Separation of cobalt by oxidative hydrolysis

The use of a low solubility product of trivalent cobalt hydroxide to oxidatively hydrolyze and precipitate cobalt is a common method for producing nickel and cobalt in a separation solution.

In the acidic solution, Co ^{2 +} is preferentially oxidized than Ni ^{2 +} , and the solubility product of Co(OH) ₃ and the pH of the hydrolyzed precipitate are significantly lower than Ni(OH) ₃ . Under the action of strong oxidant, Co ^{2 +} is Oxidation and hydrolysis precipitation. In the process of oxidative hydrolysis of cobalt, even if Ni ^{2 + is} oxidized to form Ni(OH) ₃ precipitate, it still has oxidation effect on Co ^{2 +} , and a substitution reaction occurs to produce Co(OH) ₃ precipitation, and Ni ^{2 +} enters. Solution. The commonly used strong oxidant is chlorine or sub-modified sodium chlorate.

H ^{+ is} produced during the hydrolysis and precipitation, and alkali must be added for neutralization.

In production applications, in order to separate cobalt and nickel well, the following basic principles should be followed:

(1) Adding an excess of oxidizing agent and a base, such as sodium hypochlorite for oxidation, should be made NaCl:Na ₂ CO ₃ = (1.1 to 1.2):1.

(2) Controlling the appropriate cobalt deposition rate, the cobalt deposition rate may be higher when the solution contains cobalt.

(3) Substituting a counter-cobalt with a second counter-cobalt to obtain cobalt hydroxide of higher purity.

The cobalt-cobalt operation is completed in an air agitation tank. When NaClO is used as the oxidant, the process of secondary cobalt deposition is: one time sinking cobalt→pressure filtration→the filter residue is washed with the second set of cobalt mother liquor→reduction and dissolution→secondary cobalt deposition→pressure filtration, as shown in Fig. 1. The basic technical parameters of the secondary cobalt deposition are shown in Table 1.

Figure 1 Process flow chart for producing electrocobalt from cobalt hydroxide

Table 1 Main technical parameters of secondary cobalt precipitation

In the cobalt-cobalt process, the solution is stirred evenly with air, and the oxidant must be sprayed evenly on the liquid surface by means of compressed air. In the cobalt hydroxide obtained by once cobalt precipitation, Co∕Ni≥10; in the cobalt hydroxide obtained by the second sinking cobalt, Ca∕Ni≥350, Co∕Cu≥200, Co∕Fe≥100. If it is required to produce No. 1 electrocobalt, the Co∕Ni ratio must be greater than 600.

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