258.15 K下五元体系Li+,Na+,Mg^(2+)//SO_(4)^(2-),Cl^(-)-H_(2)O相平衡研究

Study on phase equilibrium of quinary system of Li+,Na+,Mg^(2+)//SO_(4)^(2-),Cl^(-)-H_(2)O at 258.15 K

中国含锂盐湖大部分位于青藏、新疆等干旱少雨、冬季寒冷且漫长的地区。为指导低温提锂工艺的开发和设计、利用冬季冷能进行目标离子的富集及明确含锂盐湖在低温下的析盐规律,采用等温溶解平衡法对258.15 K、二水氯化钠饱和条件下的交互五元体系Li+,Na+,Mg^(2+)∥SO_(4)^(2-),Cl^(-)-H_(2)O相平衡关系进行研究并构建等温平衡相图。结果表明,相图中有4个共饱点、6个两盐结晶区(NaCl·2H_(2)O+Na_(2)SO_(4)·10H_(2)O、NaCl·2H_(2)O+MgCl_(2)·8H_(2)O、NaCl·2H_(2)O+MgSO4·7H_(2)O、NaCl·2H_(2)O+Li_(2)SO_(4)·H_(2)O、NaCl·2H_(2)O+LiCl·2H_(2)O、NaCl·2H_(2)O+LiCl·MgCl_(2)·7H_(2)O)、9条单变量溶解度曲线;6个结晶区中,只存在一种复盐为LiCl·MgCl_(2)·7H_(2)O,其结晶区最小,Na_(2)SO_(4)·10H_(2)O结晶区最大。与该体系在273.15 K下的稳定相图相比,硫酸盐型复盐消失,复盐结晶区减少到1个,共饱点减少至4个,相图结构得以简化。因此,将涩聂湖卤水降温至258.15 K时能有效脱除硫酸根,从而实现富集锂离子的目的。

Most lithium salt lakes in China are located in areas with drought,little rain,cold and long winters,such as Qinghai Tibet and Xinjiang.To guide the process of lithium extraction at low temperature,enrich the target ions by using cold energy in winter and clarify the salt precipitation law of lithium-containing salt lake at low temperature,the phase equilibrium of the interactive quinary system of Li+,Na+,Mg^(2+)∥SO_(4)^(2-),Cl^(-)-H_(2)O under saturated NaCl·2H_(2)O at 258.15 K was investigated by isothermal dissolution method and the phase diagram was constructed.There were four invariant points,six two-salt crystallization fields(NaCl·2H_(2)O+Na_(2)SO_(4)·10H_(2)O,NaCl·2H_(2)O+MgCl_(2)·8H_(2)O,NaCl·2H_(2)O+MgSO4·7H_(2)O,NaCl·2H_(2)O+Li_(2)SO_(4)·H_(2)O,NaCl·2H_(2)O+LiCl·2H_(2)O,NaCl·2H_(2)O+LiCl·MgCl_(2)·7H_(2)O)and nine univariate solubility curves in the phase diagram.LiCl·MgCl_(2)·7H_(2)O was the only double salt in the phase diagram,and its crystallization field was the smallest.The crystallization field of Na_(2)SO_(4)·10H_(2)O was the largest in the phase diagram.Compared with the stable phase diagram of the quinary system at 273.15 K,the sulfate type double salt was disappeared,the double salt crystallization zone was reduced to1,and the invariant point was reduced to 4,and the correlation system was simplified.Cooling the brine of Seniehu lake to258.15 K could effectively separate sulfate and achieve the purpose of enriching lithium.