UPTAKE OF URANYL IONS BY NEW SORBING POLYMERS - DISCUSSION OF ADSORPTION-ISOTHERMS AND PH EFFECT

Chitosan is a natural polymer well known for its efficient uptake of h eavy metals. The modification of this polymer by the substitution of f unctional groups from organic acids allows new sorbents with high sorp tion capacities to be obtained: NDTC with ascorbic acid and glutamate glucan with oxo-2-glutaric acid. The mechanism of sorption is investig ated and several sorption models are applied such as the Freundlich, L angmuir and Temkin models which fit experimental results well. These r esults are explained by the heterogeneity of the polymer surface, the variability of metal species in solution and possible interactions bet ween the molecules sorbed. The effects of several parameters such as p H and metal ion concentration are examined and demonstrate the relativ e importance of metal speciation on sorption performances and mechanis ms. The grafting of functional groups creates some heterogeneity of so rption energy, which explains the selectivity seen in the best models. Metal ions are firstly bound onto more energetic sites (nitrogen grou ps) and later onto other substituting functions.