TVAOSTEGSTRYCKURLAKNINGSFOERFARANDE FOER ZINK- OCH JAERNHALTIGA SULFIDMINERALIER

Direct pressure leaching of zinc and iron containing mineral sulphides in dilute H2SO4 is carried out in a two-stage countercurrent process in which finely divided sulphides are leached in a first leaching stage with solution from the second leaching stage to produce a first stage leach solution containing a high zinc concentration and low iron and H2SO4 concentrations. The first stage solution, after suitable purification treatment, may be treated for zinc recovery by conventional electrowinning. The residue from the first stage leach is pressure leached with return electrolyte from the electrowinning operation with the leach end solution being passed to the first stage leach as already stated. The acid and sulphides concentrations in each of the first and second leaching stage is controlled such that (1) sufficient acid and sulphides enter the leaching circuit to ensure that the final leach solution exiting from the first leaching stage will contain sufficient dissolved zinc, e.g., 140-180 g.p.l., to make it suitable for treatment by electrolysis for recovery of zinc therefrom, (2) the quantity of sulphides entering the first stage leach is in excess of the quantity required to react with all available acid in the solution recycled from the second leaching stage and (3) the quantity of free acid entering the second leaching stage is in excess of the quantity required to react stoichiometrically with all acid reactive constituents in the residue passed from the first leaching stage to the second leaching stage.