Abstract
With the target of recovering rare earth elements (REEs) from acidic leachates, a new functionalized hydrogel was designed, based on the phosphorylation of algal/polyethyleneimine beads. The functionalization strongly increased the sorption efficiency of the raw material for Pr(III) and Tm(III). Diverse techniques were used for characterizing this new material and correlating the sorption performances and mechanisms to the physicochemical structure of the sorbent. First, the work characterized the sorption properties from synthetic solutions with the usual procedures (study of pH effect, uptake kinetics, sorption isotherms, metal desorption and sorbent recycling, and selectivity from multi-element solutions). Optimum pH was found close to 5; sorption isotherms were fitted by the Langmuir equation (maximum sorption capacities close to 2.14 mmol Pr g−1 and 1.57 mmol Tm g−1). Fast uptake kinetics were modeled by the pseudo-second order rate equation. The sorbent was highly selective for REEs against alkali-earth and base metals. The sorbent was remarkably stable for sorption and desorption operation (using 0.2 M HCl/0.5 M CaCl2 solutions). The sorbent was successfully applied to the leachates of Egyptian ore (pug leaching) after a series of pre-treatments (precipitation steps), sorption, and elution. The selective precipitation of REEs using oxalic acid allows for the recovery of a pure REE precipitate.
Highlights
The chemical modifications contributed to altering the surface of the beads that became more porous at the level of thee external layers
The combination of different analytical tools allowed for characterizing the physical (BET, TGA, Scanning Electron Microscopy (SEM)) and chemical (EDX, FTIR, XPS, titration) properties of the different materials
Successful functionalization was demonstrated, but these techniques confirmed the contribution of different reactive groups on the binding of a light rare earth elements (REEs) (i.e., Pr(III)) and a heavy REE (i.e., Tm(III)) as free REE3+ or as a sulfate complex
Summary
Thulium is an expensive REE that is used for designing x-ray emitters, medical and astronautic lasers [3], high-temperature superconductors, ferrite alloys, and ceramic magnetic materials in microwave equipment. In addition to their relatively expensive costs, the geopolitical distribution of resources and exploitation facilities of these metals are making these elements strategic targets, so there is great attention toward developing recovery processes from low-grade minerals and/or from industrial wastes [4]. Their rarefaction, cost, and weak recycling rate (less than 10% for both Tm and Pr, [5]) justify the importance of designing new processes for their recovery from low-grade resources [6]
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