Influence of Chemical Weathering on Basal Spacings of Clay Minerals
1969
Conyers, E. S. | Wilding, L. P. | McLean, E. O.
Illite, vermiculite, montmorillonite, kaolinite, and a Brookston soil clay were weathered by H-, HO-, and H-resin; sodium tetraphenyl-boron + resin; and boiling 1N nitric acid + resin treatments. X-ray diffractograms of the treated clays suggest the following effects on the mineral structures. Resin caused relatively minor changes compared to unweathered specimens. NaBPh₄ removed interlayer K from 10A and 10–14A interstratified components of illite, vermiculite, and Brookston soil clay resulting in partial expansion of 10–14A components as evidenced by diffractograms of glycolated samples. HNO₃ dissolved less stable components of the illite specimen and/or favored preferred orientation of aggregates as indicated by marked increases in the intensity of mica basal reflections. Estimations of K content of mica from 10:5A peak-intensity and area ratios indicated that mica remnants in acid-treated illite were lower in K than those in unweathered or NaBPh₄-treated illite. Treatment with HNO₃ severely altered the expansibility of vermiculite, transforming a part of the specimen into an expanding lattice structure and dissolving much of the remainder. The 10A and 14A components of Brookston soil clay were less altered by HNO₃ treatment; however, the 17–18A peak in the glycolated sample was sharper, and thermally stable interlayer components were less evident after acid treatment. HNO₃- and NaBPh₄-treated kaolinite and montmorillonite basal spacings remained essentially the same as untreated samples. These data are evaluated in terms of mechanisms of K-release from the weathered clays and subsequent K-content found in soybean plants (Glycine max L.) grown in the clay residues.
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