Preparation Of High Purity Diammonium Phosphate With Wet-process Phosphoric Acid

Pure diammonium phosphate (DAP) is a white crystalline substance, it is an important industrial product. It can be used for industrial, food additives, pharmaceuticals, electronics, production of high nitrogen and phosphorus compound fertilizer, wood, paper, but also can be used for fiber processing and dye industries. Its purity directly affects its application area and value, so the preparation of high purity DAP has important economic benefits. At the same time it is the precursor material of high degree polymerization preparation of ammonium phosphate (APP), so its synthesis and process optimization studies are significant.This study based on a two-step wet-process phosphoric acid synthetic method of preparation of DAP process. Because wet-process phosphoric contents a large amount of impurities due to its production methods, the preparation of DAP must reduce these impurities effectively. The research firstly remove arsenic and lead to purify phosphoric acid initially, and then use two-step method to prepare diammonium phosphate, and purify diammonium phosphate in the crystallization process. Different concentrations and pH were tried to prepare DAP, analylize the impurities contents and yield of product.In two-step method of preparation of high purity DAP by wet process phosphoric acid, not only remove most metal cations in the phosphoric acid, but also increased P2O5 utilization rate compared to the process of purifying wet-process phosphoric. Final DAP product impurity content:Fe content 2.9ppm, Mg 3.27 ppm, aluminum 2.31ppm, arsenic 8.28ppm, lead 1.54ppm, DAP content reach to 98.0% which reached the requirement of food-grade. In the present process, the final removal efficiency of Fe, Mg, Al reached 99% or more, arsenic removal efficiency reached 97%, lead removal rate is 88%, removal rate of impurities is high, and P2O5 conversion rate reached 70% or more, so use two-step method to synthesis high purity DAP by phosphoric acid process route is feasible.This article also studied the crystallization process of diammonium phosphate, studied crystallization thermodynamics and kinetics of diammonium phosphate. Studied the influence on metastable zone width by temperature, stirring rate and cooling rate and other factors, estimated its heat of solution depending on experimental data. In the process of diammonium phosphate crystal, studied the influence on crystal form and crystal particle size distribution of diammonium phosphate by temperature, stirring rate and temperature cooling rate, provide a theoretical support for diammonium phosphate preparation, reactor design and production scale up.