Adsorption of Cu and Mn on covalently cross-linked alginate gel beads

The covalently cross-linked alginate gel beads were prepared by the reactions of Ca2+-doped alginate gel beads, which were formed by spraying a viscous alginate solution into a calcium chloride solution, with cyanogen bromide and following 1,6-diaminohexane. The cross-linking of alginate matrix decreased the mean bead diameter by about 30% and made the beads durable in some extent under alkaline conditions. The adsorption of metal ions on the covalently crosslinked alginate gel beads was rapid and reached at equilibrium within 30 min at 25 degreesC. Adsorption isotherms of Cu(II), Mn(II), and Ca2+ on the beads possessed a stepwise shape, which was firstly determined by Rorrer et al. [Ind. Eng. Chem. Res. 32 (1993) 2170] for cross-linked chitosan gel beads and explained by a pore-blockage mechanism. Higher selectivity was determined against Cu(II) over Mn(II) and Ca2+, especially at a low concentration region. These metal adsorption profiles for the covalently cross-linked alginate gel beads was almost the same as those for the un-crosslinked beads, indicating that the cross-linking reactions were performed without interfering the adsorption characteristics of alginate gel beads. (C) 2003 Elsevier Ltd. All rights reserved.