Ionic Relationships in Clay Suspensions and Dialyzates: I. Rubidium‐86 as a Tracer for Potassium

Highly significant linear correlations were found to exist between radiotracer quantities of Rb 86 and the K concentrations of the dialyzate phases of clay‐water membrane equilibrium systems. The systems extended over a wide range of Ca/K saturation ratios, electrolyte concentrations, and pH values. The linear regression lines for bentonite, illite, kaolinite, and vermiculite systems had similar slopes. The actual amounts of K in the dialyzate phases were about 1.4 times the values indicated by the Rb tracer. Of the four clay minerals only the vermiculite presented problems because of specific fixation of K or Rb. Uptake of K 42 by excised barley, corn, and soybean roots from bentonite systems was also significantly correlated with uptake of Rb 86 . It appeared that Rb 86 could be used in tracer quantities to reflect relative changes in the K distribution in these systems.