Nd(III) sorption using aminophosphonate-based sorbents – Sorption properties and application to the treatment of REE concentrate

The rare earth elements (REEs) recovery of becomes a strategic issue due to intense use in high-tech industry. One of the most important challenge in the valorization of minerals or waste resources concerns the REEs separation from heavy metals as well as their proper separation within the REEs' family. Two aminophosphates (AP) derivatives were previously prepared for uranium recovery from wastes by one-pot reaction of p-phthalaldehyde, trimethylphosphite and thiocarbazide (in different proportions, leading to Mono-AP and Bis-AP sorbents). Herein, these sorbents are successfully tested for sorption of Nd(III).). For Mono-AP and Bis-AP, the maximal sorption capacity reaches 1.3 and 1.4 mmol Nd g−1, respectively at optimum pH (i.e., 4.5). The functionalization grade weakly affects sorption property at equilibrium (equilibrium is attained in 120–180 min). Uptake kinetics is described by PFORE). Sorption isotherms are fitted by the Sips equation. Neodymium sorption is exothermic and spontaneous, the entropy change remains below 6 J mol−1 K−1 (being higher for Bis-AP). Metal desorption is successfully operated with HCl (0.2 M) solutions and at the sixth cycle, the reduction in sorption and desorption efficiencies do not exceed 7% and 4%. The materials are tested for the REEs recovery of from pre-treated acid leachate of monazite concentrate. In this work which focuses on the REEs recovery, the sorbents show first a marked (unexpected, in terms of physicochemical characteristics) preference for Nd, but also (to a lesser extent) for La>Ce>Pr (i.e., heavy REEs). The mechanisms involved in Nd(III) sorption (investigated utilizing XPS and FTIR analyses) affirm the cross contributions of phosphonate moieties, amine groups (and to a lesser extent thiocarbonyl) with differences between Mono-AP and Bis-AP in terms of relative contributions.