Optimization of pyrolysis conditions and adsorption properties of bone char for fluoride removal from water

• Pyrolysis conditions for bone char synthesis have been optimized for water defluoridation.
• Pyrolysis temperature has the major effect on fluoride adsorption using bone char.
• 700 °C is the optimum pyrolysis temperature for improving fluoride uptakes of bone char.
• Optimized bone char showed a maximum fluoride uptake of 7.32 mg/g at 30 °C and pH 7.

This study reports the optimization of a pyrolysis process for the synthesis of bone char for fluoride removal from water. Specifically, we have performed a detailed analysis of the adsorption properties of bone char samples obtained at different operating conditions of pyrolysis. Results show that the pyrolysis temperature plays a major role to synthetize an effective bone char for water defluoridation. In particular, the best adsorption properties of bone char for fluoride removal are obtained with those samples synthetized at 700 °C. Pyrolysis temperatures higher than 700 °C cause the dehydroxylation of the hydroxyapatite of bone char reducing its fluoride adsorption capacity. The maximum fluoride adsorption capacity of the bone char obtained in this study (i.e., 7.32 mg/g) is higher than those reported for commercial bone chars. Finally, adsorption experiments were performed using the optimized bone char for determining kinetic, equilibrium and thermodynamic parameters of the fluoride removal from water using this adsorbent. In summary, this study shows that the optimization of pyrolysis conditions for the synthesis of bone char is useful to obtain an effective adsorbent for fluoride removal from water.