Bench scale percolation tests on radioactive Cs-contaminated soil in Fukushima and soil modified with water-absorbing polymer agent

Abstract

The reuse of removed soil generated from decontamination projects in Fukushima as a recycled material for the construction of embankments has been under consideration for the sake of reducing the volume of this soil for its final disposal. Agents containing water-absorbing polymers are used in Fukushima to modify the removed soil in order to increase the separation efficiency of foreign materials and to improve the easiness of handling. As the reuse of modified soil containing organic water-absorbing materials, such as a superabsorbent polymer, is rather rare in the geotechnical field, it necessitates an investigation into the impact of the modifying agent on the leachate quality to ensure the environmental safety of the recycling project. In this study, therefore, bench scale percolation tests were conducted to examine the changes in the leachate quality of the removed soil with and without modification by an agent containing a superabsorbent polymer. The tests lasted for more than 950 days (liquid/solid ratio of over 10). The peak 137Cs concentration in the leachate from the removed soil was 8.6 Bq/L and the accumulated leaching ratio was 0.243 %. The leaching of 137Cs from the modified soil decreased by 60 % after mixing the removed soil with a 3 % water-absorbing polymer agent. The leaching of K+ and ammonia nitrogen (NH4+-N) was 40 % and 60 % lower, respectively, after the soil modification, while the accumulated amount of leaching of the dissolved organic carbon in the initial stage was 60 % higher. The total leachate amount collected from the modified soil was 4 % lower than that collected from the removed soil.

Keywords

• Removed soil
• Water-absorbing polymer modifying agent
• Lysimeter
• Leachate quality
• Radioactive cesium