Defluoridation of drinking water using a novel sorbent: lanthanum-impregnated green sand

A novel adsorbent, lanthanum-impregnated green sand (LIGS), was investigated as an adsorbent for removal of fluoride from water. LIGS was prepared by thermally impregnating lanthanum onto green sand at 950 degrees C. It exhibited high fluoride removal capabilities than most other conventionally used sorbents. LIGS was characterized using X-ray powder diffraction and scanning electron microscopy techniques to understand its physicochemical properties. Agitated non-flow batch adsorption experiments were conducted for fluoride removal using LIGS as sorbent. Controlling parameters such as equilibrium sorbent dose, kinetics, influence of pH, and competition of anions were investigated. Isothermal data were analyzed using Langmuir, Freundlich, BET, Sips, and Dubinin-Radushkevich isotherm models to know the sorption potential as well as the mechanism involved in sorption. Regeneration experiments were carried out to assess the reusability of sorbent. It was observed that LIGS could efficiently remove fluoride from various initial concentrations to permissible limits. More than 90% of fluoride was found to be removed in 240min from normally occurring initial fluoride values of 10mg L-1. The sorption was found to follow pseudo-second-order equation model, suggesting chemisorption. Normally occurring pH conditions were found favorable for fluoride sorption. Sips isotherm model was found to fit well and the maximum adsorption capacity of LIGS for fluoride removal was found to be 3.74 (mg g(-1)). Though most ions did not interfere much, competition was evidenced from the anions, nitrates, and bicarbonates for fluoride sorption onto LIGS.