铝酸钠溶液中钠铝萃取分离新方法基础研究

Bayer process is the main method to produce alumina, but in this process the seeded precipitation unit has the disadvantage of low decomposition efficiency, causing about a half of the alumina being recycled in Bayer process. Consequently, this unit is believed to be an important bottleneck. In order to solve the sodium and aluminium separation problem, novel method of liquid-liquid extraction separation of sodium and aluminium for sodium aluminate solution was proposed, realizing the coupling of seeded precipitation and extraction. By using this method, the transfer of sodium from the liquid phase of sodium aluminate solution to another phase can be achieved. And the remaining liquid phase with lowered molar ratio can be further decomposed to extract alumina by seeded precipitation. Based on the electronic effect features of different substituents, the relationships of the extractant structure with the acidity, the acidity with the sodium extraction ability will be studied, then guiding the optimal design of the extraction system. And the structure change of organic phase and the water transfer rules between two phases during the extraction and back-extraction will be investigated deeply. Furthermore, the extraction thermodynamics and kinetics by using the optimized extractant will be researched, and the optimal extraction conditions will be concluded and used. Novel method of deep decomposition of Bayer liquid will be established by this project, which possess the ability to promote the alumina productivity and recycle efficiency of Bayer process, and will play a very important role in enhancing the alumina production technology level of our nation. And the research result can provide theoretical basis for the foundation of novel alkali extraction separation method.

拜耳法是氧化铝生产的主要方法，但其种分工序氧化铝分解率低，使得有近一半的氧化铝在拜耳法系统进行无效循环，成为拜耳法的重要技术瓶颈。本项目针对拜耳法系统钠铝难分离的难题，将种分与萃取相耦合，提出铝酸钠溶液中钠铝高效萃取分离新方法，通过萃取实现高分子铝酸钠母液中钠的相转移，获得低分子比铝酸钠溶液，实现母液中铝的进一步种分提取。本项目将基于萃取剂基团的电子效应，通过研究萃取剂结构与其酸性、萃取剂酸性与其萃钠性能之间的关系，对萃取体系进行优化设计；深入开展萃取过程有机相结构变化、水的迁移规律等萃机理研究；采用优化设计的萃取体系开展萃取热力学、动力学研究，设计最佳的萃取工艺并进行试验验证。本项目将建立拜耳法母液深度分解新方法，可望大幅度提高拜耳法系统氧化铝产出率及循环效率，对提升我国氧化铝生产技术水平具有重要意义，并可望拓展建立碱介质液液萃取分离新方法共性基础。

拜耳法是氧化铝生产的主要方法，但其种分工序氧化铝分解率低，使得有近一半的氧化铝在拜耳法系统进行无效循环，成为拜耳法的重要技术瓶颈。本项目针对拜耳法系统钠铝难分离的难题，将种分与萃取相耦合，提出铝酸钠溶液中钠铝高效萃取分离新方法，通过萃取实现高分子铝酸钠母液中钠的相转移，获得低分子比铝酸钠溶液，实现母液中铝的进一步种分提取。本项目基于酸性萃取剂非功能基团结构与萃取剂酸度(pKa)的关系研究，以及酸性萃取剂酸度(pKa)与萃取剂萃取碱液中钠性能的系统研究数据，完成了主体酸性萃取剂的结构优选。在此基础上，进一步研究了稀释剂对萃钠性能的影响规律，指导了稀释剂的优选。项目最终设计采用了 pKa 值约 11.6、以 2-叔丁基苯酚为特征构架的烷基酚萃取剂，并优选出极性强、水溶性小、黏度适中的辛醇作为稀释剂，优化设计的萃取体系在拜耳法碱浓度区间具有高萃取容量。采用优选的萃取体系，开展了各关键因素对萃取平衡热力学影响的系统研究测定，指导了萃取工艺的设计，完成了多级逆流萃取分离工艺试验。结果表明，温度与萃取剂浓度对萃取容量影响显著，所设计的萃取体系具有显著的温度和碱浓度摆动效应，利用低温萃取/高温反萃可进一步增加萃取容量；对铝酸根离子无化学萃取作用，以正辛醇作稀释剂的萃取体系更适用于拜耳法碱浓度区间。优化的非连续二级逆流萃取实验结果表明，所设计的萃取体系在拜耳法碱浓度区间的萃取容量是 C12~C18 烷基酚体系的 10 倍以上，并可获得分子比大于 100 的碱液用于水热法高效回收赤泥中的氧化铝和碱。开展了萃取过程相关机理的研究，明确了共萃水在萃取过程中的关键作用。根据萃取平衡热力学规律，该技术思路可在全碱范围内推广，并已成功应用于钾系，形成了碱介质萃取分离的平台方法。本项目对提升我国氧化铝生产技术水平具有重要意义。