基于烧结法非化学计量硅酸钙生成转化机理及其稳定性的基础研究

The sinter process for alumina production has been increasingly showing strong capability in dealing with the great number of Al-containing resources with the decreasing grade of bauxites and the increasing amounts of solid residues such as fly ash and red mud. However, the application of the traditional sinter process is restricted by the defects of the high consumption of calcium, large amount of slag and low extraction efficiency of Al2O3. The former research results show that the lacking calcium and the doping Na2O can decrease the lime addition to form the calcium aluminates and increase the Al2O3 leaching efficiency of clinkers. Decreasing the calcium content in calcium silicate compounds and keeping their stability in the alkaline solution will greatly promote the application of the sinter process to utilize the low-grade Al-containing resources. The project aims to study the high temperature formation thermodynamics and kinetics, the solid solution and multi-state transformation of elements, the formation mechanism and stability of non-stoichiometric calcium silicate compounds using the modern physical chemistry, crystal chemistry, defect chemistry and the First-principles. The migration and transformation behaviors of elements such as calcium, silicon and other elements and activation methods in non-stoichiometric calcium silicate compounds will be clarified. This research will create the processing technology to control the formation process of low activity non-stoichiometric calcium silicate compounds, establish the modern theoretical system to deal with the low-grade Al-containing resources by the sinter process with low energy consumption and high efficiency, and finally give the scientific directions to the development and utilization of low-grade Al-containing resources in China.

随着我国铝土矿品位的急剧降低和粉煤灰、赤泥等低品位含铝固废的不断增加，烧结法生产氧化铝技术日益显示出强大的资源处理能力，但配钙量大、弃渣量大和氧化铝回收率较低等问题制约该工艺的进一步发展。前期结果表明，钙配入不足和Na2O掺杂能够大幅降低铝酸钙的配钙比和提高氧化铝浸出率，如果能够生成低配钙比硅酸钙并保证其稳定性，则可为烧结法处理低品位含铝资源的工业应用发挥强力助推作用。本项目拟利用现代物理化学、结晶化学、缺陷化学和第一性原理等研究非化学计量硅酸钙高温生成热力学与动力学、元素固溶与多态转化规律、晶体缺陷形成机制及其稳定性行为，阐明Ca、Si元素及他种元素和活化方式在非化学计量状态下形成硅酸钙化合物的元素迁移行为和时空演变规律，建立非化学计量低活性硅酸钙形成的调控方法和机制，进一步构建烧结法低耗高效处理低品位含铝资源的现代冶金工艺体系，为开发利用我国储量巨大的低品位含铝资源提供理论科学基础。

利用现代物理化学、结晶化学、缺陷化学和第一性原理研究了非化学计量硅酸钙化合物生成热力学与动力学、晶体缺陷形成机制和稳定性行为，阐明了非化学计量硅酸钙形成的元素迁移行为和时空演变规律，建立了低活性硅酸钙形成的调控方法和机制，为烧结法低耗高效处理低品位铝资源提供了科学基础。.研究了Na2O及MgO存在下对C2S高温形成机制、自粉性能及稳定性影响。当C/S为2.0、温度为1400oC时，随N/S增加，烧结产物中β-C2S含量升高，自粉性能下降；C2S在铝酸钠溶液中的稳定性降低。当N/S为0.1、温度为1300 ~1400℃时，随时间延长，烧结产物结晶度增加；C2S在铝酸钠溶液中的稳定性提高。当N/S为0.05时，添加3%MgO可消除Na2O对烧结产物自粉性能产生的负作用；当N/S为0.2时，MgO可添加使烧结产物自粉率提升50%。.研究了Na2O-CaO-SiO2系不同化学计量硅酸钙钠化合物的生成热力学及其稳定性。900~1400℃时各种硅酸钙钠吉布斯生成自由能均为负值。在温度为1100℃、时间为60min、N/S和C/S分别为0.5时，烧结产物主要物相为Na6Ca3Si6O18，其在铝酸钠溶液中的分解率仅为4.94%。不同硅酸钙钠在铝酸钠溶液中的稳定性顺序为：Na6Ca3Si6O18＞Na2Ca2Si2O7＞Na2CaSiO4＞Na2Ca3Si2O8。.计算了CaO-SiO2系不同化学计量硅酸钙化合物生成与转化过程热力学，并研究了低钙比硅酸钙的形成机制及其稳定性。当C/S为1.0和1.5时，硅酸钙最稳定相分别为CS和C3S2。在C/S为1.0时，C2S先生成，并逐渐转化为α-CS。在C/S为1.5时，CS和C2S先生成，然后转化为C3S2，最后再分解为CS和C2S，其中C3S2含量最高达75.9%。随着钙比增加，硅酸钙在铝酸钠溶液中的稳定性逐渐降低，其中CS最稳定，且随反应时间变化不大。在C/S为1.5不同温度烧结产物在铝酸钠溶液中的稳定性随C3S2含量的升高而增强。.通过MS软件建立了完整CS的晶体结构，并对Ca空位及Na掺杂CS晶体进行几何优化模拟。Ca空位以及Na掺杂对CS结构稳定性影响显著，随着Ca空位和掺杂Na原子数目增加，CS晶格参数和晶胞体积逐渐增大，自由能增加，O-Ca键布居值减小，键长增加，在费米能级处的态密度增加，赝能隙变窄，CS晶体稳定性逐渐下降。