Oxidative hydrothermal treatment of bovine bones: A lower CO2 emission process to obtain high specific surface area hydroxyapatite.

Hydroxyapatite (HA) is known to be the main component of the mineral part of bones. Due to its properties HA is studied for various applications such as bone graft, drug carrier, heterogeneous catalyst or sorbent for waste water treatment. HA can be synthesized or valorized from bone wastes, as the food industry produce billions of kilograms of animal bones. The oxidative hydrothermal treatment presented in this work offers an alternative to the conventional calcination in order to remove the organic matter contained in bones. The impact of adding dioxygen into the hydrothermal system on the degradation of organic matter was studied by varying the partial O2 pressure from 0 to 30 bar. In addition, the influence of temperature (220, 250, and 280 °C) and dwelling time (0 and 2 h) at these temperatures was investigated. The degradation of the organic matter was proved by TGA-DSC and FTIR. The presence of organic compounds dissolved in water was assessed by TOC measurements and the production of CO2 was followed by Raman spectroscopy. A hydroxyapatite powder with an organic content <1 wt% has been successfully recovered at a lower temperature, for a shorter duration and with a lower production of CO2 compared to calcination. In addition, the recovered HA has a much higher specific surface area (up to 164 m2/g) compared to calcined bones (up to 83.1 m2/g), which is favorable for biomedical and sorbent applications.