Three-liquid-phase partition behaviors of Pt(IV), Pd(II) and Rh(III): Influences of phase-forming components

Three-liquid-phase extraction is a new technique to separate Pt(IV), Pd(II) and Rh(III) from their hydrochloric acid leaching solutions. The selection of phase-forming components is crucial to induce a stable three-liquid-phase system and the controllable three-phase partitioning of Pt(IV), Pd(II) and Rh(III). In present work, various phase-forming salts with different cations and anions, amphiphilic block copolymers with different molecular weight and PPO content, organic extractants with different metal-selective functional groups were investigated to discuss their influence on three-phase mass transfer behaviors of three platinum metals. Experimental results indicated that the formation of three-layered coexisting liquid phases in system of S201/nonane-EOPO2500-Na2SO4-H2O resulted in three-liquid-phase selective partitioning of Pt(IV), Pd(II) and Rh(III). Most of Pt(IV) and Pd(II) were extracted into EOPO-rich phase with the two-phase splitting of EOPO2500-Na2SO4 mixtures, whereas Rh(III) remained in bottom salt aqueous phase. Addition of S201/nonane promoted the separation between Pd(II) and Pt(IV), and most of Pd(II) transferred from EOPO-rich phase into S201 organic top phase of TLPS. Under the optimal conditions, 98.5% of Pd(II), 90.8% of Pt(IV) and 87.1% of Rh(III) were enriched into the top organic, middle polymer and bottom salt aqueous phases, respectively.

► S201, EOPO, Na2SO4 are suitable components for three-phase separation of Pt, Pd, Rh. ► ATPS of EOPO-Na2SO4 provides high selectivity for Pt and Pd. ► Addition of S201 promotes the separation between Pt and Pd. ► 98.5% of Pd, 90.8% of Pt and 87.1% of Rh were separated into three respective phases.