Diammonium phosphate refers to the standard product containing N18%, P2O548%, crystal shape is oblique prism, solubility in 25C water is 71%, its saturated solution pH reaches 8, much higher than monoammonium phosphate. Diammonium phosphate can be prepared by reaction of phosphate rock powder with excessive NH, F solution, pH 6 7 and temperature of 100. However, the process developed by the Tennessee Valley Authority (TVA) in the United States is generally adopted, that is, ammonia neutralizing mixed phosphoric acid (containing 30% and 54% of phosphoric acid of P2a) is used to pre-neutralize the molecule ratio of ammonia to phosphoric acid at about 1.4, continue to control the molecule ratio of ammonia to phosphoric acid at 2, feed ammonia vapor and keep the solution pH above 7.5 to produce diammonium phosphate. Because the saturated solution of diammonium phosphate is alkaline, the application of diammonium phosphate on acidic soil can reduce the fixation of iron and aluminium to phosphorus, and make phosphorus keep high availability. Therefore, it is advocated that diammonium phosphate be used on acidic soil.
