Abstract
Palladium (Pd) electroplating is widely practiced in the manufacture of advanced electronic devices. The Pd(II) present in spent electroplating solutions is treated by cementation with zinc (Zn) metal powder. In order to recover pure Pd from the cemented Pd, a process that consisted of leaching followed by solvent extraction was investigated. For this purpose, solvent extraction experiments using synthesized ionic liquids (ILs) with organic and inorganic anions were performed to find separation conditions at which selective extraction of Pd(II) over Zn(II) from synthetic H2SO4 leaching solutions is possible. The concentration of sulfuric acid was varied from 0.5 to 9 M. The complete separation of Pd(II) over Zn(II) by ILs such as ALi–CY301 (N-methyl-N,N,N-trioctylammonium bis(2,4,4-trimethylpentyl) dithiophosphinic), ALi–SCN (N-methyl-N,N,N-trioctylammonium thiocyanate), ALi–I (N-methyl-N,N,N-trioctylammonium iodide) and ALi–Br (N-methyl-N,N,N-trioctylammonium bromide) depends on H2SO4 concentration, while ALi–LIX63 (N-methyl-N,N,N-trioctylammonium 5,8-diethyl-7-hydroxydodecane-6-oxime) and ALi–LIX84 (N-methyl-N,N,N-trioctylammonium 2-hydroxy-5-nonylacetophenone oxime) can completely separate Pd(II) irrespective of H2SO4 concentration. Additionally, the mixture of HCl and thiourea, aqua regia solution, NH3 solution and the mixture of NH4Cl and NH3 are powerful stripping agents for Pd(II) from the loaded ALi–LIX63/ALi–LIX84, ALi–CY301, ALi–Br/ALi–I and ALi–SCN, respectively. However, application of the separation conditions to the real 5 M sulfuric acid leaching solutions of cemented Pd indicated that it was difficult to separate the two ions by extraction with ALi–LIX63 and ALi–LIX84. Use of NaClO as an oxidizing agent during the sulfuric acid leaching of real cemented Pd resulted in an enhancement of Zn(II) extraction by ALi–LIX63 and ALi–LIX84. Therefore, removal of chloride ions from the sulfuric acid leaching solutions is necessary to apply the separation conditions obtained from synthetic sulfuric acid leaching solutions.
Highlights
Palladium electrodeposition has some advantages, such as easy control, versatile operating conditions, good throwing power and crack-free smooth and adherent coatings with high purity, and is employed in the manufacture of electronic devices and advanced materials [1,2]
The experiments were performed in triplicate and the errors associated with the extraction and stripping percentages were within ±5%
The separation of Pd(II) and Zn(II) from synthetic sulfuric acid leaching solutions of cemented Pd from spent electroplating solutions was investigated by solvent extraction with synthesized ionic liquids (ILs)
Summary
Palladium electrodeposition has some advantages, such as easy control, versatile operating conditions, good throwing power and crack-free smooth and adherent coatings with high purity, and is employed in the manufacture of electronic devices and advanced materials [1,2]. There are many kinds of ions in the diverse spent electroplating solutions, and the concentration of Pd(II) in these solutions is not high. In order to recover Pd(II) in the spent electroplating solutions, cementation with zinc (Zn) metal powder is generally practiced in order to concentrate Pd(II) [2]. Zinc metal powders with fine size are employed for the cementation kinetics. Once Pd(II) and Zn(II) are completely dissolved, it is necessary to separate these two metal ions to recover Pd(II) with high purity
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