DEVELOPMENT OF INORGANIC COMPOSITES FOR WATER DEFLUORIDATIONPRAVEEN TYAGI AND R.P. SINGHAbstract For the removal of fluoride ions from groundwater to make it fit for drinking or industrial use, the main aim of this research was to prepare four types of inorganic composites based on carbon, calcium, silica, and magnesium namely carbon inorganic composite (CIC), calcium inorganic composite (CaIC), silica inorganic composite (SiO2IC), and magnesium inorganic composite (MgIC) respectively, and to test the feasibility of their use in defluoridation of water. The sorptive capacity of most effective four ICs (CaIC, MgIC, SiO2IC, and CIC), commercial activated alumina (AA), activated carbon (AC), and an anion exchange resin (AER) Ceralite IR 400 (Cl- form) were evaluated for fluoride removal under steady-state and transient rate batch processes under different conditions of fluoride concentration, time, sorbent dose, pH and temperature. Sorbents were analyzed and their capacities were compared with AA, AC, and AER. The modified sorbents were better than ordinary sorbents. CaIC showed comparable results to AER. Defluoridation was in the order AER > CaIC > MgIC > AA > SiO2IC > CIC > AC over a wide range of initial concentration 1- 10 mg/l at sorbent dose range 1-20 g/l, pH 6.0, temperature 25 oC, rpm 150 for 5 hours. Under these conditions from 3.8 mg/l fluoride solution, they could remove 91.7, 90.2, 88.6, 80.4, 75.2, 71.2, and 66.6% fluoride removal. This order of ICs, i.e. CaIC > MgIC > SiO2IC > CIC was probably due to several factors such as particle size, ionic potential, pH, surface area, and environmental conditions. The sorption increased with increasing contact time and sorbent dose, but the equilibrium was attained in 2 hours for MgIC and AA, 2.5 hours for AC. The higher uptake at lower initial concentration can be attributed to the availability of more isolated fluoride ions. The sorption rate was very rapid during the initial period of contact. Groundwater samples revealed 3 to 12% lesser removal when correlated to standard sodium fluoride solutions under identical conditions. CaIC was found to be the best of all the fluoride removing ICs studied here. The maximum removal was at pH 6 or slightly lower 5.7 but for others, it was a slightly higher pH than 6. Thus, the weakly acidic medium favored the removal. CaIC showed better sorption than AA and comparable removal to AER. |