Effect of interlayer cation and relative humidity on the hydration properties of a dioctahedral smectite

Abstract

This paper aims at characterizing the structural evolution of a dioctahedral smec- tite (i.e. Wyoming montmorillonite) saturated by Na + , Cu 2+ or Pb 2+ . Hydration properties of the <2μm size fraction of Wyoming montmorillonite smectite (SWy) source clay (low charge i.e. 0.35) were studied by modelling of X-ray diffraction (XRD) patterns recorded under controlled relative humidity (RH) conditions on Na, Cu or Pb saturated specimens. The Cation Exchange Capacity (CEC) of the starting sample was first Na + saturated to guarantee better dispersion, followed by exchanges with the cations Cu 2+ or Pb 2+ . The resulting com- plexes were respectively labelled Wy- Na, Wy-Cu and Wy-Pb. The qualitative analysis of XRD patterns obtained under room pressure and temperature conditions showed that all complexes have one water layer hydration state. In order to highlight the specific hydration properties of each complex, we studied the XRD patterns under controlled relative humidity (%RH). The quantitative analysis of XRD patterns is achieved using an indirect method based on the comparison of experimental XRD patterns with calculated ones. This quantita- tive study showed that for Wy- Na, Wy-Cu and Wy-Pb at low RH (≈15%) the d001 spacing corresponds to a low hydration state characterized by one water layer, whereas for higher studied rates of relative humidity (75%), differences of hydration state can be distinguished for Wy-Na, Wy-Cu and Wy-Pb samples.