Solvent extraction separation of Au(III) from Pd(II), Cu(II), Ni(II) in HCl solution using cationic, neutral and basic extractants

BACKGROUND: Etching solutions of spent printed circuit boards (PCBs) contain precious metal ions like Au(III) and Pd(II) together with Cu(II). Therefore, it is crucial to recover Au(III) and Pd(II) from these solutions. To investigate the possibility of separating Au(III) from the etching solutions, solvent extraction experiments were conducted using synthetic hydrochloric acid solutions containing Au(III), Pd(II), Cu(II), and Ni(II). The solvent extraction behavior of these four metal ions was investigated by using cationic (Cyanex 301, LIX 63), neutral (Cyanex 923 and TBP), and basic (Alamine 336 and Aliquat 336) extractants in the HCl concentration range from 1 to 9 M.RESULTS: TBP and Cyanex 923 were successful in separating Au(III) from other metal ions when the HCl concentration was higher than 7 M. When the concentrations of Au(III) and Pd(II) changed from 0.1 to 5 g L-1, TBP was able to selectively extract Au(III) from 7 M HCl solution, while Cyanex 923 was effective in separating Au(III) from 9 M HCl solution. However, Au(III) and Pd(II) were co-extracted by Alamine 336 and Aliquat 336 from 1 M HCl solution. Thiourea or a mixture of thiourea and HCl solution effectively stripped Au(III) from the loaded organic phases of TBP, Cyanex 923, and amines.CONCLUSIONS: Among the six kinds of the extractants employed in this work, TBP was recommended as an extractant for the selective extraction of Au(III) from the HCl solutions containing Cu(II), Ni(II) and Pd(II) on the basis of high separation degree.(c) 2023 Society of Chemical Industry (SCI).