Synthesis and physicochemical characterization of Zn/Al chloride layered double hydroxide and evaluation of its nitrate removal efficiency

Deleterious effects of nitrate on health are well known. A laboratory study was conducted to investigate the ability of Zn–Al–Cl layered double hydroxide for the removal of nitrate from synthetic nitrate solution. In the present study Zn–Al–Cl LDH was synthesized by co-precipitation method and was characterized using SEM, XRD, FTIR and TGA–DSC. To know the practical applicability, a detailed nitrate removal study was carried out. The removal of nitrate was 85.5% under neutral conditions, using 0.3 g of LDH in 100 mL of nitrate solution having initial concentration of 10 mg/L. Adsorption kinetic study revealed that the adsorption process followed first order kinetics. Adsorption data were fitted to linearly transformed Langmuir isotherm with R2 (correlation coefficient) >0.99. Thermodynamic parameters were also calculated to study the effect of temperature on the removal process. In order to understand the adsorption type, equilibrium data were tested with Dubinin–Radushkevich isotherm. The percentage removal was found to decrease gradually with increase in pH and the optimum pH was found to be 6. The presence of competitive anions reduced the nitrate adsorption in the order of carbonate > phosphate > chloride > sulphate. The Zn–Al–Cl LDH exhibited low desorption and poor regeneration.