Separation of Pd(II) and Zn(II) by Solvent Extraction using Commercial Extractants from Hydrochloric Acid Leaching Solution of Cemented Pd from Spent Electroplating Solutions

Abstract

The demand for palladium (Pd) has increased and this has made it necessary to recover pure Pd from diverse secondary resources. To recover the small amount of Pd(II) present in spent electroplating solutions, Pd(II) is concentrated by cementation with zinc metal. In this work, a hydrometallurgical process consisting of leaching and solvent extraction was developed to recover Pd from the cemented Pd. The extraction behavior of Pd(II) and Zn(II) from synthetic HCl solution by commercial extractants such as LIX 63, Cyanex301, DOS, TBP, Alamin 308, Alamine 336 and Aliquat 336 was investigated by varying HCl concentration. The results showed that LIX 63, Cyanex 301 and DOS selectively extracted Pd(II) over Zn(II). These three extractants were employed to separate Pd(II) and Zn(II) from actual leaching solutions with cemented Pd using a mixture of 7.0 M HCl and 0.5% M H2O2 with 2 g/L pulp density at 60oC for 120 min. Cyanex 301 and DOS selectively extracted Pd(II) over Zn(II) from the leaching solution, while a small amount of Zn(II) was co-extracted with Pd(II) by LIX 63. A two stage counter-current extraction of actual leaching solution with LIX 63 resulted in the co-extraction of Zn(II) with Pd(II). The complete stripping of Pd(II) from the loaded Cyanex301 was achieved using either diluted aqua regia or a mixed solution of 5 M HCl and 0.5% NaClO at an A/O ratio of ten. The hydrometallurgical process is proposed to recover a pure Pd(II) solution from cemented Pd.