柴达木盆地富锂铷铯老卤硫酸盐体系多温稳定相图研究

The four salt lakes (Yiliping Salt Lake, East Taijinaier Salt Lake, West Taijinaier Salt Lake, and the Bieletan Regions of the Qarhan Salt Lake), located in Qaidam Basin, are belong to magnesium sulfate type and aboundant with lithium, rubidium and cesium. The main component of the old brine can be described as the complex system Li+, Na+, K+, Rb+,Cs+,Mg2+/Cl-, SO42- - H2O. In the above mentioned aqueous system, the chloride and sulfate of alkalis, alkaline earth element can easily form various hydrated salts, solid solution, and double salt, which increase the difficulty of the separation and extraction technique. It is well known that phase diagram is the basis and guidance of utilization of liquid mineral resources and separation techniques of salts. Therefore, the stable phase equilibria on the aqueous system containing lithium, potassium, rubidium, and cesium at multi-temperature are essential. To the best of our knowledge, the research on the chloride system has been supported by NSFC, however the research aimed at the multi component sulfate system has not been reported in the literature yet. Accordingly, the stable phase equilibrium of the seven – component system Li+, Na+, K+, Rb+,Cs+,Mg2+/SO42- - H2O at 0-75 ℃ will be investigated. Meanwhile, the research about the thermodynamics of the sulfate double salts for alkalis, such as the formulation condition, spectroscopy characterization, crystalline structure, and solubility idiosyncrasy, will be done. The research results will enrich the thermodynamic basis data, give guidance to the seperation and extraction of the trace elements, and also take another step on the research road to the eight- component system mentioned above.

柴达木盆地一里坪等四大盐湖区属硫酸镁亚型卤水，富含锂铷铯等稀有元素，其老卤的主要组分可用八元体系Li+, Na+, K+, Rb+,Cs+,Mg2+/Cl-, SO42- - H2O加以描述。因碱金属和镁的氯化物、硫酸盐间极易形成水合物、复盐或固溶体，按常规盐类提取分离技术，难以彻底分离，急需含锂钾铷铯的高元体系多温相图研究成果作指导。碱（土）金属氯化物体系已有基金资助，而富含锂铷铯的硫酸盐体系多温相图研究还未见报道。本课题拟开展七元体系Li+, Na+, K+, Rb+,Cs+,Mg2+/ SO42- - H2O及其子体系0 ℃-75 ℃范围内的稳定相图研究；同时全面系统地研究碱金属硫酸盐复盐的生成条件、光谱学特性、晶体结构及水溶解特性，拟建立碱金属硫酸盐复盐热力学数据库，为硫酸镁亚型盐湖老卤稀有元素的分离提取提供科学依据，同时也为复杂八元体系的研究打下基础。

柴达木盆地硫酸镁亚型盐湖卤水资源丰富，除富含锂外，还富含钾铷铯等多种有用组分，极具开发价值。本项目针对柴达木盆地硫酸镁亚型盐湖卤水组成特征和蕴藏特征，采用等温溶解平衡法，开展了含锂铷铯七元体系Li+, Na+, K+, Rb+, Cs+, Mg2+ // SO42- - H2O相关的五元、四元和三元子体系（0-75）℃多温相平衡研究。主要成果如下：（1）测定了锂铷铯等的硫酸盐在不同温度下的溶解度数据及密度、折光率等物化性质，明确了各盐的溶解析出规律及平衡固相盐的存在形式，解析了锂、铷、铯等的硫酸盐在不同温度、不同离子相互作用下的溶解和析出特性，确定了各种盐的结晶区大小及其随温度变化的趋势。（2）联用Schreinemarkers湿渣法、X-ray粉晶衍射(XRD)、偏光显微镜(PM)，扫描电子显微镜(SEM)和能量色散光谱(EDS)等方法改进了析出盐鉴定技术，建立了复杂碱（土）金属硫酸盐体系相图的固相鉴定方法。（3）发现了碱（土）硫酸盐的结晶析盐规律及相互之间的盐类作用关系：钾、铷、铯的硫酸盐间极易形成固溶体[(K, Rb)2SO4]、[(K, Cs)2SO4]、[(Rb, Cs)2SO4]；Li2SO4与其他碱金属硫酸盐间易形成多种形式的复盐：3Li2SO4·Cs2SO4·2H2O、Li2SO4·Cs2SO4、3Li2SO4·Rb2SO4·2H2O、Li2SO4·Rb2SO4、Li2SO4·K2SO4、3Na2SO4·Li2SO4·12H2O；除Li2SO4外，碱金属硫酸盐和MgSO4间易形成多种形式的复盐：Na2SO4·MgSO4·4H2O、 K2SO4·MgSO4·6H2O、K2SO4·MgSO4·4H2O、Cs2SO4·MgSO4·6H2O、Rb2SO4·MgSO4·6H2O，其中软钾镁矾(K2SO4·MgSO4·6H2O)结晶形式随温度升高变为钾镁矾(K2SO4·MgSO4·4H2O)；随着温度升高，Na2SO4·10H2O结晶形式转变为Na2SO4，MgSO4·7H2O结晶形式转变为MgSO4·6H2O。研究成果可用于指导制定富锂铷铯硫酸盐型老卤的节能、高效综合利用工艺路线，为成盐元素的富集规律等研究提供基础热力学数据。