Cyanide-free recovery of metals from polymetallic and refractory gold concentrates by the KellGold process

Abstract

A patented hydrometallurgical approach (KellGold) for high-yield, cyanide-free recovery of metals from refractory gold and polymetallic concentrates is summarized. Drivers include elimination of atmospheric emissions of SO2, As2O3 and Hg produced by smelters and roasters, as well as cyanide risks arising from transportation, operations and detoxification activities.The Kell process comprises several commercially proven unit operations. Sulphur and other soluble metals are first selectively removed by use of a pressure oxidation leaching step during which the dissolution of precious metals such as Au, Ag and platinum group metals (PGM) is minimized. The residue from pressure oxidation may be subjected to further conditioning by HCl leaching and/or thermal treatment to ensure efficient precious metals recovery by subsequent chlorination leaching from a clean leachate. Subsequent metal recovery steps provide marketable end products close to the mine site.Testwork on a range of concentrate types typically shows >95% recovery of gold, silver, copper, cobalt, zinc, lead, antimony, and, if present in economic quantities, other value elements, including PGM (Pt, Pd, Rh, Ir, Ru). Engineering studies have been successfully completed for two KellGold applications, while KellPGM studies have been completed to definitive feasibility level. Centralized concentrate processing plants are under active consideration in several countries. KellPGM has been demonstrated in a nine-week integrated pilot campaign at 1:1000 scale, supporting a bankable feasibility study for a ~ 1110 ktpa plant now at the financing stage, treating a PGM concentrate at a South African PGM mine site.