钾铷铯氯化物盐聚乙二醇-水双水相五元体系25℃相平衡与相图研究

Salt lake brine in the Qaidam Basin, abundant with minerals as sodium, potassium, boron, lithium, rubidium, and cesium, is one kind of important natural liquid resource and possess great development value. Whereas the solid solution can be easily formed between potassium, rubidium, and cesium in the chloride solution, which increase the difficulty of the separation and extraction technique, restrict the process of comprehensive utilization of the salt lake, extraction rubidium and cesium from the potassium rich salt lake is one of technique knotty problem unsolved. Based on the difference of distribution coefficient of the salt KCl, RbCl, and CsCl in the polyethylene glycol (PEG) - H2O aqueous two phase system, those three salts above mentioned can be separated and purified. Accordingly, the phase equilibria and phase diagram in the PEG - H2O aqueous two phase quinary system with potassium, rubidium, cesium, and chloride ions at 25℃ will be investigated, the physicochemical properties (densities and refractive indices) and the solubilities of the chlorides of potassium, rubidium, cesium under the condition of different ions concentration and different molecular weight of PEG will also be determined. Meanwhile, the tie lines will be correlated by the Othmer-Tobias, Bancroft’s, and Eisen-Joffe equation. The phase equilibria of the quaternary and quinary system will be predicted by using the Pitzer model. Based on the measured data, the phase diagrams can be constructed. The rule of dissolving - precipitating of the salts and the crystallization form of the salts can be obtained from the phase diagrams. Through the above research, the thermodynamics basis data will be more plentiful and can be give guidance about the potassium, rubidium, and cesium resource extraction process.

柴达木盆地盐湖卤水富含钠、钾、硼、锂、铷、铯等资源，极具开发价值。钾、铷、铯的氯化物盐间极易形成固溶体，增加了钾、铷、铯盐的分离提取难度，在富钾卤水中分离提取铷、铯是尚未解决的技术难题。利用钾铷铯氯化物盐在聚乙二醇-水双水相体系中分配系数的不同，有望实现三者的分离提取。本项目拟开展钾铷铯氯化物盐聚乙二醇-水双水相五元体系25℃相平衡研究，测定钾铷铯氯化物盐在不同离子浓度、不同聚乙二醇分子量下的溶解度以及密度、折光率等物化性质，同时采用Othmer-Tobias和Bancroft’s方程以及修正过的Eisen-Joffe方程对体系结线测定数据进行关联，并应用Pitzer电解质溶液理论模型对四元、五元体系进行相平衡理论模拟和计算，绘制相应的相图，获取钾、铷、铯氯化物的析出区间和析出盐形式，从而为氯化物型卤水钾、铷、铯盐的分离提取工艺制定提供科学依据。

碱金属盐-混合溶剂体系相平衡研究成果对于卤水中碱金属盐的提纯开发利用具有重要意义。本项目针对氯化物型卤水中钾铷铯盐易形成固溶体导致盐类难以分离纯化特点，选择环境友好的聚乙二醇(分子量为1000,4000,6000,8000,10000,20000)与水组成混合溶剂，开展了钾铷铯共存氯化物盐-聚乙二醇(PEG)-水混合溶剂体系25℃相平衡研究，获取了钾铷铯氯化物盐在纯水和混合溶剂中的结晶析盐规律，为氯化物型卤水中钾铷铯盐的分离纯化提供重要的热力学基础数据。研究成果如下：(1)建立了折光率组成法(低元体系)和分光光度法(高元体系)测定PEG-盐-水体系中PEG含量的方法；通过加入电离抑制剂，优化了钾铷铯共存体系中铯的AAS测定方法。(2)采用等温溶解法完成了四元体系K+,Rb+,Cs+//Cl- - H2O及三元子体系25℃相平衡研究，获得了溶解度数据、液相物化性质，绘制了相应体系的稳定相图。采用Schreinemakers湿渣法及X-ray粉晶衍射法确定了平衡固相组成，结果显示：3个三元子体系中分别有固溶体[(K, Rb)Cl]、[(K, Cs)Cl]和[(Rb, Cs)Cl]生成。(3)采用等温溶解法和浊点法完成了KCl/RbCl/CsCl-PEG 1000/4000/6000/8000/10000/20000-H2O体系相关的6个五元体系、18个四元子体系和18个三元子体系25℃相平衡研究，绘制了研究体系的完整相图。采用非线性方程对双液线数据进行了拟合，采用Othmer-Tobias方程和Bancroft方程对结线数据进行了计算。结果显示：随着混合溶剂中PEG含量增加盐类溶解度减小，PEG对盐具有明显盐析效应。本项目研究体系中，KCl-PEG-H2O体系未分层，只存在固液平衡；PEG分子量大于1000时，RbCl/CsCl-PEG-H2O体系形成明显的双水相，同时存在固液和液液平衡，RbCl分层能力强于CsCl。(4)基于朱自强教授修正的Pitzer模型，引入Fowler-Guggenheim表达式，同时考虑聚合物-聚合物、聚合物-盐的相互影响，构建了钾铷铯氯化物-聚乙二醇-水混合溶剂体系溶解度理论计算的Pitzer模型，并对部分体系进行了溶解度和结线计算。(5)依托本项目，发表学术论文18篇（含接收1篇），其中SCI收录8篇，会议论文6篇，培养在读研究生3名。