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Temperature Effects on Interlayer Potassium Exchange in Micaceous Minerals¹

ABSTRACT

The potential range of temperatures that can be used with NaCl-NaTPB solutions for the extraction of interlayer K in micaceous minerals has been established. Temperatures up to 45C proved suitable for all minerals and prolonged extraction periods. Higher temperatures have limited use, particularly with dioctahedral micas, because changes in TPB stability and KTPB solubility occur. For short contact periods, however, temperatures up to 105C may be used with trioctahedral micas.

The release of K by dioctahedral and trioctahedral mica samples and by illite and soil fractions was determined with solutions that contained NaTPB to minimize K blocking and were maintained at 5, 25, or 45C. In coarsely-ground samples of mica, where edge weathering was the dominant mechanism of K release, the rate of interlayer K exchange increased with the temperature. With finely-ground mica samples there was no temperature effect on the initial release of K by layer weathering, but once K release by layer weathering was completed, temperature affected the rate of K release from small particles as well. Such differences in the effect of temperature on K release by edge and layer weathering provide a means of identifying the release mechanism involved in a particular mineral sample. Accordingly, it was found that fractions of Grundite, illite, and Marshall soil are unlike finely-ground micas in that they do not release a major portion of their K by layer weathering. Changes in reaction temperature do not alter the limited degree of K exchange encountered with small mica particles.

¹ Journal Paper no. J-7045 of the Iowa Agr. & Home Econ. Exp. Sta., Ames, Iowa 50010. Project no. 1722. This work was supported in part by the US Atomic Energy Commission under contract AT(11-1)-1680. Presented before Div. S-9, Soil Sci. Soc. of Amer., Tucson, Ariz., Aug. 26, 1970.

² Postdoctoral Associate and Professor of Soils, respectively.

Received for publication August 30, 1971. Accepted for publication January 24, 1972.