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 conden-sation of guanidine and amino hydroxynaphthalene sulfonic acid, mediated by formaldehyde) allows synthe-sizing 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 suc-cessfully 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 ex-periments 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.