复杂铝电解质体系锂钾元素酸法浸出提取的基础问题

The complex bath composition in aluminum reduction cell with high lithium and potassium content has many adverse effects on the aluminum production in China. Based on this situation, we propose an acid leaching method to recover lithium and potassium in the aluminum electrolyte. Focusing on some fundamental problems in the acid leaching process, the following issues will be studies: the thermodynamics and dynamics of phase stability and phase transformation in complex bath composition, the stability of various bath phases in the acid solution, and the relationship between the composition and structure of acid leaching bath solution. There are two key scientific issues to be solved. One is the law of thermodynamics and dynamics of phase transformation in complex bath composition. Another is the relationship between the stability and structure of acid leaching bath phase. This work aims to understand the phase transformation rules and conditions of bath compositions in acid leaching solution, and reveal the relationship between the composition and structure. As a result, the valuable elements can be selectively leached, and the phase transformation of bath compositions can be oriented, which is contributed to the theoretical foundation for the solution treatment.

针对我国高锂、钾含量的复杂铝电解质体系对铝电解生产过程中带来诸多不利影响的现状，申请者提出了酸浸法处理回收铝电解质中锂和钾的方法，研究酸法浸出过程中的基础问题。本项目拟开展复杂铝电解质体系物相转变的热力学与动力学规律、不同电解质物相组成在酸性体系中稳定性及复杂铝电解质体系酸浸液成分与结构之间的关系等三方面的研究。通过研究拟解决两个关键科学问题：一是复杂铝电解质体系各物相稳定性及相互转化的热力学基础和动力学规律，二是酸性浸出液结构及稳定性关系问题。本项目旨在弄清复杂铝电解质各物相组分在酸性介质内稳定存在的规律及条件，揭示酸浸液组成与结构的关系，实现有价元素的选择性浸出和电解质物相组分的定向控制，为溶液后续处理提供理论基础。

本项目针对工业复杂铝电解质中锂钾元素富集的问题，采用高温转型-酸法浸出方法对其进行回收。首先研究了复杂电解质体系中含锂钾物物相及其物相转变规律，发现复杂铝电解质经氟化焙烧后，电解质中的含锂物相从难溶性的Na2LiAlF6转化成为可溶性的简单相LiF，而含钾物相K2NaAlF6焙烧前后并未发生改变；然后研究了该焙烧产物在水及酸性体系中的溶解规律，发现氟化锂在硝酸溶液中随着温度的升高而不断增加，加入铝酸钠溶液会促进LiF的溶解，同时生成新的含锂冰晶石相Li3Na3Al2F12，而加入硅酸钠会使得溶液中的氢离子减少，降低LiF的溶解度；其次发现复杂电解质经酸化焙烧后，随着焙烧温度的升高，复杂铝电解质中冰晶石相的转化模式为：Na3AlF6→Na5Al3F14→AlF3。以无水Al2(SO4)3和Al2(SO4)3·17H2O作为酸性焙烧介质，复杂铝电解质中的含锂钾不可溶性盐转化为可溶性锂盐和钾盐，该酸化焙烧产物在水及酸性体系中表现出很好的溶解性能，锂和钾的浸出率均在95%以上。在理论研究基础上，进行了高温焙烧-选择性浸出技术的开发，完成了百公斤级扩大试验，优化了工艺，实现了专利成果的技术转让，技术转让额为1亿元（现金）。