Separation of scandium from the other rare earth elements with a novel macro-porous silica-polymer based adsorbent HDEHP/SiO2-P

A novel macro-porous silica-polymer (SiO2-P) based di(2-ethylhexyl) phosphonate adsorbent (HDEHP/SiO2-P) was synthesized by vacuum impregnation method for separating Sc from the other rare earth elements (REEs). The as-prepared HDEHP/SiO2-P exhibited excellent selectivity towards Sc (III) over the other REEs(III) with SF(Sc/M )over 50 in 0.1-5 M H2SO4 solutions. The adsorption was spontaneous and endothermic with the capacity of 14.1, 14.8, 15.5 mg Sc/g in 5 M H2SO4 solution at 298 K, 308 K, 318 K, respectively. The adsorption equilibrium was obtained within 5 min. Moreover, the FT-IR, XPS analysis and IC test suggested that the adsorption mechanism of Sc(III) performed through ion exchange at low acidity (<= 0.5 M H2SO4) while the solvation effect by sharing the electron pairs in the oxygen atoms from P=O dominated at high acidity, which was very different from that of the other REEs such as Lu(III) whose adsorption mechanism is dominated by ion exchange at the experimental acidity (pH 2.39-4 M H2SO4). The relatively fast adsorption kinetics, high adsorption capacity and high selectivity of HDEHP/SiO2-P towards Sc(III) indicate its potential candidate for separating Sc(III) from the other REEs(III).