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Abstract
Glutaraldehyde cross‐linked chitosan exhibits a great affinity for osmium at pH 2: the sorption capacity can reach up to 3 mmol Os g−1 and the initial slope of the isotherm curve confirms that strong interactions exist between the biopolymer and osmium ions. In the case of iridium sorption, the affinity and the maximum sorption capacities are considerably lower than the levels we reached with osmium. The modification of the sorbent by grafting new amine groups [poly(ethyleneimine)] allows the sorption capacities to be increased while the grafting of thiourea did not significantly change sorption capacities. At the low sorbent dosage used in this study more than 90% of the total sorption was reached within the first six hours of contact. However, in the case of iridium after 12 hours of contact a significant release of metal is observed, it confirms that the interactions of the polymer with iridium are significantly weaker than those established between chitosan and osmium ions. Rhodium, rhenium, ruthenium are not significantly adsorbed indicating that a kind of sorption selectivity may be expected in the uptake of osmium, iridium but also platinum and palladium against rhodium, ruthenium, and rhenium.
Acknowledgments
The authors thank the European Commission for the financial support under the Competitive and Sustainable Growth Program (EU Contract No. GRD‐CT‐2000‐00300). This work has been supported by the Spanish Ministry of Education and Culture CICYT (QUI99‐0749) and DURSI (SGR2000‐00075). M. Ruiz also acknowledges CIRIT for the fellowship and the French Embassy for financial contribution received during her stay in France.