Oxidative pressure leaching of zinc concentrates

CIM Bulletin, Vol. 74, No. 829, 1981

E.G. PARKER Senior Research Chemist, Cominco Ltd. Trail, British Columbia

Sherritt's zinc pressure leaching process converts zinc sulphide concentrates directly to zinc sulphate solutions and elemental sulphur. Thus, one pressure process step replaces both the roasting and leaching operations of the conventional roast-leach route. In addition, high single-pass extractions eliminate the need for residue treatments to recover unleached zinc. Because pressure leaching produces elemental sulphur, rather than sulphur dioxide, acid plants and smoke stacks are not required, and air pollution control and work-place hygiene are greatly improved.In 1977, Cominco Ltd. and Sherritt Gordon Mines Limited jointly operated a three-tonne-per-day pilot plant to demonstrate pressure oxidative leaching of Sullivan zinc concentrate and the subsequent separation of elemental sulphur. The process consisted of regrinding the concentrate, continuous leaching at 150°C at elevated oxygen pressures in a four-compartment autoclave and the subsequent recovery of elemental sulphur, either in the molten liquid form from a decantation autoclave or as a flotation concentrate. Of the zinc contained in the concentrate, 97% was extracted in 90 minutes, and 96% of the sulphur was converted to the elemental form.Following the successful pilot campaign, Cominco began building the world's first commercial zinc pressure leaching plant. This plant, which was in operation by late 1980, will eventually treat about 25% of Cominco's planned zinc capacity of 270,000 tonnes per year.This paper describes the general process principles, the results obtained from the pilot plant and the integration of the process into Cominco's operations at Trail. The application of pressure leaching to a "grass-roots" plant is also discussed, and compared with conventional roast-leaching.
Keywords: Leaching, Pressure leaching, Oxidative pressure leaching, Zinc pressure leaching, Extractive metallurgy, Sulphur separation, Flotation, Trail Operations, Cominco Ltd., Sherritt Gordon Mines Ltd.