Time-Resolved Diffraction Studies of Soil-Forming Mineral Reactions

智力上的功绩。这项提议的主要研究人员(PI)正在寻求资金，以将时间分辨衍射的推力扩展到对土壤中金属循环至关重要的三个领域：1)生物矿化；2)氢氧化物的成核和生长；以及3)氧化还原反应期间稳定的同位素分馏。事实证明，在环境反应池设计和X射线衍射(XRD)数据收集方面的最新进展，使我们能够将速率定律与支配矿物与流体和气体相互作用的结晶学机制结合起来。PI对时间分辨的X射线衍射数据进行了密集的Rietveld分析，提供了层状氧化锰(水钠锰矿)交换一种阳离子物种时发生的结构变化的动态、原子尺度表示。这项工作证实了用高时间分辨率成像矿物反应的必要性，以便捕捉被传统方法忽视的中间反应产物，特别是在具有临界区特征的低温和压力下。笼罩着地球？S表面。在接下来的三年里，PI们建议探索长期存在于静态X射线衍射边界之外的问题。经过大量的实验，他们成功地设计了一种反应池，在该反应池中，一种常见的土壤细菌--黑氏希瓦氏菌的总膜部分可以在缺氧条件下催化水钠锰矿中锰的还原和生物沉淀菱锰矿。他们将使用TRX射线探索溶解和沉淀，以产生与酶和电子供体浓度有关的速率定律。此外，PI正在使用高温反应池来检查二氧化钛系统的结构转变。通过跟踪锐钛矿和金红石成核和生长，从纳米颗粒到宏观晶体，他们提取的结构变化作为颗粒大小的函数。结合分子建模，这些研究将测试假设，以表面结构的自由能解释晶体生长过程中的多态稳定性逆转。第三，PI将铜同位素分馏与铜辉铜矿(Cu2S)向铜铜矿(CuS)相继转变过程中伴随的结构转变联系起来。他们希望证明，在将分馏过程与固体状态转换联系在一起方面，tr-x射线衍射仪是独一无二的。更广泛的影响。PIS正在将他们的TRX射线研究中的时间元素转化为3维动画，动态地说明当土壤矿物与合成地下水反应时发生的原子结构变化。这些图形将被纳入宾夕法尼亚州立博物馆由环境动力学分析中心赞助的展览中。我们正试图将分子尺度化学作为解决酸性矿山废物和污染金属迁移的解决方案，这些问题对宾夕法尼亚州的居民来说是众所周知的。

Intellectual Merit. The principal investigators (PIs) of this proposal are seeking funds to extend the thrust of time‐resolved diffraction to three areas of critical importance to the cycling of metals in soils: 1) biomineralization; 2) nucleation and growth of oxyhydroxides; and 3) stable isotope fractionation during redox reactions. Recent developments in the design of environmental reaction cells and in the collection of X‐ray diffraction (XRD) data are proving transformative in allowing us to couple rate laws with the crystallographic mechanisms that govern the interactions of minerals with fluids and gases. Intensive Rietveld analyses of time‐resolved (TR) XRD data by the PIs have provided dynamic, atomic‐scale representations of the structural changes that occur when a layered Mn oxide (birnessite) exchanges one cationic species for another. This work confirms the necessity of imaging mineral reactions with high time resolution in order to capture intermediate reaction products that are overlooked by traditional approaches, particularly at the low temperatures and pressures that characterize the ?critical zone? enveloping Earth?s surface. Over the next 3 years, the PIs propose to explore issues that have long lain outside the boundaries of static X‐ray diffraction. Following much experimentation, they have succeeded in designing a reaction cell in which the total membrane fraction of a common soil bacterium, Shewanella oneidensis, can catalyze the reduction of Mn in birnessite and bioprecipitate rhodochrosite under anoxic conditions. They will explore dissolution and precipitation using TR XRD to generate rate laws with respect to enzyme and electron donor concentrations. In addition, the PIs are using high‐temperature reaction cells to examine structural transitions in the TiO2 system. By following anatase and rutile nucleation and growth from nanoparticles to macroscopic crystals with TR XRD, they are extracting structural variations as a function of particle size. In combination with molecular modeling, these studies will test hypotheses that explain polymorphic stability reversals during crystal growth in terms of free energies of surface structures. Third, the PIs will correlate Cu isotopic fractionation with structural transitions that accompany Cu oxidation during the sequential transformation of chalcocite (Cu2S) to covellite (CuS). They hope to demonstrate that TR XRD is uniquely poised to tie fractionation processes to solid‐state transformations. Broader Impacts. The PIs are translating the temporal element of their TR XRD studies into 3‐dimensional animations that dynamically illustrate the changes in atomic structure that occur when soil minerals react with synthetic groundwaters. These graphics will be incorporated into a Penn State museum exhibit sponsored by the Center for Environmental Kinetics Analysis. We are attempting to frame molecular scale chemistry as a solution to acid mine waste and contaminant metal migration ‐‐ problems that are well known to residents of Pennsylvania.