Cobalt extraction

The calcine is subsequently leached with sulfuric acid from the spent copper recovery electrolyte.

Oxide concentrates are introduced at this leaching step to maintain the acid balance in the circuit.

Sodium hydrosulfide (NaHS) is added (along with some metallic cobalt as a catalyst) to precipitate nickel sulfide (NiS).

The solution is then further reduced with more sulfuric acid and cobalt metal powder is added to aid in the nucleation of precipitants (seeding).

Addition of hydrogen gas to saturation precipitates cobalt powder with a purity of approximately 99.6%.

Iron and lighter impurities float to the surface as solid dross or are expelled from the melt as gas.

Concentrations of cobalt oxide (Co3O4) may also be reduced by the aluminothermic reaction or with carbon in a blast furnace.

When purifying by electrolysis, an aqueous sulfate solution at 50 to 70 °C is typically used with a lead anode (corrosion products from which will not contaminate the cobalt oxy-hydroxide (CoOOH) electrolyte solution) and a stainless steel cathode which will allow for the easy removal of the deposited cobalt.

[5] Electro refining in a chloride or sulfate medium at −0.3 V will make a cathode coating of 99.98% cobalt.