Abstract
A hydrobiotite (HBT) clay contains more cesium (Cs)-specific adsorption sites than illitic clay, and the capacity of frayed edge sites can increase as the weathering of micaceous minerals proceeds. Thus, Cs can be selectively adsorbed to HBT clay. In this study, we investigated the removal efficiency of non-radioactive (133Cs) and radioactive (137Cs) Cs from HBT, using oxalic acid. We found the minimum optimal concentration of 0.15 M oxalic acid removed more than 90% of Cs. Subsequently, cations and Cs ions were removed using Ca(OH)2 and sodium tetraphenylborate (NaTPB) to treat the washing wastewater generated at the optimum concentration of the desorbent (0.15 M oxalic acid). In order to remove cations and heavy metal ions in the waste solution, Ca(OH)2 was treated at a mass ratio of 0.025 g/mL and pH 9–10 to derive optimal conditions. As a final step, to remove Cs, NaTPB was treated with a mass ratio of 2 mg/mL and reduced to below 0.1 mg/L Cs to find the optimal dose. The novelty of this study is that the amount of radioactive waste can be drastically reduced by removing the non-radioactive cations and heavy metals separately in the first step and removing the remaining radioactive Cs in the second step.
Highlights
The widespread radioactive contamination following the 2011 Fukushima nuclear power plant disaster has spurred research on the removal of radionuclides from soil to reduce radioactivity in contaminated areas
Cesium is generally adsorbed to the interlayer of these clay minerals, and irreversible adsorption occurs in the frayed edge sites (FES) and is barely removed by conventional soil treatment methods
Nakao et al (2008) observed that vermiculitic clay contained more Cs-specific adsorption sites than illitic clay based on radiocesium interception potential analysis, and the capacity of FES can increase as the weathering of micaceous minerals proceeds [8]
Summary
The widespread radioactive contamination following the 2011 Fukushima nuclear power plant disaster has spurred research on the removal of radionuclides from soil to reduce radioactivity in contaminated areas. Cesium (Cs) remains the most concerning radionuclide due to its strong affinity with clay minerals in soil and the fact that it continues to accumulate in topsoil [1,2]. Cesium is generally adsorbed to the interlayer of these clay minerals, and irreversible adsorption occurs in the frayed edge sites (FES) and is barely removed by conventional soil treatment methods. Yamada et al (2014) reported that the Cs adsorption capacity of clay increased with the degree of biotite weathering [7]. Nakao et al (2008) observed that vermiculitic clay contained more Cs-specific adsorption sites than illitic clay based on radiocesium interception potential analysis, and the capacity of FES can increase as the weathering of micaceous minerals proceeds [8].
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