REMOVAL OF CESIUM IONS FROM RADIOACTIVELY CONTAMINATED SOILS USING MICROWAVE TREATMENT

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<p>Radioactively contaminated soils sampled at Fukushima (Japan) underwent microwave treatment to remove cesium ions. An aqueous suspension (20 mL) containing 5.0 g of the soil (7.2×105 Bq/kg) and one of three chemical reagents was sealed in a Teflon vessel (4.0 cm i.d.×5.0 cm). The effects of the following three reagents were examined: 3.0 M Mg(NO3)2, 6.5 M NH4F/HF, and 1.5 M H2SO4. The vessel was irradiated with microwaves at 800 W for 3 min. After the vessel was cooled to room temperature, the contents were removed and centrifuged, and the radioactivity of the solid precipitate was measured. The elemental composition of the filtrate was determined using ICP-MS. The XRD patterns of the solid precipitates were recorded before and after the treatment. Results indicated that: (i) in the radioactive Cs+ ions leaching experiment with 3.0 M Mg(NO3)2 from a reference saponite, 85% 137Cs+ ions were desorbed after 3 min of microwave irradiation, indicating the effectiveness of the microwave treatment for radioactively contaminated soils, (ii) less than 5% of the radioactive Cs+ (or 137Cs+) ions were eliminated through ion-exchange with 3.0 M Mg(NO3)2; (iii) more than 90% of the 137Cs+ ions were effectively eliminated with 6.5 M NH4F/HF via dissolution of silica; (iv) approximately 70% of the 137Cs+ ions were eliminated with 1.5 M H2SO4 via dissolution of alumina. These results demonstrated that 137Cs+ ions in the soil were fixed firmly in clay minerals (possibly weathered biotite) and could be removed only when their adsorbing structures were disrupted.</p>

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