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Influence of Chemical Weathering on Basal Spacings of Clay Minerals¹

ABSTRACT

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.

¹ Published with the permission of the Director of the Ohio Agricultural Research & Development Center as Journal Article no. 21-69. Presented before Div. S-2 Soil Science Society of America, Stillwater, Okla., August 1966. The results are in part contained in a Ph.D. Thesis, The Ohio State University, 1966.

² Former Research Assistant, Associate Professor, and Professor, respectively, The Ohio State University and The Ohio Agr. Res. & Devel. Center.

Received for publication July 26, 1968. Accepted for publication March 10, 1969.