Sorption and retardation of strontium in saturated Chinese loess: experimental results and model analysis

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• 作者：Lijuan Huo^a ; ^b ; Tianwei Qian^a ; ^{twqian@yahoo.com} ; Junting Hao^a ; Dongye Zhao^b ; ^{zhaodon@auburn.edu}
• 关键词：Radionuclides ; Retardation factor (Rd) ; Strontium (Sr) ; Flow velocity ; Chinese loess
• 刊名：Journal of Environmental Radioactivity
• 出版年：2013
• 出版时间：February, 2013
• 年：2013
• 卷：116
• 期：Complete
• 页码：19-27
• 全文大小：421 K

文摘

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?cm³/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 SrCl₂ was used as a surrogate for the radioactive isotope (⁹⁹Sr) 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.