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.

Arsenic is a common pollutant and impurity present in complex gold ores. In the pressure oxidation (POX) of refractory gold-bearing sulfides, a major environmental challenge is the treatment of the hazardous waste released from arsenic-bearing minerals during processing. While the bulk removal of arsenic from solution can occur during POX, the formation of stable arsenates relies on the operating conditions during POX and the subsequent curing stage. Herein, response surface methodology (RSM) and central composite design have been investigated as viable approaches for optimizing arsenic fixation during the curing of the POX product of arsenopyrite. Curing time (0–24 h) and temperature (60–120°C) were examined as the model variables for RSM optimization, and the performance was assessed via arsenic and iron precipitation, along with the change in free acid and sulfate concentrations. Experimental validation of the optimized model conditions demonstrated good agreement with the simulated outputs and provided a 10% increase in arsenic removal over the best model input. The formation of basic ferric arsenate sulfate and scorodite under these conditions was supported by RSM and confirmed via characterization. In the investigated system, the maximum arsenic removal occurs at a critical threshold temperature of 107°C, over which the scorodite formation decreases with temperature. Thermodynamic modeling revealed the preferable formation of soluble FeHAsO₄⁺ complexes over scorodite above this threshold temperature, decreasing arsenic fixation at higher temperatures.