Na^+,K^+,Mg^(2+)//Cl^-,SO_4^(2-)-H_2O五元体系15℃介稳相图研究

Studies on the Metastable Phase Equilibrium of Na^+, K^+,Mg^+ //Cl^-, SO_4^(2-)-H_2O Quinary System at 15℃

得到Ｎａ＋,Ｋ＋,Ｍｇ２＋//Ｃｌ－,ＳＯ_４_(２－)－Ｈ２Ｏ五元体系１５℃时的介稳溶解度数据,绘制了该体系１５℃的介稳相图,共有９个为氯化钠所饱和的结晶区域:氯化钾、硫酸钠、钾钠芒硝、软钾镁矾、白钠镁矾、光卤石、七水硫酸镁、六水硫酸镁和水氯镁石．所得１５℃介稳相图和Ｖａｎ'ｔ Ｈｏｆｆ稳定相图比较有较大区别;在１５℃介稳相图中钾镁矾、钾盐镁矾以及五水硫酸镁和四水硫酸镁结晶区域消失,而软钾镁矾结晶区域显著扩大．比较作者所作该五元体系１５℃,２５℃及３５℃介稳相图,发现软钾镁矾(包括钾镁矾)相区以２５℃时最大,３５℃时最小;随温度升高,钾钠芒硝结晶相区依次向ＫＣｌ相区平行移动,导致ＫＣｌ相区缩小,Ｎａ２ＳＯ４相区扩大;随温度升高相应点的钠含量和水含量依次减小．

This paper presents the experimental date of metastable phase equilibrium of Na+, K+, Mg2+//Cl-, SO_4^(2-)-H2O quinary system at 15 ℃, from which the metastable phase diagram is drawn. lt con-sists of nine rigions of crystallization saturated with sodium chloride: potassium chloride, thenardite(Na2SO4), glasserite(3K2SO4·Na2SO4), schoenit(K2SO4·MgSO4·6H2O), astrankit(MgSO4·Na2SO4·4H2O), carnallite (KCl· MgCl2· 6H2O), epsomite (MgSO4·7H2O), hexahydrite (MgSO4·6H2O)and bischofit(MgCl2·6H2O). A large difference is found between the obtained metastable phase diagramat 15℃ and Van't Hoff's stable phase diagram at 25℃. The crystallization of leonite(K2SO4·MgSO4·4H2O), kainite(KCl·MgSO4·3H2O), magnesium sulfate quinhydrate(MgSO4·5H2O) and starkeyite(MgSO4·4H2O) disapear and the crystallization regions of schoenit greatly increased. Comparing themetastable phase diagram of Na+, K+, Mg2+ //Cl-, SO_4^(2-) at 15 ℃ with the metastable phase dia-gram at 25℃ and 35℃ by the authors, it is found the crystallization region of schonite (includingleonite) at 25℃ is the largest, and at 35℃ is the smallest with the temperature rising from 15℃ to 35℃, the crystallization regions of glasserite parallelly moved toward KCl region, which made the KCl regiondecreasing and the Na2SO4 region increasing; with the temperature rising from 15℃, 25℃ to 35℃, thesodium containing and water containing decrease consequently.