What is meant by ammonia leaching ?

Explanation

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(NH_(3))_(6)]^(2+), [Cu(NH_(3))_(4)]^(2+)`, and `[Co(NH_(3))_(5)H_(2)O]^(3+)` respectively from the ore leaving hehind the gangue, iron (III) oxides/hydroxides and aluminosilicate.