Kinetic and Thermodynamic Requirements to Extend Solvent Compatibility in Thermal-Assisted Extraction of Inert Platinum Group Metals

The extraction behavior of inert platinum group metals (PGMs) like Ru(III) and Rh(III) has been investigated in a HNO₃(aq)/1-octanol system with a pyridinediamide. As a result, low efficiency of Ru(III) extraction arose from its slow kinetics at 298 K, while the situation was not improved very much even at 356 K. Addition of a hydrophobic anion like Tf₂N^- increased Ru(III) extraction up to 95% within 3 h at 356 K, where a synergistic effect would be present. Extraction of a more inert PGM like Rh(III) was also enhanced up to 90% within 2 h at 356 K in the presence of Tf₂N^-. We have successfully demonstrated the rapid and efficient extraction of inert PGMs from HNO₃(aq) to 1-octanol, which is one of the ordinary organic solvents.