Phyllosilicates such as clay minerals (talc, kaolinite, smectites...) and micas (muscovite, biotite...) appear generally as flat particles, parallel to the (001) basal faces. Using low-pressure argon adsorption, it is possible to analyse adsorption phenomena on basal and edges faces and to derive quantitative information on the corresponding surface areas [1,3]. Argon adsorption results obtained for different phyllosilicates with controlled surface chemistry present different specific features depending on the nature and the density of surface cations. Indeed, specific interactions were observed between argon and surface cations of basal faces, the argon adsorption peak is displaced towards higher energies when the size of the cation increases. In addition, using synthetic clay minerals, it was concluded that cation density has only little influences on peak position, compared to cation nature. In the specific case of talc, without cations on basal surfaces, additional high-energy adsorption sites were revelled and from quantitative analysis of the derivatives isotherms, it was concluded that these sites correspond to hexagonal ditrigonal holes defined by the SiO44- tetrahedral network. In order to better understand the argon adsorption phenomena and confirm the assignment of derivative isotherms analyses, Grand Canonical Monte Carlo simulations are carried out on two minerals: talc and muscovite. For the first trials, bulk crystal structures were used to test several potential models and to determine the influence of surface cations. In the present poster, the obtained results in the low-pressure region are discussed in view of experimental data obtained on natural samples. [1] F. Villiéras et al., Langmuir, 8 (1992) 1789. [2] F. Villiéras et al., C.R. Géoscience, 334 (2002) 597. [3] M. Sayed Hassan et al., Langmuir, 21 (2005) 12283.
