Selective Sorption of Heavy Metals by Renewable Polysaccharides.

Renewable and biodegradable polysaccharides have attracted interest for their wide applicability, among them their use as sorbents for heavy metal ions. Their high sorption capacity is due mainly to the acidic groups that populate the polysaccharide backbone, for example, carboxylic groups in alginate and sulfate ester groups in the iota and lambda carrageenans. In this study, these three polysaccharides were employed, alone or in different mixtures, to recover different heavy metal ions from aqueous solutions. All three polysaccharides were capable of adsorbing Eu3+, Sm3+, Er3+, or UO22+ and their mixtures, findings that were also confirmed using XPS, TGA, and FTIR analyses. In addition, the highest sorption yields of all the metal ions were obtained using alginate, alone or in mixtures. While the alginate with carboxylic and hydroxyl groups adsorbed different ions with the same selectivity, carrageenans with sulfate ester and hydroxyl groups exhibited higher adsorption selectivity for lanthanides than for uranyl, indicating that the activity of the sulfate ester groups toward trivalent and smaller ions was higher.

Biosorption of uranyl ions from aqueous solutions by soluble renewable polysaccharides.

Polysaccharides derived from natural sources have been offered as environment friendly sorbents for the adsorption of heavy metals. We present a simple technique to remove uranyl ions from aqueous solutions by using representative polysaccharides. The adsorption efficiency of UO22+ decreased in the following order: xanthan gum > kappa > iota/guar gum, for instance, the efficiencies after sorption of 30 min with 500 mg per L uranyl acetate and 0.03 g of the corresponding polysaccharide were: 89.7%, 85.2%, 79.1% and 77.1%. Lowering the acidity in the system decreased the sorption efficiency with all the polysaccharides, and reducing the ratio between the amount of uranyl ions and the amount of polysaccharide increased the sorption efficiencies, e.g., using 500 mg per L uranyl acetate and 0.05 g of the corresponding polysaccharide (xanthan gum, kappa, iota, guar gum) yielded after 30 min sorption efficiencies of 94.3%, 91.5%, 89.0% and 87.7%, respectively. FTIR, SEM-EDS and TGA analyses verified the presence of uranium in the polysaccharides and showed that the uranyl ions were interacting with the different functional groups. Moreover, the addition of uranyl ions to the polysaccharides caused a sharp decrease in viscometry measurements. In addition, the measurements showed that the addition of uranyl lowered both modules, G' and G'', and made the solution more liquid.