Al3+、Na+和Mg2+对二水硫酸钙结晶的影响

采用CaHPO₄·2H₂O-H₂SO₄-H₃PO₄-H₂O体系模拟湿法磷酸生产过程，以磷矿浆成分为依据，在单因素条件下分别研究Al³⁺、Na⁺和Mg²⁺对结晶和CaSO₄·2H₂O水洗速率的影响。研究发现：添加Al³⁺有利于CaSO₄·2H₂O晶体粒径增加；添加Na⁺使得0.9% Na₂O含量的Na⁺引起CaSO₄·2H₂O晶体团聚，有利于水洗；Mg²⁺增加溶液黏度，严重影响晶体生长和水洗速率。通过X射线衍射、扫描电子显微镜对CaSO₄·2H₂O进行表征，发现其晶体生长符合非完整光滑突变界面模型，杂质离子影响反应速率和晶面生长速度。

Influence of Al3+, Na+ and Mg2+ on crystallization of calcium sulfate dihydrate

The system, including CaHPO₄·2H₂O-H₂SO₄-H₃PO₄-H₂O, is utilized to simulate wet process for phosphoric acid production. Based upon the slurry composition of phosphate mineral analysis, according to single factor experimental demands, the influence of Al³⁺, Na⁺and Mg²⁺ on crystallization and washing rate of CaSO₄·2H₂O were investigated. The result indicated that, it is beneficial for the size of CaSO₄·2H₂O crystals when adding Al³⁺into the system. Na⁺as the form of 0.9% (mass) Na₂O in the slurry also caused agglomeration of CaSO₄·2H₂O crystals. We also found that it is helpful for the washing rate. But when Mg²⁺ was added into the system, the unfavorable impact such as increasing the viscosity of solution, seriously influencing crystal growth and washing rate. For our target production, CaSO₄·2H₂O crystal, XRD, SEM were adopted to characterize the products during the process. The results showed that crystal growth conforms to Burton-Cabrera-Frank model. The impurity ions change the reaction rate and crystal plane growth rate.