Thermal decomposition process of dypingite Mg5(CO3)4(OH)2•5H2O

Dypingite is one of the most common phases of crystalline magnesium carbonate hydrates, which are considered potential targets for CO2 mineral sequestration. Ex-situ high-temperature X-ray diffraction and ex-situ high temperature synchrotron X-ray scattering experiments with pair distribution function analysis were used to explore the thermal transformation process of dypingite. Dypingite transformed to hydromagnesite until 100 degrees C, but its local structure remained unchanged. At the temperature range from 250 degrees C to 350 degrees C, where the amorphous phase was predominant, the second and third coordination spheres were continuously modified and crystallized to MgO at 400 degrees C. Although the local structure of dypingite was as that of hydromagnesite, dypingite exhibited a different thermal transformation pathway from hydromagnesite.