Precipitation of Kaolinite at 25°C and 1 atm*

J. A. Kittrick
Department of Agronomy, Washington State University, Pullman, Wash. 99163
* Most of the analyses in this investigation were done by Mr. E. W. Hope, with the assistance of Mr. C. E. Ricketts and Mr. J. Dollhausen. This investigation was started in 1965 at Harvard University while the author was on sabbatical leave from Washington State University and was supported in part by a grant of funds to Dr. R. M. Garrels from the petroleum Research Fund of the American Chemical Society. Completion of the work was supported in part by grant 16060DGK from the Federal Water Pollution Control Administration. This work is published as Scientific Paper No. 3398, College of Agriculture, Washington State University, Pullman. Project 1885.

Abstract: The 0·2–5µ particle size fraction of montmorillonite from three sources was equilibrated with various solutions at room temperature. After 3–4 yr, kaolinite was found in some of the samples that were supersaturated with respect to kaolinite, but not in any of the undersaturated samples or in the original montmorillonite. X-ray diffraction analysis of the precipitated kaolinite showed no interlayer expansion of glycerated, oriented samples. Random powder samples indicated a poor crystallinity. The thermal stability of the precipitated material was indistinguishable from that of crystalline kaolinite. The electron microscope did not reveal any distinctive sizes or shapes.

Equilibration behavior of several samples defined a single kaolinite solubility line at or above which kaolinite apparently begins to precipitate. The solubility line is equivalent to a standard free energy of formation (ΔG) of −904·2 kcal per mole of kaolinite. This represents highly crystalline kaolinite. The stability of kaolinite actually precipitated at room temperature probably depends upon precipitation conditions. Thus kaolinite stability could range from poorly crystalline up to the equivalent of the kaolinite solubility line at which initial precipitation begins.

Clays and Clay Minerals; December 1970 v. 18; no. 5; p. 261-267; DOI: 10.1346/CCMN.1970.0180504
© 1970, The Clay Minerals Society
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