The disposal of titanogypsum, also known as red gypsum, which is generated during the titanium dioxide sulfate process, has become a significant environmental challenge. We propose a new process to recover iron impurities such as FeCl₂·4H₂O and to convert titanogypsum to saleable hemihydrate gypsum. For this purpose, we use HCl–FeCl₂ solution generated via the reaction of H₂SO₄–FeSO₄ with CaCl₂ to leach iron hydroxide from titanogypsum. The hemihydrate precipitation and phase-transition kinetics of the reaction of HCl–H₂SO₄–FeSO₄ with CaCl₂ are experimentally investigated at 353 K. The common ion effect of CaCl₂ in the FeCl₂ solution for FeCl₂·4H₂O crystallization is predicted by NRTL modeling of the solid–liquid equilibria of the FeCl₂–CaCl₂–H₂O system. High-quality, saleable α-gypsum and FeCl₂·4H₂O solids obtained by treating titanogypsum samples provided by a commercial processing plant further shows that the new process is feasible.

中文翻译：

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利用弱酸和CaCl2修复钛石膏（红石膏）生产可销售的α-石膏和FeCl2·4H2O的工艺


在二氧化钛硫酸盐工艺过程中产生的钛石膏（也称为红石膏）的处置已成为一项重大的环境挑战。我们提出了一种新工艺来回收 FeCl ₂ ·4H ₂ O 等铁杂质，并将钛石膏转化为可销售的半水石膏。为此，我们使用 H ₂ SO ₄ –FeSO ₄ 与 CaCl < 反应生成的 HCl–FeCl ₂ 溶液。 b6>从钛石膏中浸出氢氧化铁。 HCl–H ₂ SO ₄ –FeSO ₄ 与 CaCl ₂ 反应的半水合物沉淀和相变动力学实验在 353 K 下进行了研究。CaCl ₂ 在 FeCl ₂ 溶液中对 FeCl ₂ ·4H ₂ O 结晶的共同离子效应为通过 FeCl ₂ –CaCl ₂ –H ₂ O 系统固液平衡的 NRTL 模型进行预测。通过处理商业加工厂提供的钛石膏样品获得高质量、可销售的α-石膏和FeCl ₂ ·4H ₂ O固体，进一步表明新工艺是可行的。