Pacific Northwest National Laboratory, Richland, Washington, 99352 United States.
Environ Sci Technol. 2014;48(3):1745-52. doi: 10.1021/es404224j. Epub 2014 Jan 13.
The effect of subgrid heterogeneity in sediment properties on the rate of uranyl[U(VI)] desorption was investigated using a sediment collected from the U.S. Department of Energy Hanford site. The sediment was sieved into 7 grain size fractions that each exhibited different U(VI) desorption properties. Six columns were assembled using the sediment with its grain size fractions arranged in different spatial configurations to mimic subgrid heterogeneity in reactive transport properties. The apparent rate of U(VI) desorption varied significantly in the columns. Those columns with sediment structures leading to preferential transport had much lower rates of U(VI) desorption than those with relatively homogeneous transport. Modeling analysis indicated that the U(VI) desorption model and parameters characterized from well-mixed reactors significantly overpredicted the measured U(VI) desorption in the columns with preferential transport. A dual domain model, which operationally separates reactive transport properties into two subgrid domains, improved the predictions significantly. A similar effect of subgrid heterogeneity, albeit to a lesser degree, was observed for denitrification, which also occurred in the columns. The results imply that subgrid heterogeneity is an important consideration in extrapolating reaction rates from the laboratory to field.
使用取自美国能源部汉福德场地的沉积物，研究了亚网格尺度上沉积物性质的不均匀性对铀酰[U(VI)]解吸速率的影响。将沉积物筛分为 7 个粒级，每个粒级均表现出不同的 U(VI)解吸性质。使用具有不同空间配置的粒级来组装 6 根柱，以模拟反应传输性质的亚网格不均匀性。柱中的 U(VI)解吸速率明显不同。那些导致优先传输的沉积物结构的柱子的 U(VI)解吸速率远低于那些具有相对均匀传输的柱子。模型分析表明，从充分混合的反应器中得到的 U(VI)解吸模型和参数显著高估了优先传输柱中测量的 U(VI)解吸速率。操作上将反应传输性质分离为两个亚网格域的双域模型显著改善了预测结果。亚网格不均匀性也对反硝化产生了类似的影响，尽管程度较小，反硝化也发生在这些柱中。结果表明，在将反应速率从实验室外推到现场时，亚网格不均匀性是一个重要的考虑因素。
