Sorption Behavior of Selenium(-II) on Rocks under Reducing Conditions

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The sorption of radionuclides on rocks is an important factor for performance assessment of geologic disposal of radioactive wastes. Batch sorption experiments under reducing conditions were carried out to investigate the sorption behavior of selenium onto granodiorite, sandy mudstone, tuffaceous sandstone, and their major constituent minerals and accessory minerals. Rock cores and groundwater employed in the experiments were sampled with special care to avoid exposing the cores and groundwater to air to minimize their oxidation. Selenium was spiked as HSe− and Se42− in the experimental solutions, and reducing conditions were maintained throughout the sorption periods. Distribution coefficients, Kd (m3 kg−1), were obtained in the ranges of 2.2×10−4 to 4.0×10−3 m3 kg−1 for granodiorite, 3.3×10−2 to 5.6×10−2 m3 kg−1 for sandy mudstone, and 2.9×10−2 to 8.2×10−2 m3 kg−1 for tuffaceous sandstone at pHs 8.5 to 11.5. The dominant sorbent minerals for selenium over a neutral to alkaline pH range were determined to be biotite for the granodiorite samples and pyrite for the sandy mudstone and tuffaceous sandstone samples.
2011-02-01