Chlorine leaching of Au from copper anode slimes using the response surface method in an agitated reactor

The response surface methodology (RSM) was employed to study the interactions among different factors (i.e. temperature, liquid to solid ratio, HCl concentration and chlorine gas flowrate) involved in the leaching of Au from copper anode slimes. The interactions such as liquid to solid ratio, chlorine gas flowrate×temperature and HCl concentration×temperature were found to be statistically significant. Under the optimum operational conditions of Cl₂ = 1·99 L min⁻¹, 10 000/T = 28·7 K⁻¹, L/S = 12·57 L kg⁻¹, HCl = 2·74 mol L⁻¹ in a semi-pilot 3-L agitated reactor, the maximum recovery achieved for Au was around 93% using the second polynomial equation. This led to a selectivity factor (i.e. the ratio of ‘Au reaction fraction’ to the sum of ‘Se and Cu reaction fractions’) of 86. Process optimisation was carried out based on the maximum selectivity factor achieved. This resulted in the following optimum conditions: Cl₂ = 1·26 L min⁻¹, 10 000/T = 30·83 K⁻¹, L/S = 5 L kg⁻¹ and HCl = 2·66 mol L⁻¹, with a separation factor of 112.