Efficient extraction and selective separation of Pt(IV) and Pd(II) using TOPO based deep eutectic solvents

Recycled platinum group metals (PGMs) have become an increasingly vital component of the global PGM supply, with more than 45% of the PGMs currently in use being derived from secondary resources. To further enhance the sustainability and environmental compatibility of PGM recycling processes, we developed a novel system for separating Pt(IV) and Pd(II). A trioctylphosphine oxide (TOPO) - based deep eutectic solvent (DES) was employed as a liquid–liquid extraction medium for the selective recovery of Pt(IV) from mixed Pt(IV)/Pd(II) chloride solutions. In the preparation of these DESs, TOPO acts as a hydrogen bond acceptor (HBA), and an alcohol acts as a hydrogen bond donor (HBD). By studying the performance of these DESs and conducting organic analyses under various experimental conditions, we found that these DESs can effectively separate Pt(IV) and Pd(II) in aqueous phases with high chloride ion concentrations. Under optimized conditions ( X TOPO = 0.5, C KCl = 2–4 M, using HBDs with low solubility and high –OH charge density), the extraction efficiency of Pt(IV) exceeded 97%, while that of Pd(II) remained below 3%, demonstrating highly selective separation. By systematically investigating the effects of DES composition and aqueous-phase conditions, we found that TOPO-based DESs enable efficient separation under high-salinity and low-acidity conditions. These findings suggest that high-salinity systems can serve as a viable alternative to conventional highly acidic processes, offering improved safety and environmental compatibility for PGM recycling. • TOPO-based deep eutectic solvents enable selective Pt(IV)/Pd(II) separation. • Pt(IV) extraction exceeded 97% with Pd(II) extraction below 3%. • Hydrogen bond doner with low solubility and high charge density favor separation. • High-salinity media replace conventional highly acidic separation systems.