Conditions Affecting Cesium Fixation and Sodium Entrapment in Hydrobiotite and Vermiculite

The effect of residual and added K on Cs fixation was studied, using samples of K‐extracted Transvaal, South African hydrobiotite with 66, 60, 23, and < 1% K saturations. Fixation was measured by the availability of the cations for rapid isotopic exchange in a well‐stirred system. Over 95% of the sorbed Cs was fixed above 1% Cs saturation of the exchange capacity regardless of K levels or whether the K was in the form of residual K in hydrobiotite or K added to the vermiculite prior to addition of the Cs. In contrast, trace levels of Cs (i.e., carrier‐free 137 Cs) were fixed to a much lesser extent, indicating that it may be more available for plant uptake. X‐ray and Na entrapment results indicate that Cs saturations below 40% of the exchange capacity result largely in interstratified Na‐ and Cs‐rich layers with little edge collapse. Higher Cs saturations resulted in increased edge collapse and Na entrapment. Formation of interstratified layers vs. edge collapse of the particles tends to be associated with smaller and larger particles, respectively.