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Rapid Dissolution of Allophane and Kaolinite-Halloysite After Dehydration

Published online by Cambridge University Press:  01 January 2024

Isao Hashimoto  and
M. L. Jackson
Isao Hashimoto
Affiliation:
Department of Soils, University of Wisconsin, Madison, Wisconsin, USA
M. L. Jackson
Affiliation:
Department of Soils, University of Wisconsin, Madison, Wisconsin, USA
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Abstract

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Differential dissolution in NaOH solution was investigated as a means of purification of clay. It was discovered that a large quantity of allophane and free alumina and silica were dissolved from clay preparations in 0.5 N NaOH solution by boiling for as little as 2.5 min, provided the ratio of clay weight to solution volume was kept less than 100 mg to 100 ml. Reprecipitation of dissolved silica occurred if a more prolonged digestion or higher sample to solution ratio was employed. Also, prolonged digestion in the NaOH solution (for 80 min) dissolved as much as 50 percent of kaolinite (Merck) and 25 percent of Wyoming montmorillonite, but only a small quantity of these crystalline minerals was dissolved during the 2.5 min digestion period. Subsequent dithionite-citrate-bicarbonate treatment removed the released iron. Marked improvement of x-ray diffraction patterns of the clays resulted. This rapid and selective dissolution of allophane and free oxides greatly improves the quantitative analysis of crystalline minerals by conventional methods.

After dehydroxylation at 500°C, kaolinite and halloysite became amorphous and also dissolved by the same differential dissolution procedure. Heat-stable (aluminous) montmorillonite and chlorite were only slightly dissolved by this treatment. The selective removal of the 1 : 1 layer aluminosilicates greatly improves the quantitative analysis of the remaining crystalline components of clays by conventional methods.

Type
Article
Information
Clays and Clay Minerals (National Conference on Clays and Clay Minerals) , Volume 7 , February 1958 , pp. 102 - 113
Copyright
Copyright © Clay Minerals Society 1958

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