Determination of Layer-Charge Characteristics of Smectites

Abstract

A new method for calculation of layer charge and charge distribution of smectites is proposed. The method is based on comparisons between X-ray diffraction (XRD) patterns of K-saturated, ethylene glycol-solvated, oriented samples and calculated XRD patterns for three-component, mixed-layer systems. For the calculated patterns it is assumed that the measured patterns can be modeled as random interstratifications of fully expanding 17.1 Å layers, partially expanding 13.5 Å layers and non-expanding 9.98 Å layers. The technique was tested using 29 well characterized smectites. According to their XRD patterns, smectites were classified as group 1 (low-charge smectites) and group 2 (high-charge smectites). The boundary between the two groups is at a layer charge of À0.46 equivalents per half unit-cell. Lowcharge smectites are dominated by 17.1 Å layers, whereas high-charge smectites contain only 20% fully expandable layers on average. Smectite properties and industrial applications may be dictated by the proportion of 17.1 Å layers present. Non-expanding layers may control the behavior of smectites during weathering, facilitating the formation of illite layers after subsequent cycles of wetting and drying. The precision of the method is better than 3.5% at a layer charge of À0.50; therefore the method should be useful for basic research and for industrial purposes.

Layer Charge and Charge Distribution of Smectites: A Parameter Which Controls Important Physical Properties of Bentonites

“…Recently, Christidis and Eberl (2003) presented a novel method for determination of layer charge and charge distribution of smectites. The method is based on the comparison of XRD traces of K-saturated, ethylene-glycol solvated smectites with simulated XRD-traces calculated for threecomponent interlayering (fully expandable 17.1 Â layers, partially expandable, 13.5 Â layers and non-expandable 9.98 Â layers).…”

“…In the case of smectites characterization of layer charge is of economic and geologic importance, because layer charge strongly affects key smectite properties such as swelling (McEwan and Wilson 1980), cation exchange capacity, and ion exchange selectivity (Maes and Cremers 1977). Smectites often are compositionally and structurally heterogeneous (Stul and Mortier 1974, Lagaly and Weiss 1975, Talibudeen and Goulding 1983, Nadeau et al 1985, Decarreau et al 1987, Iwasaki and Watanabe 1988, Lagaly 1994, Christidis and Eberl 2003. This heterogeneity contributes significantly to layer charge heterogeneity, both in terms of charge location (tetrahedral or beidellitic versus octahedral or montmorillonitic charge) and charge magnitude (i.e., individual smectite 2:1 layers may differ in charge, with the total layer charge for a sample being an average of these different charges).…”

“…Smectite total layer charge and the heterogeneity of this charge from layer to layer can been measured by a variety of methods, including: (1) micro-calorimetry (Talibudeen and Goulding 1983), in which the heat released during determination of an exchange isotherm is related to different types of exchange sites and hence to charge heterogeneity; (2) measurement of the structural formula using chemical or microbeam methods (Weaver and Pollard 1973, Newman and Brown 1987, Christidis 2006, in which the oxide content of a purified smectite sample is measured and then converted into a structural formula; (3) by XRD analysis after saturation with inorganic or organic cations (Tettenhorst and Johns 1966, Cicel and Machajdik 1981, Stul and Mortier 1974, Lagaly 1981, Olis et al 1990) and (4) by computer modeling of XRD traces of K-saturated ethylene glycol solvated smectites (Christidis and Eberl 2003). Microcalorimetry does not yield quantitative estimation of the layer charge.…”

“…Alternative methods for qualitative estimation of smectite layer charge involve NH 4 + saturation and examination with FTIR (Petit et al 2006) or examination of ethylene glycol complexes with UV spectroscopy (Bujdak 2006). In this review, which contains also new data, we present some new developments on the determination of smectite layer charge proposed by Christidis and Eberl (2003) we compare them with older existing techniques and present some applications of these developments in clay mineralogy, clay geology and colloidal properties of smectites. Also the influence of these developments on the classification of smectites according to the layer charge is shown.…”

O 1sX-ray absorption spectra of Sr2RuO4and SrRuO3

“…Recently Christidis & Eberl (2003) [3] proposed a new method which calculates the layer charge and charge distribution of smectites with X-ray diffraction (XRD). The method is based on the saturation of the < 2 μm fraction with a cation of low hydration energy, mainly K, ethylene glycol solvation, subsequent X-ray diffraction and then determination of the layer charge and charge distribution of smectites by means of the LayerCharge program [3]. The method has been refined further to calculate the influence of tetrahedral charge on determination of layer charge.…”