四元体系(Li^(+),Mg^(2+)//Cl^(−),borate-H_(2)O)308.15 K相平衡与相图研究

Phase equilibria and phase diagram of the quaternary system(Li^(+),Mg^(2+)//Cl^(−),borate-H_(2)O) at 308.15 K

采用等温溶解平衡法,开展四元体系Li^(+),Mg^(2+)//Cl^(−),borate–H_(2)O固液相平衡与相图研究,测定平衡溶液的液相组成、密度、折射率和pH。该四元体系相图中存在的盐类矿物为:LiCl·H_(2)O、Li_(2)B_(4)O_(7)·3H_(2)O、MgCl_(2)·6H_(2)O、Mg_(2)B_(6)O_(11)·15H_(2)O和锂光卤石LiCl·MgCl_(2)·7H_(2)O,其中锂光卤石LiCl·MgCl_(2)·7H_(2) O是异成分复盐,溶液中MgCl 2存在下章氏硼镁石(MgB_(4)O_(7)·9H_(2)O)不稳定,转化为多水硼镁石(Mg_(2)B_(6)O_(11)·15H_(2)O)。多水硼镁石结晶区最大,表明镁硼酸盐易于结晶析出,而锂光卤石结晶区最小。采用Pitzer热力学模型对该四元体系的溶解度进行理论预测,计算相图与实验相图吻合较好。该四元体系的稳定相平衡与相图研究,可为含锂硼盐湖老卤中锂、镁、硼产品开发及其综合利用提供理论依据。

Solid-liquid phase equilibria and phase diagrams for the quaternary system(Li^(+),Mg^(2+)//Cl^(−),borate–H_(2)O)were investigated,and the compositions in liquid phase,densities,refractive indices and pH were measured experimentally by using isothermal dissolution equilibrium method.There are five minerals corresponding to LiCl·H_(2)O,Li_(2)B_(4)O_(7)·3H_(2)O,MgCl_(2)·6H_(2)O,Mg_(2)B_(6)O_(11)·15H_(2)O,and the lithium carnallite LiCl·MgCl_(2)·7H_(2)O existed in this system.Mg_(2)B_(6)O_(11)·15H_(2)O occupies the greatest part of phase region,while LiCl·MgCl_(2)·7H_(2)O covers the smallest.The mineral LiCl·MgCl_(2)·7H_(2)O belongs to the incongruent double salt,and hungchaoite(MgB_(4)O_(7)·9H_(2)O)is transformed into Mg_(2)B_(6)O 11·15H_(2)O in the concentrated MgCl_(2)aqueous solution.The crystalline area of inderite is the largest,indicating that magnesium borate is easy to crystallize,while the crystalline area of lithium carnallite is the smallest.The solubility of this quaternary system were predicted using Pitzer thermodynamics model,and the calculated solubility agreed well with experimental data.The phase equilibrium study of this quaternary system(Li^(+),Mg^(2+)//Cl^(-),borate-H_(2)O)will provide a theoretical basis to promote the development of lithium,magnesium and boron products and to guide the comprehensive utilization of this precious salt lake brine resources.