An evaluation of copper remobilization from mine tailings in sulfidic environments

Abstract

A laboratory-based assessment of copper remobilization from Cu-rich mine tailings exposed to anoxic, sulfide rich waters was performed. The results from incubation experiments, conducted over a 20 day period, were compared to thermodynamic modelling calculations of copper speciation in sulfidic waters. The tailings materials were observed to react rapidly with added sulfide, consuming 159 μmol HS − g −1 (dry wt) within a 24 h period. The consumption of sulfide was attributed to a two stage process involving the reduction of Fe-hydroxy phases by sulfide followed by reaction with available Fe 2+ and Cu 2+ resulting in the formation Fe- and Cu-sulfide phases. During incubation experiments, the dissolved copper concentrations in the absence of sulfide were approximately 0.31 μmol l −1, whereas in the presence of sulfide (0.5–5 mM) concentrations were typically 0.24 μmol l −1. The experiments did not indicate enhanced solubility owing to the formation of soluble copper sulfide species. The predictions (based on the most recent thermodynamic data for aqueous Cu-sulfide and Cu-polysulfide species) did not accurately explain the laboratory observations. Model predictions were greatly influenced by the assumptions made about the oxidation state of copper under anoxic conditions and the solid sulfide phase controlling copper solubility. The study emphasizes the limitations of modelling copper speciation in sulfidic waters and the need for laboratory or field verification of predictions.