Recovery of Pd(II) from leach solutions of automotive catalysts by solvent extraction with new thiophosphate extractants

Thiophosphate- and phosphate- based extractants, 1,3-bis(diethoxythiophosphinoyloxy)benzene (Ext 1) and 1,3-bis(diethoxyphosphinoyloxy)benzene (Ext 2), respectively, were synthesized and studied for their ability to extract Pd(II) from HCl and HNO3 media. Ext 1 (0.1 M) in 1-octanol selectively extracted 90-99.9% of Pd(II) in HCl (0.1-8.0 M) and 99.8% of Pd(II) in HNO3 (0.1-8.0 M) single-metal solutions, whereas Ext 2 demonstrated negligible Pd(II) extraction in either solution. The Pd(II) extraction rate, acid durability, optimal organic/aqueous (O/A) phase ratio, and Pd(II) loading capacity of Ext 1 were evaluated. Ext 1 was very stable in HCl and HCl/HNO3 solutions. Selective extraction of Pd(II) by Ext 1 (E% = 99%) was achieved from a solution containing Pd, Pt, Rh, rare metals, base metal ions, and leach liquors from automotive catalysts. Back-extraction of Pd(II) was performed using a solution of 0.1 M thiourea and 1.0 M HCl, allowing Ext 1 to be reused for 5 cycles. Ext 1 achieved rapid and selective extraction of Pd(II) from automotive catalyst solutions from platinum group metal refineries.