Dual strategy for enhanced and selective uranium sorption by ion-imprinting functionalized chitosan – Fast and efficient recovery from processed acid ore leachate

Uranium recovery from complex effluents requires the combination of different processes including metal sorption from low-concentration solutions containing several competitor metal ions. The design of efficient sorbents (BTC/CH(s), 2-(benzo[d]thiazol-2-yl)-N-carbamoyl acetamide grafted chitosan) that combine both high sorption capacity and high selectivity was achieved by adopting a dual strategy: (a) selecting efficient functional groups (amine, amide, thioester, and hydroxyl groups, in BTC/CH sorbents), and (b) adapting the arrangement of reactive groups appropriately to fit the specific shape of the complexes (ion-imprinting IP vs. non-ion-imprinted NIP materials). This dual strategy was applied to design a chitosan-based sorbent with high sorption capacity (≈1.5 mmol U g⁻¹), fast uptake (equilibrium: 15–20 min), remarkable stability (limited loss of performances after 10 reuse cycles), and strong selectivity (tested both on equimolar multi-component solutions and pre-treated acid leachate), at moderately acidic pH (i.e., 4). Ion-templating strategy effectively improved selectivity by 5–10-folds. Uptake kinetics was fitted by the pseudo-second order rate equation, while the sorption isotherms were finely simulated by the Temkin equation. The sorption was exothermic, spontaneous, and the ion-templating allowed reaching more organized structure. The sorbent was highly selective against base metals, alkali and alkali-earth metals, but less efficient for the separation from thorium or rare-earth elements. The sorbent was successfully used for the recovery of uranyl residues from acidic leachates pre-treated with resins (Amberlite IRA-400 and DOWEX 50, for U and rare-earth element recovery, respectively) and precipitation step (removal of Al(III)/Fe(III) at pH 4). The sorbents were characterized by elemental analysis, FTIR and XPS spectroscopy for analyzing the chemical structure of the materials and identifying their interactions with U(VI). Textural properties and pHpzc values were analyzed for supporting sorption behaviors.