Solvent extraction and stripping of gold(III) from hydrochloric acid solution using vacuum pump oil

Abstract

Vacuum pump oil (VPO) in toluene was employed as a solvent extraction reagent for Au(III) from HCl. The effects of shaking time and concentration of HCl on the extraction of Au(III) were investigated. It was found that the selectivity of VPO for Au(III) was superior even to dibutylcarbitol (DBC) which is currently employed as a commercial extactant for gold. The extraction of Au(III) with VPO is nearly quantitative over the whole HCl concentration range, while the extraction of other metal ions is nearly negligible. In addition, in case of the VPO system, the extraction of Au(III) was independent of HCl concentration regardless of the VPO concentration, while in the case of DBC, it is independent of HCl concentration only for 100% DBC. The loading capacity for Au(III) was compared between 10 % VPO in toluene and 100 % DBC. The stripping of Au(III) from the loaded VPO was also investigated using aqueous mixtures of thiourea and hydrazine in combination with varying concentrations of HCl and NaOH. It was found that complete stripping can be achieved by these combinations and that gold is recovered as solid particles in some cases.