Evolution of the microstructure of interstratified Ca-saturated clays during dehydration; SAXS and HRTEM analysis

LPM, Faculte des Sciences de Bizerte, Jarzouna, Tunisia

This paper aims at characterizing the structural and textural evolution of three mixed-layered clays in Ca-form from Southern and Central Tunisia. These samples contain various amounts of mixed-layer smectite-illite associated with crystallites of kaolinite. The clay fractions were prepared in the Ca-form and submitted to suction pressures increasing from 3.2 up to 1000 kPa. The structural and textural changes of the pastes obtained were studied by TEM and SAXS. The TEM observations and SAXS quantitative analysis on samples at low stress (3.2 kPa) showed that the thickness of the particles (number of layers per particle) and their lateral extension (in the plane of layers) decrease with increasing illite content. The textural evolution during drying, as described by SAXS, is controlled by the geometry of particles which is determined by the mineralogy of the structural units. With increasing illite content, the particles became shorter, rigid and had flat surfaces. This geometry increases their ability to associate face-to-face during dehydration. When the 2:1 fraction contains a high proportion of smectite, the architecture of the clay-water system at high water content (low stress) seems to be analogous to that of smectites. However, contrary to the behaviour of pure smectites reported in the literature, desiccation led first to a rupture of particles and a reorganization of the geometry of the pore system. This behaviour is due to the rigidity of particles caused by the presence of non-exchangeable K. The structural evolution showed that for an illite-rich sample a transition from the three-water layer to the one-water layer state occurred at 1000 kPa, whereas for smectite-rich materials, the hydration state of layers, i.e. three water layers, was not affected.

This record provided courtesy of AGI/GeoRef.