Precipitation of copper from cyanide leach solutions using sodium dimethyldithiocarbamate (SDDC)

Abstract

Production of gold from copper-rich gold ores has received particular attention due to some technical and economic challenges associated with the ready dissolution of most copper minerals during cyanide leaching. This leads to excessive consumption of cyanide by forming copper cyanide complexes, which adversely affect downstream recovery and cyanide detoxification processes. In this study, a novel method is proposed to precipitate copper from cyanide solutions using sodium dimethyldithiocarbamate (C3H6NNaS2; SDDC). The influence of various parameters (i.e., reaction period (0–360 min.), concentration of SDDC (165–992 mM), [CN−]/[Cu] ratio (3–8), pH (10–12.5) and temperature (20–60 °C) on the precipitation of copper were investigated using synthetic copper-cyanide solutions. Increasing reaction time, concentration of SDDC and temperature were found to significantly improve the precipitation of copper. Increasing the ratio of [CN−]/[Cu] adversely affected the precipitation of copper with no precipitation being occurred at ratios of ≥6. Strong alkaline conditions appeared to have a slightly negative impact on the process. In the light of these findings, the response surface methodology (i.e., central composite design; CCD) was adopted to reveal the influence and interactions of [SDDC]/[Cu] ratio (21.0–126), initial concentration of copper (50–950 mg/L) and reaction period (15–360 min.) on the precipitation of copper. The analysis of the data confirmed that statistically significant parameters affecting the process were reaction time and [SDDC]/[Cu] ratio. It was also found that initial copper concentration did not significantly influence the process. Tests on real cyanide leach solutions derived from gold ores/concentrates demonstrated that the SDDC could selectively precipitate copper (as well as zinc and silver) from gold-bearing solutions. The activation energy (i.e., ≈67 kJ/mol) calculated by Arrhenius equation has indicated that the precipitation of copper is a chemically controlled reaction. Detailed characterisation of Cu-DDC precipitates was performed using SEM-EDS, FT-IR and particle size analysis. The precipitates (d80 = 16 μm) are thin, rod-like particles in brownish colour. The recovery of copper from Cu-DDC precipitates using acid solutions (HCl, H2SO4 and HNO3) was also investigated. Complete recovery of copper was achieved using HCl and HNO3 solutions at high concentrations. The findings have suggested that SDDC is an effective reagent for selective precipitation of copper from cyanide leach solutions.