Abstract:

Hemihydrate wet process phosphoric acid can produce w(P₂O₅)>40%(mass) phosphoric acid but in the reaction stage, the phosphate ore is prone to coating formation, the crystal size of hemihydrate phosphogypsum is small, resulting in difficult filtration and reduced phosphorus recovery. Taking typical mid-and low-grade phosphate rock from Hubei province as raw material, the conditions such as SO{}_{\mathrm{4}}^{\mathrm{2}-} concentration, phosphoric acid concentration and reaction temperature in hemihydrate process were investigated, and the crystal phase and morphology and particle size change rule of semi-aqueous gypsum were obtained. In the hemihydrate reaction, with the concentration of sulfuric acid and phosphoric acid in the liquid phase increase, the hemihydrate phosphogypsum is more prone to phase transformation. The morphology of hemihydrate phosphogypsum changes from hexagonal prism to rod and flake, and the particle size decreases from 70 μm to 10 μm. Under optimal conditions, the content of P, F and other elements in hemihydrate phosphogypsum can be effectively reduced. The P₂O₅ content of hemihydrate phosphogypsum was reduced to 1.39%(mass) and the main form of P was insoluble phosphate. The F content was reduced to 0.44%(mass), which existed in hemihydrate phosphogypsum in the form of poorly soluble substances such as CaF₂ and AlF₃. The form of impurities is simple, which is convenient for the subsequent purification and utilization of gypsum. The above research brings new ideas for the stable operation of hemihydrate process and the quality improvement of hemihydrate phosphogypsum.

Key words: wet process phosphoric acid, hemihydrate process, crystallization, process control, optimization

摘要：

湿法磷酸半水工艺可生产高浓度磷酸[w(P₂O₅)>40%(质量)]，但在半水反应阶段磷矿易发生钝化，半水石膏结晶粒径小，造成工艺后端过滤困难，磷回收率降低。以湖北典型中低品位磷矿为原料，系统考察了半水工艺中SO{}_{\mathrm{4}}^{\mathrm{2}-}浓度、磷酸浓度、反应温度等条件对半水石膏结晶物相、形貌及粒径的影响规律，分析了优化条件下石膏杂质赋存与含量变化。结果表明，半水反应中液相硫酸、磷酸浓度会引起半水石膏物相、形貌、粒径变化，磷硫浓度提高会导致石膏晶体形貌由柱状变化为棒状、片状，粒径从70 μm减小到10 μm。优化工艺条件下，半水石膏较原工艺石膏P₂O₅含量降低至1.39%(质量)，磷的主要存在形式为难溶性磷酸盐，同时F含量降低至0.44%(质量)，其以CaF₂、AlF₃等难溶物形式存在于石膏，其他杂质含量均有所降低。本研究可为半水工艺生产过程参数优化及半水石膏品质提升提供参考。

关键词: 湿法磷酸, 半水工艺, 结晶, 过程控制, 优化