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我们星球过去、现在和未来演化的关键。然而，我们对结晶的科学理解--将溶解的物种转化为固体--是不完整的。最近的研究揭示了各种新的“非经典”途径和机制，晶体，特别是纳米晶体，通过中间和前体粒子的附着形成和生长。然而，我们对这些进程的理解仍然存在巨大差距。这个项目将研究形成氢氧化铁矿物施维特曼尼特的团簇的组装，以了解它是如何通过非经典路线形成的。施韦特曼因其高比表面积和对多种潜在污染物的亲和力而在酸性环境中普遍存在并引起人们的广泛兴趣。此外，由于硅灰石和其他结晶较差的矿物在地球表面和附近如此丰富和重要，了解它们的形成是解释地质记录以及生物和地质介质之间相互作用的关键。这项研究的首要目标是记录作为溶液组成和生长条件的函数的施韦特曼尼特前驱体簇的性质，然后利用该信息构建一个通用模型，说明溶解的铁和硫酸盐在溶液中如何反应形成施维特曼尼特。初步的同步辐射原位散射数据表明，形成的团簇(~1.5 nm)具有类似于施维特曼尼特的结构特征。只要溶液保持湍流(长达40小时)，这些簇合物在溶液中就是稳定的，但在静态流体条件下会迅速聚集并转化为施维特曼尼石。根据初步数据，研究人员推测，施韦特曼尼特是通过一种非经典的途径形成的，其中包括类似施韦特曼尼特的前体颗粒的自组装。他们还假设，施维特曼尼特的组成和性质应该反映出聚集的颗粒的结构和组成。研究人员将应用一套现场实验室和同步加速器矿物表征技术，研究人工合成施特曼尼特前体簇合物在溶液中的实时形成及其聚集成施维特曼尼特固体的情况。调查人员还将收集和表征来自活跃的AMD系统的水样和沉积物，并评估自然界中的施维特曼尼特形成。从这些实验中得到的结构、化学和物理数据将被用来开发一个与热力学和化学原理以及与文献和本项目中观察到的自然界中的施维特曼尼特形成相一致的施维特曼尼特的一般结晶模型。

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.