Separation of concentrated platinum(IV) and rhodium(III) in acidic chloride solution via liquid–liquid extraction using tri-octylamine.

Abstract: This research dealt with the intensification of Pt–Rh separation via liquid–liquid extraction (LLE). The stock solution contained Pt(IV) and Rh(III) at high concentration level in hydrochloric solution: 625ppm and 104ppm, respectively. Tri-octylamine (TOA) in toluene was used as an extractant. For single stage extraction, the separation factor was 135 with 8wt% TOA. The percentage of extraction was 97% for Pt(IV) and 21% for Rh(III). Soybean oil as a solvent in LLE provided good extraction performance comparable to that of toluene. Pt(IV) was almost completely removed from the organic phase when stripped by 8M nitric acid. Multi-stage extraction with direct recycling of organic phase after stripping significantly decreased the separation factor to 13 during the 5th stage. When the organic phase was washed with 1M NaOH prior to be used in the next extraction stage, the separation factor increased to 818 during the 5th stage. Finally, the Pt–Rh continuous separation process scheme is presented. [Copyright &y& Elsevier]