(261c) Selective Adsorption of Au (III) By Epichlorohydrin/Thiourea Modified Porous Alginate Beads

Xiangpeng Gao,^a Yan Zhang,^a* Yuming Zhao^b

^a Department of Process Engineering, Memorial University of Newfoundland

^b Department of Chemistry, Memorial University of Newfoundland

Abstract

Sodium alginate is an anionic polysaccharide distributed widely in the cell walls of brown algae, which can be extracted by treating algae with sodium carbonate solution and recovered by precipitation. Sodium alginate and its derivatives can be used as biosorbents to retain toxic metal ions, or recover precious metal ions from industrial wastewater. However, the dissolution of sodium alginate in aqueous solution has limited its application as a sorbent. Moreover, powder form of sodium alginate is not suitable to be packed in a column for applications at preparative scale because they may cause clogging problems, a huge pressure drop or serious hydrodynamic limitations. Therefore beads are regarded as the best form of biopolymer based sorbents for metal uptake from aqueous solutions. So far, most of the studies in biosorption area focused on the sorption of monometallic system. A major complication in the application of biosorption to industrial conditions is the presence of other metal ions in the wastewater to be treated. The effect of the co-existing metal ions on the selective adsorption of the meal of interest may be different under different scenarios. In this study, porous alginate beads were prepared by modifying epichlorohydrin and thiourea with sodium alginate, and then dropped into calcium chloride solution to form beads. The epichlorohydrin/thiourea modified alginate beads were soaked in tetraethyl orthosilicate (TEOS) sol and finally freeze dried to generate pores. Selective adsorption of Au (III) from mixed metal solutions under different acidic conditions was studied. Mathematical models were used to describe the adsorption isotherm and kinetics of Au(III). FT-IR, SEM-EDS, and XPS analyses were used to characterize the sorbent and identify the functional groups and potential biosorption mechanisms that contributed to the selective adsorption of Au (III).

Keywords: Selective adsorption; Alginate; Porous biosrobent