Synthesis of α-aminophosphonate based sorbents – Influence of inserted groups (carboxylic vs. amine) on uranyl sorption

[Display omitted] •Playing with amine precursor allows synthesizing different aminophosphonate resins.•U(VI) sorption at pH 4 is controlled by the type of precursor (best with aniline).•Sorption isotherm fitted by Langmuir equation (qm capacity up to 1.31 mmol U g−1).•Fast kinetics (equilibrium: 120 min) fitted by pseudo-first order rate equation.•Efficient desorption allows sorbent recycling for at least 5 cycles. A one-pot synthesis procedure is designed for preparing three α-aminophosphonates (R-H, R-COOH, and R-NH2); through the reaction of amine precursors (aniline, anthranilic or o-phenylene diamine, respectively) with salicylaldehyde and triphenylphosphite, under controlled conditions. These materials are first characterized by elemental analysis, FTIR, 1H NMR, 31P NMR, BET, DLS, pHzpc, TGA and titration. In a second step, the sorption properties are compared for U(VI) recovery from mildly acidic solutions. At the optimum pH (i.e., pH 4) the sorbents can be ranked according the series: R-H (1.057 mmol U g−1) > R-NH2 (0.746 mmol U g−1) > R-COOH (0.533 mmol U g−1). The isotherms are fitted by the Langmuir equation. Uranium uptake is relatively fast: under selected experimental conditions, the equilibrium is reached within 90 min of contact. The kinetic profiles are indistinctly fitted by the model of resistance to intraparticle diffusion and the pseudo-first order rate equation. The study of sorption thermodynamics shows substantial changes between the sorbents: uranyl uptake is endothermic with R-H and R-NH2 sorbents, while the reaction is exothermic with R-COOH sorbent. The diversity in functional groups and the speciation of uranyl in sulfuric acid solutions induce metal-binding through a combination of chelation and anion-exchange mechanisms (in function of pH). Sodium bicarbonate solutions achieve complete desorption of uranium from loaded-sorbents; the resins can be recycled for a minimum of 4–5 cycles with limited loss in efficiencies. The successful application of these resins for uranium recovery from acidic ore leachates demonstrates their promising properties for valorization of low-grade ores.