Mineral Formation by Cluster Self-Assembly: Schwertmannite as a Partially Crystallized Nanomineral

我们理解结晶过程的能力是解释地球过去、现在和未来进化的关键。然而，我们对结晶——溶解的物质转化为固体——的科学理解是不完整的。最近的研究揭示了多种新的“非经典”途径和机制，晶体，特别是纳米晶体，通过中间和前体颗粒的附着形成和生长。然而，我们对这些过程的理解仍然存在巨大差距。该项目将研究形成氧化铁矿物schwertmannite的簇的组装，以了解它是如何通过非经典路线形成的。schwertmanite在酸性环境中普遍存在并引起广泛的兴趣，因为它具有高表面积和对各种潜在污染物的亲和力。此外，由于schwertmanite和其他低结晶矿物在地球表面和地球表面附近非常丰富和重要，因此了解它们的形成是解释地质记录以及生物与地质介质之间相互作用的关键。本研究的首要目标是记录施魏特曼石前体簇的性质，作为溶液组成和生长条件的函数，然后利用这些信息构建一个通用模型，显示溶解的铁和硫酸盐如何在溶液中反应形成施魏特曼石。初步的原位同步加速器散射数据表明，形成的团簇（~1.5 nm）具有schwertmanite样结构特征。只要溶液保持湍流（长达40小时），这些团簇在溶液中是稳定的，但在静态流体条件下迅速聚集并转化为schwertmannite。根据初步数据，研究人员假设，schwertmanite的形成是通过一个非经典的途径，包括schwertmanite样前体粒子的自组装。他们还假设，schwertmanite的组成和性质应该反映聚集的颗粒的结构和组成。研究人员将应用一套原位实验室和同步加速器矿物表征技术来研究溶液中合成施魏特曼铁矿前体簇的实时形成及其聚集成施魏特曼铁矿固体。研究人员还将从一个活跃的AMD系统中收集和表征水样和沉积物，并评估自然界的schwertmannite形成。从这些实验中获得的结构、化学和物理数据将用于开发与热力学和化学原理一致的schwertmannite的一般结晶模型，并与文献和本项目中自然界中schwertmannite形成的观察结果相一致。

Our ability to understand crystallization processes is a key to interpreting the past, present, and future evolution of our planet. Yet our scientific understanding of crystallization - the transformation of dissolved species into solids - is incomplete. Recent research is revealing a diversity of new "nonclassical" pathways and mechanisms by which crystals, particularly nanocrystals, form and grow through attachment of intermediate and precursor particles. However, immense gaps remain in our understanding of these processes. This project will investigate the assembly of clusters to form the ferric oxyhydroxide mineral schwertmannite in order to understand how it forms via nonclassical route. Schwertmannite is pervasive and of broad interest in acidic environments because it exhibits high surface area and an affinity for a variety of potential pollutants. Additionally, because schwertmannite and other poorly crystalline minerals are so abundant and important at and near Earth's surface, understanding their formation is the key to interpreting the geologic record and the interaction between organisms and geologic media. The overarching objective of this research is to document the nature of schwertmannite precursor clusters as a function of solution composition and growth conditions, and then to use that information to construct a general model that shows how dissolved iron and sulfate react in solution forming schwertmannite. Preliminary in situ synchrotron scattering data show the formation of clusters (~1.5 nm) having schwertmannite-like structural characteristics. These clusters are stable in solution as long as the solution remains turbulent (for up to 40 hours), but quickly aggregate and transform to schwertmannite under static fluid conditions. Based on preliminary data, the investigators hypothesize that schwertmannite forms via a nonclassical pathway involving self-assembly of schwertmannite-like precursor particles. They also hypothesize that the composition and properties of schwertmannite should reflect the structure and composition of the particles that aggregate. The investigators will apply a suite of in situ laboratory and synchrotron mineral characterization techniques to study the real-time formation of synthetic schwertmannite precursor clusters in solution and their aggregation into schwertmannite solids. The investigators will also collect and characterize water samples and sediments from an active AMD system and evaluate schwertmannite formation in nature. The structural, chemical, and physical data from these experiments will be used to develop a general crystallization model for schwertmannite that is consistent with thermodynamic and chemical principles, and with observations in the literature and this project of schwertmannite formation in nature.