四元体系Li2SO4+Na2SO4+K2SO4+H2O298.2 K相平衡研究

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Li₂SO₄₊Na₂SO₄₊K₂SO₄₊H₂O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2Li₂SO₄·Na₂SO₄·K₂SO₄、Li₂SO₄·3Na₂SO₄·12H₂O、LiKSO₄、Na₂SO₄·3K₂SO₄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Na₂SO₄·3K₂SO₄结晶区最大,表明其在该体系中最易结晶析出；Li₂SO₄·H₂O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Na₂SO₄·3K₂SO₄和2Li₂SO₄·Na₂SO₄·K₂SO₄结晶形式；Na₂SO₄·10H₂O和Li₂SO₄·3Na₂SO₄·12H₂O结晶形式在323.2 K和373.2 K时转变为Na₂SO₄和Li₂SO₄·Na₂SO₄。288.2~373.2 K时随温度升高,K₂SO₄和Na₂SO₄·10H₂O结晶相区减小,Li₂SO₄·H₂O、Na₂SO₄、LiKSO₄和Li₂SO₄·Na₂SO₄结晶相区增大；Na₂SO₄·3K₂SO₄结晶相区先增大后减小,在298.2 K时结晶相区最大；2Li₂SO₄·Na₂SO₄·K₂SO₄结晶相区先减小后增大,298.2 K时结晶相区最小。

Phase Equilibria of Aqueous Quaternary System Li2SO4 + Na2SO4 + K2SO4 + H2O at 298.2 K

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 Li₂SO₄₊Na₂SO₄₊K₂SO₄₊H₂O 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 2Li₂SO₄·Na₂SO₄·K₂SO₄,Li₂SO₄·3Na₂SO₄·12H₂O,LiKSO₄,and Na₂SO₄·3K₂SO₄ formed. The phase diagram of Li₂SO₄₊Na₂SO₄₊K₂SO₄₊H₂O system consists of six invariant points,twelve isothermal dissolution curves,and seven crystallization regions. Among the crystallization regions,the crystallization region of double salt Na₂SO₄·3K₂SO₄ is the largest,which indicate that the salt is most easily crystallized from the system,while the crystallization region of Li₂SO₄·H₂O is the smallest. Comparisons between the phase diagrams of Li₂SO₄₊Na₂SO₄₊K₂SO₄₊H₂O system at (273.2 K,288.2 K,298.2 K,323.2 K,and 373.2 K),the double salts Na₂SO₄·3K₂SO₄ and 2Li₂SO₄·Na₂SO₄·K₂SO₄ were not formed at 273.2 K,the crystallization form of Na₂SO₄·10H₂O and Li₂SO₄·3Na₂SO₄·12H₂O change to Na₂SO₄ and Li₂SO₄·Na₂SO₄; when the temperatrure at 288.2 K~373.2 K,with the rise of temperature,the crystallization region of K₂SO₄ and Na₂SO₄·10H₂O decrease,while the crystallization regions of Li₂SO₄·H₂O,Na₂SO₄,LiKSO₄ and Li₂SO₄·Na₂SO₄ enlarge. The crystallization region of Na₂SO₄·3K₂SO₄ increased at first and then decreased,and reached the maximum at 298.2 K,while the crystallization region of 2Li₂SO₄·Na₂SO₄·K₂SO₄ decreased at first and then increased,and reached the minimum at 298.2 K.