This paper is part of a series of studies on the development of a multi-temperature thermodynamically consistent model for salt lake brine systems. The objective of this study is to extend the binary thermodynamic models published in our previous studies to multicomponent systems. A revised general Pitzer–Simonson–Clegg (PSC) $g^{E,\ast }$ equation for multicomponent system is proposed without limitation on the number of components. From the $g^{E,\ast }$ equation, mathematical expressions of the activity coefficient of each component as well as the excess enthalpy and excess heat capacity of the aqueous phase are derived. Based on the multicomponent PSC equations and the CALPHAD-type thermodynamic framework, a generic command-line based program, named ISLEC, was developed for the thermodynamic modeling of aqueous system. The performance of the model and program were tested using three case studies based on typical systems. In the first case study, a temperature-dependent model for a six-component system of Li⁺-Na⁺-K⁺-Mg₂+-Ca₂+-Cl^--H₂O was developed based our previous published binary models and the regressed mixing parameters developed in this study. The model well represents the phase equilibrium and activity properties of all 10 sub-ternary systems well over a wide temperature range. These ternary models are generally valid from the lowest eutectic temperature to approximately 373.15 K. For most of the studied ternary systems, the original PSC model is valid for solubility isotherm and phase diagram modeling. However, for the LiCl + KCl + H₂O and KCl + CaCl ₂+ H₂O ternary systems, the revised PSC equations are advantageous in describing the solid-liquid phase equilibria, especially at elevated temperatures. Using the parameters determined in binary and ternary systems, the Li⁺-Na⁺-K⁺-Mg²⁺-Ca²⁺-Cl^--H₂O model system reproduces the phase diagrams of its 10 sub-quaternary and two of its sub-quinary systems (LiCl + NaCl + KCl + MgCl₂+H₂O and NaCl + KCl + MgCl₂+CaCl₂+H₂O) generally well at various temperatures. However, the reliability of our model predictions of the thermal properties of multicomponent aqueous mixture cannot be assured, and the differences from experimental data are usually large. Thus, the thermal data generated from our model should be used with caution for multicomponent systems. The evaporation and cooling crystallization processes of Dead Sea brine, which is a six-component Li⁺–Na⁺–K⁺–Mg₂+-Ca₂+-Cl^--H₂O system, were simulated to test the ISLEC program. The results demonstrate the satisfactory performance of the ISLEC program for solving multiphase equilibria in systems containing at least six components. In the second case study, the PSC equations were applied to model the solubility isotherms in a neutral-solute-containing system: H₃BO₃+NaCl + H₂O. The results are excellent, but additional H₃BO₃-containing systems should be studied for further validation. In the last case study, mass and energy balance simulations were performed for the process of KCl production using sylvinite as the raw material, thus revealing the applications of ISLEC for process design and simulation.

本文是盐湖盐水系统多温度热力学一致性模型开发系列研究的一部分。这项研究的目的是将我们先前研究中发布的二元热力学模型扩展到多组分系统。修改后的一般Pitzer–Simonson–Clegg（PSC）$G^{Ë，\ast }$提出了用于多组分系统的方程式，而不限制组分的数量。来自$G^{Ë，\ast }$通过方程式，可以推导出每种成分的活度系数以及水相的过量焓和过量热容的数学表达式。基于多组分PSC方程和CALPHAD型热力学框架，开发了一个基于命令行的通用程序ISLEC，用于水系统的热力学建模。使用基于典型系统的三个案例研究测试了模型和程序的性能。在第一个案例研究中，Li ⁺ -Na ⁺ -K ⁺ -Mg ₂ + -Ca ₂ + -Cl ^-- H ₂六组分系统的温度依赖模型O是根据我们先前发布的二进制模型和本研究中开发的回归混合参数开发的。该模型很好地表示了在宽温度范围内所有10个三元系统的相平衡和活性。这些三元模型通常在最低的共晶温度到大约373.15 K时有效。对于大多数研究的三元系统，原始PSC模型对于溶解度等温线和相图建模都是有效的。然而，对于LiCl + KCl + H ₂ O和KCl + CaCl  ₂ + H ₂ O三元体系，修改后的PSC方程式在描述固液相平衡方面是有利的，尤其是在高温下。利用二元和三元系统中确定的参数，Li⁺ -Na ⁺ -K ⁺ -Mg ²⁺ -Ca ²⁺ -Cl ^-- H ₂ O模型系统复制了其10个亚四级体系和其中两个亚五级体系（LiCl + NaCl + KCl + MgCl ₂ + H ₂ O和NaCl + KCl + MgCl ₂ + CaCl ₂ + H ₂O）在各种温度下通常都很好。但是，我们不能保证模型预测多组分水性混合物热性能的可靠性，并且与实验数据的差异通常很大。因此，对于多组分系统，应谨慎使用从我们的模型生成的热数据。死海盐水的蒸发和冷却结晶过程，该过程为六组分Li ⁺ -Na ⁺ -K ⁺ -Mg ₂ + -Ca ₂ + -Cl ^-- H ₂O系统，进行了仿真以测试ISLEC程序。结果表明，ISLEC程序在解决包含至少六个组件的系统中的多相平衡方面具有令人满意的性能。在第二种情况下研究中，PSC方程应用于在含有中性溶质的系统中的溶解度等温线模型：H ₃ BO _3个+的NaCl + H ₂ O的结果是极好的，但附加H ₃ BO ₃的含系统应该进行研究以进一步验证。在最后一个案例研究中，对以Sylvinite为原料的KCl生产过程进行了质量和能量平衡模拟，从而揭示了ISLEC在过程设计和模拟中的应用。