Titanium gypsum is a solid waste produced when titanium dioxide manufacturers use sulfuric acid and neutralize the waste acid with lime. The global production of titanium gypsum waste has reached 10 million tons annually. To address the environmental hazards, this study proposes a cost-effective ($2.39/ton), emission-free method to sustainably produce high-value α-hemihydrate gypsum by consuming large quantities of titanium gypsum. The primary iron impurity in titanium gypsum was separated (> 80 %) using titanium white waste acid, yielding high-value red iron oxide (Fe2O3) and green vitriol, i.e., hydrated iron(II) sulfate (FeSO4·7H2O). Additionally, the thermodynamic process of in-situ dehydration of titanium gypsum at atmospheric pressure in a chlorine-free salt solution was studied, producing large α-hemihydrate gypsum particles of 20 μm size through hydration-recrystallization. This work enhances resource utilization efficiency, reduces environmental contamination from titanium dioxide waste acid and titanium gypsum, and exemplifies an environmentally responsible process with significant implications for the sustainable development of the titanium dioxide industry.

中文翻译：

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使用酸性钛白废水可持续处理固体钛石膏废料，生产高价值的 α 半水石膏

钛石膏是钛白粉制造商使用硫酸并用石灰中和废酸时产生的固体废物。全球钛石膏废料的产量已达到每年 1000 万吨。为了解决环境危害，本研究提出了一种经济高效（2.39 美元/吨）、零排放的方法，通过消耗大量钛石膏来可持续地生产高价值的 α 半水石膏。使用钛白废酸分离钛石膏中的初级铁杂质 （> 80 %），得到高价值的红色氧化铁 （Fe2O3） 和绿色硫酸盐，即水合硫酸铁 （II） （FeSO4·7H2O）。此外，还研究了钛石膏在大气压下在无氯盐溶液中原位脱水的热力学过程，通过水合再结晶生产 20 μm 大小的α半水石膏大颗粒。这项工作提高了资源利用效率，减少了钛白粉废酸和钛石膏对环境的污染，并体现了对环境负责的工艺，对钛白粉行业的可持续发展具有重要意义。