Adsorption of nitrate and nitrite from aqueous solution by magnetic Mg/Fe hydrotalcite

In this study, magnetic Mg/Fe hydrotalcite calcined material (M-CHT) was synthesized through the co-precipitation and calcination method, and was used to effectively remove nitrate and nitrite from water. M-CHT can restore its original layered structure after the adsorption of nitrate or nitrite, and can be easily separated by an applied magnetic field. The first-order and pseudo-second-order kinetic models (R2 ≥ 0.97) can better describe the adsorption kinetic process. The equilibrium isotherm showed that the Langmuir model provided a better fit to the experimental data than the Freundlich model for nitrates and nitrites. With temperature increased from 298 to 308 K, the maximum adsorption capacity obtained by the Langmuir model increased from 10.60 to 16.90 mg-N/g for nitrate and 7.89 to 14.28 mg-N/g for nitrite, respectively. The adverse effect of coexisting anions ranked in the order of ClO4− > Cl− > SO42− > F− > CO32− > PO43−. The actual Fe2+/Fe3+ value of M-CHT (0.56) is nearly consistent with the theoretical value of 0.5, and the saturation magnetic strength value of M-CHT is 9.15 emu/g, greatly contributing to the solid–liquid separation. Overall, M-CHT with features of magnetic properties and satisfactory adsorption capacity exhibits great promise for application in wastewater purification.