Manufacture of Mono, Di-Ammonium and Nitro-Phosphate

After reading this article you will learn about the manufacture of mono, di-ammonium and nitro-phosphate.

Mono and Di-ammonium Phosphate:

Mono Ammonium Phosphate is manufactured by slowly neutralizing orthophosphoric acid with ammonia gas as shown in the following equation:

A considerable amount of heat is generated in this reaction. Consequently the liquid mono ammonium phosphate is thickened. When this is cooled, the mono ammonium phosphate crystallizes out. The mother liquor is drained and the crystals are dried and bagged.

Di-ammonium phosphate is produced, when an excess of ammonium gas is passed through orthophosphoric acid in order to maintain the pH of the slurry at 5.8 to 6.0 as shown below:

Both mono and di-ammonium phosphate are soluble in water. Mono ammonium phosphate is a light grey material. Di-ammonium phosphate is a dark brown material. They absorb a little moisture from the atmosphere and are acidic fertilisers.

The acidity caused by the application of every 100 pounds of mono ammonium phosphate can be neutralized by adding about 55 pounds of powdered limestone to the soil. The acidity caused by adding every 100 pounds of Di-ammonium phosphate can be neutralized by adding about 77 pounds of powdered limestone to the soil.

Mono and Di-ammonium phosphate can be used in alkaline and calcareous soils. Mono Ammonium Phosphate contain 11.0 per cent N and 48.0 per cent P₂O₅ Di-ammonium Phosphate contains 21.0 per cent N and 54.0 per cent P₂O₅.

Manufacture of Nitro-Phosphate:

This is manufactured by treating apatite with a mixture of nitric and sulphuric acids.

They react together as shown below:

Liquid ammonia is then added to the slurry and then react together as shown below:

Nitro-phosphate is a granulated fertiliser containing a stabilizer which prevents the reversion of citrate soluble phosphate to insoluble tricalcium phosphate. It contains nitrogen and phosphorus in various proportions. If it is necessary, potassium salts are also added to it. Three types of nitro phosphates (Trade Name SUPHALA) 20:20:2, 18:18:9 and 15:15:15 are manufactured.

Usually about one-third of the phosphate contained in these is water soluble and the rest of the two thirds is citrate soluble. The water soluble phosphate is readily available and hence useful in the early stages of crop growth, while the citrate soluble phosphate helps the crop to grow and attain maturity. Nitro phosphate contains ammoniacal and nitrate nitrogen.