Potassium Fixation by Clay Minerals during Hydrothermal Treatment

Atsuyuki Inoue
Geological Institute, College of Arts and Sciences, Chiba University, Chiba 260, Japan

Abstract: The amount of K fixed in K- and Ca-saturated montmorillonite, vermiculite (trioctahedral), rectorite-type and IMII-ordered mica/montmorillonites was measured as a function of time (1–64 days), temperature (25°–300°C), pH (6.0, 9.7, and 10.7), and K-concentration (0.02 and 1.0 M) in solution. The amount of K fixed by the clays generally increased with increasing temperature, pH, and K-concentration and reached saturation in response to each experimental condition in 5 or 6 days. The K-montmorillonite and K-vermiculite fixed considerable amounts of K even at 25°C. Fixed K in montmorillonite increased with an increase of the layer charge which is also influenced significantly by the interlayer cation. In detail, the behavior in K-fixation was specific to each clay.

The type of structural transformation with K-fixation was different for each clay. In montmorillonite, especially, the type of transformation was related to the cationic composition of the system; in K homoionic system, montmorillonite transformed rapidly into illite/montmorillonite with about 40% expandable layers at 300°C and in a mixed cation system with Ca and K, it reacted gradually to random illite/montmorillonites with increasing temperature. These data indicate that the cation-exchange process of a natural pore solution plays an important role in the gradual transformation of detrital montmorillonite to illite.

Key Words: Diagenesis • Fixation • Hydrothermal • Interstratification • Montmorillonite • Potassium • Rectorite

Clays and Clay Minerals; April 1983 v. 31; no. 2; p. 81-91; DOI: 10.1346/CCMN.1983.0310201
© 1983, The Clay Minerals Society
Clay Minerals Society (www.clays.org)