Cesium-adsorption Behavior of Weathered Biotite from Fukushima Prefecture Depends on the Degree of Vermiculitization

Abstract

We investigated the Cs-adsorption behavior of weathered biotites collected from Domeki, Mankei, Tozawa, and Yatsuzaku (in Ono-Niimachi, Tamura-Gun, Fukushima Prefecture) by changing the initial concentration of Cs in a solution. The degree of weathering (i.e. vermiculitization) of the samples increased in the following order: Domeki sample Tozawa Mankei Yatsuzaku. A characteristic feature of the Domeki sample was distortion of the biotite layer. The Tozawa sample had an even greater degree of distortion of the biotite layer. In the Mankei sample, hydrobiotite and randomly interstratified biotite-vermiculite were observed with distorted biotite. The Yatsuzaku sample contained vermiculite with hydrobiotite and distorted biotite. The Cs adsorption ratio was associated with the initial Cs concentration of the solution. The Cs adsorption ratio of samples in an initial solution of 1 to 100 ppm Cs was about 99%; it decreased with increasing Cs concentration in the solution. Dependency of Cs adsorption behavior on the degree of weathering of biotite was clearly observed in the Cs concentration range of 300 to 1000 ppm. With increasing degree of weathering, the rate of decrease in Cs adsorption ratio with increasing initial Cs concentration in the solution became slower and the maximum amount of Cs adsorbed by the sample increased. These results confirm that weathered phyllosilicates, vermiculite, interstratified biotite-vermiculite, and distorted biotite play important roles in Cs adsorption.