The covalently cross-linked alginate gel beads were prepared by the reactions of Ca2þ-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 C. Adsorption isotherms of Cu(II),
Mn(II), and Ca2þ 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 Ca2þ, 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.