Extraction of rhodium and iridium with 4-(non-5-yl) pyridine

The extraction of rhodium and iridium with 4-(non-5-yl)pyridine (NP) was investigated. The rate of rhodium extraction increases with increasing concentration of NP and chloride ions. Spectroscopic studies indicate that the extracted species is an ion pair, RhCl^3?₆ 3HNP⁺. Under the conditions of optimum Rh extraction ([Cl^?]=3.7 M, [NP]=0.3 M, [H]=0.08 M), iridium is also extracted by NP with similar efficiency in the form of IrCl^3?₆ 3HNP⁺. The use of hypophosphorous acid to labilize rhodium results in a better extraction of rhodium without significantly changing the extraction of iridium. The efficiency and kinetics of the rhodium extraction improve with increasing chloride concentration. For [Cl^?] ? 3.7 M, [H₃PO₂]=2.5 M, [NP]=0.3 M and Ph ≈ 1.6, 82% of rhodium is extracted in 4 min and 95% in 30 min.