Add time:09/26/2019         Source:sciencedirect.com

A one-pot synthesis procedure was used for preparing two derivatives of chitosan bearing α-aminophosphonate moieties. Chitosan functionalization was performed by reacting chitosan with glutaraldehyde and triphenylphosphite or trimethylphosphite under selected experimental conditions. The materials (CS-Ph and CS-Me, respectively) were characterized using different analytical procedures for confirming their suggested structures: scanning electron microscopy (coupled to energy dispersive X-ray analysis), Fourier-transform infra-red spectroscopy, X-ray diffraction and X-ray photoelectron spectroscopy analyses, thermogravimetric analysis and elemental analysis. The sorption properties of these materials were compared for U(VI) recovery through the study of pH effect, sorption isotherms, thermodynamics, uptake kinetics and sorbent recycling (metal desorption and sorbent re-use). The sorption isotherms were modeled using the Langmuir and the Sips equations while the kinetic profiles were preferentially fitted by the pseudo-second order rate equation. The comparison of sorption properties shows that the methyl α-aminophosphonate derivative is much more effective in uranium recovery than the phenyl derivative: maximum sorption capacities reached at pH 5 around 245 mg U g−1 and 114 mg U g−1, respectively. Tentative explanations are suggested associated to the acid-base properties, the steric hindrance and the donor/acceptor behavior of reactive groups. Experimental data show that uranyl sorption process proceeds via an exothermic and spontaneous reaction for the two sorbents. Metal desorption was successfully tested using sodium bicarbonate solutions and the sorbent was recycled four times: the sorption and desorption efficiencies progressively decreased but remained relatively high at the fourth cycle (sorption: 88–90% of initial sorption and desorption decreasing by 5% between the first and the fourth cycles). Finally, the sorbents were efficiently tested on acidic ore leachate.

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