固液反萃湿法磷酸生产磷铵的工艺研究

通过连续逆流萃取对原料湿法磷酸先进行净化，萃取后的有机溶剂相直接用氨反萃取生成磷铵晶体，再沉降使晶体与有机萃取剂分离，实现磷铵直接反萃结晶和萃取剂的循环利用。结果表明用氨直接固液反萃湿法磷酸生产磷铵的最佳工艺条件是：萃取剂组成为V(磷酸三丁酯)∶V(稀释剂)=1∶1，原料磷酸浓度为w（P₂O₅）=40%～50%，萃取剂用量为V(萃取剂)∶V(原料磷酸)≈3∶1，萃取搅拌时间约为5 min，氨用量控制为氨反萃结晶后的液相pH≈7，固液反萃-结晶温度为15～20 ℃。最终所得的磷铵晶体中w(氮)＞20%、w(五氧化二磷)＞50%，原料湿法磷酸中的五氧化二磷一次性利用率接近50%。该法所得磷铵晶体中氮磷含量均接近工业磷酸二铵(98%)标准，远大于国家肥料级农用磷铵产品标准。

Research on process of producing ammonium phosphate with solid-liquid back-extraction of phosphoric acid by wet process

Method of continuous countercurrent extraction was used to purify raw material phosphoric acid by wet process at first.Then ammonia was used to directly back-extract the organic solvent after extraction to produce ammonium phosphate crystals.Finally the crystals were separated from the organic extraction agent by deposition to achieve the aim of recycling utilization of organic extraction agent and direct crystallization of ammonium phosphate through back-extraction.Experiment results showed that the optimum technological conditions of producing ammonium phosphate with the method of solid-liquid back-extraction of wet process phosphoric acid were as follows:extractants′ composition was V(tributyl phosphate)∶V(diluent)=1 ∶1,mass fraction of P2O5 in raw material phosphoric acid was at 40%~50%,volume ratio of extractants to phosphoric acid was about 3∶1,extraction stirring time was about 5 min,ammonia amount was that control pH≈7 of the liquid phase after back-extracted crystallization,and stripping-crystallization temperature was 15~20 ℃.Ultimately in the obtained ammonium phosphate crystals w(N)>20% and w(P2O5)>50%,and one-time utilization ratio of P2O5 in the phosphoric acid by wet process approached 50%.Contents of N and P in ammonium phosphate crystals made by this method were both close to the industrial DAP(98%) standard and were much higher than national fertilizer-grade ammonium phosphate product standard.