结晶法脱除高浓度正磷酸中硫酸根的研究

研究了以工业级湿法磷酸净化酸浓缩生产的质量分数为98%的正磷酸为原料，采用冷却结晶方式脱除正磷酸中的阴离子硫酸根（SO42-）。考察了降温速率、搅拌转速、助长剂用量、养晶时间对正磷酸中硫酸根脱除的影响。确定了最佳工艺条件：搅拌转速为300 r/min，降温速率为每15 min降温1 ℃，助长剂用量为5 g，养晶时间为 1.5 h。在最佳工艺条件下，正磷酸中硫酸根去除率达到82.1%，硫酸根质量分数小于20 mg/kg，达到85%食品级磷酸对硫酸根的质量要求，提高了磷酸产品的附加值。同时，该方法为生产低硫酸根含量的正磷酸提供了一条可行途径。

Removal of SO42- in high concentration orthophosphoric acid by crystallization

Anion SO42- in orthophosphoric acid  was removed by cooling crystallization method with the 98%（H3PO4，mass fraction） orthophosphoric acid got from the purification and concentration of industrial grade wet-process phosphoric acid as raw material.The influences of cooling rate，stirring speed，crystal growth substance dosage，and crystal maturing time on the removal effect were investigated.The optimum technological conditions were comfirmed as follows：the stirring speed was 300 r/min，the cooling rate was 1 ℃ per 15 min，the growth substance dosage was 5 g，and the crystal maturing was 1.5 h.Under the best process conditions，SO42- of orthophosphoric acid removal rate reached 82.1%，mass fraction of  SO42- less than 20 mg/kg， meeting the 85% quality requirement for SO42- of food grade phosphoric acid，and improved the added-value of products.At the same time，this method provided a feasible way for the production of orthophosphoric acid with low content of SO42-.