Palladium(II) extraction from acidic chloride media using an ionic liquid-based aqueous two-phase system (IL-ATPS) in the presence of dipotassium hydrogen phosphate salting-out agent and reductive stripping with hydrazine hydrate to recover palladium metal

Abstract

Aqueous two-phase systems (ATPSs) based on ionic liquids (ILs) are efficient and green extraction systems. In this study, ATPSs consisted of three hydrophilic imidazolium-based ionic liquids ([C4mim]Br, [C6mim]Br, and [C8mim]Br) with phosphate, which were employed for Pd(II) extraction in acidic solutions. The obtained results showed that IL-ATPSs exhibited excellent Pd(II) extraction performance in acidic media, and Pd(II) was concentrated into ionic liquid rich upper phase. Palladium(II) extraction efficiencies of the three imidazolium-based ILs in acidic media were >98%, and the order of extraction efficiencies was: [C4mim]Br > [C6mim]Br > [C8mim]Br. Palladium(II) concentrated in IL-rich phase was recovered via direct reduction with hydrazine hydrate. Fourier transform infrared spectrometer (FT-IR) and mass spectrometry characterization indicated that Pd(II) migration into IL-rich phase followed an ion-exchange mechanism. Furthermore, transmission electron microscopy showed that “oil-in-water” micelles were formed during Pd(II) extraction.