Chemo-morphological coupling during serpentine heat treatment for carbon mineralization

One of the safest and permanent routes for potentially capturing and storing CO2 is via carbon mineralization which involves converting CO2 into environmentally benign and thermodynamically stable calcium and magnesium carbonates. One of the most abundant Mg-bearing minerals in the world suitable for carbon mineralization is serpentine (Mg3Si2O5(OH)4). To enhance the reactivity of serpentine with CO2, dehydroxylation by heating to temperatures in the range of 600 °C-700 °C was proposed. To establish a fundamental structural and morphological basis for the enhanced reactivity of serpentine (e.g. lizardite) on heating to temperatures in this range, in-operando synchrotron multi-scale X-ray scattering measurements were performed, with complementary analyses of the changes in the porosity, particle size, and surface morphology. The detailed transformation of lamellar serpentine to a pseudo-amorphous state on heating to temperatures in the range of 600 °C-700 °C, and the subsequent conversion to denser crystalline phases such as Al2.35Si0.64O4.82 (mullite), SiO2 (cristobalite), Mg2SiO4 (forsterite), and Fe0.3Mg0.7(SiO3) (enstatite) was determined from the wide and small angle X-ray scattering measurements. Increasing roughness of the pore-solid interface on heating to 700 °C followed by enhanced smoothness due to the formation of crystalline phases at higher temperatures was established from the combined ultra small and small angle X-ray scattering measurements. The transformation of lamellar lizardite to its pseudo-amorphous state corresponded to an increase in the porosity and surface area, while the formation of crystalline phases reduced the porosity and surface area while increasing the particle size.