Preparation of Lanthanum Impregnated Pumice for defluoridation of water: Batch and column experiments

In this study, a novel low-cost adsorbent Lanthanum Impregnated Pumice (LIP) was developed, to study the synergistic influence of Lanthanum and Pumice on removal of fluoride from water. Lanthanum loading onto Pumice was varied and evaluated for its defluoridation capacity. Characterization studies were performed using SEM, XRD and FTIR analysis. Equilibrium batch studies, continuous flow studies and mechanistic aspects involved in the adsorption process were explored. It was observed that, at an optimal 2.5 wt% loading of Lanthanum on Pumice, the fluoride adsorption capacity was 7.18 mg/g. Characterization studies confirmed the presence of Lanthanum on Pumice after impregnation. BET surface area increased significantly to 21.4 m2/g after impregnation. pHzpc of the synthesized sorbent, LIP was found to be 7.9. Equilibrium isothermal and kinetic data was tested for suitability with various standard models. Non-linear method of fitting was adopted, using Root Mean Square (RMSE) analysis. Adsorption data fitted well with pseudo-second-order kinetic model, indicating chemisorption, whereas for equilibrium isothermal data, Sips model suited best. Continuous flow studies revealed that a column of 2.54 cm diameter, 30 cm bed depth, flow rate 15 ml/min and influent fluoride concentration of 10 mg/L could treat 36.45 L of fluoride laden water optimally up to permissible limit of 1.5 mg/L. Thomas and BDST models fitted well with the results of column studies. Thus the synthesized low-cost sorbent LIP was able to effectively remove fluoride from water.