Adsorption Studies for the Removal of Nitrate Using Modified Lignite Granular Activated Carbon

The removal of nitrate (NO3-) on ZnCl2 modified lignite granular activated carbon (LGAC) was investigated. The LGAC was modified with varying chemical impregnation ratios (ZnCl2: LGAC) and activation temperatures. Modified LGAC (LGAC5), with a 2: 1 chemical impregnation ratio and a 500 degrees C activation temperature had the optimum adsorption capacity for NO3-, at a 200 mg/L initial concentration. The initial pH of the testing solutions significantly influenced the adsorption capacity of LGAC5. The contact time studies showed the effectiveness of LGAC5, up to 50 mg/L initial NO3- concentration with 30 min of equilibration time. Isotherm studies revealed the highest values of the Langmuir constant (b), confirming strong affinity of LGAC5 for NO3- ions. Thermodynamics studies verified the endothermic nature of the adsorption process with randomness at the solid/solution interface. Competitive ion testing demonstrated that interfering anions, such as Cl-, CO32-, and PO43-, significantly reduced NO3- adsorption on LGAC5.