Physicochemical characterization of hydroxyapatite and its application towards removal of nitrate from water.

A laboratory study was conducted to investigate the efficiency of hydroxyapatite (HAP) towards removal of nitrate from synthetic nitrate solution. In the present research HAP synthesized from egg-shell was characterized using SEM, XRD, FTIR and TGA-DSC. The removal of nitrate was 96% under neutral conditions, using 0.3 g of adsorbent in 100 mL of nitrate solution having an initial concentration of 100 mg/L. An adsorption kinetic study revealed that the adsorption process followed first order kinetics. Adsorption data were fitted to a linearly transformed Langmuir isotherm with correlation coefficient (R(2))>0.98. Thermodynamic parameters were also calculated to study the effect of temperature on the removal process. In order to understand the adsorption type, equilibrium data were tested with the Dubinin-Radushkevich isotherm. The process was rapid and equilibrium was established within the first 40 min.