Interaction of natural and thermally processed vermiculites with gaseous carbon dioxide during mechanical activation

The interaction of natural and thermally processed (exfoliated and heated) vermiculites with CO₂ during mechanical activation in a planetary ball mill (in-situ) and in an autoclave after mechanical activation (ex-situ) was investigated using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), surface area analyses and total carbon analyses. Mechanical activation under an air or a CO₂ atmosphere, especially in wet mode, increased the surface area and pore volume of the studied vermiculites. Moreover, activation under a CO₂ atmosphere resulted in a higher degree of amorphisation (comparing the basal reflections in the XRD patterns of the vermiculites milled under air or CO₂), indicating that CO₂ interacted with the sample during activation. From this type of interaction, a maximum CO₂ content of 2.74% was determined for the heated vermiculite sample that was mechanically activated in dry mode under a CO₂ atmosphere. If the interaction with CO₂ was performed in an autoclave following mechanical activation, hydromagnesite crystallisation occurred, and a maximum CO₂ content of 3.22% was found for the thermally exfoliated sample.In the FT-IR spectra, the observed bands attributed to carbonate in the range of 1430-1550cm^-1 were singlets (for the natural and thermally exfoliated vermiculites) or split (for the heated vermiculite). This effect is likely due to structural breakdown and increased amorphisation created by heating and mechanical activation.