A novel alum impregnated CaO/ carbon composite for de-fluoridation of water

Abstract

Abstract Excessive fluoride concentration (>1.5\xa0mg/L) in water adversely affects human teeth and bones. The present study focuses on the development of a fluoride adsorbentvia wet chemical method, by treating activated carbon and CaO (derived from rice straw and egg shell respectively) with alum. The prepared adsorbents were characterized for various physico-chemical parameters and fluoride adsorption test. The optimized composite with highest fluoride adsorption capacity was further subjected to batch adsorption study. The adsorbent followed second order kinetic model with intra-particle diffusion revealing that the adsorption was controlled by pore diffusion along with the other process, i.e. electrostatic interaction between opposite charges. This has been explained by a mechanism which in turn is supported by XPS data. Langmuir isotherm fitted well with experimental data suggesting homogenous and monolayer adsorption of fluoride. The adsorption capacity obtained from Langmuir isotherm model is 48.78\xa0mg/g. Thus the adsorbent is highly effective in removing fluoride from the initial concentration of 10\xa0ppm to less than 0.2\xa0ppm which is safe for drinking purpose.