Solvent extraction of platinum group metals.

A survey has been made of previous work on the application of solvent extraction and gaseous reduction processes to refining of platinum group metals. Amine extraction processes have been investigated by chemical shake-up tests and distribution ratios determined with all classes of amines and quaternary ammonium compound for rhodium, iridium, palladium, platinum, ruthenium, osmium and gold using radio tracer techniques. Proposed schemes for separation of platinum metals from base metals using primary amine and separation of Pt/Pd from Ir/Rh using tertiary amine were examined using commercially useful reagents, and specific processes defined. A continuous counter-current testing rig using mixer-settler contactors was built and the performance of the extraction processes determined, Extraction and separation by these processes was successful but continuous re-extraction of platinum rnetals from the solvent suggested certain limitations in progressing to full pilot-scale operation. It is suggested that gaseous-reduction of the metal from the organic phase in situ could be employed.