University of Leeds, UK.
National Nuclear Laboratory Ltd., Sellafield, CA20 1PG, UK.
J Environ Radioact. 2024 Jul;277:107451. doi: 10.1016/j.jenvrad.2024.107451. Epub 2024 Jun 7.
Strontium-90 (Sr) is a major contaminant at nuclear legacy sites. The mobility of Sr is primarily governed by sorption reactions with sediments controlled by high surface area phases such as clay and iron oxides. Sr adsorption was investigated in heterogeneous unconsolidated aquifer sediments, analogous to those underlying the UK Sellafield nuclear site, with grainsizes ranging from gravels to clays. Batch sorption tests showed that a linear K adsorption model was applicable to all grainsize fractions up to equilibrium [Sr] of 0.28 mmol L. Sr sorption values (K; Langmuir q) correlated well with bulk sediment properties such as cation exchange capacity and surface area. Electron microscopy showed that heterogeneous sediments contained porous sandstone clasts with clay minerals (i.e. chlorite) providing an additional adsorption capacity. Therefore, gravel corrections that assumed that the > 2 mm fractions are inert were not appropriate and underestimated K adsorption coefficients. However, K values measured from sieved sediment fractions, were effectively adjusted to within error of K using a surface area dependant gravel correction based on particle size distribution data. Amphoteric pH dependent Sr sorption behaviour observed in batch experiments was consistent with cation exchange modelling between pH 2-7 derived from the measured cation exchange capacities. Above pH 7 model fits were improved by invoking a coupled cation exchange/surface complexation which allowed for addition sorption to iron oxide phases. The overall trends in Sr sorption (at pH 6.5-7) produced by increasing solution ionic strength was also reproduced in cation exchange models. Overall, the results showed that Sr sorption to heterogeneous sediment units could be estimated from K data using appropriate gravel corrections, and effectively modelled using coupled cation exchange and surface complexation processes.
锶-90 (Sr) 是核遗留场址的主要污染物。Sr 的迁移性主要受吸附反应控制，而吸附反应则由粘土和氧化铁等高表面积相控制。在类似于英国塞拉菲尔德核场址下面的非固结含水层沉积物中，对 Sr 吸附进行了研究，颗粒大小从砾石到粘土不等。批式吸附试验表明，线性 K 吸附模型适用于所有颗粒大小分数，直至达到 0.28 mmol L 的平衡 [Sr]。Sr 吸附值 (K; Langmuir q) 与阳离子交换容量和表面积等大量沉积物特性密切相关。电子显微镜显示，非均匀沉积物含有多孔砂岩碎屑和粘土矿物（即绿泥石），提供了额外的吸附能力。因此，假设 > 2 mm 级分惰性的砾石校正并不合适，并且低估了 K 吸附系数。然而，通过使用基于粒径分布数据的表面积相关砾石校正，可以有效地将筛分沉积物级分测量的 K 值调整到误差范围内。在批处理实验中观察到的两性 pH 依赖 Sr 吸附行为与 pH 2-7 之间的阳离子交换模型一致，该模型源自测量的阳离子交换容量。在 pH 7 以上，通过调用允许向氧化铁相添加吸附的耦合阳离子交换/表面络合，模型拟合得到了改善。在增加溶液离子强度时，Sr 吸附（在 pH 6.5-7 时）的总体趋势也在阳离子交换模型中得到了重现。总体而言，结果表明，可以使用适当的砾石校正从 K 值估算非均匀沉积物单元中的 Sr 吸附，并且可以通过耦合阳离子交换和表面络合过程有效地对其进行建模。
