Time-Resolved Diffraction Studies of Soil-Forming Mineral Reactions

智力优势。该提案的主要研究者（PI）正在寻求资金，以延长时间‐解析衍射的三个领域的至关重要的循环金属在土壤中：1）生物矿化; 2）成核和生长的羟基氧化物;和3）稳定同位素分馏过程中的氧化还原反应。环境反应池设计和收集&X#8208;射线衍射（XRD）数据被证明是变革性的，使我们能够将速率定律与控制矿物与流体和气体相互作用的晶体学机制结合起来。由PI对时间分辨（TR）XRD数据进行的深入Rietveld分析提供了层状锰氧化物（水钠锰矿）交换一种阳离子物质时发生的结构变化的动态原子尺度表示。这项工作证实了高时间分辨率的成像矿物反应的必要性，以捕捉中间反应产物被忽视的传统方法，特别是在低温和低压下的特点？临界区？包围着地球s表面。在接下来的3年里，PI计划探索长期以来一直处于静态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个反应池，其中一个常见的土壤细菌，希瓦氏菌oneidensis的总膜部分，可以催化还原锰水钠锰矿和生物沉淀菱锰矿缺氧条件下。他们将使用TR XRD探索溶解和沉淀，以生成酶和电子供体浓度的速率定律。此外，PI正在使用高温反应池来检查TiO 2系统中的结构转变。通过使用TR XRD跟踪从纳米颗粒到宏观晶体的金红石和金红石成核和生长，他们提取了作为粒度函数的结构变化。结合分子建模，这些研究将测试的假设，解释在晶体生长过程中的表面结构的自由能的多晶型稳定性逆转。第三，PI将铜同位素分馏与结构转变，伴随着铜氧化过程中的辉铜矿（Cu 2S）铜蓝（CuS）的顺序转换。他们希望证明，TR XRD是唯一准备将分馏过程与固态转变联系起来的方法。更广泛的影响。PI正在将其TR XRD研究的时间元素转换为3& #8208;三维动画，动态地说明了原子结构的变化时发生的土壤矿物质与合成地下水反应。这些图形将被纳入由环境动力学分析中心赞助的宾夕法尼亚州立大学博物馆展览。我们正试图将分子尺度化学框架作为宾夕法尼亚州居民所熟知的酸性矿山废物和污染物金属迁移问题的解决方案。

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.