三元体系MgCl_2+NH_4Cl+H_2O 298.15K稳定相平衡

Stable phase equilibrium in aqueous ternary system MgCl_2+NH_4Cl+H_2O at 298.15 K

采用等温溶解平衡法研究了三元体系MgCl2+NH4Cl+H2O 298.15 K的稳定相平衡,测定了平衡时各组分的溶解度及平衡液相的密度、折光率等物化性质。该三元体系在298.15 K时的稳定相图含有2个共饱点E1,E2,3条单变量曲线AE1,E1E2,E2B,3个结晶区。3个结晶区分别对应MgCl2.6H2O,NH4Cl及复盐铵光卤石(NH4Cl.MgCl2.6H2O)。2个共饱点中,E1为不相称共饱点,对应的平衡固相为NH4Cl.MgCl2.6H2O+NH4Cl,平衡液相组成为w(NH4Cl)=7.79%,w(MgCl2)=21.90%;E2为相称共饱点,对应的平衡固相为NH4Cl.MgCl2.6H2O+MgCl2.6H2O,平衡液相组成为w(NH4Cl)=0.21%,w(MgCl2)=32.27%。研究结果表明:该三元体系为复杂三元体系,有不相称复盐NH4Cl.MgCl2.6H2O生成。MgCl2对NH4Cl有强烈的盐析作用。平衡液相的密度和折光率随着溶液中MgCl2质量分数的增加而增大。采用经验公式对密度和折光率进行计算,计算值与实验值吻合度较好,相对偏差小于0.012。

The stable phase equilibrium of the ternary system MgCl2 ＋ NH4 Cl ＋ H2O at 298.15 K was investigated by using isothermal dissolution equilibrium method. The solubility of each component and the physicochemical properties such as density and refractive index of the equilibrium liquid were determined. The stable phase diagram and the physicochemical properties versus composition diagrams of the ternary system were constructed. The stable phase diagram consists of two invariant points E1 and EE, three univariant curves AEI, E1E2, EEB, and three crystallization regions corresponding to single salts MgCl2·6H2O, NH4Cl and the double salt NH4Cl · MgCla· 6H2O. Point E1 is an incommensurate invariant point, while point E2 is a commensurate invariant point. Point El is saturated with NH4Cl ~ MgCl2·6HEO and NH4Cl, and the mass fraction composition of the corresponding liquid phase is w（NH4Cl） = 7.79%, w（MgCl2 ） = 21.90%. Point E2 is saturated with NH4Cl· MgCl2·6H2O and MgCl2·6H2O, the composition of the corresponding liquid phase is w（NH4Cl） = 0.21%, w（ MgCla） = 32.27%. The results show that the system MgCla ＋ NH4Cl ＋ H2O is a complex ternary system with an incommensurate double salt NH4Cl · MgCl2·6H2O formed at 298.15 K. Salt MgCl2 has strong salting-out effect on salt NH4Cl in the solution. The density and refractive index of the equilibrium liquid both increase with the increase of the mass fraction of MgCl2. The calculated values of density and refractive index by using empirical equation are in good agreement with the experimental data, and the relative deviation is less than 0.012.