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.

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The influence of polyethylene glycol (PEG) having different molecular weight to the aging phenomenon of smectite dispersion was investigated by measuring viscosity and birefringence. PEG whose molecular weight is bigger than 4000 improved depressiveness of smectite in water and suppressed orientation of platelet smectite particles. This is caused by the bridging effect of PEG between smectite particles. PEG also suppressed dissolution of divalent ion from the smectite dispersion of which pH was adjusted neutral. This resulted in suppression of viscosity increase with time and decrease of water release from clay dispersion.

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