Defluoridation of water using Brushite: Equilibrium, kinetic and thermodynamic studies

In this study, the adsorption potential of Brushite for the removal of fluoride from aqueous solution has been investigated by using batch mode experiments. The effects of different parameters such as pH, adsorbent dosage, initial fluoride concentration, contact time, temperature and co-existing ions have been studied to understand the adsorption behavior of the adsorbent under various conditions. The adsorbent has been characterized by pHpzc measurement, FTIR. XRD and TEM with EDAX analysis. The Langmuir Freundlich, and Temkin models are found to be the best to describe the equilibrium isotherm data, with a maximum monolayer adsorption capacity of 6.59 mg g(-1) at 310 K. Thermodynamic parameters including the Gibbs free energy Delta G degrees, enthalpy Delta H degrees, and entropy Delta S degrees have revealed that the adsorption of fluoride ions on the Brushite is feasible, spontaneous and endothermic. Among the kinetic models tested for Brushite, pseudo-second-order model fits the kinetic data well. It has been found that the adequate time for the adsorption equilibrium of fluoride is only 60 min. The results of this study have demonstrated the effectiveness and feasibility of Brushite for the removal of fluoride ions from aqueous solution. (C) 2011 Elsevier B.V. All rights reserved.