四元体系Li_(2)SO_(4)+Na_(2)SO_(4)+K_(2)SO_(4)+H_(2)O 298.2 K相平衡研究

Phase Equilibria of Aqueous Quaternary System Li_(2)SO_(4)+Na_(2)SO_(4)+K_(2)SO_(4)+H_(2)O at 298.2 K

为了获取锂钠钾共存硫酸盐体系298.2 K下各盐结晶形式,采用等温溶解平衡法研究了298.2 K下四元体系Li_(2)SO_(4)+Na_(2)SO_(4)+K_(2)SO_(4)+H_(2)O的相平衡关系,测定了该体系的溶解度和密度,采用X-ray粉晶衍射法测定了平衡固相组成,并绘制了相应的稳定相图和多温对比图。研究表明,298.2 K下该四元体系为复杂四元体系,有复盐2Li_(2)SO_(4)·Na_(2)SO_(4)·K_(2)SO_(4)、Li_(2)SO_(4)·3Na_(2)SO_(4)·12H_(2)O、LiKSO_(4)、Na_(2)SO_(4)·3K_(2)SO_(4)生成。其稳定相图由6个四元共饱点、12条单变量曲线以及7个结晶区组成。其中,复盐Na_(2)SO_(4)·3K_(2)SO_(4)结晶区最大,表明其在该体系中最易结晶析出;Li_(2)SO_(4)·H_(2)O结晶区最小。对比273.2 K、288.2 K、298.2 K、323.2 K、373.2 K四元体系多温相图可知,273.2 K时未发现复盐Na_(2)SO_(4)·3K_(2)SO_(4)和2Li_(2)SO_(4)·Na_(2)SO_(4)·K_(2)SO_(4)结晶形式;Na_(2)SO_(4)·10H_(2)O和Li_(2)SO_(4)·3Na_(2)SO_(4)·12H_(2)O结晶形式在323.2 K和373.2 K时转变为Na_(2)SO_(4)和Li_(2)SO_(4)·Na_(2)SO_(4)。288.2~373.2 K时随温度升高,K_(2)SO_(4)和Na_(2)SO_(4)·10H_(2)O结晶相区减小,Li_(2)SO_(4)·H_(2)O、Na_(2)SO_(4)、LiKSO_(4)和Li_(2)SO_(4)·Na_(2)SO_(4)结晶相区增大;Na_(2)SO_(4)·3K_(2)SO_(4)结晶相区先增大后减小,在298.2 K时结晶相区最大;2Li_(2)SO_(4)·Na_(2)SO_(4)·K_(2)SO_(4)结晶相区先减小后增大,298.2 K时结晶相区最小。

To obtain the crystallization form of the salts in the system containing with lithium,sodium,potassium,and sulfate at 298.2 K,the stable phase equilibrium for the quaternary system Li_(2)SO_(4)+Na_(2)SO_(4)+K_(2)SO_(4)+H_(2)O at 298.2 K was studied by using isothermal dissolution equilibrium method.The solubilities and densities of the aqueous quaternary system were determined,the solid phases were identified by using X-ray diffraction method.Meanwhile,the stable phase diagram at 298.2 K and the comparison diagram of the system at 273.2 K,288.2 K,298.2 K,323.2 K,and 373.2 K were constructed.Results show that the stable phase diagram of this quaternary system at 298.2 K belongs to complex type with double salts 2Li_(2)SO_(4)·Na_(2)SO_(4)·K_(2)SO_(4),Li_(2)SO_(4)·3 Na_(2)SO_(4)·12H_(2)O,LiKSO_(4),and Na_(2)SO_(4)·3K_(2)SO_(4)formed.The phase diagram of Li_(2)SO_(4)+Na_(2)SO_(4)+K_(2)SO_(4)+H_(2)O system consists of six invariant points,twelve isothermal dissolution curves,and seven crystallization regions.Among the crystallization regions,the crystallization region of double salt Na_(2)SO_(4)·3K_(2)SO_(4)is the largest,which indicate that the salt is most easily crystallized from the system,while the crystallization region of Li_(2)SO_(4)·H_(2)O is the smallest.Comparisons between the phase diagrams of Li_(2)SO_(4)+Na_(2)SO_(4)+K_(2)SO_(4)+H_(2)O system at(273.2 K,288.2 K,298.2 K,323.2 K,and 373.2 K),the double salts Na_(2)SO_(4)·3K_(2)SO_(4)and 2Li_(2)SO_(4)·Na_(2)SO_(4)·K_(2)SO_(4)were not formed at 273.2 K,the crystallization form of Na_(2)SO_(4)·10H_(2)O and Li_(2)SO_(4)·3Na_(2)SO_(4)·12H_(2)O change to Na_(2)SO_(4)and Li_(2)SO_(4)·Na_(2)SO_(4);when the temperatrure at 288.2 K~373.2 K,with the rise of temperature,the crystallization region of K_(2)SO_(4)and Na_(2)SO_(4)·10H_(2)O decrease,while the crystallization regions of Li_(2)SO_(4)·H_(2)O,Na_(2)SO_(4),LiKSO_(4)and Li_(2)SO_(4)·Na_(2)SO_(4)enlarge.The crystallization region of Na_(2)SO_(4)·3K_(2)SO_(4)increased at first and then decreased,and reached the maximum at 298.2 K,while the crystallization region of 2Li_(2)SO_(4)·Na_(2)SO_(4)·K_(2)SO_(4)decreased at first and then increased,and reached the minimum at 298.2 K.