Effect of pH on competitive adsorption of Cu(II), Ni(II), and Zn(II) from water onto chitosan beads

The amounts of adsorption of Cu²⁺, Ni²⁺, and Zn²⁺ from single, binary, and tertiary nitrate solutions onto glutaraldehyde cross-linked chitosan beads were measured. The beads had an average particle size and pore volume of 2 mm and 0.06 cm³/g, respectively, and had a BET surface area of 60 m²/g. All experiments were performed at 298 K as a function of initial pH (2.0-5.0), total metal concentration (0.77-17.0 mol/m³), and molar concentration ratio (0.25-4) in the aqueous phase. It was shown that the amount of metal adsorption generally increased with increasing solution pH. Competitive adsorption was significant in binary and tertiary systems when Cu²⁺ was present. The selectivity factor reached maximum in an equilibrium pH range of 5.1-5.3 and 4.5-4.9 for the Cu-Ni and Cu-Zn binary systems, respectively. This adsorbent provided a possibility for selective separation of Cu²⁺ from such multi-component solutions.