Sorption and fractionation of rare earth element ions onto nanoscale zerovalent iron particles

Abstract

The removal behaviour of rare earth element (REE), (Sc, Y, La-Lu), ions onto nanoscale zerovalent iron (nZVI) particles has been investigated. Batch sorption isotherms were conducted using REE-bearing acid mine drainage (AMD) and a range of different synthetic REE solutions, which were exposed to nZVI at 0.1–4.0 g/L. Maximum adsorption capacity of Yb and La was 410 and 61 mg/g respectively (1000 mg/L LaCl 3 and YbCl 3 starting concentration, initial pH = 4.5, T = 294 K), the highest currently reported in the literature. Aqueous REE removal to ultratrace concentrations ( < 1 µg/L, > 99.9% removal) was also recorded after 30 min (the first sampling interval) exposure of ≥0.5 g/L nZVI to 10 mg/L aqueous REE solutions (nitrate counterion). Similar rapidity and near-total removal ability was recorded for the exposure of nZVI to the AMD, however, a greater nZVI concentration was required, with the removal of all REEs (with the exception of La, Ce, Nd and Gd) to < 1 µg/L when exposed to nZVI at 4.0 g/L for 30 min. In all systems nZVI was selective for the removal of HREE ions in preference to LREE ions, with the mechanism determined using HRTEM-EDS and XPS analysis as via surface mediated precipitation. Overall the results demonstrate nZVI as exhibiting great promise as an effective and versatile agent for simultaneous REE ion recovery and fractionation.