Kinetic and isotherm studies of nitrate adsorption on granular Fe–Zr–chitosan complex and electrochemical reduction of nitrate from the spent regenerant solution

Abstract

In this study, a granular Fe–Zr–chitosan complex was synthesized to remove nitrate from aqueous solution and an undivided cylindrical electrochemical cell was constructed to treat the spent regenerant solution, thus achieving separation and conversion. Adsorbent characterization was conducted by SEM, XRD, BET, FTIR and XPS. The effects of pH and co-existing anions on nitrate adsorption were investigated. The results indicated that nitrate adsorption on Fe–Zr–chitosan complex followed the first-order kinetic model and the two-site Langmuir isotherm model. The specific surface area of Fe–Zr–chitosan complex was 23.6 m² g⁻¹ and the maximum adsorption capacity reached 10.60 ± 0.74 mg g⁻¹ (as N). The point of zero charge of Fe–Zr–chitosan complex occurred at a pH of 6.3. No significant changes in nitrate removal efficiency were observed over a wide pH range of 3.0–11.0. Sulphate and phosphate seriously interfered in nitrate removal. The developed electrochemical method might have a potential of practical application for the treatment of the spent regenerant solution.