盐卤硼酸盐化学——XⅦ.MgO-B_2O_3-28%MgCl_2-H_2O体系20℃热力学非平衡态液固相关系研究  

Chemistry of Borate in Salt Lake Brine XVII. Study on Liquid-Solid Phase Diagram of Thermodynamic Non-Equilibrium of MgO-B_2O-3-28%MgCl_2-H2_O System at 20℃

作　　者：高世扬[1] 姚占力[1] 夏树屏[1] 

机构地区：[1]中国科学院青海盐湖研究所,西宁810008

出　　处：《化学学报》1994年第1期10-22,共13页Acta Chimica Sinica

基　　金：国家自然科学基金资助的课题;中国科学院基础研究重点资助课题

摘　　要：用动力学方法对MgO·nB_2O_3在28%MgCl_2-H_2O浓盐溶液中形成的过饱和溶液的结晶过程进行研究,首次得到MgO-B_2O_3-MgCl_2-H_2O体系过饱和区内的液固相关系图,即热力学非平衡态液固相关系图.该相图有六个相区:H_3BO_3,MgO·3B_2O_3·7.5H_2O,MgO·3B_2O_3·7H_2O,2MgO·2B_2O_3·MgCl_2·14H_2O,3Mg(OH)_2·MgCl_2·8H_2O和5Mg(OH)_2·MgCl_2·8H_2O.拟合得到各结晶过程的动力学方程,同时对结晶机制进行了探讨.The MgO-B2O3-MgCl2-H2O supersaturated solutions containing 28% MgCl2 and different mole ratio MgO:B2O3 were prepared and kept at 20℃. The crystallization processes of Mg borates from the solutions have been studied with the kinetic method. When a solid began to crystallize out from the solution, the solution samples were taken at different time for determing their densities, pH values and compositions until the density did not change basically. Finally, the solid phase was seperated, washed, dryed at room temperature and identified by IR spectra, powder X-ray diffraction, thermal analysis and chemical analysis.With the aid of simplex method and digital integration as well as Runge-Kutta digital solution of differential equation system, we fitted the experimental data and evaluated the kinetic parameters of the chosen models with computer. The crystallization kinetic equations have been given. The calculated results show that when MgO:B2O3 in initial solutions are 1.5:1, 1:2, 1:4, 1:6 and 1:9, the mechanism of crystallization are polynuclear layer controlled growth. When MgO:B2O3 are 3:1 and 2:1, the mechanism of crystallization are mononuclear layer controlled growth. We also disscussed the crystallization reaction processes.In this paper, we obtain the liquid-solid phase diagram of supersaturated solutions of MgO-B2O3-28%MgCl2-H2O system at 20℃for the first time and call it a phase diagram of thermodynamic non-equilibrium state. There are six solid phases in the diagram. They are H3BO3, MgO-3B2O3-7.5H2O, MgO-3B2O3·7H2O, 2MgO·2B2O3·MgCl2·14H2O, 8Mg(OH)2·MgCl2-8H2O and 5Mg(OH)2·MgCl2-8H2O respectively.

关 键 词：硼酸盐 结晶动力学 热力学 盐卤 

分 类 号：O613.81[理学—无机化学]