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Abstract
Copper is often associated with arsenic in mixed sulphide minerals such as enargite (Cu3AsS4) and tennantite (Cu12As4S13). Enargite, in particular, is the principal mineral in many deep epithermal copper–gold deposits. Most mining companies avoid exploiting such resources, because the arsenic can become a serious environmental liability or may considerably reduce the resource value due to hefty treatment charges. The few enargite deposits that have been exploited so far are usually rich in gold and silver. The first challenge in the exploitation of copper–arsenic sulphides is the effective separation of arsenic phases from other valuable minerals. In the last decade, though, it was shown that this is possible by pulp-potential adjustment (oxidative conditions) combined with pH adjustments (basic conditions) prior to flotation. In this way, two types of concentrate can be produced: one rich in arsenic and another low in arsenic but rich in other valuable metals. Arsenic-rich concentrates have traditionally been processed pyrometallurgically by reduction roasting to gaseous arsenic sulphide, which is then converted to arsenic trioxide. New pyrometallurgical technologies for the treatment of copper–arsenic sulphides include sulphidization roasting, sulphidization roasting and halogenation, and carbothermic reduction to copper arsenide. The hydrometallurgical treatment of copper–arsenic-antimony resources has been done by atmospheric leaching in alkaline sodium-sulphide solutions. Ultrafine grinding and ferric oxidation at atmospheric pressure, total pressure oxidation at temperatures above 220°C, and bacterial leaching have recently been tried on copper–arsenic sulphides, some with considerable success.
ACKNOWLEDGEMENTS
The authors would like to thank many investigators, particularly Profs. S. H. Castro (Universidad de Concepción, Chile) and W.-T. Yen (Queen's University, Ontario, Canada), who kindly provided copies of their publications for this review. Dr. Robert (Bob) R. Seal II (United States Geological Survey, Virginia, USA) provided some clarifications with regard to enargite thermodynamics. Dr. T.-C. Cheng (formerly with McGill University, Montreal, Quebec, Canada; now with the Royal Mint of Canada, Ottawa, Ontario, Canada) helped the authors to locate several references cited herein.