Smectite fraction assessment in complex natural clay rocks from interlayer water content determined by thermogravimetric and thermoporometry analysis.

The smectite content is a key parameter to be determined for various applications of clays and clay-rich rocks. The quantity of interlayer water characteristic of swelling domains can be used to assess the smectite content in clays. We propose in this study to use a simple approach to determine water distribution in clays (mainly between pores and interlayers) by means of thermoporometry and thermogravimetric analysis. Provided the interlayer water does not freeze at low temperature upon thermoporometry experiments, the difference between water quantities determined by the two techniques is assigned to interlayer water. Single-phase model clays and complex natural clay rocks and their composites in water-saturated state are characterized by this approach. The open question is the application of available thermoporometry models developed for simple pore geometry to characterize the complex pore network of clays. Depending on the approach used, different pore sizes were obtained highlighting the limit of a simplified model to describe the complex porous network. The results are more coherent when quantifying the amount of interlayer water, further used for smectite content estimation. Good agreement was obtained between smectite fraction contents deduced from the results of thermal analysis and those measured by conventional mineralogical techniques.