Optimization of capacity and kinetics for a novel bio-based arsenic sorbent, TiO2-impregnated chitosan bead

The optimization of TiO2-impregnated chitosan beads (TICB) as an arsenic adsorbent is investigated to maximize the capacity and kinetics of arsenic removal. It has been previously reported that TICB can 1) remove arsenite, 2) remove arsenate, and 3) oxidize arsenite to arsenate in the presence of UV light and oxygen. Herein, it is reported that adsorption capacity for TICB is controlled by solution pH and TiO2 loading within the bead and enhanced with exposure to UV light. Solution pH is found to be a critical parameter, whereby arsenate is effectively removed below pH 7.25 and arsenite is effectively removed below pH 9.2. A model to predict TICB capacity, based on TiO2 loading and solution pH, is presented for arsenite, arsenate, and total arsenic in the presence of UV light. The rate of removal is increased with reductions in bead size and with exposure to UV light. Phosphate is found to be a direct competitor with arsenate for adsorption sites on TICB, but other relevant common background groundwater ions do not compete with arsenate for adsorption sites. TICB can be regenerated with weak NaOH and maintain full adsorption capacity for at least three adsorption/desorption cycles.

► Bead diameter does not affect TICB equilibrium sorption capacity. ► A model to predict As sorption capacity by TICB as a function of solution pH and % TiO2 was generated. ► As removal kinetics by TICB increase with bead diameter reduction and exposure to UV irradiation. ► P competes for As sorption sites on TICB, but Ca, Mg, and Si do not. ► When regenerated with weak NaOH, TICB can be reused for at least three cycles.