Magnetic amino-sulfonic dual sorbent for uranyl sorption from aqueous solutions – Influence of light irradiation on sorption properties

The association of magnetite microparticles with bi-functional amino-sulfonate polymer (obtained by condensation of guanidine and amino hydroxynaphthalene sulfonic acid, mediated by formaldehyde) allows synthesizing a magnetic composite sorbent (M−GANS). The sorbent bearing both amine and sulfonate groups is efficient for uranyl sorption at pH 4–5. The sorption isotherms are successfully fitted by the Temkin equation, while kinetics is controlled by the pseudo-first order rate equation. The sorption properties are increased by UV irradiation in terms of both sorption capacity (by 25 %, up to 1.25 mmol U g−1) and kinetics. The sorption occurs on both amine and sulfonate groups; the improvement in sorption properties under UV irradiation is tentatively assigned to the photo-reduction of uranyl species (mediated by magnetite particles and amine groups from polymer layer). The UV irradiation improves the selectivity of M−GANS for uranium against other metal ions, tested on both synthetic and real solutions. This improvement can be correlated to the higher propensity of uranyl to be photo-reduced compared with investigated competitor ions. The recycling of the sorbent was successfully tested for five successive cycles of sorption and desorption (stably complete): the loss in sorption performances is slightly reduced (less than 1.5 % at the fifth cycle) under UV irradiation compared with experiments performed under dark conditions (loss close to 4.2 %). The uranium peroxide precipitate obtained at the end of the treatment of acid leachate of ore shows higher purity when UV irradiation was applied.