Pd and Pt recovery using chitosan gel beads. I. Influence of the drying process on diffusion properties

Abstract

Chitosan is very efficient at removing metal ions, especially precious metals. Sorption kinetics can be improved by the preparation of chitosan gel beads, using a coagulation procedure. However, this process leads to the formation of beads containing very high water yields, which prevent chitosan from being an economically competitive sorbent for large-scale industrial applications, for reasons linked to transport costs and handling. The air-drying of chitosan gel beads resulted in a decrease in the sorption rate, while the sorption performance at equilibrium was not influenced by the drying step. The influence of re-hydration was examined. The drying of beads saturated with saccharose was considered a simple alternative treatment, to prevent the restriction of the polymer network and improve sorption rate. The influence of these different treatments on both sorption kinetics and sorption isotherms was studied for the recovery of platinum and palladium from dilute solutions.

Keywords:

• Platinum
• Palladium
• Chitosan
• Glutaraldehyde cross-linking
• Sorption isotherms
• Sorption kinetics
• Drying process

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 was supported by the Spanish Ministry of Education and Culture CICYT (QUI99-0749) and DURSI (SGR2000-00075). M. Ruiz also acknowledges CIRIT for the fellowship received during her stay in France.