Thermochemical and kinetic studies of the acid attack of “B” type carbonate fluorapatites at different temperatures (25–55)°C

The thermochemical and kinetic study of the attack of “B” type carbonate fluorapatites (B-CO3-Fap) by a (19% w/w P2O5) acid solution was performed using microcalorimetry at a temperature range between 25 and 55 °C and a pH 0.6. The results were processed iteratively in order to get the kinetic constant and the enthalpy of dissolution reaction. The rise in temperature leads to an increase in the apparent rate constant and an increase in the enthalpy of dissolution between (−200 and −140 kJ mol−1) with an order of reaction close to 2. Increasing the amount of carbonate in B-CO3-Fap generates a decrease in the activation energy 16–8 kJ mol−1 suggesting that the dissolution reaction could be controlled by a diffusion phenomenon.