碱金属碳酸（氢）盐水体系相图构建与低钾高钠型卤水的单盐分离

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.

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。

本研究针对“低钾高钠”（浓度[Na+]/[K+]>5）卤水体系，研究了碱金属（Li+、Na+、K+、Rb+、Cs+）//Cl-、CO32-、HCO3--H2O）水盐体系，旨在实现碱金属单盐，特别是K+盐的分离，为我国战略性碱金属的提取提供科学依据。鉴于预研项目的时间所限，本项目重点研究了Li+、Na+、K+//Cl-、CO32-、HCO3--H2O相行为与单盐分离。通过蒸发、结晶及CO2酸化等工艺，避开了复盐（KNaCO3）生成，实现了碱金属单盐分离，并获得Rb+、Cs+浓缩液。使得K+盐提取率从4%提高一个数量级（30~75%）。并且将温度、CO2压力考虑入Pitzer电解质溶液理论，结合理论计算，为低品位钾盐卤水资源化利用提供解决方案。本研究选取Cl-为阴离子的水盐体系，考察引入CO2改变水盐体系端员，水盐相图的变化规律，获得结晶路线。具体步骤如下：首先考察了Na2CO3-K2CO3-H2O与NaHCO3-KHCO3-H2O相平衡，通过CO2酸化Na2CO3-K2CO3-H2O，获取NaHCO3-KHCO3-H2O相平衡介稳平衡。确定了变温、变PCO2条件下的蒸发、结晶、分离工艺，测定液、固相组成，密度，折光率，电导率及pH值等，绘制出CO32-及HCO3-体系高精度相图，实现了KHCO3高效分离。本研究考察了CO2对含碱金属、硼酸盐体系卤水的酸化作用，发现了Na+、K+//B4O72-、CO32--H2O的CO2碳化硼酸盐（B4O72-）增溶效应，通过萃取工艺，获得价值更大的硼酸盐提取工艺，此工艺有望产业转化。其次研究了Na+、K+//Cl-、CO32--H2O四元体系，即氯化物型低钾高钠性卤水体系，实现高钠低钾水盐体系的钾盐提取。将上述简单四元体系引入其他碱金属离子，参照实际盐湖卤水中碱金属离子活度，测定Li+、Na+、K+等多种碱金属盐在CO32-及HCO3-体系中的溶解度。考察CO2偏压等变化规律，最终获取优化工艺。另外，基于Na+、K+//Cl-、CO32--H2O四元体系的相变行为，合成了多种矿物功能材料（共生黏土、MoS2、水盐体系贵金属等），研究发现其在催化、燃料电池等领域具有广泛应用前景，发表了系列研究论文（J. Chem. Eng. Data, Adv. Mater., Adv. Energy Mater.等17篇），并申请4项发明专利。