Thermodynamic Study of Hg(II) Ion Adsorption onto Nano Hydroxyapatite from Aqueous Solution

Hydroxyapatite nanocrystals were synthesized by sol-gel combustion method for the sorption of Hg(II) ions from aqueous solutions. The effects of varying parameters such as pH, temperature, initial metal concentration, and contact time on the adsorption process were examined. Adsorption equilibrium was established in 360 minutes and the maximum adsorption of Hg(II) on the hydroxyapatite was observed to occur at pH 7.0. The adsorption data correlated with Freundlich and Langmuir isotherms. The Langmuir isotherm showed a better fit to the equilibrium data. The adsorption thermodynamic parameters (ΔG 0, Δ H 0, and Δ S 0) were calculated which showed an endothermic adsorption process. The equilibrium parameter (RL) indicated that hydroxyapatite nanocrystals are useful for Hg(II) removal from aqueous solutions.