RUI: Where does all the molybdenum go? Evaluating the role of iron sulfides in molybdenum accumulation in marine sediments

该项目将研究沉积物硫化铁在去除海洋中溶解钼方面的作用。钼（Mo）是一种在海洋沉积物中发现的微量金属。在过去，它被用作低氧和高硫化物条件的指示。了解海洋氧合的历史对于监测现代沿海水域的低氧“死亡区”和预测气候变化对海洋的影响非常重要。然而，Mo在沉积物中积聚的过程尚不清楚。这个项目将使用实验室实验来研究溶液Mo和固体硫化铁之间的相互作用。这项研究将在一所本科院校进行。该研究将为来自STEM中历史上代表性不足的群体的学生提供结构化的经历进展。它将包括一个队列导师的方法，以支持学生在他们到达校园之前，并在他们的入门科学课程。暑期研究学生（即将升学的大三学生和大四学生）将参与这个项目的各个方面。这些三年级和四年级的学生也将作为研究队列学生（即将上升的二年级学生）的同伴导师，形成一个有效的研究团队。学生接触研究生院的机会将通过与宾夕法尼亚州立大学研究小组的会议来实现。最后，对地球化学的兴趣将通过在普通化学入门课程中开发环境主题的实验室模块来培养。这项工作的目的是澄清在海洋沉积物中的相对重要性：(1)Mo对铁硫化物的吸附，(2)在黄铁矿形成过程中Mo的保留和/或在结晶黄铁矿区域生长时Mo的排除，以及(3)可能形成独特的FeMoS产物。最近的研究表明，Mo从硫化水中的去除发生在亚稳硫化物铁的初始形成过程中，而Mo在这些前驱相转变为黄铁矿的热力学稳定形式的过程中被保留下来。在此基础上，将有可能通过以下方法确定硫化铁在海洋沉积物中Mo积累中的作用：1)合成亚稳态硫化铁，并评估不同条件下这些物种对Mo的吸附，以确定Mo硫代化，硫化铁表面化学和氧化还原行为的影响；2)监测这些材料向黄铁矿的转变，以确定不同的初始条件如何改变Mo的保留或掺入；3)建立一个模型，通过这些过程来追踪莫的命运，并协调不同的文献证据。了解硫化铁及其相变在Mo积累中的作用将为Mo作为古示踪剂的工作提供坚实的基础。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

The project will study the role of sediment iron sulfides in removing dissolved molybdenum from the ocean. Molybdenum (Mo) is a trace metal found in ocean sediments. It is used as an indicator of low-oxygen and high-sulfide conditions in the past. Understanding the history of ocean oxygenation is important for monitoring low-oxygen “dead zones” in modern coastal waters and predicting the impact of climate change on the oceans. However, the processes by which Mo accumulates in sediments are not well understood. This project will use laboratory experiments to study the interactions between solution Mo and solid iron sulfides. The research will be carried out at an undergraduate institution. The study will provide a structured progression of experiences for students from historically underrepresented groups in STEM. It will include a cohort-mentor approach to support students before they arrive on campus and throughout their introductory science courses. Summer Research Students (rising juniors and seniors) will be engaged in every aspect of this project. These juniors and seniors will also serve as peer mentors for Research Cohort students (rising sophomores), forming an effective research team. Student exposure to graduate school opportunities will occur through meetings with research groups at the Pennsylvania State University. Finally, interest in geochemistry will be fostered by developing an environmentally-themed laboratory module within an introductory General Chemistry course. The goal of this work is to clarify the relative importance in marine sediments of: (1) sorption of Mo to iron sulfides, (2) retention of Mo during the formation of pyrite and/or exclusion of Mo upon growth of crystalline pyrite domains, and (3) possible formation of a distinct FeMoS product. Recent work established that Mo removal from sulfidic waters occurs with the initial formation of metastable iron sulfides and Mo is retained during the transformation of these precursor phases to the thermodynamically stable form of pyrite. With this groundwork, it should be possible to conclusively determine the role that iron sulfides play in the accumulation of Mo in marine sediments by: 1) synthesizing metastable iron sulfides and evaluating Mo adsorption to these species under various conditions to determine the impact of Mo thiolation, iron sulfide surface chemistry, and redox behavior; 2) monitoring the transformation of these materials to pyrite to determine how various initial conditions alter the retention or incorporation of Mo; and 3) developing a model that traces the fate of Mo through these processes and reconciles the disparate literature evidence. Understanding the role that iron sulfides and their phase transformations play in Mo accumulation will provide a strong foundation for work that employs Mo as a paleotracer.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.