Separation of rhodium and iridium by multiple fractional extraction

Mixtures of the chloro complexes of rhodium(III) and iridium(IV) were resolved by a nine stage multiple extraction technique. The solutes are partitioned in a hydrochloric acid-tributyl phosphate system. Rhodium is concentrated in the raffinate while iridium is concentrated in the extractant. 99% of the rhodium and 94% of the iridium are recovered free of the other metal. Experimental results agree reasonably well with the results predicted by a theoretical treatment of the distribution data.