Recovery of Pure Pd(II) from Spent Electroplating Solutions by Solvent Extraction with Ionic Liquids from Sulfuric Acid Leaching Solution of Cemented Pd

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.

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

“…In order to increase the recovery percentage of Pd from the spent electroplating solutions, excess amount of zinc metal is employed in the cementation of Pd(II). Therefore, the concentration of Pd(II) and Zn(II) in the leaching solution would depend on the composition of the cemented Pd and leaching conditions (Song et al, 2021;Nguyen et al, 2021). In this study, the concentration of Pd(II) and Zn(II) in synthetic HCl leaching solution was kept at 100 and 500 mg/L, respectively.…”

“…Our previous work showed that the complete leaching of Pd and Zn was obtained by employing the mixture of 9 M HCl in presence of 0.5% (v/v) H2O2 at 60 o C for 60 min (Nguyen et al, 2021). At this condition, the Pd and Zn metal in the cemented Pd were completely dissolved.…”

“…ALi-SCN was prepared by contacting Aliquat 336 (R4N•Cl) and an aqueous solution of 1.6 M KSCN in several times for the complete conversion of chloride to thiocyanate (Preston, 1982;Nayl, 2010). ALi-CY301, ALi-LIX 63 and Ali-LIX 84 were synthesized according to the previous work (Nguyen et al, 2021). In these cases, chloride precipitation using AgNO3 was performed to verify the transfer of the chloride ions from the organic phase to the aqueous phase.…”

“…We have done solvent extraction experiments with ILs from the synthetic sulfuric acid leaching solutions of cemented Pd (Nguyen, et al, 2021). According to this work, ALi-LIX63 (N-methyl-N,N,Ntrioctylammonium 5,8-diethyl-7-hydroxydodecane-6-oxime) and ALi-LIX84 (N-methyl-N,N,Ntrioctylammonium 2-hydroxy-5-nonylacetophenone oxime) were able to selectively extract Pd(II) over Zn(II) when sulfuric acid concentration was in the range from 0.5 to 9 M. In leaching of the cemented Pd with sulfuric acid solutions, oxidizing agent is necessary to dissolve Pd metal.…”

Selective precipitation of ammonium hexachloropalladate from leaching solutions of cemented palladium with zinc

“…In hydrometallurgical process, the target elements present in the secondary resources are dissolved by either inorganic or organic acid solutions. Since the leaching solutions contain not only the target metal ions but also some impure elements, these impure elements should be separated from the leaching solution by employing some unit operations like solvent extraction, ion exchange and precipitation [6][7][8]. In developing a process, it is necessary to find one which can meet both recovery efficiency and minimization of environmental burden.…”