碱法回收湿法磷酸萃余渣中五氧化二磷的研究

磷酸是一种重要的化工原料。目前,生产磷酸及磷酸盐的方法主要采用湿法,但湿法磷酸中含有大量的杂质,在利用溶剂萃取法净化湿法磷酸的过程中,大量金属离子杂质以不溶性磷酸盐的形式沉淀出来,其中不溶性五氧化二磷的回收利用问题受到广泛关注。采用碱解工艺设计单因素实验,考察了液固比、n（Na₂O）/n（P₂O₅）、反应温度、反应时间对氢氧化钠分解湿法磷酸萃余渣（难溶性金属磷酸盐）效果的影响,并选出适宜的反应条件范围,在此基础上通过二次回归正交实验得到最佳的反应条件。结果表明,最佳反应条件为：液固比为30 mL/g、n（Na₂O）/n（P₂O₅）为3.31、反应温度为82 ℃、反应时间为4.05 h。在最佳的工艺条件下,五氧化二磷的回收率可达到92.48%,反应碱液可进一步作为生产磷酸三钠的原料而加以利用。该研究得到了一种利用湿法磷酸萃余渣的合理方案,并给出了相关参数,为该方案的实际应用提供指导,对萃余渣的利用和环境保护具有重要意义。

Study on the recovery of phosphorus pentoxide from wet-process phosphoric acid extraction residue by alkaline process

Phosphoric acid is an important chemical raw material.At present,the method of producing phosphoric acid and phosphate mainly adopts wet-process,but wet-process phosphoric acid contains a large amount of impurities.In the process of purifying wet-process phosphoric acid by solvent extraction,a large amount of metal ion impurities precipitate in the form of insoluble phosphate precipitate,and the problem of recycling of insoluble P₂O₅ has received widespread attention.Alkaline hydrolysis process was used and single factor experiment was designed,the effect of liquid-solid ratio,n（Na₂O）/n（P₂O₅）,reac-tion temperature and reaction time on the wet-process phosphoric acid extraction residue（insoluble metal phosphate） deco-mposition were inspected,and a suitable range of reaction condition was selected.On this basis,the optimal reaction conditions were obtained through quadratic regression orthogonal experiments.The results showed that the optimum conditions were con-firmed as following：liquid-solid ratio was 30 mL/g, n（Na₂O）/n（P₂O₅）was 3.31,reaction temperature was 82 ℃ and reactiontime was 4.05 h.Under optimum conditions,the recovery rate of P₂O₅ could reach 92.48%.The reaction lye could be further used as raw material for the production of trisodium phosphate.In this study,a reasonable scheme for purifying phosphoric acid extraction residue was obtained,and related parameters were given,which provided guidance for the practical applica-tion of this program.It was of great significance for the utilization of extraction residue and environmental protection.