Effect of diffusion properties on the uranium sorption by chitosan polymers
Résumé
Chitosan is a well-known natural amino-polymer which has proved efficient in removing metal ions from dilute solutions. The uranium sorption is diffusion controlled and it occurs within a thin layer at the surface of the polymer. Sorption performances of chitosan could be increased by a substitution of functional groups on the chitosan backbone: the grafting of oxo-2-glutaric acid allowed glutamate glucan to be obtained. This modification of the chitosan promoted the formation of new chelating sites. Another impact of the modification was the change in the polymer structure which favoured metal ion diffusion in the whole mass of the sorbent. In order to estimate the influence of the modification of its structure, the chitosan was recrystallized by a dissolution/precipitation method. The performances of both polymers were compared regarding in terms of their diffusion properties. The recrystallization enhanced the mass transfer in the solid, although the process was not optimized. Scan Electron Microscopy and X-ray Energy Dispersed Analysis reveals the concentration gradient, thus confirming and the previous conclusion. The recrystallization of the chitosan produced behaviour somewhere between raw and substituted chitosan.