Indian Journal of Chemical Technology Vol. 21, January 2014, pp. 70-77 Evaluation of polymer-agglomerated granular tri-calcium phosphate for fluoride removal from drinking water C Sivasankari 1, * & A Arulanantham 2 1 Department of Chemistry, Government College of Technology, Coimbatore 641 013, India 2 Department of Chemistry, Sriguru Institute of Technology, Coimbatore 641 010, India Received 2 July 2012 ; accepted 21 July 2013 The powder and granular forms of tri-calcium phosphate have been used as adsorbents in batch studies for removal of fluoride from aqueous synthetic fluoride solutions. The effects of different operational parameters like pH, adsorbent dose, and contact time have been studied for their optimization. Results show that the fluoride removal is maximum and nearly constant in the pH range 3.0-8.0. The efficiency of fluoride removal increases with the increase in adsorbent dose and contact time. Surface morphology of the adsorbent has been examined with the scanning electron microscope. Experimental equilibrium adsorption data obtained is found to be fitted well with both Langmuir and Freundlich isotherm models. Adsorption kinetic study reveals that the adsorption process follows pseudo second – order kinetics. Column experiments are performed using granular tri-calcium phosphate (GTCP) to find out the optimum flow rate, bed height and the effect of co-existing anions in water. The optimum fluoride removal capacity in column study is found to be 2.1005 mg of fluoride per gram of GTCP. Regeneration of the adsorbent for repeated use has also been studied in column operation and it is established that complete regeneration could be achieved with 0.5% aluminium sulphate solution for 8 cycles without loss of efficiency. Keywords: Adsorption, Agglomeration, Column studies, Freundlich isotherm, Fluoride removal, Langmuir isotherm, Tri-calcium phosphate Widespread occurrence of fluoride above the prescribed limit in water meant for human consumption has caused detrimental effects on health 1 . The recommended limits of concentration of fluoride vary among countries. WHO has set a limit range 0.5-1 mg L -1 and Bureau of Indian Standards 2 has prescribed a permissible limit of 0.6-1.2 mg L -1 Mohapatra et al .3 have reviewed various techniques available for the removal of fluoride from drinking water. The methods reported for the removal of excess fluoride from drinking water include chemical treatment, ion exchange, electro-dialysis, adsorption, membrane separation, electrolytic defluoridation and Nalgonda technique. Among various treatment methods available, adsorption has been found to be the cheapest and the most effective. Tri-calcium phosphate adsorbent has been used to remove fluoride from drinking water since 1930’s. It has been reported that tri-calcium phosphate has approximately twice the capacity as that of alumina 4 . However, it has not been widely exploited for fluoride removal. He and Cao 5 compared the fluoride removal efficiency of calcium phosphate systems like bone char, synthetic hydroxyapatite, and tri-calcium phosphate and concluded that the relative efficiency was maximum with tri-calcium phosphate. In the powder form, tri-calcium phosphate exhibits increased adsorption potential for fluoride due to enhanced surface active sites. However, practical problems like handling and separation of the adsorbent from solution are said to be associated with fine powders. To overcome these difficulties, in this study an attempt has been made to agglomerate powder tri calcium phosphate with a neutral non-toxic polymer. Arulanantham et al. 6 have used poly vinyl acetate for agglomeration of powdered carbon for heavy metal removal. In a similar way, powder tri- calcium phosphate was agglomerated with a neutral non-toxic polymer poly (vinyl acetate) to granular form. The potential of the granular tri-calcium phosphate for the removal of fluoride from aqueous solution has been investigated and compared with that of powder tri-calcium phosphate. The effect of pH, adsorbent dose, contact time, kinetics of adsorption and adsorption isotherms has been —————— *Corresponding author. E-mail: sivasankarigct@gmail.com