Determination, Graphics Expression And Calculation Of Freezing Point And Eutectic Point In Salt-water Systems

In this paper,aiming at two quaternary salt-water systems of K⁺,Na⁺,Mg²⁺//SO₄^2--H₂O,K⁺,Mg²⁺,Li⁺//SO₄^2--H₂O and some ternary salt-water systems,such as Mg²⁺,Na⁺//SO₄^2--H₂O,Mg²⁺,K⁺//SO₄^2--H₂O,Li⁺,Mg²⁺//SO₄^2--H₂O,Li⁺,K⁺//SO₄^2--H₂O,K⁺//Cl-,NO₃^--H₂O,Na⁺//Cl-,NO₃^--H₂O,Li⁺,Na⁺//SO₄^2--H₂O,Na⁺//Cl-,SO₄^2--H₂O,Na⁺,K⁺//Cl--H₂O,Na⁺,K⁺//NO₃^--H₂O,Na⁺//NO₃^-,SO₄^2--H₂O,K⁺//Cl-,SO₄^2--H₂O,Na⁺,K⁺//SO₄^2--H₂O and K⁺//NO₃^-,SO₄^2--H₂O,the relationships between freezing points,eutectic points and compositions of solutions have been investigated.According to experimental data,the three-dimensional phase diagrams of salt-water systems were plotted at different temperature.The calculation formulas of predicting the freezing points and eutectic points were obtained.The results show:?1?The three-dimensional phase diagram of ternary salt-water systems at different temperature can be used to describe the relationships among the crystalline regions,freezing points or eutectic points and the compositions of liquids for the ternary salt-water systems visually,and to determine the precipitation processes of salts or ice as cooling solution.In the three-dimensional phase diagram of ternary salt-water systems at different temperature,the crystalline region of salt or ice has a fault.On the two sides of the fault,although the compositions of solutions are close,the crystallization temperature and the crystallization regularities of salts or ice are very different.?2?The double salts don't appear at the eutectic point temperature in the ternary salt-water systems of Mg²⁺,Na⁺//SO₄^2--H₂O,Li⁺,Mg²⁺//SO₄^2--H₂O and Li⁺,Na⁺// SO₄^2--H₂O,and there is an eutectic point with two single salts and ice,the eutectic point temperature is lower than the corresponding two kinds of single salts.Two eutectic lines with single salt and ice,two crystallization zones with single salt?the zone of the hydrated single salt is combined with that of the corresponding anhydrous single salt?and a crystallization zone with ice.?3?One double salt exists at the eutectic point temperature in the ternary salt-water system of Mg²⁺,K⁺//SO₄^2--H₂O and Li⁺,K⁺//SO₄^2--H₂O respectively,and there are two eutectic points with single salt,double salt and ice.At least,the temperature of one of the eutecticpoint is lower than the corresponding two kinds of single salts.There are two eutectic lines with single salt and ice,one eutectic line with double salt and ice,a crystallization zone with ice,two crystallization zones with single salt and a crystallization zone with double salt.?4?Aiming at the ternary salt-water systems studied in this paper,the calculation formulas of predicting the freezing points and eutectic points were obtained.The freezing points and eutectic points predicted are in good agreement with the experimental ones.?5?The double salt K₂SO₄·MgSO₄·6H₂O exists at the eutectic point temperature in quaternary salt-water system of K⁺,Na⁺,Mg²⁺//SO₄^2--H₂O,and there are two eutectic points with two single salts,double salt and ice.Two eutectic lines with two single salts and ice,three eutectic lines with single salt,double salt and ice.Three eutectic surfaces with single salt and ice,one eutectic surface with double salt and ice.?6?The double salts of KLiSO₄ and K₂SO₄·MgSO₄·6H₂O exist at the eutectic point temperature in the quaternary salt-water system of K⁺,Mg²⁺,Li⁺//SO₄^2--H₂O,There is an eutectic point with two single salts,double salt and ice,two eutectic points with single salt,two double salts and ice.One eutectic line with two single salts and ice,five eutectic lines with single salt,double salt and ice,one eutectic line with two double salts and ice.Three eutectic surfaces with single salt and ice,two eutectic surfaces with double salts and ice.