A new sustainable process was developed to recycle FeSO₄·7H₂O produced from the sulfate process for titanium dioxide production. In this process, FeSO₄·H₂O was crystallized out from a subsequent cooling crystallization operation rather than FeSO₄·7H₂O. In order to better develop the new process and provide a theoretical basis for ferrous sulfate dehydration, the study of the phase equilibrium of the FeSO₄–H₂SO₄–HCl–H₂O system is necessary. For this purpose, the solubility of FeSO₄·7H₂O in the H₂SO₄–HCl–H₂O system was determined at a temperature range from 278.15 to 313.15 K using a dynamic method. By raising temperature and the concentration of HCl, more FeSO₄·7H₂O can be dissolved in this system. However, with the addition of H₂SO₄, the solubility of FeSO₄·7H₂O is found to decrease due to common-ion effect. A speciation-based model equipped with middle-range parameters was established by regressing the experimental and reported solubility of FeSO₄·7H₂O under varying conditions. The phase transition temperature of FeSO₄·7H₂O to FeSO₄·H₂O was successfully predicted by the new model, which was found to decrease with increasing concentration of both H₂SO₄ and HCl.

中文翻译：

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H ₂ SO ₄ -HCl–H ₂ O体系中FeSO ₄ ·7H ₂ O到FeSO ₄ ·H ₂ O的相变建模

一个新的过程可持续的开发是为了再循环的FeSO ₄ ·7H ₂从二氧化钛生产硫酸盐法产生的O操作。在这个过程中，的FeSO ₄ ·H ₂ O的从后续冷却结晶操作结晶出来，而不是的FeSO ₄ ·7H ₂ O.为了更好地开发新进程和硫酸亚铁脱水提供理论基础，的研究FeSO ₄ –H ₂ SO ₄ –HCl–H ₂ O系统的相平衡是必要的。为此目的，FeSO ₄ ·7H ₂ O在H ₂ SO中的溶解度使用动态方法在278.15至313.15 K的温度范围内测定了₄ –HCl–H ₂ O系统。通过提高温度和HCl的浓度，更多的FeSO ₄ ·7H ₂ O可以溶解在该系统中。然而，发现由于添加了H ₂ SO ₄，FeSO ₄ ·7H ₂ O的溶解度由于共离子效应而降低。通过回归实验和报道的FeSO ₄ ·7H ₂ O在不同条件下的溶解度，建立了带有中间范围参数的基于物种的模型。FeSO ₄ ·7H ₂ O转变为FeSO的相变温度新模型成功预测了₄ ·H ₂ O，发现随着H ₂ SO ₄和HCl浓度的增加，H ₂ O会降低。