Study On Phase Equilibria Of The Quinary Systems Na⁺,K⁺//Cl^-,Br^-,B₄O₇^2--H₂O,Na⁺,K⁺//Br^-,So₄^2-,B₄O

Phase equilibria of reciprocal quinary systems Na⁺,K⁺//Cl^-,Br^-,B₄O₇^2--H₂O,Na⁺,K⁺//Cl^-,SO₄^2-,B₄O₇^2--H₂O and their subsystems at multi-temperature were studied.These systems included one ternary system NaBr-Na₂SO₄-H₂O at 348 K;two ternary systems NaCl-NaBr-H₂O and KCl-KBr-H₂O at 348 K;two ternary systems NaCl-NaBr-H₂O and KCl-KBr-H₂O at 373 K;and quaternary system KCl-KBr-K₂B₄O₇-H₂O at 323 K and 348 K;reciprocal quinary systems Na⁺,K⁺//Cl^-,Br^-,B₄O₇^2--H₂O at 373 K and Na⁺,K⁺//Cl^-,SO₄^2-,B₄O₇^2--H₂O at 348 K.All systems were conducted by isothermal solution equilibrium method.The solubilities and densities of these systems listed at corresponding temperature were mensurated.According to the experimental data,the isothermal equilibria phase diagram of the quinary system Na⁺,K⁺//Cl^-,Br^-,B₄O₇^2--H₂O at 373 K?saturated with Na₂B₄O₇?,the isothermal equilibria phase diagram of the quinary system Na⁺,K⁺//Cl^-,SO₄^2-,B₄O₇^2--H₂O at 348 K,sodium content diagrams and water content diagrams of quinary systems were plotted.The isothermal equilibria phase diagrams and water content diagrams of quaternary systems were finished.The isothermal equilibria phase diagrams of the ternary systems were drew,and density-composition diagrams of the relevant systems were also plotted.The experimental results show that the isothermal phase diagram of the ternary system Na Br-Na₂SO₄-H₂O at 348 K was a simple common saturation and without complex salt and solid solution.The isothermal phase diagram consists of one invariant point,two univariant curves and three fields of crystallization.The equibrium solid phases of the invariant point E were NaBr+Na₂SO₄[w?NaBr?=53.12%,w?Na₂SO₄?=0.53%],the equibrium solid phases of three fields of crystallization were NaBr,Na₂SO₄ and?NaBr+Na₂SO₄?.Analyzing the isothermal phase diagram and the solubilities in the table,It can be observed that NaBr has a strong salting-out effect on Na₂SO₄.The ternary system NaCl-NaBr-H₂O at 348 K and 373 K both belonged to solid solution type,the solid solution Na?Cl,Br?was formed,and no complex salt was found.The isothermal phase diagrams of the system NaCl-NaBr-H₂O at 323 K and348 K are similar;the two phase diagrams comprised one field of crystallization[Na?Cl,Br?],one univariant curve and no invariant point.The ternary system KCl-KBr-H₂O at 348 K and 373 K also belonged to solid solution type,the solid solution K?Cl,Br?was formed,and no complex salt was found in the system at the two temperatures.The isothermal phase diagrams of the system KCl-KBr-H₂O at323 K and 348 K are also similar;the two phase diagrams contained one field of crystallization[K?Cl,Br?],one univariant curve and no invariant point too.The quaternary system KCl-KBr-K₂B₄O₇-H₂O at 323 K and 348 K both contained solid solution K?Cl,Br?,their solubility diagram has no invariant point,but has a univariant dissolution curve,without any invariant point of quaternary system and two crystallization regions corresponding to K?Cl,Br?and potassium borate quahydrate?K₂B₄O₇·4H₂O?.Compared to the isothermal phase diagram at 323K,the crystallization field of K?Cl,Br?increased at 348 K,and this showed that the solubility of K?Cl,Br?in the quinary system KCl-KBr-K₂B₄O₇-H₂O was smaller at348 K than at 323 K;the crystallization field of K₂B₄O₇·4H₂O decreased,and this showed that in the quinary system KCl-KBr-K₂B₄O₇-H₂O the solubility of K₂B₄O₇·4H₂O was larger at 348 K than at 323 K.Moreover,in the water content diagrams,the variation trend of water content was the same,but the water content at348 K was smaller as a whole.In the density-composition diagrams,the variation trend of density-composition was semblable,but the density at 348 K was largerer in the whole.The ionic crystal radius ratio of Cl^-/K⁺is closer to 1.4 than the counterpart of Br^-/K⁺,therefore the hydration capacity of KBr is greater than the counterpart of KCl,and the law of solubility variation is that KBr has a strong salt-out effect on KCl.As the experimental results showed,the reciprocal quinary system Na⁺,K⁺//Cl^-,Br^-,B₄O₇^2--H₂O 373 K contained solid solutions,the solid solutions Na?Cl,Br?was found,and no complex salt was formed.The isothermal phase diagrams of reciprocal quinary system Na⁺,K⁺//Cl^-,Br^-,B₄O₇^2--H₂O at 373 K?saturated with Na₂B₄O₇?comprised two invariant points,five univariant curves and four fields of crystallization.The equibrium solid phases of four fields of crystallization were K₂B₄O₇·4H₂O,KBr,Na?Cl,Br?and KCl.The isothermal phase diagrams of reciprocal quinary system Na⁺,K⁺//Cl^-,SO₄^2-,B₄O₇^2--H₂O at 348 K,the double salt Na₂SO₄·3K₂SO₄ was formed,and no solid solutions was found.The phase diagrams comprised seven uninvariant curves,three invariant points,and five crystallization fields?saturated with NaCl?:[Na₂SO₄,Na₂ B₄O₇·5H₂O,Na₂SO₄·3K₂SO₄?Gla?,K₂B₄O₇·4H₂O and KCl].