Processing of rice straw to derive carbon with efficient de-fluoridation properties for drinking water treatment

Drinking water with excessive fluoride concentration (> 1 mg/l) has detrimental effect on bones and teeth. Out of the several de-fluoridation methodologies, the present study is focused on the adsorption technique. Rice straw was processed in different ways before converting it into carbon to enhance its fluoride adsorption capacity. The adsorbents were subjected to various physico-chemical characterizations and adsorption tests. Alumina impregnated activated carbon (AIAC) was found to be the most efficient adsorbent and further batch adsorption studies, column studies, and regeneration studies were carried out with the same. It follows the second order kinetics model. The intra-particle diffusion model suggest pore diffusion to be a major contributor along with other processes, which may be operating simultaneously The D-R and Temkin Isotherm models reveal physical adsorption due to the electrostatic interaction between the opposite charges present in the adsorbate and adsorbent. This has been illustrated through a mechanism and further supported by XPS results. The adsorbent could effectively remove fluoride to less than 0.4 ppm when the initial fluoride concentration in water was 10 ppm. Further, the fluoride adsorbed AIAC was successfully reused as effective filler in developing particle board material.