Adsorption removal of ammonium from aqueous solution using Mg/Al layered double hydroxides-zeolite composite

Natural zeolites have widely been applied in the removal of contaminants from water while Mg/Al layered double hydroxide (LDH) zeolite (Mg/Al LDH-zeolite) composite is a relatively new material with promising features in wastewater treatment. This study evaluated the performance of a material combined between natural zeolite and Mg/Al LDH in the adsorption of ammonium from aqueous solutions. The characterization data of Mg/Al LDH zeolite composite, including BET, SEM, TEM, XRD, EDX, and FTIR show superior traits for adsorption with higher heterogeneity compared to conventional zeolites. Batch experiments demonstrated the effects of the parameters including pH, reaction time, reaction temperature and the initial ammonium concentration onto NH4+ adsorption by Mg/Al LDH zeolite. The optimal conditions adsorption of NH4+ onto Mg/Al LDH zeolite were at solution pH of 8.0, reaction time of 60 min, and an initial ammonium concentration of 40 mg/L. The NH4+ adsorption by Mg/Al LDH zeolite increased when temperature grew, suggesting NH4+ adsorption process was endothermic in nature The maximum adsorption capacity of Mg/Al LDH-zeolite was 17.81 mg/g corresponding to the NH4+ removal efficiency of 89.03%. Kinetics of NH4+ adsorption fit well with the pseudo second order and Elovich models. While NH4+ adsorption isotherms were described better by the Sips model. Characterization, kinetic, and isothermal studies suggest the main mechanisms of NH4+ adsorption onto Mg/Al LDH-zeolite involved ion exchange, surface complexation and π-cation interaction.