FI71771C - FOERFARANDE FOER FRAMSTAELLNING AV ETT TAETT KOBOLTPULVER. - Google Patents

Description

1 71771

Method for preparing a dense cobalt powder

The invention relates to a process for preparing a dense cobalt powder having a coarse relatively uniform particle size by reducing a cobalt-containing solution with hydrogen under pressure in the presence of cobalt powder and then reducing new batches of solutions in the presence of the formed cobalt powder.

Hydrogen-reduced elemental cobalt-10 powder is a commercial product. One currently available product of this type is known to be prepared by reducing aqueous solutions of cobalt amine ammonium sulfate with hydrogen using a catalyst, for example sodium sulfite / sodium cyanide. The crystallization of the cobalt powder 15 in this system is irregular, resulting in the formation of a powder with a bulk density of 0.6 to 1 g / cm 3. To obtain a more dense commercial product, repeated cycles of compaction are used, which precipitate more cobalt on the initially formed powder-20 from the fresh cobalt-containing solution. In this way, the particle size increases so that possibly n.

60% of the product has a particle size greater than 200 mesh on a Tyler screen (75 microns), and the bulk density of the product increases to about 3.2 g / cm 2. The cobalt-adhesive-25 ma per reduction cycle is of the order of about 40 g / l.

Approximately 30% of the cobalt metal produced is recovered and redissolved in the step of reducing the cobalt (3) ions to cobalt (2) ions in a cobalt (3) -amine ammonium sulfate feed solution to obtain a starting solution for the hydrogen-30 reduction step. The average hydrogen reduction cycle is shown to last about 30 minutes. The particles of the final cobalt powder are irregular in shape and have a rough, slightly debris-covered surface.

In many cases, the powder is dark gray to 35 black in color. The prepared cobalt powder must be handled with care and exposure to air should be avoided until the powder product has cooled. Drying of the washed cobalt powder is usually performed under a hydrogen or nitrogen atmosphere.

An example of the state of the art in the art is the selective reduction scheme for nickel shown in Schaufelberger and Roy entitled "Separation of

Copper, Nickel and Cobalt by Selective Reductions from Aquenous Solution "in Transactions of the Institute of Mining and Metallurgy, London, Vol. 64, 1954-1955, pp. 375-393, and U.S. Pat. No. 10,694,005 and 2,694,006. A scheme comprising soluble cobalt (3) amine is disclosed in U.S. Patents 2,767,055 and 2,767,054. One method of hydrogen reduction in which an extraction solution is made alkaline with ammonia is described by Mitchell under the heading "Cobalt Pressure Leaching and Reduction 15 at Gardield "in Journal of Metals, March 1957, pages 343-345. Direct gas reduction of cobalt (2) oxide or hydrogen reduction of aqueous slurries to cobalt metal is described in the literature, for example, in U.S. Patent 2,805 to Schaufelbergen 20. 149 and in the writings of R. Soubirous et al., Published in CR Acid, Se., Paris, pp. 270, pp. 1595-1597 and in the writings of Dobrokhotov et al., which appeared in Cveth. Metally, 35, 1962, page 44. In many of these methods, the starting material is cobalt (3) hydroxide, which must be converted to the cobalt (2) form. Dissolution of cobalt (3) hydroxide with an organic reducing agent such as methanol is disclosed in U.S. Patent 4,151,258 and L. Syper, entitled "Oxidation of Some Organic Compounds by Cobalt (III) Hydroxide", in Roczniki Chemii, Vol.

47, no. 1, pp. 43-48, (1973). The use of crystalline nucleating agents in hydrogen reduction processes is described in U.S. Patents 2,767,081, 2,767,082 and 2,767,083.

It would be desirable to be able to produce a cobalt powder having a higher bulk density than the currently available product, and the present invention is based on the finding that such a cobalt powder can be obtained by reducing a cobalt solution with hydrogen under certain conditions.

3,71771

The process according to the invention for producing a dense cobalt powder having a coarse, relatively uniform particle size is characterized in that a portion of the cobalt (2) sulphate solution is subjected to hydrogen reduction at a hydrogen partial pressure of at least one megapascal and at a temperature of at least 180 ° C. in the presence of seed cobalt powder in the form of fine, discrete particles of an average size not exceeding 20 micrometres, while maintaining the pH of the solution at not more than 10 by adding alkali metal hydroxide solution in an amount not substantially exceeding molar equivalents of hydrogen reduction from hydrogen reduction, to reduce a substantial portion of the cobalt content of this portion to give a final reduction solution and a cobalt powder, and this hydrogen reduction is repeated periodically with fresh successive portions of a cobalt (2) sulfate solution, each successive reduction being performed in the presence of cobalt powder, n formed in the previous cycle, to give a concentrated cobalt powder product.

The cobalt sulphate solution generally contains about 50-100 g / l of cobalt and the hydrogen reduction is preferably stopped when about 80-95% of the cobalt has been reduced. The cobalt adhesion per reduction cycle can be up to 90 g / l.

The process according to the invention gives a product comprising coarse cobalt particles with smooth surfaces 3 and a density of about 4.5-5.5 g / cm 3. At this density, the cobalt powder is found to be compacted so that 98% or more of the particles exceed a screen number of 200 mesh on a Tyler screen scale (0.075 mm). The parts have a flat 30 spherical shape and look bright to the eye.

The number of compaction steps used, i.e. the hydrogen reduction steps, is not important because the process is continued until the desired particle size and powder density are reached.

35 The product can be washed and dried in the presence of air.

The final reduction liquid does not contain any ammonium sulfate and the remaining dissolved cobalt can be recovered by simple hydrolysis. The average duration of the reduction cycle can be as short as 30 minutes.

5 The inoculant cobalt powder used to initiate the precipitation of cobalt during hydrogen reduction must be finely divided and consist of discrete particles not exceeding 20 microns in size. It is preferred to use a fine, discrete particle inoculum powder having an average particle size of about 1-5 microns. For example, a particularly fine cobalt powder having an average particle size of 1 to 20 microns and known under the trade name "Afrimet" powder can be used. Alternatively, a cobalt powder prepared by thermally decomposing cobalt oxalate, for example by heating cobalt oxalate at 500 ° C under a nitrogen atmosphere for 15 minutes, may be used. The very small needle-like particles and large surface area characteristic of Afrimet cobalt powder make it a preferred starting material. Thermal decomposition of cobalt oxalate also gives fine needle-like particles, but not as fine as Afrimet.

In contrast, the cobalt powder prepared by crystallization using sodium cyanide and sodium sulfide as catalysts is irregular in shape and has a large particle size. During the hydrogen reduction, the self-crystallized cobalt powder consists of large porous particles. When finely divided needle-like initial powders allow compaction by growing individual particles or particle agglomerates during reduction, the use of porous cobalt powder envelopes tends to precipitate hydrogen-reduced cobalt in the cavities of large cobalt envelope particles, resulting in a smaller area of available cobalt. In subsequent compaction steps, care must therefore be taken not to add too much base and, in general, the amount of base added in a given compaction step should be less than the amount added in the previous step to compensate for less cobalt reduction (and thus sulfuric acid formation). is due to the smaller pin-5 ta area on which fresh cobalt can precipitate. However, the products thus obtained have a lower bulk density than products inoculated with a fine, discrete particulate cobalt powder.

It is clear that in the process one mole of sulfuric acid is formed for every 10 moles of cobalt sulphate hardened. It is important that the amount of alkali metal hydroxide added does not exceed the amount required to neutralize the sulfuric acid as it is formed. Thus, for example, if sulfuric acid is generated at a rate of 200 g / h (2.40 mol-15 l / h), sodium hydroxide should be added at a rate not substantially higher than 164 g (4.1 mol) / h.

If the amount of sodium hydroxide added exceeds the amount necessary to neutralize the sulfuric acid formed, cobalt (2) hydroxide may be formed, which tends to produce self-crystallized cobalt powder and interferes with the compaction of the cobalt powder already present. To reduce the risk of precipitation of cobalt (2) hydroxide, the pH of the solution is preferably not higher than 4 during any of the hydrogen reduction steps.

To avoid dilution of the solution, the alkali metal hydroxide is preferably added as a saturated, NaOH or KOH solution. By using alkali metal hydroxide instead of the ammonia previously proposed, the problems associated with the separation of ammonium sulphate from the solution remaining after the hydrogen reduction are avoided.

The source of the cobalt sulfate feed solution to be treated according to the invention is irrelevant. It is desirable that the feed solution be substantially free of impurities that are reduced or precipitated with cobalt during the hydrogen reduction. Thus, the concentrations of nickel, copper, iron and lead should be as low as possible. In addition, the concentration of 6,71771 different ion species such as chloride ion should be very low, e.g., less than 100 parts per million (ppm), as such ions tend to corrode the autoclave. In addition, unsaturated sulfur species, i.e., all sulfur-5 compounds except sulfate that can lead to sulfur contamination of the cobalt product, e.g., dithionate ions, should be removed.

The invention is preferably used to recover cobalt from cobalt (3) oxide hydrate obtained by oxidation precipitation of 10 cobalt from process extraction solutions using sodium hypochlorite and a base. Treatment of cobalt (3) hydrate to obtain a cobalt sulfate feed solution suitable for recovering cobalt as a cobalt powder in accordance with this invention comprises the steps of: 1) treating Co (OH) 2 with water and water at 60 ° C; for 30 minutes with suitable stirring and aeration to remove soluble Cl as Cl 2 according to the following reaction: 2Co (OH) 3 + 6H + + 2Cl "^ ^ 2Co ++ + Cl2 + 61 ^ 0 (the reaction is preferred only at pH _ <1.5, preferably 0.5-1.0) 2) To the dechlorinated slurry is added 25 methanol in the presence of a sufficient amount of i 2 SO 4 (already added in step 1) to dissolve Co +++ as Co +++ at 60 ° C according to the following reaction: 6Co (OH) 3 + 6H2SO4 + CH3OH - ^ 6CoSO4 + CC> 2 + 17 ^ 0 30 (However, this reaction does not proceed completely unless large excesses of H2SO4 * and CH2OH are added. In the presence of a stoichiometric amount of H2SO4 and 1.2 times the stoichiometric amount of CH3OH, 85-90% (i.e. at least about 35%) of the Co dissolves together. per hour at 60 ° C with a final pH of 1.5-2.0).

il 7 71771 3) A small amount of H 2 ° 2 is added to the extraction slurry to complete the dissolution of Co (OH) 2 according to the following reaction: 5 2 Co (OH) 3 + 2H 2 SO 4 + H 2 O 2 -2CoSC> 4 + 6H 2 O 2 O 2

Complete dissolution of Co (OH) 2 is achieved by keeping the pH below about 2.5.

4) 0.5-1.0 g / l BaCO 2 is added to precipitate Pb at 60 ° C and pH about 2.5.

5) Excess H 2 SO 4 is neutralized with CoCO 3 or Na 2 O 4 to pH 5.5. At this point, Fe and Cu precipitate on the hydroxy-deine.

6) The extraction liquid is separated by filtration from the extraction residue-15 containing metals Pb, Fe and Cu.

7) The extraction solution is treated by passing it through a Cu, Ni-selective ion exchange resin (such as Dow Chemical Company XF-4195) to remove residual Cu and the required amount of Ni.

8) Co is recovered in elemental form from the purified extraction solution by the method of the invention.

The process of the invention will now be described in more detail by way of example and with reference to the accompanying photomicrographs, in which: Figure 1 is a photomicrograph taken at a magnification of 200 of a fine, commercial cobalt powder useful in inoculants in the process of the invention; Figure 2 is a photomicrograph taken at magnification 30 at a ratio of 200 of a powder prepared by the method of the present invention after two compacts using the seed powder shown in Figure 1; Figure 3 is a photomicrograph taken at a magnification of 200 of a powder prepared by the method of the invention 35 after four compactions, starting with the seed powder of Figure 1; Fig. 8 71771 is a photomicrograph taken at a magnification of 200 of a powder prepared by the method of the invention after six compacts, starting with the inoculum powder of Fig. 1; Fig. 5 is a photomicrograph taken at a magnification of 200 of cobalt powder obtained as a result of self-crystallization; and Figure 6 is a photomicrograph taken at a magnification ratio of 200 of a product powder obtained after six compacts using the powder of Figure 5 as an inoculum powder by a method not in accordance with the present invention.

Example I

6.3 kg wet Co (OH) 3 cake containing 27.6 wt% Co, 0.48 wt%, Ni, 0.06 wt% Fe, 0.003 wt% Cu, 0.001 wt% Zu and 0.2 wt% Cl, was slurried with water and 3 kg of concentrated H 2 SO 4 to a volume of 15 L. The slurry was heated to 60 ° C and stirred while air was blown through it for 30 minutes to remove the chloride ion content as gaseous chlorine. At this point, the pH of the slurry was 0.1 and less than 5% of the cobalt in the cake was dissolved.

The dechlorinated slurry was then subjected to reductive extraction by the addition of pure methanol solution at a rate of 600 ml / h for 15 minutes. The extraction of edis-25 sea buckthorn was monitored by monitoring the pH, which rose from 0.1 to 1.5 in one hour. At pH 1.5, about 85% of the feed Co (OH) 3 was dissolved and further dissolution of Co (OH) 3 was very slow due to the lack of H 2 SO 4 and methanol. A complete reaction with methanol would require not only an excess of methanol, but also a large excess of H 2 SO 4 (pH not greater than 1 in the final leach liquid), which must be neutralized with a base. This step would be expensive.

Methanol was therefore replaced with H 2 O 2, which reacts with Co (OH) 3 as a reducing agent below pH 4. To the extraction-35 slurry was added 30% H 2 O 2 solution at a rate of 75 ml / h for 140 minutes. At this point, the end of the extraction was observed by a sharp discoloration from black to pink. During the completion of the extraction, the pH was maintained at 1.5 with H 2 SO 4 as needed. This pH is preferred for the subsequent Pb removal step. Lead was removed from solution 5 by adding 0.5 g of BaCO 2 / l solution. After 30 minutes at 0-60 ° C, the solution was neutralized to pH 5.5 using a 100 g / l CoCO 2 slurry. After filtration, the liquid was passed through a Ni-selective IX resin to remove Ni. The final purified solution contained 96 g / l 10 Co and 0.038 g / l Ni as well as 1 mg / l Cu, <0.3 mg / l Pb, 1 mg / l Fe, 5 mg / l Zn and 30 mg / l Cl.

An extraction solution prepared as described above containing 92.2 g / l Co, 1.3 g / l Ni, 0.3 mg / l Cu, 0.3 mg / l Pb and 0.5 mg / l Fe was treated with cobalt to recover 15 as a powder in elemental form as follows: 0.8 l of extraction solution and 10 g of fine, discrete Co-powder 3 with a bulk density of 0.6 g / cm were placed and sealed in a 2-liter Parr car made entirely of Ti. -clave equipped with a twin-propeller stirrer 20 at a speed of 1000 rpm in all experiments. The suspension was heated to 200 ° C and H 2 was charged to the autoclave at a partial pressure of 1.3 MPa (total pressure 3 MPa). A 9.4 N NaOH solution was then pumped into the autoclave at a rate of 150 ml / h for 90 minutes, representing a rate of NaOH addition of 1.1 moles per mole of cobalt per hour. The pH of the solution during the addition of NaOH was 2.0-3.0. The reduction was continued after the addition of NaOH for 20 minutes to ensure complete removal of Co (OH) 2. The final reduction solution was cooled to 80 ° C and removed from the autoclave through a carbon-30 filter, leaving the Co powder in the autoclave. Approximately 100 ml of final pupellant was left in the autoclave.

0.8 L of fresh CoSO 4 feed extract solution was pumped into the autoclave and the H 2 reduction cycle was repeated as above.

After 6 cycles (or compaction), all of the Co powder was washed and air dried at room temperature. The final powder contained 97% cobalt, 2% nickel, <15 ppm copper, <40 ppm iron, 14 ppm zinc, 170 ppm sulfur, 10 71 771 and 590 ppm carbon. Table I describes the compaction achieved by 6 cycles.

Table I

5 _Cobalt powder__

Reduction-% Volume- Reduced Reduced Co cycle S weight Co inoculum Co _ (g / cm3) _ (£) _ (g / q) __ 10 1 0.058 2.0 56 5.6 2 0.024 4.1 104 10, 4 4 0.019 5.2 209 20.9 6 0.017 5.5 300 30.0 15 The structure of the fine cobalt seed powder used in this example is shown in Figure 1 and the structure of the product powder 2, 4 and 6 after compaction is shown in Figures 2, 3 and 4. , all at a magnification of 200. The correspondence between density and particle size is significant.

20 Example II

The H2 reduction procedure used in Example I was repeated, but using a feed extraction solution containing 85.5 g / l Co, 0.13 g / l Ni, 0.2 mg / l Cu, 0.3 mg / l Pb and 0.9 mg / 1 Fe. After 8 reduction cycles, the cobalt powder was washed 25 and air dried. The cobalt powder product contained 99% by weight cobalt, 0.32% nickel, 7 ppm copper, 20 ppm iron, <10 ppm lead, <5 ppm zinc, 280 ppm sulfur and 630 ppm carbon. Table II describes the condensation achieved during 8 cycles.

30

Table II

_Cobalt Powder____

Reduction% Apparent Reduced Reduced Co cycle S specific gravity Co inoculum Co 35 _ (g / cm3) _ {£) _ (g / g) _ 2 0.024 2.35 77.9 7.8 4 0.025 4.59 156, 1 15.6 71 771 11

Table II (continued)

The cobalt powder

Reduction% Apparent Reduced Reduced Co cycle S specific gravity Co inoculum Co 5 _ (g / cm3) __ (g / g) __ 6 0.027 5.4a 218.0 21.8 8 0.028 5.50 273.5 27.4

Example III

An extraction solution containing 96 g / l Co, 0.038 g / l Ni, 0.3 mg / l Cu, 0.2 mg / l Pb, 1.3 mg / l Pe and 5 mg / l Zn was treated to recover Corn in powdered elemental form as follows: 0.8 l of extraction solution and 40 g of fine discrete cobalt powder (Afrimet) in a pan-15 ti in 2 l Parr Ti autoclave. The suspension was heated with stirring to 200 ° C and H 2 O was introduced into the vessel at a partial pressure of 1.2 MPa (total pressure 3MPa). The 9.4 N NaOH solution was pumped into the autoclave at a rate of 780 ml / h (5.5 moles of NaOH per mole of cobalt per hour) for 18 minutes 20 seconds-20 n. The pH of the solution during NaOH addition was between 2-3. The reduction was then continued for a further 11 minutes 40 seconds (total time 30 minutes). The final reduction liquid was cooled and removed from the autoclave through a Ti feed tube equipped with a carbon filter. OF.

25 100 ml of final reduction liquid and reduced Co powder were left in the autoclave.

0.8 L of fresh CoSO 4 feed extraction solution was pumped into the autoclave and the hydrogen reduction cycle was repeated under the above conditions. After 11 such cycles, all 30 Co powder was removed, washed and air dried at room temperature. The powder contained 99% by weight of cobalt, 0.042% by weight of nickel, 5 ppm of copper, 33 ppm of iron, 2 ppm of lead, 2 ppm of zinc and 210 ppm of sulfur.

The results are shown in Table III. Again, the S content of the Co-35 powder decreased and the bulk density increased with increasing number of cycles.

71771 12

Table III

_ Cobalt powder__

Reduction-% Volume- Reduced Reduced Co cycle S weight Co inoculum Co 5 _ (g / cm3) _ (£) _ (g / g) _ 1 0.083 0.8 51 1.3 3 0.040 1.9 160 4, 0 6 0.018 3.8 310 7.8 8 0.026 4.3 420 10.5 10 11 0.021 4.7 560 14.0

Example IV

CoSO 4 feed extract solution prepared by the method described in Example I and containing 92 g / l 15 Co, 0.035 g / l Ni, <0.1 mg / l Cu, 1.1 mg / l Fe, 0.25 mg / l 1 Pb and 2 mg / l Zn, were treated with H 2 reduction for the recovery of Co as follows: 0.8 l of CoSO 4 extraction solution and 30 g of Co powder prepared by decomposing cobalt oxalate crystals at 500 ° C: for 15 to 20 minutes, was placed in a 2 L Parr-Ti autoclave. The suspension was heated to about 200 ° C and introduced into the autoclave at a partial pressure of 1.3 PMa (total pressure 3MPa).

The 9.95 N NaOH solution was then pumped into the autoclave at 150 ml / h for 90 minutes. The pH of the solution during the NaOH-li-25 addition was between 2.5-3.5. The reduction was then continued for a further 30 minutes, during which time the pH of the solution dropped to 2.5. The final reduction liquid was cooled to 80 ° C and removed from the autoclave through a Ti feed tube equipped with a carbon filter. 0.8 L of fresh CoSO 4 solution was fed to the autoclave and the H 2 reduction cycle was repeated as before 11 times. At the end of the 11th cycle, the Co powder was washed and air dried. The cobalt powder contained .99 wt% cobalt, 0.089 wt% nickel, 12 ppm copper, 32 ppm iron, 9 ppm lead, 4 ppm zinc and 518 35 ppm sulfur.

Achieved satisfactory condensations are described in Table IV.

13,717 71

Table IV

_Kobolttijauhe__

Reduction-% Volume- Reduced Reduced Co cycle S weight Co inoculum Co 5__ (g / cm3) _ (_ a _) _ (g / q) _ 3 - 3.3 155 5.2 6 - 4.3 271 9.0 11 0.05 4.7 518 17.3 10 To illustrate the unsatisfactory results obtained when sodium hydroxide is introduced during the reduction in an amount substantially exceeding the amount of sulfuric acid formed, the following three examples are given:

Example A

A 15 SO 4 feed extract solution containing 86 g / l Co, 0.046 g / l Ni, 0.3 mg / l Cu, 0.4 mg / l Pb and 2 mg / l Fe was treated to recover Co. in a crude manner: 0.7 l of CoSO 4 extraction solution and 10 g of Afrimet-Co powder were placed in a 2 L Parr-Ti autoclave.

The suspension was heated to 200 ° C and introduced into a vessel at a partial pressure of 1.3 MPa (total pressure 3 MPa). The 10 N NaOH solution was then pumped into the autoclave at a rate of 1.44 L / h (12 moles NaOH moles cobalt per hour) for 7 minutes 30 seconds. The pH of the solution increased from 2.0 to 7.0 during the addition of NaOH. The reduction was continued until the pH of the solution was below about 3. This took about n.

110 minutes. The final reduction liquid was cooled to 80 ° C and removed from the autoclave through a Ti feed tube equipped with carbon filters. The autoclave was charged with 0.7 L of fresh CoSO 4 solution and the H 2 reduction cycle was repeated as before 8 times. At the end of the 8th cycle, the resulting Co powder was washed and air dried. The co-powder was light and porous. About 3% of the Co had decayed into the interior of the autoclave. The powder contained 99 wt% cobalt, 0.05 wt% 35 nickel, 5 ppm copper, 30 ppm iron, <5 ppm lead, 6 ppm zinc, 1000 ppm sulfur and 500 ppm carbon.

14 71 771

The results are shown in Table A. Apparently due to the rapid addition of NaOH and only 10 g of Afrime t-inoculated powder, the bulk density of the Co powder was much lower than in the tests described in the previous examples.

Table A

_Kobolttijauhe_

Reduction% Volume Reduced Reduced Co cycle S weight Co inoculum Co 10 _ (g / cm3) _ [gj_ (g / g) _ 8 0.10 1.7 4.3 41.3

Example B

An extraction solution containing 96 g / l Co, 0.038 g / l Ni, 15 <0.3 mg / l Cu, <0.3 ml / l Pb, 1.3 mg / l Fe and 5 mg / l Zn - sealed to recover the cobalt powder as follows: 0.7 l of the extraction solution was sealed in a 2 l Ti autoclave and heated to 200 ° C. 1.3 MPa of partial pressure H 2 and 0.1 l of a solution containing 20 g / l of 20 NaCN and 2 g / l of Na 2 S were introduced into the autoclave. 9.4 N NaOH solution was then added at a rate of 780 ml / h for 18 minutes 36 seconds. The reduction was continued after the addition of NaOH for about 12 minutes. The contents of the autoclave were cooled to 80 ° C and the solution was removed from the vessel through a Ti-feed tube equipped with a carbon filter.

The autoclave was pumped with 0.7 L of fresh CoSO 4 feed extract solution, heated to 200 ° C and pressurized with H 2 to a total pressure of 3 MPa (manometer). The autoclave was then pumped with 9.4 N NaOH at 30,780 ml / h for 16 minutes and the reduction was continued together for 30 minutes. After cooling and removing the solution, the reduction cycle was repeated 5 times. The pH of the solution during the NaOH addition was between 2.5-3.0. After the 5th cycle, the Co powder was washed and air dried. Powder si-35 contained 99% by weight of cobalt, 0.05% by weight of nickel, 4 ppm of copper, 150 ppm of iron, <10 ppm of lead, <10 ppm of zinc and 450 ppm of sulfur.

71 771 15

The compaction results are shown in Table B.

Table B

_Kobolttijauhe_

Reduction% Volume Reduction Reduced Co 5 cycle S weight Co crystallized Co _ (g / cm3) _ (£) _ (g / g) _ 0 crystallization 63 2 0.152 1.15 155 2.46 5 0.045 2.50 274 4.35 10

Example C

An extraction solution containing 92 g / l Co, 0.032 g / l Ni,> 0.1 mg / l Cu, 1 mg / l Fe, <0.25 mg / l Pb and 2 mg / l Zn was treated to recover cobalt powder as follows: -15 ti: 0.8 l of CoSO 4 extraction solution was heated in an autoclave to 200 ° C and derivatized at a partial pressure of 1.3 MPa.

The 9.4 N NaOH solution was pumped into the autoclave at 1.2 L / h for 15 minutes (equivalent to 99% as Corsta Co (OH) 2) and the reduction was then continued for another 20 to 35 minutes. After cooling, the final reduction liquid was pumped out and 0.8 L of fresh CoSO 4 feed solution was pumped in. After heating to 200 ° C, 1 * 2 was introduced at a partial pressure of 1.3 MPa (total pressure 3 MPa) and a 9.4 N NaOH solution was pumped in at 0.7 l / h for 17 minutes. After the addition of NaOH, the pH of the reducing liquid varied between 2.7 and 3.9. The final reduction liquid was cooled and removed through a Ti feed tube equipped with a carbon filter. After the addition of 0.8 L 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 air dried. The powder contained 99% by weight of cobalt, 0.09% by weight of nickel, 240 ppm of copper, 240 ppm of iron, <10 ppm of lead, <10 ppm of zinc and 1000 ppm of sulfur.

35 The compaction results are given in Table C.

16 71 771

Table C

_Kobolttijauhe_

Reduction% Apparent Reduced Reduced Co cycle S specific- Co crystallized Co 5 weight (g) (g / g) _ (g / cm3) _ 0 crystallization - - 72 3 0.046 3.6 220 3.0 6 0.100 3, 6,350 5.0 10

The structure of the inoculum powder is shown at a magnification ratio of 200 in Figure 5. The large amount of cavity space is clear. The powder structure obtained after six compacts is shown in Figure 6. The powder is still porous and the tendency for precipitated reduced cobalt to precipitate in the cavity of the seed particles has been described. The density of the product is remarkably low. It was believed that the reason why the powder produced in Examples B and C is not particularly dense is that the seed particles are large and porous. Cobalt precipitates in the cavities in such particles 20 and this results in a reduction in the surface area available for cobalt precipitation in later stages. The state of the art can be compared to the methods described above, in which the surface area increases in successive compaction when small compact inoculum parts are used.

The addition of sodium hydroxide at the same rate in all steps using porous inoculated cobalt results in an excessive addition in the later steps, as the rate of sulfuric acid evolution in these later steps is lower than in the earlier steps as a result of a slower reaction rate . When the porous inoculated powder of formula 5 is subjected to light grinding, such as in a ball mill, fine loose powder particles are formed which are satisfactory for producing a dense cobalt powder product of the inoculated powder after a series of compactings have been carried out in accordance with this invention.

Claims (5)

17 71 771 A process for preparing a dense cobalt powder having a coarse, relatively uniform particle size by reducing a cobalt-containing solution with hydrogen under pressure in the presence of cobalt powder and then reducing new batches of solution in the presence of cobalt powder formed, characterized in that a dose of cobalt at a partial pressure of hydrogen of at least one megapascal and at a temperature of at least 180 ° C in the presence of seed cobalt powder in the form of fine, discrete particles of an average size not exceeding 20 microns, while maintaining the pH of the solution at not more than than 4, by adding an alkali metal hydroxide solution in an amount not substantially exceeding the molar equivalent of the amount of sulfuric acid formed in the hydrogen reduction, the hydrogen reduction is continued to reduce a substantial portion of the cobalt content of this portion to give a final reduction solution and cobalt powder, and this is reduced with fresh successive doses of cobalt (2) sulphate solution, each successive reduction being carried out in the presence of the cobalt powder formed in the previous cycle to give a concentrated cobalt powder product. Process according to Claim 1, characterized in that the average particle size of the seed cobalt powder is 1 to 5 microns. Process according to Claim 1 or 2, characterized in that the seed cobalt powder is in the form of needle-like particles. Process according to one of Claims 1 to 3, characterized in that the cobalt (2) sulphate solution contains 50 to 100 g / l of cobalt. Process according to one of Claims 1 to 4, characterized in that the hydrogen reduction is stopped when 80 to 95% of the cobalt in solution has been reduced. 71 771