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

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: 625 ppm and 104 ppm, respectively. Tri-octylamine (TOA) in toluene was used as an extractant. For single stage extraction, the separation factor was 135 with 8 wt% 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 8 M 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 1 M 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.