Clay minerals sorbing radiocesium in Fukushima. Investigation by IP autoradiography and electron microscopy

Although more than four years have passed after the accident at the Fukushima-Daiichi nuclear power plant, the state of radioactive cesium, which is the main source of the high radioactivity in the environment of Fukushima, is not well understood yet. To advance this situation, we tried to specify radioactive soil particles using IP autoradiography and electron microscopy. As a result, the radioactive soil particles were classified into three types from their morphologies and chemical compositions: (1) conglomerates of fine clay minerals, (2) organic matter containing clay mineral particles, and (3) weathered biotite with a platy shape originated from granite. The weathered biotite is actually a biotite-vermiculite mixed layer mineral, forming a porous structure with well-developed cleavage, and kaolinite filling the cleavage spaces. It was indicated that radioactive cesium is located uniformly in the weathered biotite, rather than concentrated around the edge of the platy shape. (author)