Salting-out induced three-liquid-phase separation of Pt(IV), Pd(II) and Rh(III) in system of S201−acetonitrile−NaCl−water

Abstract

Salting-out induced three-liquid-phase system (TLPS) of diisopentyl sulfide (S201)−acetonitrile−NaCl−water was explored to extract and separate platinum, palladium and rhodium with one-step method. The influences of phase-forming behaviors of TLPS on partition of platinum-group metal (PGM) ions were investigated by changing the phase-forming salt and its concentration, HCl concentration in equilibrating salt aqueous phases and the initial volume ratio of acetonitrile to aqueous NaCl solution. Experimental results indicated Pd(II), Pt(IV) and Rh(III) were selectively concentrated into the S201 organic top phase, acetonitrile-rich middle phase and NaCl aqueous bottom phase respectively. The three-liquid-phase partition of platinum metal ions occurred with the salting-out induced two-phase splitting of acetonitrile–water mixtures. A micro-mechanism model is proposed to explain the influence of salting-out induced phase splitting behavior of three-liquid-phase system on mass transfer of PGM ions. Appearance of microscopic molecular aggregates accounts for the micro-phase enrichment of platinum metal ions. The competition of two opposite processes, salting-out induced dehydration of acetonitrile molecules in aqueous solutions while strong re-hydration of salting-out acetonitrile molecules in separated acetonitrile-rich phase, plays an important role in affecting the phase-forming behaviors and three-liquid-phase mass transfer of different platinum metal ions.