Ammonium phosphates acidulant

Nitric Phosphate. Fertilizers that are referred to as nitric phosphate or nitrophos-phate are produced by acidulation of phosphate rock with nitric acid or with mixtures of nitric and sulfuric or phosphoric acids. The primary advantage of nitric phosphate processes is that no sulfur or less sulfur is required as compared with superphosphates or ammonium phosphates this is particularly important during a shortage of sulfur, or in locations where sulfur must be shipped long distances. A variety of processes and equipment have been used in Europe since the late 1930s.3,12 Also there are a number of plants in Central and South America and in Asia. The production of nitric phosphates is complex. Simple substitution of nitric acid in a superphosphate-type acid-rock reaction is not feasible because (1) decomposition of the nitric acid would occur and cause noxious fumes and loss of nitrogen and (2) the product would be extremely hygroscopic and unstable. 

Alternatively, the ammonium sulfite-bisulfite solution may be acidulated with phosphoric acid, producing an ammonium phosphate solution. There are nurnerous other tail-gas scrubbing processes that produce various byproducts or waste products [5]. 

Many plants outside of North America pfill or granulate a mixture of ammonium nitrate and calcium carbonate. Production of this mixture, often called calcium ammonium nitrate, essentially removes any explosion hazard. In many cases calcium nitrate recovered from acidulation of phosphate rock (see Phosphoric acid and the phosphates) is reacted with ammonia and carbon dioxide to give a calcium carbonate—ammonium nitrate mixture containing 21 to 26% nitrogen (23). 

Heavy Metals. — The solution of 2 gm. of sodium phosphate in 20 cc. of water, acidulated with 1 cc. of hydrochloric acid, should appear unchanged on the addition of hydrogen sulphide water. On now adding to the liquid 5 cc. of ammonia water and a few drops of ammonium sulphide solution, no precipitate should form, nor should a green color develop. 

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