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

在这个由美国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污染环境中有毒金属的迁移性。新方法可以更好地预测许多金属的运输和命运，但这里的重点是钨(W)，最近被美国环保署宣布为“令人担忧的新兴污染物”。这种方法利用了钨稳定同位素比率的变化（例如，W-183/W-182），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。稳定同位素系统用于探测环境中实际浓度下溶解W和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）分析无法实现。与此同时，印第安纳大学发起了一项创新的信息努力，向校园社区宣传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害和后果。在科学拓展办公室和Wasylenki教授的研究学生的帮助下，印第安纳大学可持续发展办公室的实习生开发了一系列带有测试问题和QR（二次残数）代码链接的校园标牌。简单的吸附实验和精确的同位素分析得到了W在四种常见吸附剂相上吸附过程中同位素分馏的定量信息。研究首先在高浓度下进行，其中EXAFS直接提供有关配位化学和吸附机制的信息，然后在现场相关条件下进行，同位素可能是限制吸附机制的唯一方法。计算量子力学建模补充实验，同位素分析和EXAFS分析。模型研究预测了单体和聚合物W之间的预期同位素偏移量，它们在溶液中形成并作为吸附复合物。这项工作推进了对钨的环境化学的了解，并使稳定的金属同位素能够用作跟踪金属污染物的运输和命运的工具。

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.