Selective zinc extraction from complex copper/zinc sulphide concentrates by pressure oxidation

Abstract

Currently the world demand for non-ferrous metals can still be met by simple ores treated in a conventional manner. However, mineral resources are finite and as these reserves become depleted, attention must be focused on utilizing the more complex sulphide deposits. Frequently complex sulphide ores exhibit poor metallurgical response to conventional froth flotation. Since hydrometallurgical processes can tolerate lower metal grades and higher impurity levels than can conventional pyrometallurgical processes, treatment of bulk flotation concentrates is conducive to hydrometallurgical methods. The application of bulk flotation results in a simplified milling flowsheet and is capable of producing higher metal recoveries and revenues with respect to conventional smelter contracts. The primary objective was to develop hydrometallurgical process conditions which would enable selective pressure leaching of copper/zinc bulk flotation concentrates to extract zinc producing a zinc electrolytic solution. The upgraded leach residue containing the unreacted copper sulphide and precious metals would be treatable by conventional copper smelting. Zinc was selectively extracted from several complex Cu/Zn concentrates by utilizing various combinations of temperature and oxygen concentration in the pressure leaching process. A bulk concentrate grading 12.2% Cu, 3.8% Pb, 22.2% Zn, 1.4 g/t Au and 184 g/t Ag was pressure leached at 210°C with a 50% oxygen concentration at an over-pressure of 689 KPa with a retention time of 180 minutes. Extractions of zinc, and copper from the concentrate were 99%, and 0.32% respectively. The grade of the residue produced was approximately: 26% copper, 8.8% lead, 0.5% zinc, 435 g/t silver, 3.5 g/t gold and 42% iron. Similar results were also obtained from two bulk concentrates of different ore deposits.