Optimization of Arsenic Fixation in the Pressure Oxidation of Arsenopyrite Using Response Surface Methodology

ABSTRACT

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.

KEYWORDS:

• Arsenic fixation
• scorodite
• pressure oxidation
• response surface methodology
• thermodynamic modeling

Acknowledgement

The authors would like to acknowledge the financial support provided by Zijin Mining, the State Key Laboratory of Comprehensive Utilization of Low-Grade Refractory Gold Ores, and the Australian Research Council Linkage Project grant (ARC LP160101760) for this work. We are thankful to Nadia Zakhartchouk, Bebeto Lay, Stephen Grist, Steven Priver, Lydon Alexandrou, Susan Holden, Ruth Cepriano-Hall, Sandro Longano, and the Centre for Advanced Materials and Industrial Chemistry (CAMIC) high pressure research facility for training and the use of equipment.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

The work was supported by the Australian Research Council [ARC LP 160101760]