Method for recovering cobalt from hexammine cobaltic (111) solutions

A method is disclosed for recovering cobalt, which comprises adding ammonia to a cobalt chloride solution to a pH of from about 8.8 to about 9.6 with oxidation, to form hexammine cobalt (III) chloride, adding to the resulting solution of hexammine cobalt (III) chloride, sodium chloride in an amount sufficient to result in the precipitation of at least about 98% by weight of the cobalt as cobalt hexammine (III) chloride at a temperature of no greater than about 40.degree. C., separating the precipitate of cobalt hexammine (III) chloride from the resulting mother liquor which contains the balance of the cobalt, adding to the mother liquor, aluminum powder in an amount sufficient to result in the precipitation of the balance of the cobalt as cobalt metal, and separating the cobalt metal from the resulting spent liquor.

This invention relates to a method for recovering cobalt from solutions of 
cobalt hexammine (III) ion as a precipitate of cobalt hexammine (III) 
chloride. By the method of the present invention, the amount of 
hydrochloric acid and ammonia is reduced from the amount used in previous 
methods. The mother liquor from the precipitation of the hexammine is then 
treated with aluminum metal to cement the cobalt contained therein. 
BACKGROUND OF THE INVENTION 
Oxidation of cobaltous chloride ion to the cobaltic ammine ion is 
accomplished in an ammoniacal-ammonium chloride solution in the presence 
of an activated charcoal catalyst. The reaction mixture is essentially 
buffered at a pH of from about 9.0 to about 9.4. After a period of 
aeration, &gt;98% by weight of the Co ions have been oxidized to 
Co(NH.sub.3).sub.6.sup.3+. Much of the Co at this point precipitates as 
[Co(NH.sub.3).sub.6 ]Cl.sub.3 due to the initial high concentration of 
chloride ion. However, in order to recover &gt;98% by weight of the cobalt as 
the solid ammine complex additional chloride ion must be added to the 
mixture. At the present time, HCl is used as the source of chloride ion. 
This is described in U.S. Pat. No. 4,612,039. Hydrochloric acid is added 
to a pH of about 0.5 at which &gt;98% by weight of the cobalt can be 
recovered by way of filtration. (The solid hexammine compound is further 
processed to extra fine cobalt metal powder.) The mother liquor from this 
filtration can contain up to about 5% of the initial cobalt (although 
generally about 2% or less) and, therefore, is treated in a separate step 
to recover the cobalt. This is accomplished by raising the pH to 8.0 to 
8.5 with NH.sub.4 OH and then cementing the cobalt out of solution with 
aluminum metal powder. After the cobalt is removed, the liquor is sent to 
a steam stripper for ammonia recovery. The recovered cobalt is then 
redigested in HCl and recycled to the beginning of the process. In the 
above process, much acid and ammonia are consumed. This results in high 
cost for materials and for extra processing. 
Therefore, a process in which less acid and ammonia are used would be 
advantageous both from an economical and an environmental standpoint. 
The following U.S. Patents relate to cobalt processing: 
U.S. Pat. No. 4,184,868 relates to a method for producing extra fine cobalt 
metal powder by digesting cobalt pentammine chloride in ammonium hydroxide 
to obtain a black precipitate which contains cobalt and which is 
thereafter reduced to metal powder. U.S. Pat. Nos. 4,214,894, 4,214,896, 
4,233,063, and 4,278,463 relate to improvements in U.S. Pat. No. 4,184,868 
in which the ammonia solutions are processed to recover any cobalt 
therein. U.S. Pat. Nos. 4,395,278 and 4,469,505 relate to improvements in 
U.S. Pat. No. 4,184,868 in which fine cobalt metal powder is 10 produced 
having reduced tailings. 
U.S. Pat. No. 4,214,895 relates to a process for producing cobalt metal 
powder which involves treating an aqueous solution of a soluble cobaltic 
ammine halide with a sufficient amount of a soluble metallic hydroxide to 
form a cobalt containing precipitate which is thereafter reduced to 
metallic cobalt. 
U.S. Pat. Nos. 4,218,240 and 4,690,710 relate to methods for producing 
cobalt metal powder by forming a solution of a cobalt hexammine compound 
and treating the solution with a metallic hydroxide to form a precipitate 
which is reduced to cobalt metal powder. U.S. Pat. Nos. 4,348,224 and 
4,381,937 relate to improvements in the process described in U.S. Pat. No. 
4,218,240 which involve removal of copper and silver from the cobalt. U.S. 
Pat. No. 4,452,633 relates to an improvement in the processes described in 
U.S. Pat. Nos. 4,218,240 and 4,348,224 in which the silver is recovered. 
U.S. Pat. No. 4,612,039 relates to a process for recovering cobalt in which 
cobalt is first reduced to the metal followed by ammonia-ammonium chloride 
digestion to form an hexammine cobalt (III) chloride while hydrochloric 
acid is added to precipitate the hexammine cobalt (III) chloride. The 
mother liquor is therefore acid and ammonium hydroxide is required to 
raise the pH to further recover any cobalt which remains in the mother 
liquor. 
U.S. Pat. Nos. 4,608,084 and 4,608,235 relate to processes for recovering 
cobalt from stellite material. 
U.S. Pat. No. 4,606,885 relates to producing a pure cobalt article. 
U.S. Pat. No. 4,594,230 relates to a process for recovering cobalt from 
cobalt material by digestion in hydrochloric acid followed by 
precipitation of cobalt oxalate. 
U.S. Pat. No. 4,578,251 relates to a process for separating chrominum from 
cobalt. 
U.S. Pat. No. 4,093,450 to Doyle et al describes a process for producing 
fine particle size cobalt metal powder by the hydrogen reduction of cobalt 
oxide obtained from a cobalt pentammine carbonate solution. The 
precipitate is formed by heating the solution to drive off ammonia and 
carbon dioxide to form a precipitate of cobalt oxide. 
U.S. Pat. No. 4,329,169 relates to a process for producing fine cobalt 
metal powder absent tailings by heating an aqueous solution of soluble 
cobalt ammine halide to decompose the halide and form a cobalt containing 
precipitate which is reduced to the cobalt metal powder. 
U.S. Pat. No. 4,409,019 relates to a process for producing fine cobalt 
metal powder from pieces of relatively pure cobalt by dissolving the 
cobalt pieces in an aqueous solution of hydrogen iodide and iodine and 
forming a cobalt containing solid which is subsequently reduced to a fine 
cobalt metal powder. 
SUMMARY OF THE INVENTION 
In accordance with one aspect of this invention, there is provided a method 
for recovering cobalt, which comprises adding ammonia to a cobalt chloride 
solution to a pH of from about 8.8 to about 9.6 with oxidation to form 
hexammine cobalt (III) chloride, adding to the resulting solution of 
hexammine cobalt (III) chloride, sodium chloride in an amount sufficient 
to result in the precipitation of at least about 98% by weight of the 
cobalt as hexammine cobalt (III) chloride at a temperature of no greater 
than about 40.degree. C., separating the precipitate of hexammine cobalt 
(III) chloride from the resulting mother liquor which contains the balance 
of the cobalt, adding to the mother liquor, aluminum powder in an amount 
sufficient to result in the precipitation of the balance of the cobalt as 
cobalt metal, and separating the cobalt metal from the resulting spent 
liquor. 
DETAILED DESCRIPTION OF THE INVENTION 
For a better understanding of the present invention, together with other 
and further objects, advantages and capabilities thereof, reference is 
made to the following disclosure and appended claims in connection with 
the above description of some of the aspects of the invention. 
This invention relates to a process for recovering cobalt from solutions in 
which cobalt is present as cobaltic hexammine (III) ion. This is done by 
adding sufficient chloride ion in the form of sodium chloride to insure 
the precipitation of at least about 98% by weight of the cobalt contained 
therein. The balance of the cobalt is recovered by adding aluminum metal 
to the mother liquor to result in the formation of cobalt metal. The 
cobalt hexammine (III) chloride is then processed by existing methods to 
cobalt metal powder. The formation of the cobalt (III) hexammine is 
accomplished without hydrochloric acid as has been done prior to this 
invention as described in U.S. Pat. No. 4,612,039. This is advantageous 
both economically and environmentally because the acid does not have to be 
removed. This would be done by neutralizing with ammonia. The mother 
liquor from the precipitation is treated with aluminum metal to recover 
the balance of the cobalt by cementation. As a result of not using HCl in 
the formation of the hexammine, there is less volume of mother liquor and 
the mother liquor is at the desired pH for the cementation. Therefore less 
processing is required to recover the balance of the cobalt. 
The starting cobalt solution is a solution of cobalt chloride having a 
cobalt concentration of typically from about 50 to about 120 g Co/l. 
Ammonia is added usually in the form of ammonium hydroxide to a pH of from 
about 8.8 to about 9.6 to form hexammine cobalt (III) chloride. This is 
done with oxidation which is usually air oxidation. Activated charcoal is 
present as a catalyst. The solution is kept at room temperature, that is 
less than about 40.degree. C. and most typically about 20.degree. C. for 
the subsequent precipitation. 
To the resulting hexammine cobalt (III) chloride solution is added sodium 
chloride in an amount sufficient to result in the precipitation of at 
least about 98% by weight of the cobalt contained therein as hexammine 
cobalt (III) chloride. The sodium chloride is added preferably in the 
solid form to maintain the solution concentration of cobalt. The balance 
of the cobalt remains in the resulting mother liquof. 
The precipitate is then separated from the mother liquor by any standard 
technique such as filtration. 
The precipitate of hexammine cobalt (III) chloride can then be processed by 
existing technology to the metal powder. 
To the mother liquor is added aluminum metal typically in powder form in an 
amount sufficient to result in the precipitation of the balance of the 
cobalt as cobalt metal. This process is known as the cementation of 
cobalt. In this step, there is no required pH adjustment with ammonia. The 
liquor is already at the desired pH whereas is HCl were used in the 
hexammine formation step, pH adjustment would be necessary. Also the 
volume of mother liquor to be treated with alumina is less than if HCl 
were used and this results in a simpler handling. 
The cobalt metal is then separated form the cobalt depleted mother liquor 
by standard techniques such as filtration. 
The recovered cobalt metal can then be further processed if necessary 
according to known methods depending on the desired use.

To more fully illustrate this invention, the following non-limiting example 
is presented. 
EXAMPLE 
Five tests are run in which the effect of adding HCl or NaCl at the end of 
the oxidation are compared. Oxidation conditions are identical in all five 
tests. Only the amounts of HCl or NaCl which are added to precipitate the 
hexammine cobalt (III) chloride are varied. The initial cobalt chloride 
solution contains about 110 g Co/l, about 28 g Ni/l, about 8.6 g Fe/l, 
about 41 g NH.sub.3 /l, and about 310 g Cl.sup.- /l. These tests are shown 
below in the Table. 
TABLE 
______________________________________ 
Chloride Chloride Mother liquor 
Test ion ion Vol. g/l 
# Added Moles ml pH Co Ni Fe Cl- 
______________________________________ 
1 None 0 410 9.4 3.3 12 &lt;0.005 
52 
2 110 ml 1.3 700 0.5 1.2 8 2.2 91 
HCl(*) 
3 29.2 g 0.5 520 9.3 1.7 9 &lt;0.005 
73 
NaCl 
4 43.8 g 0.75 420 9.4 0.8 9 &lt;0.005 
110 
NaCl 
5 58.4 g 1.0 400 9.2 0.6 12 &lt;0.005 
130 
NaCl 
______________________________________ 
(*)to pH 0.5 
The amount of chloride ion needed to substantially precipitate hexammine 
cobalt (III) chloride with NaCl is about half the amount needed using HCl 
where the pH is adjusted to about 0.5. See tests 1 and 2. Treatment of the 
resulting mother liquors from Tests 3, 4, and 5 can be accomplished simply 
by adding Aluminum powder to cement the cobalt. The volume decreases in 
the mother liquor when NaCl is used as opposed to HCl by about 25-40%. See 
Tests 2 and 4. 
While there has been shown and described what are at present considered the 
preferred embodiments of the invention, it will be obvious to those 
skilled in the art that various changes and modifications may be made 
therein without departing from the scope of the invention as defined by 
the appended claims.