Adsorption mechanism of boric acid on chitosan resin modified by saccharides

This study aims to develop an environmentally-friendly resin for boron recovery. To this end, the adsorption characteristics of boron on chitosan resins chemically modified by saccharides are investigated for the purpose of the removal of boron from a boron mine and the desulfurizing equipment in coal-fired steam power stations, and compared with those of a commercial resin (Duolite ES371). First, chitosan derivatives incorporating saccharides were synthesized by reductive N-alkylation, and the products were crosslinked with ethylene glycol diglycidil ether. The resulting products (SMC resins) were found to exhibit dissolubility in acidic and basic solutions. From the adsorption experiment on the resins (SMC and Duolite resins), it is found that the adsorption mechanism is a complex formation between boron which exists as boric acid or borate in an aqueous solution and the vicinal diol groups of the branched saccharide. The apparent adsorption equilibrium constants of boric acid-diol complex and borate-diol salt complex are determined. The adsorption isotherms of boron correlate well with the Langmuir equation, and the order of the saturated adsorption capacity of boron on SMC resins corresponds to that of the degree of substitution on SMC resins.