was evidenced by an abrupt color change from black to pink. Upon completion of the leaching, the PH was maintained at 1.5 with H ₂ SO ₄ if necessary.
This PH is favorable for the subsequent Pb removal operation. Lead was removed from the solution by adding 0.5 g BaCO ₃ per solution. 30 at 60℃
After minutes, the solution was neutralized to pH 5 with a CoCO ₃ slurry containing 100 g/Co. After this period, the liquid is passed through Ni Select IX resin for Ni removal.
The final purified solution contains 96 g/Co and 0.038 g/
of Ni, and Cu of 1 mg/mg/, respectively.
Pb<0.3, Fe was 1, Zn was 5, and Cl ^- was 30. Created in the same manner as above, but with 92.2g/Co,
0.3g/Ni, 0.3mg/Cu, 0.3mg/
A soaking solution containing 100% Pb and 0.6mg/Fe was processed as follows for the recovery of elemental powdered cobalt. i.e. 0.8 leaching solution and 0.6 g
Fine, discrete particles with an apparent density of m/cc
10 g of Co powder was placed in a 2 capacity Parr all-Ti autoclave equipped with a twin propeller stirrer and sealed. The stirrer has a full speed of 1000r.p.
Rotated by m. Heat the suspension to 200 °C and add _H2 into the autoclave to a partial pressure of 1.3 MPa (3 MPa
or 450 psig total pressure). Next, add 150ml/h of 9.4N NaOH solution into the autoclave.
was pumped for 90 minutes at a rate of . This corresponds to a NaOH addition rate of 1.1 mol per mol of cobalt per hour. The solution pH during NaOH addition was 2.0 to 3.0. To ensure complete removal of Co(OH) ₂ ,
Reduction was continued for 20 minutes after NaOH addition. The final reduced solution was cooled to 80°C and extracted from the autoclave through a carbon filter, leaving the Co powder in the autoclave. Approximately 100 ml of final reductant was left in the autoclave. 0.8 fresh _CoSO4 leachate was pumped into the autoclave and purified with _H2 as described above.
The reduction cycle was repeated. After 6 cycles (densification), the entire amount of Co powder was washed and dried in air at room temperature. The final powder is 97% cobalt, 2
% nickel, and ppm <15 copper, <40 iron,
It contained 14 parts zinc, 170 parts sulfur, and 590 parts carbon. The table below shows the densification obtained during 6 cycles. [Table] The structure of the fine cobalt nuclide powder used in this example is illustrated in FIG.
The structure of the product powder after 6 times of densification is illustrated in Figures 2, 3 and 4, all at 200x magnification. The correlation between density and particle size is noteworthy. Example The H ₂ reduction method used in the example was repeated. However, 85.5g/Co.0.13g/Ni, 0.2mg/
A leaching feed solution with an analysis of 50% Cu, 0.3mg/Pb, and 0.9mg/Fe was used. After eight reduction cycles, the cobalt powder was washed and dried in air. The cobalt powder product is 99% cobalt by weight, 0.32% nickel, ppm basis, 7
of copper, 20% Cu, <10% lead, <5% zinc, 280% sulfur, and 630% carbon. The table below shows the densification obtained during 8 cycles. [Table] Example: For the recovery of elemental powdered Co, 96g/Co,
0.038g/Ni, 0.3mg/Cu, 0.2mg/
A leaching solution with analytical values of Pb, 1.3 mg/Fe, and 5 mg/Zn was treated as follows. 0.8 g of leaching solution and 40 g of fine, loose cobalt powder (Afrimet) were placed in a 2-volume Parr type Ti autoclave. The suspension was heated with stirring to 200 °C, and H ₂ was added at a partial pressure of 1.2 MPa (3 MPa
(total pressure)) into the autoclave. 9.4N
of NaOH solution was pumped into the autoclave at a rate of 780 ml/h (5.5 mol of NaOH per mol of cobalt per hour) for 18 minutes and 20 seconds. The pH of the solution during NaOH addition was between 2 and 3. After that, the reduction continues for another 11 minutes and 40 seconds (the total reduction time is 30 minutes).
minutes). The final reduced liquid is cooled and extracted from the autoclave through a Ti inlet tube equipped with a carbon filter. Approximately 100 ml of final reducing solution and reduced Co powder were left in the autoclave. 0.8 of fresh CoSO ₄ leach feed was pumped into the autoclave and the H ₂ reduction cycle was repeated at the above conditions. After 11 cycles like this,
The entire amount of Co powder was extracted, washed, and dried in air at room temperature. The powder contains 99% cobalt by weight,
0.042% nickel, 5 ppm copper, 33 iron,
It contained 2 parts of lead, 2 parts of zinc, and 210 parts of sulfur. The results are shown in the table. In this case too, the S content decreased and the apparent specific gravity of the Co powder increased with increasing number of cycles. [Table] Example Made by the method of example, 92g/Co, 0.035
g/Ni, <0.1mg/Cu, 1.1mg/Fe,
A CoSO ₄ leach feed having an analysis of <0.25 mg/Pb, 2 mg/Zn was processed for Co recovery by H ₂ reduction as follows. 0.8
_CoSO4 leaching solution and 500 °C for 15 min under _N2 atmosphere.
30 g of Co powder made by decomposing cobalt oxalate crystals with a capacity of 2 Parr type Ti
placed in an autoclave. suspension ~200
℃ and H ₂ was introduced into the autoclave at 1.3 MPa (3 MPa total pressure). Then 9.95N
The NaOH solution was pumped into the autoclave at a rate of 150 ml/h for 90 minutes. The pH of the solution during NaOH addition was within the range of 2.5-3.5. Reduction was then carried out for another 30 minutes, during which time the solution
PH decreased to 2.5. The final reduced solution was cooled to 80°C and extracted from the autoclave through a Ti inlet tube equipped with a carbon filter. 0.8 fresh CoSO ₄ solution was introduced into the autoclave and the H ₂ reduction cycle was repeated 11 times as before.
At the end of 11 cycles, the Co powder was washed and dried in air. The cobalt powder contained 99% cobalt, 0.089% nickel, 12 copper, 32 iron, 9 lead, 4 zinc, and 518 sulfur in ppm by weight. . Satisfactory densification was achieved as shown in the table below. Table The following example is given to demonstrate that unsatisfactory results were obtained by introducing sodium hydroxide during reduction at a rate that greatly exceeded the rate of sulfuric acid production. Example A 86g/Co, 0.046g/Ni, 0.3mg/
A CoSO ₄ leach feed having an analysis of Cu, 0.4 mg/Pb, 2 mg/Fe was processed as follows for Co recovery by H ₂ reduction. 0.7 CoSO ₄ leaching solution and 10 g Afrimet Co powder were placed into a 2 capacity Parr type Ti autoclave. suspension
It was heated to 200 °C and H ₂ was introduced into the autoclave at a partial pressure of 1.3 MPa (total pressure of 3 MPa). then 10N
A NaOH solution was introduced into the autoclave at a rate of 1.44/h (12 mol NaOH per mol of cobalt per hour) for 7 minutes and 30 seconds. During the NaOH addition, the pH of the solution increased from 2.0 to 7.0. Thereafter, reduction was carried out until the pH in the solution became approximately 3 or less. This took approximately 110 minutes. The final reduced solution was cooled to 80°C and extracted from the autoclave through a Ti inlet tube equipped with a carbon filter. 0.7 of fresh CoSO ₄ was introduced into the autoclave and the H ₂ reduction cycle was repeated 8 times as described above.
At the end of 8 cycles, the produced Co powder was washed and dried in air. This Co powder was light and porous. Approximately 3% Co was deposited inside the autoclave. Cobalt powder contains 99% cobalt, 0.05% nickel, 5 ppm copper, 30 iron, <5 lead, 6 zinc, and 1000 sulfur.
It contained 500 carbon atoms. The results are shown in Table A below. It is clear that when using rapid NaOH addition and only 10 g of Afrimet nuclide powder, the apparent density of the Co powder was much lower than in the test described in the previous example. That is, in the above example according to the present invention, the caustic soda aqueous solution was slowly added at a rate of 150 ml/h, that is, at a rate that did not greatly exceed the sulfuric acid production rate by hydrogen reduction. 5.2 g/cm ³ after, 5.5 g/cm 3 after 6 reduction cycles
According to the method of the present invention, it is possible to obtain cobalt powder with a high apparent density of 5.48 g/cm ³ after 6 times, and 5.50 g/cm ³ after 8 times. Cobalt powder with high density (4.5-5.5) could be obtained with fewer reduction cycles. On the contrary,
According to Table A, in Example A according to the prior art, as a result of adding the caustic soda aqueous solution at a very high rate at a rate of 1.44/h, only a small amount was added after 8 reduction cycles.
It is clear that only a low apparent density cobalt powder of 1.7 g/cm ³ could be obtained. TABLE Two tests using self-nucleating seed powder to produce hydrogen-reduced cobalt powder yielded unsatisfactory results, as shown in Examples B and C below. Example B 96g/Co, 0.038g/Ni, <0.3mg/
Cu, <0.3mg/Pb, 1.3mg/Fe, 5mg/
The leaching solution with a Zn analysis result of 10% was processed as follows for cobalt powder recovery. Seal the leaching solution of 0.7 in a 2Ti autoclave,
Heated to 200°C. for autoclave
Introducing H ₂ with a partial pressure of 1.3 MPa and 20 g/
Solution 1 containing NaCN and 2 g/Na ₂ S
was pumped in. This was followed by the addition of 9.4N NaOH solution at a rate of 780 ml/h for 18 minutes 36 seconds.
After NaOH addition, reduction continued for approximately 12 minutes.
The autoclave contents were cooled to 80°C and the solution was extracted from the autoclave through a Ti inlet tube equipped with a carbon filter. Heated to 200℃ and 3MPa total pressure (450psig)
During autoclaving pressurized with _H2 up to 0.7
of fresh CoSO ₄ leach feed solution was pumped in.
Reduction is carried out by pumping 9.4N NaOH for 16 minutes at a rate of 780 ml/h for a total of 30 minutes. After cooling and solution extraction, the reduction cycle was repeated five times.
The solution PH during NaOH addition was within the range of 2.5 and 3.0. After 5 cycles, the Co powder was washed and dried in air. This powder contains 99% cobalt by weight, 0.05% nickel, 4 ppm copper, 150%
of iron, <10% lead, <10% tin, and 450% sulfur. The densification results are shown in Table B below. [Table] Example C 92g/Co, 0.032g/Ni, <0.1mg/
A leaching solution with an analysis of 50% Cu, 1 mg/Fe, <0.25 mg/Pb, and 2 mg/Zn was processed as follows for cobalt powder recovery. 0.8
The _CoSO4 leaching solution was heated to 200 °C in an autoclave and _H2 was introduced at a partial pressure of 1.3 MPa. 9.4N
The NaOH solution was pumped in at a rate of 1.2/h for 15 minutes (corresponding to 99% of Co as Co(OH) ₂ ), after which the reduction was continued for a further 35 minutes. After cooling, the final reductant was pumped out and a fresh CoSO ₄ charge of 0.8 was pumped in. After heating to 200℃,
_H2 was introduced at a partial pressure of 1.3 MPa (total pressure of 3 MPa),
A 9.4N NaOH solution was pumped in at a rate of 0.7/h for 17 minutes. Thereafter, the reduction was continued for 23 minutes. During NaOH addition, the pH of the reducing solution varied between 2.7 and 3.9. The final reduced liquid was cooled and removed through a Ti inlet tube equipped with a carbon filter. After adding 0.8 of fresh CoSO ₄ feed solution, the reduction cycle was repeated under the same conditions. After 6 cycles,
The Co powder was removed, washed and dried in air.
The powder is 99% cobalt, 0.09% nickel (wt%), and ppm 240 copper, 240 iron, <10 lead, <10
of zinc and 1,000 of sulfur. The densification results are shown in Table C. [Table] Figure 5 shows the structure of the nuclide powder at 200x magnification. A large amount of voids can be seen. The powder structure obtained after 6 cycles of densification is shown in FIG. This powder is still porous and tends to deposit reduced cobalt within the voids of the seed particles. The density of the product is significantly lower. However, when the porous nuclide powder shown in Figure 5 is lightly ground in a ball mill, for example, fine discrete powder particles are created, which can be used to obtain a dense cobalt powder after multiple densification treatments. Satisfied as a powder. The present invention is not limited to the above description, and can be modified or implemented as desired within the scope of the spirit thereof.

[Brief explanation of drawings]

Figure 1 is a 200x micrograph of fine commercially available cobalt powder that can be used as nuclide particles in the method of the present invention.
Figure 3 is a 200x micrograph of the product powder after densification has been carried out 4 times. Figure 4 is a 200x microscope photograph of the product powder after densification has been carried out 4 times. of the product powder after carrying out
200x micrograph, Figure 5 is a 200x micrograph of cobalt powder obtained as a result of self-nucleation,
In addition, Figure 6 shows 6
FIG. 2 is a 200x micrograph of the product powder after double densification.

Claims (1)

[Claims] 1. While introducing an aqueous sodium hydroxide solution at a rate that does not substantially exceed the rate of sulfuric acid production due to hydrogen reduction,
In the presence of a metallic cobalt initiator, a hydrogen partial pressure of at least 1 megapascal and a hydrogen partial pressure of at least 180
carrying out hydrogen reduction on a portion of a cobaltous sulfate solution containing 50 to 100 grams of cobalt per liter of water at a temperature of at least PH 4; reducing substantially the entire cobalt content of the solution portion to simultaneously produce a final reduced solution and cobalt powder; extracting the final reduced solution and adding fresh cobaltous sulfate solution sequentially to periodically reduce the hydrogen content; The reduction is repeated, with each successive reduction cycle being carried out in the presence of substantially all of the cobalt powder formed in the previous cycle and in the absence of any initiator other than that used in the first reduction. and producing a densified cobalt powder product of coarse uniform particle size. 2. Process according to claim 1, characterized in that the reaction initiator is a fine, loose cobalt powder with a particle size not exceeding 20 microns. 3. A method according to claim 2, characterized in that the cobalt powder has an average particle size in the range of 1 micron to 5 microns. 4 Coarse, relatively uniform particle size cobalt powder having an apparent density in the range of 4.5 grams to 5.5 grams per cubic centimeter, at least 98% of the particles having smooth surfaces, and having a particle size greater than 75 microns.