Magnetic flocculants and selective adsorbents for the decontamination of radioactive and acidic soil-washing effluent

Abstract

We demonstrate that radioactive 137Cs-suspended soil and 137Cs+ ions in the effluent can be sequentially removed, enabling the effluent to be reused or released. Specially synthesized coagulant-flocculants and adsorbents were used to remove Cs-suspended soils and Cs+ ions under strongly acidic conditions. Polyethyleneimine coated magnetic nanoparticles (PEI-MNPs) was found to be the best coagulant-flocculants for removing Cs-suspended soil among various coagulant-flocculants, including inorganic, organic, and organic-inorganic ones. To optimize the separation conditions, such as the dosage and composition of the coagulant-flocculants and adsorbents, a nickel potassium hexacyanoferrate -embedded polyacrylonitrile (NiFC/PAN)-3.5, defined as a NiFC/PAN weight ratio of 3.5, was used to successfully remove Cs+ ions in nonradioactive and radioactive tests, meeting the release criterion of 50 Bq L−1 (South Korea). In the first step, the radioactivity of the effluent was reduced from 380 to 300 Bq L−1 by separating 137Cs-suspended soils with PEI-MNP coagulant-flocculants. In the next step, 137Cs ions were substantially removed using NiFC/PAN, resulting in a decrease of the radioactivity from 300 to 20 Bq L−1, which meets the release criterion. These results suggest that the proposed process is a potentially useful and effective method for treating radioactive effluent after soil washing.