典型纳米硅酸盐矿物水铝英石和埃洛石的结构与表面基团受酸、碱作用影响的机理研究

Globular allophane and tubular halloysite are two representative nano-sized silicate minerals, and they are usually associated at their occurrence in geological environments. Exploring the changes in the structure and surface reactivity of surface groups of allophane and halloysite in acid or alkaline aqueous solutions is of essential meaning not only for the interface reactions and the geochemistry performance of these two mentioned nanominerals, but also for their industrial applications as important resources. Unfortunately, the related studies are still at an very early stage and more efforts thus need to be made for that. Accordingly, the objectives of this work are to make clear the mechanism concerning the changes of microstructure and surface properties of allophane and halloysite under various acid or alkaline aqueous solutions, to clarify how the local structures and coordination environments of silicon and aluminum atoms induce the types of surface groups as well as the related surface properties, and to understand in depth the main factors, the key conditions, and the assessment criterions resulting in the structure and property changes of allophane and halloysite as well as their thermally treated products under the influences of the structure characteristics and specific conditions of acid or alkaline treatments. For those mentioned purposes, some research methods, especially the microscopic and spectroscopic ones with high resolution and at real state for the micromorphology and microstructure in nanoscale, will be carefully selected and used on the basis on the already obtained understanding on the nano-sized globular and tubular structures of allophane and halloysite, respectively. It is anticipated that the fundamental information derived from the currently proposed project is of significance both theoretically and experimentally in providing a key basis for the well understanding of the interface reactions of allophane and halloysite in geological environments and for developing novel mineral-based materials or creating new applications of the mineral resources in the related mine engineering domains.

水铝英石和管状埃洛石是两种典型的纳米硅酸盐矿物，地质产状上二者常共生产出。探索酸、碱作用下水铝英石和埃洛石的结构和表面基团性质变化，对二者的矿物界面作用、地球化学行为和资源利用都很关键，但相关研究目前还十分薄弱。为此，本项目拟采用原位、高分辨电子显微与谱学研究手段，探明纳米水铝英石和埃洛石在不同酸、碱介质条件下发生微结构和表面基团性质变化的机理，重点揭示硅、铝原子局域结构、配位环境变化乃至微区相变对表面基团类型及相关表面性质的制约机制，掌握水铝英石、埃洛石及二者的热处理产物受自身矿物结构特性和酸/碱处理反应影响发生结构-性质改变的主要因素、关键条件、参数范围和判别依据。相关结果不仅将为地质作用中水铝英石和埃洛石所涉界面反应机理奠定理论基础，而且为相关的矿物加工、矿物材料和资源利用新工艺方法的研发提供理论和实验依据。

水铝英石和埃洛石是两种典型的铝硅酸盐纳米矿物，二者在地质产状上常共生产出。探索酸、碱介质下水铝英石和埃洛石的结构和表面基团性质变化，对理解二者的矿物界面作用、地球化学行为和资源利用都很关键，但相关研究目前还十分薄弱。为此，本项目采用了原位、高分辨电子显微学与谱学研究手段，探明了水铝英石和埃洛石在不同酸、碱介质条件下发生微结构和表面基团性质变化的机理，重点揭示了硅、铝原子局域结构、配位环境变化乃至微区相变对表面基团类型及相关表面性质的制约机制，掌握了水铝英石、埃洛石及二者的热处理产物受自身矿物结构特性和酸/碱处理反应影响发生结构-性质改变的主要因素、关键条件、参数范围和判别依据。主要发现包含：对水铝英石及其对比矿物伊毛缟石的合成而言，原料的硅铝摩尔比是最重要的影响因素；伊毛缟石的形成生长过程可划分为五个阶段，首次发现伊毛缟石形成初期易发生球状（原水铝英石）到管状（原伊毛缟石）的形态转化；水铝英石在热处理条件下发生复杂而独特的物相结构、微观形貌和孔性等变化，确证了1000°C左右的热处理产物为莫来石；水铝英石在较弱酸、碱性pH值介质（pH ≥ 3或pH ≤ 11）中，只有少量Si和Al溶出，纳米空心球结构基本不发生变化；而在较强酸、碱pH介质（pH < 3或pH >11）中，Si和Al均大量溶出，纳米空心球结构明显破坏甚至坍塌，在酸性介质中生成无定形二氧化硅而在碱性介质中生成硅铝凝胶；埃洛石及其热处理产物在中高浓度强酸介质（3 M硫酸）中的溶蚀机制不同，埃洛石的溶蚀发生在内腔的铝氧八面体片，反应较慢，最终形成无定形二氧化硅颗粒组成纳米棒，而热处理埃洛石的铝氧八面体片已与硅氧四面体片分离，可快速发生溶蚀，最终形成无定形二氧化硅纳米管，但二者的酸处理产物均含大量微孔，具有高的比表面积和优异的苯吸附性能；埃洛石在中高浓度强碱性介质（1 M氢氧化钠）中可以保持其管状结构完整性，但表面硅羟基和缺陷增多，导致对氧化物的负载能力增强。以上结果不仅为地质作用中水铝英石和埃洛石所涉界面反应机理奠定了理论基础，而且为相关的矿物加工、矿物材料和资源利用新工艺方法的研发提供了理论和实验依据。