ADSORPTIVE REMOVAL OF FLUORIDE FROM WATER BY SURFACE MODIFIED LATERITE SOIL

Abstract

Fluoride (F−) contamination in groundwater has been recognized as one of the serious problems worldwide . Fluoride is classified as one of the contaminants of water for human consumption by the World Health Organization (WHO) , which causes large-scale health problems. Elevated fluoride concentrations in the groundwater occur in various parts of the world. Fluoride is generally released into the groundwater by slow dissolution of fluorine-containing rocks eg granite, basalt, etc. Industries like glass, semiconductor , etc also discharge effluents containing high concentrations of fluoride. High concentration of fluoride could be toxic to mankind in several ways and thus removal of fluoride is required to control fluoride concentrations within the limit. Among several treatment technologies applied for fluoride removal, adsorption process has been explored widely and offers satisfactory results. In this study we have studied fluoride removal using surface modified laterite soil as it serves as a low cost, easily available and a highly effective adsorbent. Laterite soil was brought from Burdwan district of West Bengal. It was washed with distilled water several times , crushed and sieved to get a particle size range of 250 to 350 microns. It was then treated with 2N HCl followed by treatment with 1N NaOH .The adsorbent i.e acid treated laterite soil , so developed was used for removal of fluoride and further the batch process is optimised by varying the particle size ,adsorbent dose , pH , fluoride concentration and time of contact. The acid base treatment is done to enhance the absorption characteristics .In this process 81% removal of fluoride was reported The adsorption efficiency of the acid base treated laterite was compared with acid treated laterite . Acid base treated laterite was further impregnated with FeCl3 and the efficiency increases to 85%.From EDX analysis it is clear that iron is the main component responsible for fluoride removal. The equilibrium data obtained through batch mode was fitted to Langmuir, Freundlich and Tempkin isotherm. The Tempkin isotherm fits better to the equilibrium data. Fluoride adsorption on acid base treated laterite follows pseudo second order kinetics .Column studies are done so as to study the defluoridation capacity of the adsorbent in continuous mode. The effect of flow rate , fluoride concentration and bed height is studied.