Defluoridation of Groundwater Using Raw Bauxite: Kinetics and Thermodynamics

High concentration of fluoride in drinking water causes dental and skeletal fluorosis, a slow, progressive and incurable disease. Removal of fluoride from water (defluoridation) offers a viable remedy to high fluoride content in water and fluorosis where other domestic water treatment solutions are not practicable. Conventional defluoridation technologies are either inefficient or require significant financial and technological investment. Therefore studies in developing countries have focused on local defluoridating agents for abating high fluorides and fluorosis. This study therefore investigated the efficiency of using raw bauxite in defluoridating groundwater through batch equilibrium studies. The bauxite exhibited defluoridation efficiency of up to 96.1% for groundwater with a fluoride concentration of 6.17mg/L at a bauxite dosage of 0.120kg/L. High fluoride uptake capacity of up to 275mg/kg was obtained for the raw bauxite. Gibbsite which is the main constituent of the raw bauxite was responsible for the fluoride removal. The intraparticle diffusion model revealed that fluoride sorption by the raw bauxite occurred through both surface complexation and penetrative diffusion. Ion exchange resulting in the precipitation of insoluble AlF3 might add to the fluoride removal. Fluoride sorption was spontaneous and showed first order kinetics. The activation energy and enthalpy of reaction were determined as 19.6 and 126.5kJ/mol, respectively.