Producing cobalt (III) hexammine sulfate from nickel cobalt sulfides

In a process for producing cobalt (III) hexammine sulphate, comprising leaching nickel-cobalt sulphides in a primary oxidative pressure leach in an ammoniacal ammonium sulphate solution under elevated pressure of an oxygen-bearing gas and at an elevated temperature with an ammonia to metals mole ratio effective to oxidize nickel and cobalt sulphides to sulphates, and to produce an ammoniacal leach liquor in which dissolved cobalt is predominantly in the (III) oxidation state, and a leach residue, separating the leach liquor from the leach residue and ammoniating the leach liquor by combining it with an effective amount of ammonia and cooling the ammoniated leach liquor whereby the triple salt of cobalt (III) hexammine sulphate, nickel (II) hexammine sulphate and ammonium sulphate is precipitated, recovering the precipitated triple salt from the leach liquor, and repulping the triple salt with an effective amount of water to selectively leach nickel (II) hexammine sulphate and to produce a crystalline cobalt (III) hexammine sulphate and a nickel enriched leach liquor, the improvement comprising:

• subjecting the leach liquor obtained from the primary oxidative pressure leach to a secondary oxidative pressure treatment at elevated temperature in the presence of an oxygen-bearing gas with an ammonia to metals mole ratio effective to produce a leach liquor whereby the formation of cobalt (III) hexammine sulphate therein has been increased.