Key Laboratory of Radiation Physics and Technology of the Ministry of Education, Institute of Nuclear Science and Technology, Sichuan University, Chengdu, 610064, PR China.
Key Laboratory of Nuclear Environmental Simulation and Evaluation Technology, China Institute for Radiation Protection, Taiyuan, 030006, PR China.
J Environ Radioact. 2024 Sep;278:107493. doi: 10.1016/j.jenvrad.2024.107493. Epub 2024 Jul 5.
The presence of carbonates or humic substances (HS) will significantly affect the species and chemical behavior of U(VI) in solution, but lacking systematic exploration of the coupling effect of carbonates and HS under near real environmental conditions at present. Herein, the sorption behavior of U(VI) on illite was systematically studied in the co-existence of carbonates and HS including both humic acid (HA) and fulvic acid (FA) by batch technique. The distribution coefficients (K) increased as function of time and temperature but decreased with increasing concentrations of initial U(VI), Ca, and Mg, as well as ion strength. At pH 2.0-10.5, the K values first increased rapidly and then decreased visibly, with its maximum value appearing at pH 5.0, owning to the changes in the interaction between illite and the dominant species of U(VI) from electrostatic attraction to electrostatic repulsion. The sorption was a heterogeneous, spontaneous, and endothermic chemical process, which could be well described by pseudo-second-order kinetic and Flory-Huggins isotherm models. When carbonates and HA/FA coexisted, the K values always increased first and then decreased as a function of pH, with the only difference for HA and FA being the key pH (pH) at which the promoting and inhibiting effects on the sorption of U(VI) onto illite undergo a transition. The carbonates and HS have a synergistic inhibitory effect on the U(VI) sorption onto illite at pH 7.8. FTIR and XPS spectra demonstrated that the hydroxyl groups on the illite surface and in the HS were involved in U(VI) sorption on illite in the presence of carbonates. These results provide valuable data for a deeper understanding of U(VI) migration in geological media.
碳酸盐或腐殖质（HS）的存在会显著影响溶液中 U(VI)的物种和化学行为，但目前缺乏在接近实际环境条件下对碳酸盐和 HS 耦合效应的系统探索。在此，通过批量技术系统研究了在碳酸盐和 HS（包括腐殖酸（HA）和富里酸（FA））共存的情况下，U(VI)在伊利石上的吸附行为。分配系数（K）随时间和温度的增加而增加，但随初始 U(VI)、Ca 和 Mg 浓度以及离子强度的增加而降低。在 pH 2.0-10.5 范围内，K 值先快速增加，然后明显下降，最大值出现在 pH 5.0，这是由于伊利石与 U(VI)的主要物种之间的相互作用从静电吸引变为静电排斥所致。吸附是一种非均相、自发和吸热的化学过程，可用准二级动力学和 Flory-Huggins 等温线模型很好地描述。当碳酸盐和 HA/FA 共存时，K 值随 pH 的变化总是先增加后减少，HA 和 FA 的唯一区别在于促进和抑制 HS 对 U(VI)在伊利石上吸附的关键 pH（pH）发生了转变。碳酸盐和 HS 对 U(VI)在伊利石上的吸附具有协同抑制作用，在 pH 7.8 时效果最为显著。FTIR 和 XPS 谱图表明，碳酸盐存在时，伊利石表面和 HS 中的羟基参与了 U(VI)在伊利石上的吸附。这些结果为深入了解 U(VI)在地质介质中的迁移提供了有价值的数据。
