Recovery of pure palladium compound from the spent electroplating solutions by hydrometallurgical method

Electroplating of palladium (Pd) is practiced in the manufacture of electronic materials. The increasing demand for Pd metal necessitates the recovery of Pd(II) from the spent electroplating solutions. In this work, the recovery of Pd compound was studied from the cemented Pd by zinc (Zn) metal from spent electroplating solutions. Initially, the selective extraction ability of ionic liquids synthesized from commercial extractants for Pd(II) over Zn(II) from the synthetic HCl solution was investigated. Pd(II) was selectively extracted over Zn(II) from 9 M HCl solution by ALi-CY301(Nmethyl-N,N,N-trioctylammonium bis(2,4,4-trimethylpentyl) dithiophosphinic) and by ALi-I (N-methylN,N,N-trioctylammonium iodide) from weak HCl solution (pH 1). Since 9 M HCl was needed to completely dissolve Pd from the cemented Pd, ALi-CY301 was employed for the separation of Pd(II) and Zn(II) from the real HCl leaching solution of the cemented Pd. Two-stages counter-current extraction of the real HCl solution with ALi-CY301 resulted in selective extraction of Pd(II). Pd(II) was effectively stripped from the loaded ALi-CY301 by a mixture of HCl and NaClO. After oxidizing Pd(II) in the stripping solution to Pd(IV) by adding NaClO, Pd(IV) compound was synthesized by adding NH4Cl as a precipitant. By comparing leaching and extraction efficiency between hydrochloric and sulfuric acid solutions, a hydrometallurgical process consisted of HCl leaching, extraction with ALiCY301 and precipitation with NH4Cl was recommended for the recovery of pure (NH4)2PdCl6 from the cemented Pd.