Effect of electrolyte composition, and of added iron(III) in the presence of selected organic complexing agents, on nickel(II) precipitation by lime

The effect of effluent composition involving the common anionic species Cl−, SO42− and CO32− on the efficiency of nickel(II) precipitation, modelling lime (CaO) as the precipitant, has been investigated using the solubility domain approach. Solubility domains were based on the phases that were found to limit metal solubility for systems representing potential effluent composition limits. These phases were found to resemble their mineralized counterparts, but with a lower degree of structural order. At higher SO42− and CO32− concentrations both gypsum (CaSO4•2H2O) and calcite (CaCO3) were formed, but these had little effect on the observed residual nickel solubility. The calculated solubility domains were found to generally encompass the experimentally determined solubilities, thereby providing quality assurance ranges for hydroxide precipitation. The effect of the complexing anions tartrate and EDTA4− on residual Ni(II) in solution as well as the effects of the addition of Fe(III) on the removal of Ni(II) complexed by these species are described.