An evaluation of copper remobilization from mine tailings in sulfidic environments

A laboratory-based assessment of copper remobilization from Cu-rich mine ta ilings exposed to anoxic, sulfide rich waters was performed. The results fr om incubation experiments, conducted over a 20 day period, were compared to thermodynamic modelling calculations of copper speciation in sulfidic wate rs. The tailings materials were observed to react rapidly with added sulfid e, consuming 159 mu mol HS- g(-1) (dry wt) within a 24 h period. The consum ption of sulfide was attributed to a two stage process involving the reduct ion of Fe-hydroxy phases by sulfide followed by reaction with available Fe2 + and Cu2+ resulting in the formation Fe- and Cu-sulfide phases. During inc ubation experiments, the dissolved copper concentrations in the absence of sulfide were approximately 0.31. mu mol l(-1), whereas in the presence of s ulfide (0.5-5 mM) concentrations were typically 0.24 mu mol l(-1). The expe riments did not indicate enhanced solubility owing to the formation of solu ble copper sulfide species. The predictions(based on the most recent thermo dynamic data for aqueous Cu-sulfide and Cu-polysulfide species) did not acc urately explain the laboratory observations. Model predictions were greatly influenced by the assumptions made about the oxidation state of copper und er anoxic conditions' and the solid sulfide phase controlling copper solubi lity. The study emphasizes the limitations of modelling copper speciation i n sulfidic waters and the need for laboratory or field verification of pred ictions. (C) 1998 Elsevier Science B.V. All rights reserved.