The Fate of the Arsenic Species in the Pressure Oxidation of Refractory Gold Ores: Practical and Modelling Aspects

With the rising focus on the development of complex refractory ores, one of the major environmental challenges has been in the treatment and processing of arsenic-bearing minerals. An increasingly common approach is to immobilize arsenic as stable ferric arsenate phases during pressure oxidation, utilizing an existing process in the treatment of refractory arsenic-bearing ores. This review examines the lifecycle of the arsenic species in the pressure oxidation stage, from the source of the arsenic-bearing minerals in the feed to the various reaction products following pressure oxidation. The reactions and conditions for the formation of the different products have been detailed, with the oxidation temperature, time, feed iron-to-arsenic ratios, and pH being the main determinants for the characteristics of the arsenic-bearing phases. With an emphasis on arsenic fixation, the factors that contribute toward the formation of stable solid phases such as basic ferric arsenate sulfate and scorodite have also been examined. Subsequently, existing thermodynamic and kinetic models for the behavior of arsenic in pressure oxidation will be discussed. Future opportunities in this area have also been highlighted, including the use of in-situ techniques to probe the system at pressure oxidation conditions, the simulation of arsenic-bearing species, and further investigations on how precipitation is affected by the curing process and the presence of other cations.