Development of tungsten stable isotope analysis for constraining sorption mechanisms and tracking the transport and fate of tungsten

在这个由国家科学基金会化学部环境化学项目资助的项目中，印第安纳大学的Laura Wasylenki教授开发了一种新的方法来评估矿物颗粒的吸附如何以及在多大程度上改变了受污染环境中有毒金属的流动性。新的方法能够更好地预测许多金属的运输和命运，但这里的重点是钨(W)，它最近被美国环保局宣布为“新出现的令人担忧的污染物”。这种方法利用了钨的稳定同位素比(例如W-183/W-182)的变化，这对涉及金属原子的化学键的数量、长度和强度的差异非常敏感。稳定同位素系统学被用来探索环境中实际浓度下溶解的W与多孔介质之间的分子尺度相互作用，但传统的光谱技术如扩展X射线吸收精细结构(EXAFS)分析无法获得这些相互作用。与此同时，印第安纳大学发起了一项创新的信息工作，以教育校园社区，让他们了解日常物品中的金属来自哪里，以及从地球上获取这些资源会带来什么危险和后果。在科学外展办公室和Wasylenki教授的研究学生的帮助下，在大学可持续发展办公室的实习生们开发的一系列标牌上展示了一系列问答题和QR(二次型残留物)代码链接。简单的吸附实验和精确的同位素分析产生了关于W在四个常见吸着剂相上吸附时同位素分馏的定量信息。研究首先在高浓度下进行，在那里EXAFF直接提供关于配位化学和吸附机制的信息，然后在与场相关的条件下进行研究，在那里同位素可能是限制吸附机制的唯一途径。计算量子力学模型是对实验、同位素分析和EXAFS分析的补充。模拟研究预测了W的单体和聚合物种之间预期的同位素偏移，W在溶液中形成和作为吸附的络合物形成。这项工作推进了人们对钨环境化学的了解，并使稳定的金属同位素能够被用作追踪金属污染物的运输和去向的工具。

In this project funded by the Environmental Chemistry Program in the Chemistry Division at the National Science Foundation, Professor Laura Wasylenki of Indiana University (IU) develops a new way to assess how and to what extent sorption to mineral particles changes the mobility of toxic metals in contaminated settings. The new approach enables better prediction of the transport and fate for many metals, but the focus here is on tungsten (W), recently declared an "emerging contaminant of concern" by the US EPA. This approach takes advantage of variations in the stable isotope ratios of tungsten (e.g., W-183/W-182), which are highly sensitive to differences in the numbers, lengths, and strengths of chemical bonds involving the metal atoms. Stable isotope systematics are used to probe the molecular-scale interactions between dissolved W and porous media at realistic concentrations in the environment, but inaccessible to conventional spectroscopic techniques such as extended X-ray absorption fine structure (EXAFS) analysis. Concurrently, an innovative informational effort is launched at Indiana University to educate the campus community about where metals in everyday objects come from and what hazards and consequences are associated with taking those resources from the Earth. A series of signs are displayed on campus with quiz questions and QR (quadratic residue) code links that are developed by interns in IU's Office of Sustainability, with assistance from the Office of Science Outreach and Professor Wasylenki's research students.Simple sorption experiments and precise isotope analyses yield quantitative information about isotope fractionation during sorption of W onto four common sorbent phases. Studies are made first at high concentrations, where EXAFS provide information directly about coordination chemistry and sorption mechanisms, and then at field-relevant conditions, where isotopes may be the only way to constrain sorption mechanisms. Computational quantum mechanical modeling complement the experiments, isotope analyses, and EXAFS analyses. The modeling studies predict the expected isotope offsets between monomeric and polymeric species of W, which form in solution and as sorbed complexes. The work advances what is known about the environmental chemistry of tungsten and enables stable metal isotopes to be used as a tool for tracking transport and fate of metal contaminants.