We studied bentonites taken from outcrops around the bentonite closed-mines in Fukushima prefecture, northeastern Japan. Before 1945, bentonite was mined in the following four areas in Fukushima prefecture: the Numanodaira, Ten-ei, Takada and Aosaka areas, which are located in the Aizu region, western Fukushima prefecture. In the Numanodaira area, we have found a high-grade bentonite containing Ca-montmorillonite. The amount of methylene blue adsorbed on the sample was 121 mmol/100g and the swelling volume of the sample was 9.0 ml/2g. The 001 reflection of the sample was about 15 Å in the XRD pattern, indicating the presence of Ca-montmorillonite. The sample was obtained about 200 meters away from the estimated location of a closed mine. Thus, a promising bentonite deposit may be found around the old mine. In the Tenei area, we have found a moderate-grade bentonite containing Na-montmorillonite. The amount of methylene blue adsorbed on the sample was 53 mmol/100g and the swelling volume of the sample was 14.5 ml/2g. The 001 reflection of the sample was about 12.7 Å in the XRD pattern, indicating the presence of Na-montmorillonite. The sample was obtained from talus sediments near the river around the estimated location of a closed mine. Thus, a promising bentonite deposit may be found near the river around the old mine. No bentonite was found in the Takada area and in the Aosaka area.
