Novel phosphonate-functionalized composite sorbent for the recovery of lanthanum(III) and terbium(III) from synthetic solutions and ore leachate

Abstract

A new process of phosphorylation of algal/polyethyleneimine composite beads allows to dramatically increase the sorption of rare earth elements (La(III) and Tb(III), as light and heavy REE elements, respectively). Sorption proceeds through interactions with several functional groups (phosphonate, but also amine, and carboxylate groups). The sorption capacity at optimum pH (pH0 : 5, pHeq : 4–4.2) reaches 1.44 mmol La g−1 and 1.02 mmol Tb g−1 (increased by 4.5 to 6.7 compared with raw beads). Sorption isotherms are fitted by the Langmuir equation, while fast uptake kinetics (equilibrium within 20–30 min) is described by the pseudo-first order rate equation. Bound metal ions are quantitatively desorbed using a 0.2 M HCl/0.5 M CaCl2 solution; the recycling of the sorbent for five cycles of sorption and desorption shows high stability of sorption (loss of sorption capacity < 9%) and desorption (efficiency > 99%). The sorbent exhibits a remarkable preference for REEs against Si(IV), Ca(II), and Mg(II). The sorbent is used efficiently for the recovery of REEs from acidic leachates of a sedimentary ore. A global process is designed including acidic leaching, pre-treatment of leachates by U(VI) sorption on quaternary ammonium (QA) resin (about 94% of U content). The outlet solution of QA resin is treated at different pH values: the best results are obtained at pH0 5 (pHeq : ~4.5). The REEs are selectively recovered from the eluates by precipitation with oxalic acid: the REE-oxalate precipitate retains 70–76% of its content in the acidic leachates. After precipitation of Al(III) and Fe(III) at pH 5, residual uranium is recovered by precipitation at pH 9 (4.3% of metal leached from the ore).