萃取净化磷酸制备磷酸二氢钠过程及结晶介稳特性

Preparation of sodium dihydrogen phosphate from wet process phosphoric acid and metastable characteristics of crystallization

提出了以工业湿法磷酸和氢氧化钠为原料,以磷酸三丁酯(TBP)+煤油(稀释剂)作为萃取剂,通过萃取、反萃与结晶工艺相结合,制备磷酸二氢钠的一种新工艺过程。以完整工艺的实施为前提,结合必要的实验并确定合适的萃取温度、稀释剂加入量、反萃取条件等因素。与热法磷酸原料制备磷酸二氢钠相比,溶剂萃取磷酸中阴、阳离子质量分数的差异造成结晶过程的显著差异。文中主要考察降温速率、搅拌速率及部分杂质质量分数等因素对磷酸二氢钠结晶过程的影响,以便于选择结晶温度;实验测定了硫酸根离子,氟离子,铁离子与磷酸二氢钠溶液介稳区宽度之间的关系,并拟合了相关方程。在优化的萃取和结晶条件下,经三级萃取,萃取相中负载的五氧化二磷的收率可达95.0%,磷酸二氢钠纯度(质量分数)可达99.3%以上,Fe,As,Pb等杂质均有较高的脱除率。

Using the industrial wet process phosphoric acid（WPA） and sodium hydroxide as raw materials,tributyl phosphate（TBP）＋kerosene（diluent） as the extractant,a new process to prepare sodium dihydrogen phosphate was proposed by combining extraction,stripping and crystallization.Necessary experiments were carried out to determine appropriate extraction temperature,adding amount of diluent,back extraction condition and other factors to be applied in the whole process of industrial plant.Compared with the preparation method of sodium dihydrogen phosphate by thermal phosphoric acid,there is a significant difference in the crystallization process caused by difference in anion and cation mass fraction of extracted phosphoric acid.The effects of cooling rate,stirring rate,content（mass fraction） of part impurities,etc.on the crystallization process were mainly investigated to choose crystallization temperature.The relationship between SO4^2-,F^-,Fe^3＋ and the metastable zone width of sodium dihydrogen phosphate was determined,and the correlation equations were fitted.In the optimized conditions,the yield of phosphorus pentoxide loading in extraction phase is 95.0%,the sodium dihydrogen phosphate product purity（mass fraction） is over 99.3%,and Fe,As,Pb and other impurities have a higher removal rate after three-level extraction.