黏土矿物对水铁矿相转变过程的影响及其制约机制

The evolution of iron-bearing minerals is the core of the geochemical cycle of iron, which greatly influences the evolution of the earth and the origin of life. Ferrihydrite and clay minerals often form complexes at earth’s near-surface environment. Owing to the small particle size, abundant surface groups, and high surface reactivity, the interaction of these natural nanominerals can significantly affect the phase transformation of ferrihydrite, which has an important impact on the geochemical cycle of iron. This project intends to study the effect of clay minerals on phase transformation of ferrihydrite under near-surface environmental condition (under illumination) and the related mechanisms. In this project, we will use a combination of micro-beam/area technologies and spectroscopy to first study the interfacial interaction processes between clay minerals with different crystal chemical characteristics (kaolinite, montmorillonite, and illite) and ferrihydrite. Then, we will focus on the effect of clay minerals on the photoreductive dissolution and subsequent phase transformation of ferrihydrite, and the related mechanisms will be investigated with the help of in-situ characterization techniques. Based on the obtained results, we intend to clarify the correlation of the microstructure of clay minerals/ferrihydrite composite−the photoreductive dissolution of ferrihydrite–the transformation of ferrihydrite. The expected outcomes of the project may provide reliable experimental basis for understanding the transformation process of ferrihydrite and the evolution of the related nanominerals at earth’s near-surface environment, and provide theoretical support for revealing the geochemical cycle of iron element.

（含）铁矿物的演化是铁元素地球化学循环的核心，对地球演化、生命起源等过程有重要影响。在地表环境中，水铁矿与黏土矿物常常会形成复合体，由于这些天然纳米矿物具有粒径小、表面基团丰富、表面反应活性强等特点，它们之间的相互作用可显著制约水铁矿的相转变过程，影响铁元素的地球化学循环。本项目拟研究表生条件（光照）下，黏土矿物对水铁矿相转变过程的影响及其制约机制。将采用微束微区技术和现代谱学方法，首先研究不同晶体化学特征的黏土矿物（高岭石、蒙脱石、伊利石）与水铁矿的表/界面作用过程，重点考察黏土矿物对水铁矿光还原溶解以及后续矿物相转化过程的影响，并结合原位表征技术，探明相关作用机制。在此基础上，阐明黏土矿物与水铁矿复合体的微观结构—光还原溶解—相转变之间的耦合关系。项目预期成果可为认识地表环境中水铁矿相转变过程及相关纳米矿物的演化提供可靠的实验依据，并为揭示铁元素的地球化学循环提供理论支撑。

含铁矿物的演化是铁元素地球化学循环的核心，对地球演化、生命起源等过程有重要影响。黏土矿物在地表环境中与水铁矿广泛共存并相互作用，但黏土矿物如何制约水铁矿的相转变过程尚不清楚。鉴于此，项目聚焦表生条件下黏土矿物对水铁矿相转变过程的影响及其制约机制，采用微束微区技术和现代谱学方法，首先研究了不同黏土矿物与水铁矿的表/界面作用特征，重点考察了黏土矿物对水铁矿光还原溶解以及矿物相转化过程的影响，并结合原位表征技术，探究了相关作用机制。项目研究获得以下主要认识：1）明确了黏土矿物与水铁矿的表/界面作用特征。黏土矿物可通过静电吸引、化学键合等方式与水铁矿作用，其纳米片层可有效分离和隔离水铁矿，分散程度受黏土矿物的表面结构和膨胀性制约。2）揭示了黏土矿物对水铁矿光还原溶解和相转化过程的制约。黏土矿物可通过制约水铁矿光还原溶解过程、改变水铁矿聚集状态、影响Fe2+与水铁矿的相互作用等方式，抑制水铁矿的相转化过程，水铁矿的转化途径和产物类型显著受环境pH制约。3）揭示了水热和干热条件下黏土矿物对水铁矿相转化过程的制约。黏土矿物可通过静电吸引、化学键合、物理分散、溶出元素掺杂等方式与水铁矿作用，抑制水铁矿相转化过程，水热条件下出现不规则形状的赤铁矿颗粒，干热条件下出现磁赤铁矿中间相。4）揭示了黏土矿物/水铁矿复合体系转化过程对环境离子迁移富集的影响。黏土矿物可抑制水铁矿转化以及稳定体系pH值，进而对共存环境中阴阳离子的迁移富集产生不同的影响，抑制阳离子迁移，促进含氧阴离子迁移。上述研究工作为认识地表环境中水铁矿相转变过程及相关纳米矿物的演化提供了实验依据，并为揭示黏土矿物在地质地球化学过程中的重要作用提供了新信息。