不同来源腐殖酸与U(Ⅵ)结合特性差异的实验与分子动力学模拟

Experiments and Molecular Dynamics Simulations on Nature Differences of Humic Acids From Different Origin for Binding Characteristics of U(Ⅵ)

采用元素分析、化学滴定、光谱分析等方法对三种不同来源腐殖酸(AHA、YHA和EHA)进行了分析表征和官能团测定,系统地研究了不同pH、时间、温度和离子强度下它们与U(Ⅵ)的配位行为,并借助分子动力学模拟方法研究了不同腐殖酸模型与U(Ⅵ)相互作用的溶液动力学,探究了动力学过程、配位结构和作用机理。实验结果表明:三种不同来源腐殖酸的元素组成和官能团类型基本相似,均具有较强的芳香性和共轭双键,但也略有差异。YHA的低H/C原子比、高酸度和高官能团含量表明其腐殖化程度较高,存在高的共轭性或芳香族成分,具有较强的金属配位能力。不同来源腐殖酸与U(Ⅵ)的配位行为存在显著差异,且受pH、时间、温度和离子强度的明显影响。分子动力学模拟表明:单个腐殖酸分子与U(Ⅵ)的配位在很短时间内完成,主要的结合位点为羧基,在水溶液中可自发形成具有显著差异的HA-U(Ⅵ)配位结构,其主要驱动力为静电相互作用。上述研究结果不仅有助于进一步理解腐殖酸存在下铀在环境中的化学行为,对放射性废物的地质处置及安全性评价也具有参考价值。

Three humic acids(AHA,YHA,and EHA)from different origin were characterized by elementary analysis,UV-Vis and FTIR spectra,and the functional groups were determined by chemical titration.The effects of pH,time,temperature,and ionic strength on the complexation of three HAs with U(Ⅵ)were investigated systematically.Meanwhile,the interaction of U(Ⅵ)with three HA models in aqueous phase was studied by means of molecular dynamics(MD)simulations,and the dynamics,coordination structures,and interaction mechanism were further explored.The experimental results show that the elemental composition and functional group types of three HAs from different origin are basically similar,with strong aromaticity and conjugated double bonds,but slight differences can be also observed between them.The low H/C atom ratio,high acidity,and high content of functional groups indicate that YHA has high humification degree,high conjugation or aromatic composition,and strong metal complexation ability.The complexation behavior of three HAs with U(Ⅵ)are significantly different,which is substantially affected by pH,time,temperature,and ionic strength.MD simulations demonstrate that the complexation of single HA with U(Ⅵ)can be completed in a short time,and the main binding sites are carboxyl groups.The coordination structures formed by HAs with U(Ⅵ)in aqueous solution have quite differences,and the main driving force is electrostatic interaction.The results reported here are beneficial to further understanding the chemical behavior of uranium in the presence of HA,and provide data and reference for the geological disposal and safety evaluation of radioactive wastes.