α-半水磷石膏的晶型调控及稀土的同步释放与迁移分配机制研究

Phosphogypsum, which is mainly comprised of calcium sulfate dihydrate, is a multi-component complex industrial by-product in wet-process phosphoric acid production. At present, the cumulative stockpile of phosphogypsum in China has exceeded 500 million tons. This not only causes serious environmental pollution, but also is a great waste for the huge amount of rare earth elements contained in the phosphogypsum. The project is aimed at the low-cost, high value-added comprehensive utilization of phosphogypsum, and based on the principle that the rare earth elements can be fully released from phosphogypsum during the dissolution process of the crystal transformation from phosphogypsum to α-hemihydrate gypsum in sulfuric acid solution, and during the recrystallization process, co-crystallization and adsorption of the rare earth elements in the newly formed α-hemihydrate gypsum can be effectively reduced by controlling crystal morphology and particle size. Using sulfuric acid as the reaction medium, and succinic acid, citric acid, and disodium EDTA as the crystal modifier, the project explores the synergistic control mechanism of crystal morphology and particle size of α-hemihydrate phosphogypsum. Furthermore, the synchronous release, migration, and distribution of rare earth elements during the crystal transformation of phosphogypsum to α-hemihydrate gypsum are also investigated. Then, the collaborative relationship between the preparation of high-strength α-hemihydrate phosphogypsum and the high-efficiency leaching of rare earth elements from phosphogypsum is built, which forms the technological basis for the high-efficiency separation and recovery of rare earth elements while preparing high value-added α-hemihydrate gypsum from phosphogypsum. This project provides theoretical and technical support for further improving the economic and social benefits of phosphogypsum utilization.

磷石膏是湿法磷酸生产过程中排放的主要成分为二水硫酸钙的多组分复杂工业副产物。目前我国磷石膏累计堆存量已超过5亿吨，这不仅造成严重的环境污染，而且对于其中蕴含的巨量稀土，也是一种极大的浪费。本项目针对磷石膏的低成本高附加值综合利用，基于常压硫酸溶液中磷石膏制备α-半水石膏的溶解过程中能够充分解构稀土，同时重结晶过程中又可以通过晶体形貌和粒度的调控有效降低稀土在新形成固相中共晶和吸附的原理，以硫酸为反应介质，以丁二酸、柠檬酸、EDTA二钠为媒晶剂，研究硫酸溶液体系中α-半水磷石膏晶体形貌和粒度的协同调控机制，以及磷石膏制备α-半水石膏的晶体重构过程中稀土的同步释放和迁移分配规律，构建高强α-半水磷石膏制备与稀土高效浸出分离之间的协同关系，形成磷石膏制备高附加值α-半水石膏的同时高效分离回收稀土的技术基础，为进一步提高磷石膏利用的经济效益和社会效益提供理论和技术支持。

磷石膏是湿法磷酸生产过程中排放的主要成分为二水硫酸钙的多组分复杂工业副产物。目前我国磷石膏累计堆存量已超过5亿吨，这不仅造成严重的环境污染，而且对于其中蕴含的巨量稀土，也是一种极大的浪费。本项目针对磷石膏的低成本高附加值综合利用，以硫酸为反应介质，以EDTA二钠为媒晶剂，研究了硫酸溶液体系中石膏物相转化及相变产物形貌和粒度调控对磷石膏中稀土浸出的影响，研究发现物相转化并形成形貌规则的大粒度晶体可以有效促进稀土的浸出。当加入0.5%EDTA-2Na时，可形成规则的大粒度α-半水石膏，此时稀土浸出率可提高26%，并且规则的大粒度α-半水石膏是高附加值的高强石膏。因此本研究初步形成了磷石膏制备高附加值α-半水石膏的同时高效分离回收稀土的技术基础，为进一步提高磷石膏利用的经济效益和社会效益提供理论和技术支持。