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Ammonium phosphate is a chemical compound containing one nitrogen alongside three hydrogen atoms. Ammonium phosphate is generally neutral but can be highly acidic, and may be toxic to aquatic organisms.

Industrial production

The industrial production of ammonium phosphate is carried out as follows: An aqueous solution which contains impurities derived from starting ore of phosphorus is first added with ammonia to form ammonium phosphate. The precipitated impurities are then separated from the solution by filtration or centrifugal separation.

Phosphoric acid is then added to the resulting ammonium phosphate until diammonium hydrogenphosphate, (NH4)H2 PO4 or a mixture of these forms is formed. Then the phosphoric acid is neutralized with ammonia to obtain the resulting liquid composition, which usually consists of a major proportion of ammonium dihydrogenphosphate and a minor proportion of diammonium hydrogenphosphate.

Neutralization of phosphoric acid with ammonia is preferably carried out in the presence of an aqueous mother liquor from which the phosphor salt crystals have been removed. The resulting liquor should have a molar ratio of H3 PO4 :NH3 :NaCl of about 1:1.6-2.5:0.2-2.8, preferably 1:1.9-2.3:1.4-2.6, and a pH value of about 6.2 to 8.0, preferably 6.7 to 7.6.

The ammonium phosphate solution is then introduced into the circulating mother liquor with the addition of further ammonia, which is maintained at temperatures below 60deg C. In a further stage the sodium chloride may be added to the ammonium phosphate solution. In this case the sodium chloride may be non-purified industrial salt, since purified industrial salt brings in too many impurities and thus causes a slight increase in the discharged ammonia from the reaction system.