Cominco, Ltd.

Louis Landucci

Ernest G Parker

Donald Roderick McKay

A process for the treatment of zinc plant residue formed on leaching zinc calcine with sulphuric acid in which the residue is leached in a first leaching step with a sulphuric acid solution at atmospheric pressure, and a temperature above about 60.degree.C, in the presence of excess zinc sulphide reductant whereby ferric iron in the residue is reduced to the ferrous state, thereby forming a zinc sulphate solution containing excess acid, ferrous iron and other dissolved impurities such as germanium, indium, gallium, antimony and arsenic nd a mixture of solids containing undigested zinc residue, lead residue, and unreacted zinc sulphide. Clarified solution is separated, preferably by thickening, from the mixture of solids. The mixture of solids is leached in a second residue leaching step at atmospheric pressure and at a temperature above about 60.degree.C in a solution which is substantially higher in acid than the solution in the first leaching step, unreacted zinc sulphide from the first residue leaching step providing reducing conditions in the second residue leaching step. Slurry from the second residue leaching step is treated by flotation to separate a froth product comprising unreacted zinc sulphide and elemental sulphur, a tailings product containing gangue and a lead residue, and an acidic solution which is recycled to the first residue leaching step. A portion of the clarified zinc sulphate solution from the first residue leaching step is treated by oxidizing a small part of the ferrous iron contained therein, and neutralizing this portion of the solution with limerock to precipitate solids containing oxidized iron, gypsum, and the other impurities. These precipitated solids are separated and this portion of the solution is combined with the remainder of the clarified zinc sulphate solution. Ferrous iron in the combined solution is oxidized to precipitate ferric iron compounds which are separated from the solution to provide purified zinc sulphate solution which is recovered.

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Trail, Canada

Louis Landucci