Highly efficient and selective extraction of Au(I) from thiosulfate gold-leaching solution using diphenylphosphine

Solvent extraction has the advantages of continuous operation mode and high loading capacity, which has received some attention in the field of thiosulfate gold leaching, but current research results are not satisfactory. In this study, diphenylphosphine (DPP) diluted in benzene was used to extract gold from thiosulfate solution, and its extraction behavior and properties were investigated. The effects of the DPP concentration, pH value, contact time, and sodium thiosulfate concentration on the extraction performance were evaluated. Under the optimal conditions, 0.7 mmol/L DPP showed high gold-extraction efficiency (99%) from 0.2 mol/L S2O32- solution embracing 10 mg/L Au(I) at pH = 10.0 with an aqueous/organic (A/O) ratio of 2. A high A/O ratio (A/O = 15) can be used in the extraction stage to achieve complete recovery of gold ions from solution. In addition, DPP showed high selectivity and recovery ability in Cu-NH3-thiosulfate gold-leaching solution, and the recovery rate was higher than 99%. The mechanism of gold-ion extraction by DPP involving ligand exchange between DPP and [Au(S2O3)(2)](3-) was confirmed by X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy. The P atom in Ph2-P- plays an important role in complexation of gold ions, which was confirmed by density functional theory calculation. The extraction method with low reagent consumption and high recovery rate developed in this study will greatly promote the development of gold leaching with thiosulfate.