Influence of pH on the interlayer cationic composition and hydration state of Ca-montmorillonite: Analytical chemistry, chemical modelling and XRD profile modelling study

Abstract

To cite this version:Eric Ferrage, Christophe Tournassat, Emmanuel Rinnert, Bruno Lanson. Influence of pH on the interlayer cationic composition and hydration state of Ca-montmorillonite: analytical chemistry, chemical modelling and XRD profile modelling study.. Geochimica et Cosmochimica Acta, Elsevier, 2005Elsevier, , 69, pp.2797Elsevier, -2812Elsevier, . 10.1016Elsevier, /j.gca.2004 ABSTRACTThe hydration state of a <2 µm fraction of Ca-saturated SWy-2 montmorillonite was characterised after rapid equilibration (3 hours) under pH-controlled conditions (0.1-12.6 pH range). The solution composition was monitored together with the interlayer composition and X-ray diffraction (XRD) patterns were recorded on oriented preparations. Experimental XRD patterns were then fitted using a trial-and-error procedure to quantify the relative proportions of layers with different hydration states.The montmorillonite is mostly bi-hydrated in basic and near-neutral conditions whereas it is mostly mono-hydrated at low pH. The transition from the bi-hydrated to the mono-hydrated state occurs through very heterogeneous structures. However, the proportion of the different layer types determined from XRD profile modelling and that derived from chemical modelling using Phreeqc2 code strictly coincide. This correlation shows that the hydration modification is induced by a H 3 O + -for-Ca 2+ exchange at low pH, the two species being distributed in different interlayers. This layer-by-layer exchange process occurs randomly in the layer stack.Under alkaline conditions, results from XRD profile modelling and from near infrared diffuse reflectance spectroscopy (NIR-DRS) clearly demonstrate that there is no CaOH + -for-Ca 2+ exchange at high pH. The apparent increase in Ca sorption in smectite interlayers with increasing pH is thus probably related to the precipitation of CalciumSilicate-Hydrate (CSH) phases, which also accounts for the decrease in Si concentration under high-pH conditions. This precipitation is thermodynamically favoured.2

Adsorption of polyamine on clay minerals

“…The diffractogram of the starting Ca-montmorillonite (Fig. 5b) displays a main d 001 spacing around 15 Å typical of a dominant bilayer state (e.g., [33,34]). The addition of small amounts of F25 polymer immediately modifies the patterns for both samples.…”

Effect of pH and organic ligands on the kinetics of smectite dissolution at 25°C

“…This cannot be explained by precipitation of any secondary Mg-bearing silicate phases because outlet solutions were undersaturated with respect to any such solid phase. While the ion-exchange processes responsible for rapid release of loosely bound Ca of the interlayer sites are very well known (Ferrage et al, 2005;Metz et al, 2005a), non-stoichiometric Mg release cannot be explained by removal of exchangeable ions since there is no Mg in the interlayer positions of the SWy-2 Na-montmorillonite. Therefore, we evoke the cation-proton exchange of the octahedral-layer structural component in the way it is observed for feldspars (Casey et al, 1988;Blum and Stillings, 1995), pyroxenes (Casey et al, 1993b;Oelkers and Schott, 2001) and orthosilicates (Wogelius and Walther, 1991;Pokrovsky and Schott, 2000a,b).…”

Ion Exchanged Vermiculites with Lower Expansion Onset Temperatures

“…As a result they are able to create a richer interlayer hydration and consequent better enlargement of the interlayer space [28][29][30][31][32].…”

“…These WLHS define the basal reflection and are intrinsically related to the interlayer cation(s), relative humidity and temperature [26,31,34,35]. In natural biotite (vermiculite parent mica) the interlayer ions are potassium and the interlayer space contains no water (0-WLHS).…”