高纯铵明矾制备中杂质钠、钾及铁的去除机制研究

Ammonium alum is an important raw material for industrial production of high purity alumina (HPA). High purity ammonium alum is prepared usually by repeated recrystallization in industry. The obtained ammonium alum crystals contain high content of impurities such as sodium, potassium and iron, causing a high content of impurities in HPA. The purity of HPA is difficult to reach 4N5 or more. The precondition of producing HPA from ammonium alum is to prepare high purity ammonium alum with low impurity content. The study of the removal mechanism of impurities such as sodium, potassium and iron in the crystallization process of ammonium alum is of great theoretical significance and application guidance for producing HPA. The present proposal plans to prepare high purity ammonium alum by the method of static crystallization without stirring. Based on the isomorphous substitution of impurity ions in the crystallization of ammonium alum, effects of impurities such as sodium, potassium and iron ions on crystal nucleation and growth of ammonium alum is studied. The precipitation of impurity ions during crystallization and the mechanism of isomorphous substitution also need to be investigated. The effective removal mechanism of impurities including sodium, potassium and iron ions in the crystallization process of ammonium alum will be revealed to realize the precise control of the crystallization process and to produce gem quality high purity ammonium alum with a purity of > 99.9999%. This strategy is expected to provide a new idea and theoretical basis for solving the key problem of the high content of impurities in HPA produced from ammonium alum in industry.

铵明矾是工业上生产高纯氧化铝的一种重要原料。工业上常通过多次重结晶制备高纯铵明矾，由于制得的铵明矾晶体具有较高含量的杂质钠、钾及铁，导致高纯氧化铝中杂质含量较高，其纯度难以达到4N5以上。采用铵明矾为原料生产高纯氧化铝的前提是要制备出杂质含量低的高纯铵明矾，因此研究铵明矾结晶过程中杂质钠、钾及铁的去除机制具有重要的理论意义和应用价值。本项目拟利用无搅拌条件下的静态结晶制备高纯铵明矾，基于杂质离子在铵明矾结晶中的类质同象置换现象，深入研究杂质钠、钾及铁离子影响铵明矾晶体成核与生长的机理，揭示杂质离子在结晶中的析出规律以及类质同象置换作用机制，探究铵明矾结晶过程中主要杂质钠、钾及铁的有效去除机制，最终实现对结晶过程的精确调控，制得纯度>99.9999%的宝石级高纯铵明矾。该项目的实施，将为工业上采取铵明矾为原料生产高纯氧化铝中杂质含量高的关键问题的解决提供新思路和理论基础。

铵明矾最重要的工业用途是作为生产高纯氧化铝的原料，纯度是其产品质量的重要指标。采用铵明矾为原料制备高纯氧化铝的缺点是制备出的高纯氧化铝纯度较低，这是因为铵明矾中杂质钠、钾及铁的含量高，导致高纯氧化铝纯度较低， 因此应尽可能地去除铵明矾中的杂质。铵明矾为原料生产高纯氧化铝的优点是可以直接采用氢氧化铝为原料制备高纯氧化铝，有助于降低生产成本。研究铵明矾制备过程中杂质的去除对于工业上采用铵明矾为原料生产高纯氧化铝具有重要的意义。本项目针对采用铵明矾为原料生产高纯氧化铝中产品杂质含量高的问题，通过研究杂质钠、钾及铁在结晶过程中的析出规律，揭示了高纯铵明矾结晶中杂质钠、钾及铁的类质同象置换作用机制，采用静态结晶法来实现铵明矾结晶过程的精确调控，制得杂质钠和铁含量低于1ppm的宝石级高纯铵明矾。通过本项目的实施，可以为采用铵明矾为原料生产高纯氧化铝中降低产品杂质含量提供理论基础。