鉴于我国低品位钾盐矿床亟待开发之现状及盐湖卤水都存在“低钾高钠”特征而导致钾、钠分离的困难，本项目针对碱金属氯化物-碳酸盐卤水（Li+、Na+、K+、Rb+、Cs+//Cl(-)、CO3(-2)-H2O及其子体系，浓度[Na+]/[K+]>5），通过蒸发、结晶，CO2酸化等手段，将碳酸盐水体变成碳酸氢盐体系，改变碱金属化合物盐析顺序，避开碱金属复盐的生成，实现各单盐的有效分离。采用盐湖卤水，测定过程介稳相的物化参数（液、固相组成，密度，折光率，电导率及pH值等），优化蒸发、结晶工艺，获取水盐体系结晶分离路线图，提高单盐收率。将温度、CO2压力考虑入Pitzer电解质溶液理论或Harvie-Weare模型，计算体系中碱金属盐在变温、变压条件下的活度系数，并将理论计算与电化学等实验数据相结合，绘制高精度相图，为我国低品位钾盐卤水资源化利用及碱金属化合物的分离提供解决方案。

The project is proposed based on two reasons. One is the urgency in developing low grade of potassium mineral resources of China, i.e., the low concentrated [K+] brine waters. The other is the difficulty in separating single salts from high ratios of [Na+]/[K+] brines that were found in most salt lakes. In this project, we plan to extract alkali metal salts from the brine solutions of Li+,Na+,K+,Rb+,Cs+//Cl(-),CO3(-2)-H2O by procedures of isothermal evaporation, crystallization, filtration and CO2 acidification which would move the system of carbonate to bicarbonate. The invariant point of K2CO3•Na2CO3•xH2O which was found in solution of Li+、Na+、K+、Rb+、Cs+//Cl(-)、CO3(-2)-H2O would make one unable to obtain potassium single salts by the isothermal evaporation-crystallization-separation procedures. However, this invariant point can be avoided by procedures of CO2 acidification. The potassium bicarbonate (KHCO3) is to be precipitated because the system point is located in the crystallization area KHCO3 of the new diagram (alkaline ions// Cl(-)、HCO3(-)-H2O). During the evaporation process, the physic-chemical parameters such as solubility of dried salts, density, conductivity and pH value of the equilibrated solutions will be recorded in order to plot phase diagrams of both systems (Li+、Na+、K+、Rb+、Cs+//Cl(-)、CO3(-2)-H2O and Li+、Na+、K+、Rb+、Cs+//Cl(-)、HCO3(-)-H2O). Experiments are to be conducted to optimize procedures of evaporation-crystalization-separation-CO2 acidifications in order to achieve a higher efficiency of the single-salt seperation. For the planned theoretical study, temperatures and pressures of CO2 are to be taken into account when the Pitzer or Harvie-Weare calculation model is used to obtain values of activity coefficients for all reciprocal electrolytes. The solubility of the equilibrated salts is also to be predicted. New phase diagrams were to be constructed based on the Jänecke indexes which are derived from experiments and theoretical calculations. The developed routes for extraction of alkaline salts from these low concentrated [K+] brine waters will undoubtedly aid the on-going exploitation of salt lakes in China.