两步法制湿法磷酸过程中除氟效果的研究

Research on fluoride removal in wet-process phosphoric acid by two-step process

本文采用两步法制备湿法磷酸,第一步用磷酸酸解磷矿石得到Ca(H2PO4)2溶液,第二步用稀硫酸与Ca(H2PO4)2反应得到硫酸钙沉淀和更多的磷酸。论文研究了两步法中磷酸浓度、反应物物料比、静置时间和加酸时间对液相中氟质量分数的影响。研究结果表明,采用两步法有利于降低液相中的氟质量分数;增加反应物中磷矿石的物料比,使磷矿石过量可以显著降低液相中的氟质量分数;此外适当延长反应后的静置时间和选择合适的加酸时间均可大大降低液相中的氟质量分数。通过选择最佳的工艺条件,可将湿法磷酸中的氟磷比降低至4.32×10-4,达到了工业湿法净化磷酸行业标准[1]中合格品的要求(<4.7×10-4)。

Phosphoric acid was prepared by a two-step wet- process. Phosphate rock was decomposed into calcium dihydrogen phosphate by phosphoric acid in the first step and then the calci- um dihydrogen phosphate was reacted with sulfuric acid to form calcium sulfate sediment and more phosphoric acid in the second step. The influence of concentration of phosphoric acid, mass ra- tio of reactant, standing time, and speed of acid-dropping on the concentration of fluorine was investigated in the two-step process in this paper. The research results showed that it is conducive to reduce the fluorine concentration in the product solution by two- step process. Besides, the fluorine concentrate, on also can he re duced dramatically by increasing the mass ratio of phosphate rock to＇phosphoric acid until the extent of surplus rock phosphate is remained. In addition, the fluoride concentration also can be aba- ted greatly by choosing appropriate standing time after reaction and proper speed of acid-dropping. Under the optimal technology conditions, the mass ratio of fluorine to phosphoric acid can he decreased to as low as 4.32× 10 4, which meets the requirement of （ 〈 4. 7 × 10-4 ） for qualified products in Chinese industrial standard of Industrial Purified Wet-process Phosphoric Acid.