Separation of Au(III) from hydrochloric acid solutions containing Pd(II), Cu(II) and Ni(II) by solvent extraction with a mixture of Cyanex 272 and TBP

Etching solutions of spent printed circuit boards contain a small amount of valuable metals like Au(III) and Pd(II). In order to meet the increasing demand for gold and palladium, it is necessary to recover these metals from the etching solutions. In this work, solvent extraction experiments were done to separate Au(III) from the synthetic hydrochloric acid solutions containing Pd(II), Cu(II), and Ni(II). Single Cyanex 272 and TBP and their mixture were employed to investigate the selective extraction of Au(III) from other metal ions in the HCl concentration range from 1 to 9 M. Single Cyanex 272 and the mixture of Cyanex 272 and TBP successfully separated Au(III) from the solution, while a small amount of Pd(II), Cu(II) and Ni(II) were co-extracted with Au(III) by TBP. The mixture of Cyanex 272 and TBP showed synergism for the extraction of Au(III). The dependence of Au(III) extraction on the mole fraction of TBP in the mixture was pronounced when HCl concentration was 1 and 3 M. The Au(III) loaded into the mixture was completely stripped by low concentration of thiourea and sodium thiosulfate. Pure gold metal was recovered from the thiourea stripping solution by chemical reduction with ascorbic acid. Complete reduction of Au(III) was possible at 80 °C for 30 min when the molar ratio of ascorbic acid to Au(III) was 20.