[HCG26-P01] Effects of addition of clay minerals on the existing state of radiocesium in soil
Keywords:Fukushima, cesium, clay minerals
Soil samples were taken from a grassland polluted by RCs at the surface layer (from 0 to 5cm) in Fukushima prefecture. Zeolite and weathered biotite were selected as clay minerals. Incubation was conducted in a constant temperature (25℃) room. The clay minerals were added at 1, 5 and 10% per 50 g dried soil. Incubation duration was 7, 28 and 258 days. Soil moisture was adjusted to 86% and 120% mass water content. Effect of drying-wetting cycles was also examined.
For drying-wetting cycle, the soil was repeatedly incubated under room temperature (25℃) and 50℃ for 48 hours at each temperature condition. After drying, the samples were rewetted to be mass water content of 120%.
After the incubation, 1M ammonium acetate was added to be dry soil: solution ratio of 1:4, and shook for 6 hours. Suspension was filtered by 0.45µm membrane filter. Cs concentration (denoted as exchangeable Cs, Ex-Cs) in the filtrates were measured by a Ge semiconductor detector.
To confirm adsorption of RCs on weathered biotite, after the incubation, soil sample was washed, sieved and collected weathered biotite larger than 5 mm. Obtained weathered biotite was fixed on the paper and placed in contact with an imaging plates (IP) for 7days. The IP image was scanned to detect radioactive substances.
With increasing in amount of clay minerals added to the RCs polluted soil samples, the concentration of Ex-Cs decreased where more decrease in Ex-Cs was observed for the sample at higher water content. Incubation period had no effect under the constant mass water content condition.
After the incubation under drying-wetting cycles for 28 days (7 cycles), the sample applied weathered biotite showed more reduction in the concentration of Ex-Cs as compared to that of the zeolite. Number of drying-wetting cycles, and thus incubation period, had an effect on RCs behavior.
IP image suggested radioactive substances could have transferred from the soil to weathered biotite.
This research was supported by grants from the Project of the NARO Bio-oriented Technology Research Advancement Institution (the special scheme project on regional developing strategy) and the Japan Society for the promotion of Science grant 15H02467.