Smectites drying

High base status, high CEC clays smectite, dry season... 

Eberl, D. D., Srodon, J., and Northrop, H. R. (1986). Potassium fixation in smectite by wetting and drying. In "Geochemical Processes at Mineral Surfaces," pp. 296-325. American Chemical Society, Washington, DC, ACS Symposium Series 323. 

The Smectite Clays. The smectite-type clays are distinctive in that they expand and cause significant destruction to synthetic (human-made) structures. In this type of 2 1 clay, isomorphous substitution occurs in the aluminum sheet. If there is substitution of lower-oxidation-state metal such as magnesium, there will be an unsatisfied pair of bonding electrons in the interior of the crystal and there will be no noticeable change in the surface. Because the charge is in the interior of the crystal, its attraction for cations is diminished by distance. Thus, smectite crystals are not held together strongly by cations and are able to incorporate more water and ions between sheets when the environment is wet and less when it is dry. 

The amount of swelling and contraction in smectites is quite dramatic. Typically, soils containing large amounts of this type of clay will develop cracks that are 30 cm wide at the surface and greater than 100 cm deep, and these cracks will allow surface material to fall into them during dry periods. This characteristic is so unique that these types of soils are given their own name. They are called Vertisols the name is taken from the concept that material from the surface falls to the bottom of the cracks, resulting in inversion of the soil. 

Table III. Structural Formulae for Smectites Used in Wetting and Drying Experiments, Based on 0io(OH)2 [Formulae Calculated from Data in Table II, Unless Noted Otherwise]... 

Table IV. Percentage of Illite Layers and Interlayer Chemistry of K-Smectites Subjected to Wetting and Drying Cycles in Water at 60°C, and Then Exchanged with 0.1 N SrCl2...

Table V. Data Used to Construct Figure 6 for K-Smectites Submitted to 100 Wetting and Drying Cycles, and Then Exchanged Once and Three Times With 0.1 N SrCl2...

Shaking in water prior to each drying cycle speeds reaction. For example, a K-Kinney smectite subjected to 64 WD cycles produced 42% illite layers, with shaking, compared with 30% for K-Kinney subjected to 50 WD cycles, and 32% for K-Kinney subjected to 75 WD cycles, without shaking. 

Powder x-ray diffraction patterns of oriented clay films on glass slides were obtained for both the air-dry and fully wet Na+- and Ca +-smectites using a Philips Norelco diffractometer. 

ESR spectra of Cu + in dry smectite powders are similar to that shown in Figure 14b, but the 3/2 nuclear spin of Cu splits each g and g resonance into four peaks (6). The individual hyperfine lines of the gy resonance are easily resolved because Ay is large, but the gA resonances are not always resolved because A is small. Thus, A, g, and g can be measured from the powder spectrum. 

Figures 15, 16, and 17 depict Cu + spectra of air-dry smectites in oriented films at 0° and 90° to the applied magnetic field.

Several general observations can be made from the spectra and the calculated ESR parameters. First, the Na+- smectites possess narrower resonance line widths than the Ca +-smectites, with the exception of the saponite. Since Ca +-smectites, unlike Na+ -smectites, do not disperse into individual platelets in aqueous suspension, the Na+-smectite films formed by drying suspensions onto a smooth flat surface have the silicate surfaces more perfectly oriented in the plane of the film. As a result, less angular variation of the z-axis of Cu + relative to the plane of the film would narrow the spectra. One can see evidence of hyperfine splitting in the gj component of the Na+-smectite spectra, but not in the Ca +-smectite spectra. Saponite, unlike the other smectites, has very similar spectral linewidths for the Na+ and Ca + form (Figure 16). Since this Na+-saponite sample does not disperse completely in water (Table II), the alignment of Na+-saponite platelets in the clay film may be no better than that of the Ca +-saponite. 

Isaacson and Sawhney (60) studied the reactions of a number of phenols and smectite with transition metal (Cu, FeJ+) and nontransition metal exchangeable cations. IR spectra of the clay-phenol complexes showed that all the clays studied transformed the sorbed phenols. The transformation occurred to a much greater extent in clays with transition metal cations than in those with the non-transition metal cations. In a subsequent study, Sawhney et al. (61) studied the polymerization of 2,6-dimethylphenol on air-dried homoionic Na-, Ca-, A1-, and Fe-smectite at 50°C. A portion of the adsorbed 2,6-dimethylphenol was transformed into dimers, trimers, tetramers, and quinone-type compounds. The nature of the exchange cations had an effect on both sorption and transformation and decreased in the order Fe Al > Ca > Na. 

Fig. 1. Hydroxyl absorption bands for several smectites pillared with aluminum chlorhydroxide (ACH) soluctions A) Wyoming ACH-bentonite B) Texas ACH-bentonite C) Fe-bentonite D) ACH- Fe bentonite) E) (ACH, Fe)-bentonite and F) ACH-nontronite. Samples a) have been dried at 200 C and then loaded with pyridine and degassed at b) 200 C, c) 300 C, d) 400 C and e) 500 C in vacuo for 2 hours at each temperature.

Smectite-type materials were synthesized with a hydrothermal method [5]. The aqueous solution of sodium silicate (Si02 / NajO= 3.22) and sodium hydroxide was mixed with the aqueous solution of metal chloride to precipitate Si-M (M divalent metal cation, Si M = 8 6) hydroxides. The precipitation pH of Si-M hydroxide was controlled by changing the molar ratio of sodium hydroxide to sodium silicate. After separating and washing of Si-M hydroxide, slurries were prepared from Si-M hydroxide and water. The Si-M slurries were treated hydrothermally in an autoclave at 473 K under autogaseous water vapor pressure for 2 h. The resultant samples were dried at 353 K then we obtained smectite samples. The smectite-type materials are denoted by the divalent species in octahedral sheets and BET surface area, e.g., Ni-481 for the Ni2+ substituted smectite-type material with a surface area of 481 m2g. ... 

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