Low acidity, low solids pressure oxidative leaching of sulphidic feeds

A process for recovering one or both of copper and silver from a sulphidic feed containing iron, arsenic, copper and silver, comprising:

• a) pressure oxidizing an aqueous feed slurry of the sulphidic feed in a pressure vessel to form a liquid phase containing free sulphuric acid and aqueous copper sulphate, and to precipitate arsenic as solid iron arsenic compounds, while operating the pressure vessel at a solids content in the aqueous feed slurry such that:
• i. a free acid level below 30 g/L is maintained in the liquid phase,
• ii. heat generated by oxidizing the aqueous feed slurry provides less than 60% of the heat to the pressure vessel, and
• iii. the sulphide level in the aqueous feed slurry is below 2.5 wt %,
• wherein the solids content is maintained by adding one or more of process water, steam and a feed slurry to the pressure vessel as part of the aqueous feed slurry,
• wherein one or more of a heated feed slurry, a heated process water and steam is added to the pressure vessel as part of the aqueous feed slurry;
• and
• wherein temperature in the pressure vessel is maintained above 200° C.;
• b) withdrawing from the pressure vessel treated slurry comprising a liquid phase containing sulphuric acid and copper sulphate, and solids containing iron arsenic compounds and at least a portion of the silver;
• c) separating the liquid phase from the solids;
• and one or both of
• d) recovering copper metal from the separated liquid phase;
• and
• e) recovering silver from the solids by cyanide leaching.