Nitrate adsorption from aqueous solution using granular chitosan-Fe3+ complex

- Granular chitosan-Fe3+ complex had high performance for nitrate adsorption.
- Granular chitosan-Fe3+ complex had shorter equilibrium time (1.5 h).
- Nitrate adsorption was ascribed to ion exchange and electrostatic attraction.
- Granular chitosan-Fe3+ complex could be regenerated using NaCl solution.

In the present study, In order to efficiently remove nitrate, granular chitosan-Fe3+ complex with high chemical stability and good environmental adaptation was synthesized through precipitation method and characterized using SEM, XRD, BET and FTIR. The nitrate adsorption performance was evaluated by batch experiments. The results indicated that granular chitosan-Fe3+ complex was an amorphous and mesoporous material. The BET specific surface area and average pore size were 8.98 m2 g−1 and 56.94 Å, respectively. The point of zero charge was obtained at pH 5. The maximum adsorption capacity reached 8.35 mg NO3−-N g−1 based on Langmuir-Freundlich model. Moreover, no significant change in the nitrate removal efficiency was observed in the pH range of 3.0-10.0. The adverse influence of sulphate on nitrate removal was the most significant, followed by bicarbonate and fluoride, whereas chloride had slightly adverse effect. Adsorption process followed the pseudo-second-order kinetic model, and the experimental equilibrium data were fitted well with the Langmuir-Freundlich and D-R isotherm models. Thermodynamic parameters revealed that nitrate adsorption was a spontaneous and exothermic process. Granular chitosan-Fe3+ complex could be effectively regenerated by NaCl solution.