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 ofHg(II) ions from aqueous solutions. The effects of varying parameters such as pH, temperature, initialmetal concentration, and contact time on the adsorption process were examined. Adsorptionequilibrium was established in 360 minutes and the maximum adsorption of Hg(II) on thehydroxyapatite was observed to occur at pH 7.0. The adsorption data correlated with Freundlich andLangmuir isotherms. The Langmuir isotherm showed a better fit to the equilibrium data. Theadsorption thermodynamic parameters (ΔG 0, Δ H 0, and Δ S 0) were calculated which showed anendothermic adsorption process. The equilibrium parameter (RL) indicated that hydroxyapatitenanocrystals are useful for Hg(II) removal from aqueous solutions.