The thickness of the two-layer ethylene glycol complex of dioctahedral smectites varies under room conditions between 17.3 and 16.5 A because of such factors as layer charge density, type of interlayer cation, and relative humidity. Neglecting this variability can give up to 30% error in the X-ray powder diffraction estimation of the smectite:illite ratio of the mixed-layer structures. Three methods have been developed for the interpretation of X-ray powder diffraction patterns of glycolated mixed-layer illite/smectite which take layer-spacing variability into account. The methods include a technique for quantifying the degree of layer ordering. In addition, the proposed techniques minimize the error due to the influence of domain size on positions of reflections. The experimental error can be kept below 5% or below 1% smectite layers, depending on the method applied, provided that the peak positions are measured with the accuracy of ± 0.02°2θ.

Precise identification of illite/smectite interstratifications by X-ray powder diffraction

Mica-type layer-silicates such as montmorillonite and vermiculite are capable of exchanging their cations for other (including organic) cations, just like the zeolites. These derivatives swell in a variety of liquids. This paper presents a survey of the structures of organic derivatives of mica-type layer-silicates and illustrates some possibilities for their industrial utilization.

Organic Derivatives of Mica‐type Layer‐Silicates

................................................................................................

/pdf/the-routine-mineralogical-analysis-of-clay-bearing-samples-428r4ryl41.pdf

The Routine Mineralogical Analysis of Clay-Bearing Samples

Samples of smectites and vermiculites were evaluated to (1) determine the effects of source and amount of charge, (2) determine if a continuum of properties exists, and (3) improve the basis for differentiating criteria for identification. The montmorillonites expanded to the equivalent two-layer complex upon solvation by condensation of ethylene glycol or glycerol vapor. Beidellite exhibited the one-layer complex with glycerol vapor and the two-layer complex with ethylene glycol. The vermiculite samples did not yield regular two-layer complexes regardless of saturating cation, prior moisture or solvating agent. A number of different complexes of vermiculite were obtained depending on conditions of solvation. These corresponded to spacings of approx 13·6, 14·0, 14·3, 15·0, and 15·3 A. Two or more of the complexes may be present in the same sample. Potassium-saturated vermiculites and smectites both exhibited collapsed layers in a dry atmosphere. Hydration of smectites occurred at humidities above 20 per cent and resulted in poorly ordered diffraction maxima of 11–12 A. The K-saturated vermiculites tended to retain the collapsed lattice and exhibited diffraction maxima of 10–10·6 A with integral higher orders. Some hydration occurred as evidenced by peak asymmetry or the appearance of a small 14·3 A line at higher humidities, although the collapsed spacing predominated. The tendency of vermiculite to hydrate decreased as the exchange capacity increased. Differences in properties can be related to both source and amount of charge. Nevertheless, a continuum in the properties of expansion and collapse between the smectites and vermiculites was not observed. The data indicate two discrete populations. These properties may be used as differentiating criteria for identification.

https://link.springer.com/content/pdf/10.1346/CCMN.1967.0150117.pdf

Properties of Vermiculites and Smectites: Expansion and Collapse

Synthetic clays were prepared hydrothermally at 300° to 350°C and 15,000 psi from gels with compositions calculated to give a series of octahedrally and tetrahedrally substituted, 2:1-type layer silicates with charges of 0.5N, 1N, 1.5N, 2N, 2.5N, and 3N, where N equals the “normal” layer charge of montmorillonite. Besides montmorillonites and beidellites, the products also contained other components, kaolinite, saponite, paragonite and possibly amorphous materials, depending on the initial gel compositions. Cation exchange capacities of <2µ fractions treated for removal of amorphous constituents were within the narrow range of 0.95–1.35 meq per g rather than 0.45–2.70 meq per g as calculated from initial gel compositions. Comparisons between the expanding properties of these materials showed that the beidellites expanded less readily than the montmorillonites upon solvation with glycerol vapor and tended to give single interlayer complexes. These differences were most pronounced when Mg was the saturating ion, although they were also apparent with Ca. The K-saturated montmorillonites gave greater expansion than the beidellites on hydration at 100 per cent r. h. The montmorillonites also exhibited greater rehydration than the beidellites after heating at 400°–500°C. Beidellite exhibits properties of expansion that are intermediate between those of montmorillonite and vermiculite. The results of this investigation are consistent with the existence of somewhat stronger ionic attractions in the beidellites than in the montmorillonites. The source of the charge thus has an effect upon the properties of expansion.

Swelling Properties of Synthetic Smectites in Relation to Lattice Substitutions

X-ray diffraction results are presented to show that some montmorillonites will not retain two layers of ethylene glycol in the interiayer space when dried under atmospheric conditions. Diffraction data obtained from such samples of montmorillonite may erroneously be attributed to mixed layer minerals. Studies have shown however that this difficulty may largely be overcome by initially saturating the sample with ethylene glycol by the vaporization technique described, after which the sample is placed in a saturated atmosphere of ethylene glycol for a period of 12–24 hours to come to equilibrium and then irradiated.

G. W. Kunze

Papers

Anomalies in the Ethylene Glycol Solvation Technique used in X-ray Diffraction*