SusChEM: Collaborative Research: Influence of Fe2+- catalyzed recrystallization on Fe oxide reactivity and C stabilization

铁(Fe)是地球上第四丰富的元素，也是所有生命(从微生物到人类)的关键营养素。铁矿物是我们生活中重要的一部分：它们是我们脚下土壤的一部分；是我们汽车上的铁锈；是我们计算机上的硬盘；是地球和火星上的岩石。这些微小的、通常是纳米级的颗粒是我们周围大多数红色、黄色、绿色和黑色的原因，它们通过生物驱动的氧化亚铁(Fe3)和还原亚铁(Fe2)之间的氧化还原循环深刻地影响着我们的水、空气和土壤的质量。这些铁矿物捕获了土壤和沉积物中大量的有机碳(C)，还可以在缺氧土壤和沉积物中代替氧气进行厌氧呼吸，将有机质氧化和矿化为二氧化碳。对碳驱动的气候变化的日益关注为更好地理解管理土壤和沉积物中碳(C)储存的铁和碳过程之间的耦合提供了强大的动力。这项工作的研究成果将为陆地对气候变化的反应以及水质保护(如砷释放)和工程水处理系统提供重要的见解，从而造福社会。该项目将为高中(HS)和本科生(UG)在科学领域代表性不足的群体提供真实的研究经验。这将通过让长期的UG研究人员参与该项目来实现；为HS的初中和高年级学生提供历史上大学入学率较低的机会，以参与真正的暑期研究活动；并作为规模的一部分，为HS和UG学生提供直接的师生指导--Matters？研讨会和夏季土壤研究所。这项研究的总体目标是了解铁与有机碳土壤和沉积物之间的复杂氧化还原动力学。在还原环境中，溶解的Fe2可以催化铁氧化物重结晶成化学性质相似或截然不同的新矿物相。对于纯Fe相，已经观察到了Fe2催化的再结晶过程，但作为动员(或隔离)有机C的途径尚未被探索。此外，有机C的存在也可能改变再结晶过程，对Fe的反应性和同位素分馏具有重要意义。研究人员将调查Fe2催化的重结晶如何影响有机碳和铁矿物的反应性。为了做到这一点，研究人员将进行一系列铁同位素示踪实验，以量化由一系列铁氧化物和各种天然有机物合成的模型Fe-C组合中Fe2催化的再结晶程度。将测量Fe氧化物对微生物和化学溶解的敏感性的变化，以及Fe同位素分馏和Fe-C组合重结晶后的C有效性。

Iron (Fe) is the fourth most abundant element on Earth and a critical nutrient for all life (from microorganisms to humans). Iron minerals are an important part of our lives: they are part of the soil beneath our feet; the rust on our cars; the hard drives in our computers; and the rocks on Earth and Mars. These tiny, often nanoscale, particles are responsible for most of the red, yellow, green, and black colors around us and they profoundly influence the quality of our water, air, and soil through biologically-driven redox cycling between oxidized ferric iron (Fe3+) and reduced ferrous iron (Fe2+). These Fe minerals trap much of the organic carbon (C) in soils and sediments and can also take the place of oxygen in anaerobic respiration, oxidizing and mineralizing organic matter to CO2 in anoxic soils and sediments. Increasing concerns about carbon driven climate change provides strong motivation to better understand the coupling between Fe and C processes that govern storage of carbon (C) in soils and sediments. The research findings from this work will benefit society by providing important insights into terrestrial response to climate change, as well as water quality preservation (such as arsenic release), and engineered water treatment systems. This project will provide authentic research experiences for individuals from groups underrepresented in the sciences at the upper high school (HS) and undergraduate (UG) levels. This will be accom-plished by involving long-term UG researchers in the project; providing HS junior and seniors from schools with historically low-college enrollment opportunities to participate in authentic summer research activities; and providing direct faculty-student instruction for HS and UG students as part of a ?Scale-Matters? workshop and Summer Soil Institute. The overall goal of this research project is to understand the complex redox dynamics between Fe and organic C soils and sediments. In reducing environments, dissolved Fe2+ can catalyze Fe oxides to recrystallize into new mineral phases with similar or drastically different chemical properties. This process, Fe2+- catalyzed recrystallization, has been observed for pure Fe phases, but has yet to be explored as a pathway for mobilizing (or sequestering) organic C. Additionally, the presence of organic C is also likely to alter the recrystallization process with important implications for the Fe reactivity and isotope fractionation. The investigators will investigate how Fe2+- catalyzed recrystallization influences organic C and Fe mineral reactivity. To do this, the investigators will conduct a series of Fe isotope tracer experiments to quantify the extent of Fe2+- catalyzed recrystallization in model Fe-C assemblages synthesized from a range of Fe oxides and diversity of natural organic matter. Changes in Fe oxide susceptibility to microbial and chemical dissolution will be measured, along with Fe isotopic fractionation, and C availability following recrystallization of the Fe-C assemblages.