Um Wooyong, Serne R Jeffrey, Last George V, Clayton Ray E, Glossbrenner Ellwood T
Pacific Northwest National Laboratory, Richland, WA 99352, USA.
J Contam Hydrol. 2009 Jun 26;107(1-2):82-90. doi: 10.1016/j.jconhyd.2009.04.003. Epub 2009 Apr 16.
This manuscript addresses the consequences of the common practice of assuming that the gravel fraction of sediments does not participate in sorption reactions and thus sorption quantified by the distribution coefficient (K(d)) construct can be estimated from laboratory tests on sediments less than 2 mm size fraction. However, this common assumption can lead to inaccurate estimates of the mobility and sorption affinity of many radionuclides (e.g., Tc, U, and Np) on gravel dominated sediments at the Hanford Site and other locations. Laboratory batch sorption experiments showed that the distribution coefficients measured using only sediment less than 2 mm size fraction and correcting for inert gravel fraction were not in agreement with those obtained from the bulk sediments including gravel (larger than 2 mm size fraction), depending on the radionuclide. The least reactive radionuclide, Tc had K(d) values for bulk sediment with negligible deviations from the inert gravel corrected K(d) values measured on less than 2 mm size fraction. However, differences between measured K(d) values using sediment less than 2 mm size fraction and the K(d) values on the bulk sediment were significant for intermediately and strongly reactive radionuclides such as U and Np, especially on the sediment with gravel fractions that contained highly reactive sites. Highly reactive sites in the gravel fraction were attributed to the presence of Fe oxide coatings and/or reactive fracture faces on the gravel surfaces. Gravel correction factors that use the sum of the K(d)(,<2 mm) and K(d)(,>2 mm) values to estimate the K(d) for the bulk sediment were found to best describe K(d) values for radionuclides on the bulk sediment. Gravel correction factors should not be neglected to predict precisely the sorption capacity of the bulk sediments that contain more than 30% gravel. In addition, more detailed characterization of gravel surfaces should be conducted to identify whether higher reactive sorbents are present in the gravels.
本手稿探讨了一种常见做法的后果，即假定沉积物的砾石部分不参与吸附反应，因此通过分配系数（K(d)）构建所量化的吸附可根据对小于2毫米粒径级分的沉积物进行的实验室测试来估算。然而，这种常见假设可能导致对许多放射性核素（如锝、铀和镎）在汉福德场地及其他地点以砾石为主的沉积物上的迁移率和吸附亲和力的估计不准确。实验室批量吸附实验表明，仅使用小于2毫米粒径级分的沉积物并校正惰性砾石部分后测得的分配系数，与从包括砾石（大于2毫米粒径级分）的整体沉积物中获得的分配系数不一致，这取决于放射性核素。反应性最低的放射性核素锝，其在整体沉积物中的K(d)值与在小于2毫米粒径级分上测得的经惰性砾石校正的K(d)值偏差可忽略不计。然而，对于中等反应性和强反应性的放射性核素（如铀和镎），尤其是在含有高反应性位点的砾石部分的沉积物上，使用小于2毫米粒径级分的沉积物测得的K(d)值与整体沉积物上的K(d)值之间存在显著差异。砾石部分的高反应性位点归因于砾石表面存在铁氧化物涂层和/或反应性断裂面。发现使用K(d)(<2毫米)和K(d)(>2毫米)值之和来估算整体沉积物的K(d)的砾石校正因子最能描述放射性核素在整体沉积物上的K(d)值。为了精确预测含有超过30%砾石的整体沉积物的吸附能力，不应忽略砾石校正因子。此外，应更详细地表征砾石表面，以确定砾石中是否存在更高反应性的吸附剂。
