Synthesis of Hydroxyapatite from Eggshell for defluoridation of water by adsorption

Abstract

The present study deals with fluoride ion removal from aqueous solution by hydroxyapatite adsorbent synthesized from waste eggshell as calcium precursor and phosphoric acid through wet chemical precipitation technique. The prepared adsorbent was characterized using XRD, FT-IR and TGA techniques. Batch adsorption studies were carried out to investigate the effect of initial pH of the solution, contact time, adsorbent dose and initial fluoride concentration on the adsorption capacity of hydroxyapatite. The fluoride removal efficiency was determined using fluoride ion selective electrode. Fluoride adsorption was found to be pH dependent and 98.8%.of fluoride was removed at pH 3.0 but, at pH ~7.0, 85% of fluoride was removed. Both the Langmuir and Freundlich models were tested for the adsorption isotherm studies and the experimental results indicated that the Langmuir model was more favorable for the removal of fluoride and the reaction followed pseudo second order kinetics. The synthesized hydroxyapatite crystal has also about 81% removal efficiency for the tested real water samples.