Nitrate removal from aqueous solutions by cross-linked chitosan beads conditioned with sodium bisulfate

The investigation of adsorption of nitrate onto chitosan beads modified by cross-linking with epichlorohydrin (ECH) and surface conditioning with sodium bisulfate was performed. The results indicated that both cross-linking and conditioning increased adsorption capacity compared to normal chitosan beads. The maximum adsorption capacity was found at a cross-linking ratio of 0.4 and conditioning concentration of 0.1 mM NaHSO₄. The maximum adsorption capacity was 104.0 mg g⁻¹ for the conditioned cross-linked chitosan beads at pH 5, while it was 90.7 mg g⁻¹ for normal chitosan beads. The Langmuir isotherm model fit the equilibrium data better than the Freundlich model. The mean adsorption energies obtained from the Dubinin-Radushkevich isotherm model for all adsorption systems were in the range of 9.55–9.71 kJ mol⁻¹, indicating that physical electrostatic force was potentially involved in the adsorption process.