Separation of palladium by solvent extraction with methylamino-bis-N,N-dioctylacetamide and direct electrodeposition from loaded organic phase

Abstract

The development of solvent extraction and direct electrodeposition processes is an important task to reduce the volume of secondary wastes. In this study, the extraction of Pd(II) from hydrochloric/chloride media using methylimino-bis-N,N-dioctylacetamide (MIDOA) in three diluents (acetophenone; AP, 1,2-dichloroethane; DCE, or 1-octanol; OC) was investigated. Slope analysis revealed that the extraction reaction of Pd(II) was based on the following anion exchange:PdCl42-aq+nMIDOAorg⟺PdCl4-2nMIDOA2org2n-2+2nCl-aqThe electrochemical behavior of the extracted Pd(II) complex in the MIDOA/AP bath was investigated using an electrochemical quartz crystal microbalance (EQCM). Pd(II) was found to be reduced to Pd(0) metal via a two-electron transfer, and the cathodic reaction [Pd(MIDOA)2]2+ + 2e− → Pd(0) + 2[MIDOA] was found to proceed in the region between −2.38 V and −3.40 V based on the apparent molar mass of 105.22 evaluated by EQCM. Moreover, the alternation of Δηρ corresponded to the local decrease in the viscosity of the organic phase near the electrode. The potentiostatic electrodeposition of the extracted Pd(II) complex enabled us to recover the blackish electrodeposits, which were identified as Pd metal through SEM/EDX, XPS, and XRD analyses.