Reducing Nitrate from Water Using Lanthanum-modified Adsorbent: Optimization, Thermodynamics, Kinetics, and Isotherms

Lanthanum-modified commercial activated carbon (LMAC) adsorbent was synthesized, characterized, and then applied for reducing nitrate from aqueous solutions under various conditions. The extent of nitrate removal depended on four factors: temperature, the aqueous solution pH, initial nitrate concentration, and contact time. The Taguchi approach was used as the method of design for the experiments. Under optimal conditions ( T= 300°C, pH=3, C0=10 ppm, and t= 210 min), the removal percentages and capacity of nitrate adsorption were found to be 71.31%, and 1.43 for activated carbon (AC) and 93.31% and 1.87 for LMAC, respectively. Thermodynamic parameters, including the enthalpy, Gibbs free energy, and entropy, indicated the spontaneous and exothermic nature of the adsorption process. Various isotherms and first and second-order kinetic models were applied to investigate the adsorption process. The pseudo-second-order kinetic model and Langmuir isotherm could well describe the adsorption process.