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 322% was found for the thermally exfoliated sample.