Light, Middle, and Heavy Rare-Earth Group Separation: A New Approach via a Liquid-Liquid-Liquid Three-Phase System

The present work puts forward a new strategy to achieve group separation of light, middle, and heavy rare-earth ions by liquid-liquid-liquid three-phase systems. Experimental results indicated that heavy rare-earth ion, Yb(III), can be selectively extracted into the organic top phase, while middle rare-earth ion, Eu(III), and light rare-earth ion, La(III), can be enriched, respectively, into PEG rich middle phase and (NH4)(2)SO4-rich bottom aqueous phase of Cyanex272/PEG/(NH4)(2)SO4-H2O three-liquid-phase system. Various influences of aqueous pH, (NH4)(2)SO4 concentrations, complexing agents, polymers, and their added amount on three-liquid-phase separation of La, Eu, and Yb were investigated. Besides, a possible partitioning mechanism for three rare-earth ions was discussed. The present work highlights the possibility of employing the discrepancy in selective partitioning behaviors of different rare-earth ions (such as La, Ce, Eu, Gd, Yb, and Lu) into different liquid layers of three-liquid-phase system to achieve one-step group separation of light, middle, and heavy rare-earth ions. In comparison with traditional organic-aqueous biphasic extraction for group separation of rare-earth ions, which require multiple steps of pH adjustments and repeated separation, the three-liquid-phase approach exhibits obvious advantages for future industrial application.