Abstract:

The efficient separation of nitrogen and phosphorus in acid hydrolysis solution is one of the key technologies for the development of nitric acid wet phosphoric acid process.The research idea of using antisolvent crystallization to precipitate phosphorus in the form of calcium phosphate in the acid hydrolysis solution was put forward，so as to achieve the separation of nitrogen and phosphorus.Using isopropanol as the antislovent，the effect of antisolvent addition ratio（mass ratio of isopropanol to simulated acidolysis solution），temperature，P₂O₅ mass fraction and antisolvent time on the phase structure and phosphorus precipitation ratio of precipitated crystals was investigated by single factor experiment.The experimental results showed that the antisolvent time did not effect the phase structure of the precipitated crystals.Increasing the antisolvent addition ratio，increasing the temperature and reducing the mass fraction of P₂O₅ would change the precipitated crystals from monocalcium phosphate to dicalcium phosphate.By comparing the phosphorus precipitation ratio，it was concluded that the suitable process conditions were as follows：the antisolvent addition ratio was 3∶1，the temperature was 5.0 ℃，the mass fraction of P₂O₅ was 30%，and the antisolvent time was 1.0 h.At this time，the phosphorus precipitation ratio was 73.58%.

Key words: monocalcium phosphate, dicalcium phosphate, antisolvent crystallization, isopropanol