Nickel sulphide precipitated from waste liquors at the Yabulu plant of Queensland Nickel Pty Ltd was pressure leached under various conditions. Leaching at 130C and 700 kPa of air dissolved 95 per cent of the nickel as the sulphate in less than 2 h._x000D_
Leaching at 130C and 350 kPa of oxygen dis- solved 95 per cent of the nickel in less than 1 h. Dissolution was faster with oxygen than with the equivalent pressure of air. Crystallization of hydrated nickel sul- phate from the resulting clarified leachate is readily achieved. Because the sulphide pre- cipitate also contains minor amounts of iron, copper and cobalt, the crystallization product contains these metals in excess of the amounts required for electrolytic-grade nickel sul- phate. This grade of product could only be produced if the contaminants were removed prior to crystallization. Alternatively, the "crude" nickel sulphate could find a market as a feed for the electrolytic production of Ni-Fe coatings.