When a crushed ore containing nickel, copper and cobalt is treated with aqueous ammonia under suitable pressure, ammonia selectively leaches these metals by forming their soluble complexes viz. [Ni(NH3)6]2+, [Cu(NH3)4]2+, and [CO(NH3)5H2O]3+ respectively from the ore leaving behind the gangue, iron (III) oxides/hydroxides and aluminosilicate.
