Changes of Ca and Mg silicate minerals induced by grinding and interaction with water

Abstract: FT-IR spectroscopy, powder XRD, 29Si MAS-NMR, 13C CP/1H-decoupling MAS-NMR, BET surface area and CO2-content measurements have been used to study the processes which occur during dry grinding of Ca and Mg silicate minerals: diopside, enstatite, åkermanite, and wollastonite. In the course of grinding alongside to hydration and amorphisation considerable sorption of atmospheric CO2 by ground minerals occur. According to FT-IR spectra carbon dioxide is present in the ground minerals, in the same form as in silicate glasses after dissolution of CO2 at high temperatures and pressures relevant to the magma state. The degree of carbonisation increases with the fraction of Ca in octahedral positions in the silicate structure. The structure of silicate is less important in the carbonisation process during grinding. Water treatment of diopside leads to a significant increase of BET surface area of the mineral (8-10 times). This may be caused by an increase of surface roughness, which is a result of dissolution at dislocations or other imperfect sites on the mineral surface.