Mineralogical transformation during hydroxyapatite dissolution in simple aqueous solutions

Hydroxyapatite (HAP) is considered to be a stable mineral under surface Earth conditions and adopted as a proxy for paleo-environmental reconstructions and in choice of remediation strategies. A clear description of the solubility properties for HAP is fundamental and can be gained by understanding the basic principals governing the solid-solution interface. In this study we investigated the early stage of HAP dissolution at 25 degrees, 50 degrees and 70 degrees C using solubility and ATR-FTIR spectroscopy measurements. We found a non-stoichiometric release of calcium and total phosphorus in solution in the experimental close to neutral pH conditions. The ATR-FTIR measurements revealed the presence of new peaks corresponding to the vibrations of HPO42- group. Comparing HAP spectra of the pristine surface to those obtained after 7 days of hydration we propose the presence of monetite (CaHPO4). This rapidly formed new phase would affect the observed low solubility of HAP and its presence could validate the use of this mineral in paleo-environmental reconstructions and ecological remediation strategies.