Extraction of silica from fly ash to produce mesoporous silica materials is one of the most important utilization approaches. Mesoporous silica could not be synthesized on a large-scale by conventional sol-gel method. In this paper, facile preparation of mesoporous silica with controllable pore structure from fly ash by the template-free process via two steps of mineral phase transformation and selective acid etching was proposed. The influence of crystalline structure and acid etching degree on structure of as-synthesized mesoporous silica materials was revealed, as well as mechanism of crystalline structure transformation and pore structure formation. The results show that mullite and quartz could be transformed into acid-soluble kaliophilite when fly ash reacted with KCO at temperature of 800–1100 °C. The hexagonal kaliophilite would be transformed into orthorhombic KAlSiO–O1 phase when the temperature is controlled at 1100 °C. Mesoporous silica with specific surface area of 475.93 m/g and 642.57 m/g could be synthesized from activated fly ash with kaliophilite and KAlSiO–O1 phase crystalline structure. By controlling the degree of acid etching, mesoporous silica materials with different pore structures can be obtained. This paper provides a cost-effective and large-scale process for the preparation of mesoporous silica materials with controllable pore structure from solid waste fly ash.

中文翻译：

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粉煤灰简易制备孔结构可控介孔二氧化硅基材料的新工艺

从粉煤灰中提取二氧化硅生产介孔二氧化硅材料是最重要的利用途径之一。传统的溶胶-凝胶法无法大规模合成介孔二氧化硅。本文提出了以粉煤灰为原料，通过矿物相变和选择性酸蚀两步的无模板工艺，简便地制备具有可控孔结构的介孔二氧化硅。揭示了晶体结构和酸蚀程度对合成介孔二氧化硅材料结构的影响，以及晶体结构转变和孔结构形成的机制。结果表明，粉煤灰与碳酸钾在800~1100℃反应时，莫来石和石英可转化为酸溶性钾钙石。当温度控制在1100℃时，六方钾辉石会转变为斜方晶系KAlSiO-O1相。以具有钾钙石和 KAlSiO-O1 相晶体结构的活化粉煤灰为原料，可以合成比表面积分别为 475.93 m/g 和 642.57 m/g 的介孔二氧化硅。通过控制酸蚀程度，可以获得不同孔结构的介孔二氧化硅材料。本文提供了一种经济高效、规模化的利用固废粉煤灰制备孔结构可控的介孔二氧化硅材料的方法。