Effective removal of nitrate and phosphate anions from aqueous solutions using functionalised chitosan beads

Adsorption of nitrate and phosphate from aqueous solution on both the protonated cross-linked chitosan beads (PCB) and carboxylated cross-linked chitosan beads (CCB) was investigated in batch mode. Effects of various parameters such as contact time, dosage of adsorbent, pH of the aqueous solutions, competitive co-anions and temperature on the sorption capacity of the sorbents were studied. The reuse of sorbents was evaluated by sequential sorption–desorption cycles using 0.1 M NaOH as regenerant. Three isotherms namely Langmuir, Freundlich and Dubinin–Radushkevich were used to fit the equilibrium data, whereas the pseudo-second-order equation was used for the kinetic data. The E values obtained from the D–R isotherm at 303 K for nitrate and phosphate adsorption on PCB were 0.036 and 0.107 kJ/mol, respectively, and on CCB were 0.029 and 0.114 kJ/mol, respectively, which confirms the physical adsorption between the anions and functional moieties in PCB and CCB. ΔH° values revealed that the adsorption of nitrate is exothermic process and adsorption of phosphate is endothermic process. The sorbents were characterised by SEM and FTIR.