Solvent extraction of rhodium chloride from aqueous solutions and its separation from palladium and platinum

The extraction of Rh chlorocomplexes with trioctylamine (TOA) or with Aliquat 336 (diluted with toluene) and its subsequent separation from Pd and Pt was studied. Species distribution calculations showed that the predominant species of Rh–Cl present in 1 M HCl is Rh(H 2O)Cl 5 2−. Spectrophotometric measurements of Rh–chloride in the organic phase showed that Rh(H 2O)Cl 5 2− is being extracted and slowly converted into a dimer, Rh 2Cl 9 3−. Stripping is carried out with concentrated HCl. It is difficult to separate Rh chlorides from Pd and Pt by solvent extraction, and a gel-chromatographic method is therefore proposed in order to solve this problem.