EXTRACTABLE POTASSIUM IN GRUNDITE ILLITE

Abstract

To obtain more information about the K exchange behavior of naturally fine-grained micaceous minerals, and especially the reasons for part of the K in these minerals being nonexchangeable, samples of Grundite illite were subdivided on a particle-size basis or ground in various ways and characterized in regard to their NaTPB-extractable K. Various illite fractions that were prepared by mechanically disperising the material in water, released K at nearly the same rate and to the same degree (66 percent). These data emphasize the difficulties encountered in isolating particle-size effects in naturally fine-grained micaceous minerals, show the limited exchange of interlayer K in small particles is not confined to ground or chemically dispersed samples, and establish the level of K exchange to be used in assessing the effects of particle size in this mineral. Since these fractions appeared to be made up of aggregates, portions of the illite were dispersed by chemical treatments that were shown to not alter the K-release behavior of the mineral. With these chemically dispersed size-fractions, the rate of K exchange increased and the degree of exchange decreased as the particle size decreased. While this K-release behavior of illite fractions is similar to that observed with ground micas, the limitations on K exchange imposed by particle size is far greater with illite (only 48 percent of the K in <0.08 μ illite particles being exchangeable) and no illite fraction released all its K. The effects of grinding illite by wet and dry procedures were evaluated in terms of the changes induced in both the nonoxidizable N (by NaOBr) and the nonextractable K. The wet procedure had little effect on the mineral but a simulataneous increase in N oxidation and K exchange was achieved by dry grinding. Part of the K and N in this mineral seem to occur together in contracted interlayers and are rendered inaccessible by the same small particle-size effect. Unlike the results obtained with ground micas, a net increase in the accessibility of the interlayer components was achieved by fracturing illite particles. However, even dry grinding failed to expose 9 me K per 100 g and 147 ppm N.