Electrochemical remediation of metal-bearing wastewaters Part II: Corrosion-based inhibition of copper removal by iron (III)

A hitherto undocumented inhibition to electrodeposition of Cu(II) from dilute (<200 mg L-1 wastewaters was traced to the presence of Fe(III) at concentrations comparable to those. of copper ion. This inhibition was found to differ from heterogeneous side-reduction of Fe(III) that is well known to decrease faradaic efficiency for copper removal. Based on bench-scale electrolysis as well as cyclic voltammetry studies, an inhibition mechanism was qualitatively identified that involved copper corrosion by Fe(III). This corrosion process was found to be strongly favoured by sluggish heterogeneous reduction of Fe(III) at carbon electrode materials. One procedure shown to substantially improve copper removal from solutions demonstrating corrosion inhibition was alkali precipitation of iron. Real mine drainage wastewater that was pretreated in this manner was consistently depleted of copper by flow-through electrolysis to levels below 50 mu g L-1.