Abstract: The microencapsulated alginate ionotropic gels[alginate-chitosan-alginate(ACA) microcapsules, a kind of novel ion adsorbents] are prepared and employed to examine their ion exchange properties. FTIR spectra reveal that ACA has a capsular structure composed of capsular membrane with alginate-chitosan polyelectrolyte complex and intracapsular alginate solution. ACA microcapsules particle sizes are about 400-450 μm, its smooth surface and clear capsular membrane was observed by optical microscope. The membrane thickness is 8-10 μm determined by SEM. The SEM analysis proves that the process of adsorption of ACA on heavy metals is sol-gel transition process and the process of desorption of ACA on heavy metals is gel-sol transition process. So ACA is a kind of ionotropic gels. As novel ion adsorbents, ACA microcapsules have a higher percent adsorption, lower limiting adsorption concentration, higher enrichment capacity than usual ion exchange resins on Pb²⁺. The highest percent adsorption is 99.90%. The limiting adsorption concentration is 0.021 6 mg/L. The weight exchange capacity is 311 mg(Pb)/g at an equilibrium concentration of 1.5 mmol/L Pb²⁺ ions. Especially ACA microcapsules have much faster ion exchange velocity than D418 chelating resin and D113 polyacrylate resin in the controlled experiments. The mutual diffusion of metal ions and alginate molecules decreases the diffusion distance of exchange ions and increasingly enhances ion exchange velocity. At last, it is proved that ACA can be used for many times.

Key words: Ion adsorbents, Alginate, Microencapsulation, Ionotropic Gels