Arsenic(V) sorption on molybdate-impregnated chitosan beads

A new adsorption process for As(V) ion removal from an aqueous solution was studied using molybdate impregnated chitosan beads (MICB). Arsenate ions were strongly adsorbed in the pH range from 2 to 4 with a minimum release of molybdate ions. The sorption mechanism is a complexation between arsenate ions and molybdate ions. Even at low equilibrium concentration, the sorption capacity is high, and allows the process to be used as a finishing treatment. Phosphate ions significantly depressed arsenate collection because of a competing reaction for the active sites. Simultaneously with the arsenate sorption, molybdate is released to a significant extent. This release can be reduced using a treatment of MICB with orthophosphoric acid (to obtain MICB-PO4). The treatment allows weakly bound molybdenum to be removed from the sorbent during As sorption: molybdate release does not exceed 2%. The Langmuir equation fits best the experimental data for As(V) sorption on MICB-PO4 at pH 3 up to equilibrium concentration of 80 mg l−1. A selective and total elution can be carried out using a 0.05–1 mol l−1 orthophosphoric acid solution. Three sorption/desorption cycles were performed with no significant decrease in uptake performance.