There is provided an improvement in a process for producing cobalt (III) hexammine
sulphate which process comprises oxidatively pressure leaching nickel cobalt sulphides
in an ammoniacal ammonium sulphate solution. The nickel and cobalt sulphides are
oxidized to sulphates, and an ammoniacal leach liquor in which dissolved cobalt
is predominantly in the (III) oxidation state is produced. The ammoniacal leach
liquor is combined with ammonia to precipitate the triple salt of cobalt (III)
hexammine sulphate, nickel (II) hexammine and ammonium sulphate which is further
treated to produce a crystalline cobalt (III) hexammine sulphate and a nickel enriched
leach liquor. The improvement involves the provision of a second oxidative pressure
treatment effective to maximize the formation of the desired cobalt (III) hexammine
ion, prior to the triple salt precipitation step.