Platinum and palladium sorption on chitosan derivatives

Chitosan is a unique biopolymer due to its cationic properties in acidic solutions. Protonation of the amino groups induces ion-exchange properties that can be used for anion recovery. As this sorbent is soluble in acidic media, it may be necessary to reinforce its chemical stability using a glutaraldehyde cross-linking treatment. Sorption properties are strongly influenced by the pH of the solution and the presence of competitor anions, especially sulfate anions. This competitor effect may be decreased by the grafting of sulfur derivatives on the chitosan backbone using glutaraldehyde as a linker between the polysaccharide chains and the substituent. Several techniques such as FTIR and SEM-EDAX were used for the chemical characterization of chitosan substitution and for the location of PGM sorption on the sorbent. Sorption isotherms and kinetics were investigated and compared for cross-linked materials and substituted polymers, and special attention was given to the influence of competitor anions. The grafting of sulfur compounds increased sorption capacities and decreased the competition of sulfate and chloride anions. While cross-linked materials sorbed platinum and palladium through anion exchange, the grafting of sulfur moities gave chelating functionalities to the ion-exchange resin.