Abstract: A method of pressure leaching nickel and cobalt from sulphidic precipitates is provided, wherein such precipitates are leached with chlorine at a controlled redox potential of between 400 and 550 mV (Ag/AgCl), catalysed by copper, and at a temperature of between 120.degree. and 160.degree. C., to dissolve at least 80% of cobalt and to oxidize less than 10% of sulphur to sulphate.

Abstract: Sulphuric acid leaching has been used in the treatment of lateritic ores for the recovery of nickel and cobalt therefrom. However, in order to obtain good extraction from these ores, prolonged treatment using acid of high strength and also using high pressures and recycling steps have been necessary. In the improved method of the invention nickel and cobalt is solubilized from high-magnesia nickeliferous serpentine ores by leaching the ore with an aqueous solution of sulphuric acid while adding to the solution a reducing agent to maintain the redox potential of the solution at a value between 200 and 400 millivolts, measured against the saturated calomel electrode. This improved procedure increases the reactivity of the serpentine and results in maximum extraction of nickel consistent with minimum extraction of iron and magnesia and minimum acid consumption.