COLUMN DEFLUORIDATION OF GROUNDWATER USING MODIFIED INORGANIC COMPOSITESPraveen Tyagi and R. P. Singh
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 by the column processat different fluoride concentrations, bed heights, pH and flow rates. The sorptive capacity of the 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. 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 BH 30 cm, pH 6.0, temperature 25oC, flow rate 10 mL per minute. Under these conditions from 3.8 mg/l solution, they could remove 19.7, 17.2, 16.6, 15.4, 14.7, 13.2, and 12.6% fluoride removal. This order of ICs i.e., CaIC>MgIC> SiO2IC > CIC is probably due to several factors such as particle size, ionic potential, pH, surface area, and environmental conditions. The sorption of fluoride ions increased as their concentration decreases from 9.5 to 1.9 mg/l. Leaching increased as the flow rate increased. The solution pH considerably affected the quantity of pollutant elimination. Most of the sorbents showed the maximum fluoride removal percent at pH 6. The sorption increased with increasing BH, but the equilibrium was attained in 2 hours for MgIC and AA, 2.5 hours for AC. Leaching increases considerably as the flow rate increases. It was concluded that CaIC, MgIC, SiO2IC, and CIC are effective sorbents for F- ions. CaIC and MgIC are especially effective at a high concentration of fluoride (F-) ion in water. A mixed solution containing 0.14 mol/l calcium chloride and 0.08 mol/L sodium dihydrogen phosphate with pH adjusted to about 3 can be profitably used to regenerate the spent sorbent. CaIC, MgIC, SiO2IC, and CIC are ecofriendly sorbents, and their sorption ability is much higher than others. They can be further modified to have enhanced fluoride sorption capacity to be used as a primary remediate of fluoride in wastewater or groundwater like AER.