Roasting of Sulfide Minerals

Abstract

In addition to common metals like copper, lead, zinc, and nickel a number of other metals such as antimony, bismuth, cadmium, cobalt, mercury, and molybdenum occur as sulfide minerals. Sulfides are not reduced with the most widely used reducing agents, carbon and hydrogen, because the free energy change for the reactions 2MS + C = 2M + CS2 and MS + H2 = M + H2S is positive due to the lesser stability of CS2 and H2S, compared to most sulfides. Reduction of sulfides with metals is not economical. Furthermore, from most sulfide minerals the metal value is not brought into aqueous solution by leaching with common acids and alkalis. In the presence of an oxidant, chalcocite is leached quickly in dilute sulfuric acid whereas bornite and covellite are leached slowly. Leaching is speeded up in the presence of bacteria. But chalcopyrite, the major source of copper is not leached. Commercially, pentlandite, a nickel sulfide mineral, is treated with ammonia under pressure (8 atm) at 105 °C to dissolve nickel. Nickel is precipitated by blowing hydrogen at 30 atm in the purified leach liquor at 170 °C. Otherwise, by and large, the hydrometallurgical route for treatment of sulfides has failed. Under the circumstances, the only alternative seems to be the conversion of sulfide concentrates into oxides by dead roasting [1–3], which can be easily reduced with carbon (production of lead and zinc) or into mixed oxide and sulfate by partial roasting and sintering, which can be dissolved in dilute sulfuric acid, and the resultant solution is subjected to electrowinning (extraction of zinc). © 2021, The Minerals, Metals & Materials Society.