Study On The Process Conditions Of Preparing Ammonium Phosphate With Hydrochloric Acid-Double Salt Precipitation

In this dissertation,faced to the key technical problems existing in the hydrochloric acid method wet-process phosphoric acid process,such as,the difficulty in the separation of water-soluble calcium chloride and phosphoric acid and the subsequent disposal of the calcium chloride waste liquid,based on a great deal of literature and pre-laboratory research work,an innovative process of preparing ammonium phosphate salt via the "hydrochloric acid-double salt precipitation method" was proposed because melamine performs high stability in structure and can react with phosphoric acid to form an insoluble melamine phosphate.The study was focused on the leaching of phosphorite by hydrochloric acid,the preparation of melamine phosphate and the optimization of the above processes.The main work and the obtained conclusions were as follows:（1）The detection of physicochemical properties of the phosphorite showed that the phosphorite powder used in the experiments was medium-grade phosphorite,mainly composed of apatite,dolomite and silica with P₂O₅ content of 27.86%.（2）The optimum conditions of the leaching process were as follows:reaction temperature 40℃,reaction time 60min,acid ratio 1.1:1,concentration of hydrochloric acid solution 7mol·L^-1.The repeated experiments under the optimum process condition showed that the average leaching rate of P₂O₅ reached 96.70%.（3）The suitable process conditions of the precipitation of melamine phosphate were as follows:reaction temperature 70℃,concentration of phosphoric acid solution 0.6mol· L^-1,the molar ratio of C₃H₆N₆ to H₃PO₄ 1.5:1,reaction time 1.5h.The repeated experiments under the suitable process condition showed that the precipitation rate of phosphoric acid in the acid leach liquor reached 98.27%.（4）The preliminary experimental results showed that the ammonolysis of melamine phosphate by ammonium hydroxide to prepare ammonium phosphate was feasible.The decomposition rate of melamine phosphate was up to 92.40%and the recovery rate of the melamine was up to 99.60%.The characterization results showed that the recovered melamine was pure with monoclinic phase and the prepared ammonium phosphate sample was ammonium dihydrogen phosphate.