Institute of Environmental Science, Taiyuan University of Science and Technology, Taiyuan, Shanxi 030024, PR China.
J Environ Radioact. 2013 Feb;116:19-27. doi: 10.1016/j.jenvrad.2012.09.002. Epub 2012 Oct 18.
Geological burial and landfill have been widely practiced for disposal of nuclear wastes. However, radionuclides in the waste leachate from landfill facilities can contaminate soil and groundwater. Chinese loess is widely distributed in China and has been involved in large-scale disposal of nuclear wastes. Consequently, there has been an urgent need for understanding and predicting the fate and transport of contaminants in both vadose and saturated zones in the loess. In this paper, the distribution coefficient (K(d)) values of Strontium between a Chinese loess and groundwater were determined in batch experiments. The isotherm could be described with nearly linear isotherm model, which resulted in a K(d) value of 40.0 cm(3)/g. Based on this K(d) value, the retardation factor (R(d), the ratio of pore water velocity to solute transport velocity) value was calculated to be 112.6. As an alternative approach, the R(d) value was also determined through independent column experiments and transport modeling. Bromide (Br(-)) was used as a non-reactive tracer, and reagent SrCl(2) was used as a surrogate for the radioactive isotope ((99)Sr) in the experiment because they share the same adsorption and transportation characteristics. An equilibrium-based model and a two-region non-equilibrium model were employed to interpret the column sorption data of Sr. The computer program, CXTFIT 2.1, was used to estimate the parameters by simulating the breakthrough and retention curves of Br and Sr, respectively. The resultant D (dispersion coefficient) value for Sr transport was much lower than that of Br(-), indicating the important effect of chemical non-equilibrium of Sr in the loess system. The observed Sr retention curves in the loess were best modeled by the two-site transport model. The R(d) value determined from batch equilibrium tests differed markedly from that determined from the column transport experiments, and the R(d) value decreased with increasing pore-water velocity. The relationship between D and pore water flow velocity (v) was determined as a D = 1.192v(1.26). The results from this work indicate that the strong flow and non-equilibrium effects on the transport parameters (R(d) and D) must be taken into account in Sr transport modeling.
地质埋藏和垃圾填埋场已被广泛用于处理核废料。然而，垃圾填埋场设施中的放射性核素沥滤液会污染土壤和地下水。中国黄土广泛分布在中国，并已参与大规模处理核废料。因此，迫切需要了解和预测黄土中饱水带和非饱水带中污染物的运移和归宿。在本文中，通过批量实验确定了 Sr 在黄土与地下水之间的分配系数（Kd）值。等温线可以用近乎线性的等温线模型来描述，从而得到 Kd 值为 40.0 cm3/g。基于此 Kd 值，计算得到阻滞因子（Rd，即孔隙水速度与溶质运移速度之比）值为 112.6。作为替代方法，还通过独立柱实验和运移模型确定了 Rd 值。溴化物（Br-）用作非反应示踪剂，而试剂 SrCl2 用作实验中放射性同位素（99Sr）的替代物，因为它们具有相同的吸附和运移特征。采用基于平衡的模型和两区非平衡模型来解释 Sr 的柱吸附数据。使用程序 CXTFIT 2.1 通过模拟 Br 和 Sr 的穿透和保留曲线来分别估计参数。Sr 传输的 D（弥散系数）值远低于 Br-，表明 Sr 在黄土系统中的化学非平衡的重要影响。观察到的 Sr 在黄土中的保留曲线通过两位置传输模型得到了很好的模拟。通过批量平衡测试确定的 Rd 值与通过柱传输实验确定的值有明显差异，并且 Rd 值随孔隙水速度的增加而降低。D 与孔隙水流速度（v）之间的关系为 D = 1.192v（1.26）。该研究结果表明，在 Sr 运移建模中必须考虑到强流和非平衡效应对运移参数（Rd 和 D）的影响。
