Abstract: Industrial organo-sulfonic acid wastewater contains high concentrations of inorganic salts and various organo-sulfonates, causing significant challenges for their efficient removal, separation, and recovery. These waste streams often arise from complex industrial processes, and their intricate compositions make effective treatment and recycling more difficult. Herein, the phase equilibrium data for the sodium benzenesulfonate (BSNa)-sodium sulfate (Na2SO4)-water (H2O) ternary system were measured at temperatures of 273.15, 283.15, and 313.15 K using both the isothermal dissolution equilibrium method and Schreinemakers' wet residue method. Thermodynamic analysis of the dissolution process was performed using the van't Hoff equation, offering valuable insights into the system's behavior under different temperature conditions. At 313.15 K, the phase diagram indicated one invariant point, two univariant curves, and three distinct crystallization regions, corresponding to Na2SO4, BSNa, and their co-crystal mixture. However, at the lower temperatures of 273.15 and 283.15 K, the system displayed only one invariant point, one univariant curve, and two crystallization regions, specifically for Na2SO4?10H2O and a co-crystal region consisting of Na2SO4?10H2O and BSNa. Notably, no distinct crystallization region or solubility curve for BSNa was observed at these lower temperature ranges. Additionally, freeze crystallization experiments demonstrated no evidence of double salts or eutectic mixtures forming within the ternary system. This suggested that separating the components at lower temperatures, particularly around 283.15 K, was not only more efficient but also more cost-effective for obtaining pure salts. The thermodynamic analysis further revealed that the dissolution of Na2SO4 in this system was an endothermic, non-spontaneous process with an increase in entropy. The changes in enthalpy significantly influence the Gibbs free energy of dissolution, impacting the separation process. This research provided insight into the effective separation and recovery of BSNa and Na2SO4 from industrial wastewater, offering a solid foundation and practical guidance for improving wastewater treatment processes in industrial applications.

Key words: organo-sulfonate, phase equilibrium, thermodynamics, sodium sulfate, freeze crystallization

摘要： 工业有机磺酸废水中含有高浓度的无机盐和多种磺酸盐，对其有效处理和分离回收面临挑战。因此，本工作采用等温溶解平衡法和湿固相法探究了苯磺酸钠(BSNa)-硫酸钠(Na2SO4)-水(H2O)三元体系在273.15, 283.15和313.15 K下的相平衡数据，并利用van't Hoff方程对其溶解过程的热力学进行了研究。相平衡研究表明，该体系在313.15 K时存在1个共饱和点、2个单变量曲线及由BSNa, Na2SO4及其共晶组成的3个结晶区。而在273.15和283.15 K下，该体系仅存在1个共饱和点、1条单变量曲线和2个结晶区，对应于Na2SO4?10H2O及BSNa和Na2SO4?10H2O的共晶，未见BSNa的结晶区和溶解度曲线，表明该体系在低温下分离更易得到纯盐，且在283.15 K下进行分离的能效比更高。热力学研究表明，在该三元体系中，Na2SO4的溶解是一个非自发的吸热熵增过程，焓变对溶解Gibbs自由能的影响较大。本研究为高浓度有机废水中BSNa和Na2SO4的分离和回收奠定了基础。

关键词: 有机磺酸, 相平衡, 热力学, 硫酸钠, 冷冻结晶