Abstract
Soil washing is seen as a volume reduction/waste minimization technology for treatment of radiocesium (radio-Cs) contaminated soils. However, little information relative to specific application and potential effectiveness of the soil washing process exists that applies to radio-Cs contaminated soils in Fukushima. The objective of this experimental study was to understand the performance and validity of soil washing for the radio-Cs contaminated soils. Soil washing performance with a trade-off between the removal efficiency of radio-Cs and the volume reduction rate of feed soils was evaluated after an examination of each radio-Cs balance at every stage of soil washing, namely wet-sieving, hydrocyclone, and scrubbing-flotation.
As a result of this study, following observations were made; 1) the removal efficiencies of cyclone system were at around 70% of radio-Cs, and the efficiencies were greatly improved to 84~87%, when the cyclone system was combined with the scrubbing-flotation system, 2) the sludge volume was slightly increased when the cyclone system was combined with the ‘chemical scrubbing-flotation’. 3) ‘chemical scrubbing-flotation’ was useful for improving the removal efficiencies of radio-Cs as well as minimizing the sludge volume, 4) the treated water was good for reuse, because the radio-Cs was below the detectable level (< 10 Bq/kg), 5) the radio-Cs content of clean products was less than 3,000 Bq/kg as compared to the feed soils of approximate 20,000 Bq/kg, 6) the volume reduction rate of feed soils ranged from 70 to 80%, and 7) most of the organic matter in feed soils was concentrated into sludge cake.
The above results indicate that the soil washing system with the chemical scrubbing flotation makes it possible to achieve both high removal efficiency of radio-Cs and a high volume reduction rate of feed soils, and can be practically used in Fukushima for remediation of soils.
