TOXICITY AND STABILITY OF IRON-ARSENIC ALLOY

Abstract

Iron-arsenic alloy is a waste-form of a novel gold recovery technology from gold-arsenicbearing concentrates. This study investigates toxicity and solubility of Fe-As alloy in aqueous solutions. Results of the TCLP-like test, to evaluate the potential toxicity of a solid Fe-As alloy, suggest that the alloy is not stable in acidic conditions (pH 2.88), and releases As in concentrations exceeding the TC threshold level by more than four times. Calcium arsenate dust toxicity has been also evaluated for comparison. It was found to release 40 times more As than iron-arsenic alloy. Concentrations of As in the SPLP-like test leachates were well within the regulatory limit, thus demonstrating the relative stability of the Fe-As alloy in normal meteoric waters (pH 5). Long-term leaching tests in the environmentally-relevant pH range of 5 to 9 at 22°С demonstrate that FeAs alloy is very susceptible to acidic pH conditions. Arsenic solubilization was high under acidic conditions (at pH5 and pH6), which suggests that in the long term it can be mobilized within the environment if exposed to meteoric waters, and certainly to acid rain. However, at the neutral and alkaline pH conditions typical of monofills it appears to be stable over the long term.