-15℃下Na~＋,K~＋,Mg^(2＋)//Cl^-,SO_4^(2-)-H_2O体系相平衡

Liquid-solid phase equilibrium of Na^+, K^+, Mg^(2+)// Cl^-, SO_4^(2-)-H_2O system at -15℃

采用等温溶解平衡法,研究了Na+,K+,Mg2+//Cl-,24 2SO-H2O五元水盐体系在-15℃下Na Cl·2H2O饱和时的相平衡关系,测定了溶解度和密度,并绘制出相应的相图。研究结果表明:该五元体系平衡相图中有3个四盐共饱点,7条单变量溶解度曲线及5个两盐结晶区,5个两盐结晶区分别对应于KCl+Na Cl·2H2O、Na2SO4·10H2O+Na Cl·2H2O、Mg SO4·7H2O+Na Cl·2H2O、Mg Cl2·8H2O+Na Cl·2H2O、KCl·Mg Cl2·6H2O+Na Cl·2H2O;所得-15℃相图和25℃下相图相比,相图结构大为简化:K2SO4·Mg SO4·4H2O、KCl·Mg SO4·3H2O、Na2SO4·3K2SO4、Na2SO4·Mg SO4·4H2O、Mg SO4·(4~6)H2O、K2SO4·Mg SO4·6H2O结晶区均消失,Na2SO4结晶区转变为Na2SO4·10H2O且结晶区扩大,KCl、Mg SO4·7H2O、KCl·Mg Cl2·6H2O结晶区缩小,Mg Cl2·6H2O结晶区转变为Mg Cl2·8H2O。在此基础上研究了不同组成的盐湖卤水在降温过程中的结晶规律,为低温盐田工艺的开发提供了理论依据。

Solubilities and densities in the system Na＋, K＋, Mg2＋// Cl-, 24 2SO-H O- saturated with Na Cl·2H2O were investigated with the isothermal method at -15℃. Based on experimental data, phase diagram and densitycomposition diagram were drawn. The equilibrium phase diagram of quinary system consisted of three invariant points, seven univariant curves and five crystallization fields, corresponding to solids of KCl＋Na Cl·2H2O, Na2SO4·10H2O＋Na Cl·2H2O, Mg SO4·7H2O＋Na Cl·2H2O, Mg Cl2·8H2O＋Na Cl·2H2O and KCl·Mg Cl2·6H2O＋ Na Cl·2H2O. Compared with the phase diagram at 25℃, in the phase diagram at -15℃, the crystalline regions of K2SO4·Mg SO4·4H2O, KCl·Mg SO4·3H2O, Na2SO4·3K2SO4, Na2SO4·Mg SO4·4H2O, Mg SO4·（4—6）H2O, K2SO4·Mg SO4·6H2O did not exist, the crystalline region of Na2SO4 converted into the crystallization field of Na2SO4·10H2O and became larger, the crystallization fields of KCl, Mg SO4·7H2O, KCl·Mg Cl2·6H2O decreased and the crystalline region of Mg Cl2·6H2O converted into the crystallization field of Mg Cl2·8H2O. The crystallization behavior of brines with different concentrations in the cooling process was studied. Such information could provide theoretical guidance for comprehensive utilization of salt-lake resource.