The solid–liquid equilibrium data of the aqueous NaOH–Na₂CO₃–Na₂SO₄–H₂O, NaOH–Na₂CO₃–NaCl–H₂O, and NaOH–Na₂SO₄–NaCl–H₂O quaternary systems at 363.15 K were measured. The equilibrium solid phases and solubilities of salts in the three systems and its subsystems were determined. The densities of the saturated solutions were also determined. The experimental data are used to plot the solubility diagrams and water content diagrams of the systems. It was found that the NaOH–Na₂CO₃–Na₂SO₄–H₂O system contains the solid solution of γ-salt (mNa₂SO₄·nNa₂CO₃) and the other two systems Na₂CO₃–NaOH–NaCl–H₂O and NaOH–Na₂SO₄–NaCl–H₂O have the complex salts S1 (Na₂SO₄·NaOH) and S3 (Na₂SO₄·NaCl·NaOH). On the basis of Xu’s activity coefficient model, a model was constructed for the correlation of solid–liquid equilibrium in electrolyte solutions to calculate the solubilities of salts in these systems at 363.15 K. The calculated solubilities are in agreement with the experimental values.

中文翻译：

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四元体系中的相平衡NaOH + Na ₂ CO ₃ + Na ₂ SO ₄ + H ₂ O，Na ₂ CO ₃ + NaOH + NaCl + H ₂ O和NaOH + Na ₂ SO ₄ + NaCl + H ₂ O在363.15 ķ

NaOH–Na ₂ CO ₃ –Na ₂ SO ₄ –H ₂ O，NaOH–Na ₂ CO ₃ –NaCl–H ₂ O和NaOH–Na ₂ SO ₄ –NaCl–H ₂水溶液的固液平衡数据测量了363.15 K的O四元系统。确定了这三个系统及其子系统中平衡固相和盐的溶解度。还确定了饱和溶液的密度。实验数据用于绘制系统的溶解度图和水含量图。发现NaOH–Na ₂ CO ₃ –Na ₂SO ₄ -H ₂ O系统包含γ-盐的固溶体（m Na ₂ SO ₄ · n Na ₂ CO ₃）和其他两个系统Na ₂ CO ₃ -NaOH-NaCl-H ₂ O和NaOH-Na ₂ SO ₄ –NaCl–H ₂ O具有复合盐S1（Na ₂ SO ₄ ·NaOH）和S3（Na ₂ SO ₄·NaCl·NaOH）。在徐的活度系数模型的基础上，建立了电解质溶液中固液平衡相关性的模型，以计算在363.15 K下这些系统中盐的溶解度。计算的溶解度与实验值一致。