Non-equilibrium kinetic separation of thulium, yttrium and erbium on the surface of freely rising oil droplets

Abstract

It is difficult to achieve selective separation and enrichment of different rare earths from high abundance yttrium ores efficiently only dependent on their discrepancy in thermodynamic properties. The present work suggests a new strategy based on non-equilibrium kinetic separation of Er and Tm on the surface of freely rising oil droplets to control the separation order of Y. It is revealed that the mutual separation of Er/Tm is significantly promoted with the separation coefficient of 2.89 during the non-equilibrium extraction with the addition of diethylenetriaminepentaacetic acid (DTPA). The extraction sequence of Tm, Er and Y can be controlled as Tm > Y > Er, thus Y can be selectively enriched during the process of separation of Er and Tm. Such a sequence is subject to the controllable dissociation rates of RE(III)–DTPA complexes and extraction abilities of P507 with the three RE(III) ions. The dissociation rate is dependent on the stabilities of RE(III)–DTPA complexes and follows the sequence of Y(III)–DTPA < Tm(III)–DTPA < Er(III)–DTPA. However, the extraction abilities of the three RE(III) ions follow the sequence of Y(III)–P507<Er(III)–P507<Tm(III)–P507. The competition complexation of DTPA and P507 at the interface of oil droplets results in an obvious change in the separation order of Y from Tm > Er > Y to Tm > Y > Er.