Removal of fluoride using the adsorbents produced from mining waste

The capability of the use of the adsorbent produced from coal mining wastes for uptaking fluoride from aqueous solutions was investigated. Experiments were carried out as a function of initial concentration, time, and pH. Lagergren equation was used to describe the adsorption rate of fluoride and rate constant was calculated. The effect of kinetic mechanism was also investigated. Both intraparticle diffusion and film diffusion played roles in the adsorption of fluoride. The equilibrium data were fitted to the Langmuir and Freundlich isotherms. The values of Q and k obtained from the Langmuir and Freundlich equations were found to be 15.67 mg/g and 8.55. Data obtained at various pH indicated that the removal of fluoride was favourable at low pH. The optimum pH for fluoride adsorption was found to be 3.5. The capacity of the adsorbent was compared with other adsorbents. The results showed that the capacity of the adsorbents were higher than alum sludge, lignite, bituminous coal, fine coke, spent bleaching earth, lantanum impregnated silica gel, activated alumina