Solvent extraction of palladium(II) with newly synthesized asymmetric branched alkyl sulfoxides from hydrochloric acid

A group of new asymmetric branched alkyl sulfoxides was synthesized and applied in palladium(II) extraction for the first time. According to the experimental data, the concentration of hydrochloric acid in aqueous phase greatly influenced Pd(II) extraction, which could be interpreted by different mechanisms (ligand substitution mechanism at low acidity and ion association mechanism at high acidity). In regard to structure effect, the steric hindrance of branched alkyl showed remarkable influence on the extraction performance of sulfoxides. On the basis of thermodynamic analysis, it was demonstrated that higher temperature exerted positive influence on the Pd(II) extraction reaction. As for the separation of Pd(II) and Pt(IV), low concentration of hydrochloric acid was considered to be appropriate for highly effective separation. Furthermore, ammonia solution was proven to be an efficient stripping agent for palladium recovery from organic phase.