Development of new inorganic-biomass adsorbents using sol-gel method and establishment of innovative separation process for critical metals

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New adsorbents using chitosan with the primary amine and lignin with phenolic and hydroxyl groups were developed to elucidate the relationship between their chemical structures and selectivity for critical metals. We also found that the adsorbents prepared by the ion-imprinting method were able to recognize not the ion-size of target metal ion but its complex structure. The hybrid adsorbents of silica/chitosan derivatives with through-pores also were obtained by cross-linking the chitosan derivatives with silica (TEOS) using the sol-gel method. The hybrid adsorbents exhibited the high selectivity for precious metals while those on lignin exhibited the selective adsorption for base metals such as Pb, Cd and Zn. Silica/chitosan derivatives achieved the space velocity (SV) of 50-500 folds over the conventional SV in column method. Chitosan-coated filter was also prepared by a dipping method, and selective recovery of In over Ga from industrial wastes was established using this filter.