Recovery of Palladium by Extraction-electrodeposition Using N, N, N’, N’, N”, N”- Hexaoctyl-nitrilotriacetamide

Abstract

ABSTRACT It is essential to develop solvent extraction (SX), and electrodeposition (ED) processes for palladium to reduce the volume of acid and organic media. In this study, the extraction reaction of Pd(II) in chloride media using of N, N, N’, N’, N”, N”-hexaoctyl-nitrilotriacetamide (NTAamide(C8)) as a novel extractant has been demonstrated. Three diluents with high dielectric constants (acetophenone (AP), 1,2-dichloroethane (DCE), and 1-octanol (OC)) were used for the solvent extraction reaction. The slope analysis indicated that the anion exchange extraction reaction of Pd(II) was consistent with an approximately 2:1 stoichiometry for the NTAamide(C8)/AP and NTAamide(C8)/DCE systems, and 1:1 for NTAamide(C8)/OC. Moreover, the ED behavior of the extracted Pd(II) complex was investigated using cyclic voltammetry (CV). Palladium reduction was found to be an irreversible process based on analysis of the standard rate constant. A semi-integral analysis of the voltammogram determined the diffusion coefficients of the extracted Pd(II) complex in the AP, DCE, and OC systems to be 3.7 ± 0.1 × 10−10, 2.8 ± 0.1 × 10−10 and 1.5 ± 0.2 × 10−10 m2 s−1, respectively. Furthermore, consecutive extraction-electrodeposition processes using the NTAamide(C8)/AP system were carried out for five cycles. High extraction percentage (E > 91%) and current efficiency (ε > 83.1%) were attained in all cycles. The electrodeposits recovered from the extraction-electrodeposition process were identified as Pd metal through X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) analyses.