Nitrophosphate Processes

This is possible with the Odda-type processes, in which the solution is cooled so that most of the calcium nitrate crystallizes. About 60% of the calcium is removed from the solution at 20 C and S5%-90% at -5 C. 

Alternatively, the calcium can be precipitated chemically by adding ammonium sulfate to the solution. In this case only calcium rather than nitrate is removed therefore, the range of grades that can be produced is restricted to the higher erxi of the N P range. 

It is also possible to precipitate only the calcium using carbon dioxide. 

In this case, care has to be taken to suppress reversion to tricaldum phosphate, which is citrate-insoluble and water-insoluble. 

Other ways to influence the N P205 ratio are to use a mixture of nitric and sulfuric or phosphoric acids or to remove the calcium by ion exchange. These alternatives will be discussed later. 

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Nitric Phosphate. About 15% of worldwide phosphate fertilizer production is by processes that are based on solubilization of phosphate rock with nitric acid iastead of sulfuric or phosphoric acids (64). These processes, known collectively as nitric phosphate or nitrophosphate processes are important, mainly because of the iadependence from sulfur as a raw material and because of the freedom from the environmental problem of gypsum disposal that accompanies phosphoric acid-based processes. These two characteristics are expected to promote eventual iacrease ia the use of nitric phosphate processes, as sulfur resources diminish and/or environmental restrictions are tightened. 

There is extensive Hterature on nitrophosphates (65,66). A description of the Norsk Hydo nitrophosphate process, ie, using calcium adjustment by crystallization of calcium nitrate, emphasizing the environmental advantages is also available (64). 

H. Storen, "The Nitrophosphate Process—an Alternative Route to Phosphate Fertilizers," ia proceedings of Phosphate Eertilicyers and the Environment, International Fertilizer Development Center, Muscle Shoals, Ala., 1992. 

Hignett, T. P. Nitrophosphate Process Advantages and Disadvantages, in Proc. I5th Annual Meeting Fert. Ind. Round Table, pp. 92-95, 1965. 

B. Use of calcium nitrate tetrahydrate byproduct separated from nitrophosphate processes. The separated tetrahydrate can be remelted in its own crystal water by wasteheat, which gives a solution of about... 

These reactions go substantially to completion in most granulation processes, in nitrophosphate processes, and in liquid compound fertilizer processes. Ando et al. found that ammonium chloride was one of the most common forms of nitrogen in representative grades of NPK granular fertilizers in the United States 165], Thus, the production and use of compound fertilizers containing ammonium chloride is well established on a worldwide basis even though some people in the industry are not aware of it. 

Phosphate rock can be dissolved by several organic and inorganic acids to produce phosphoric acid. The use of nitric acid for this purpose is described in Chapter 13. Commercial nitrophosphate processes produce phosphoric arid that contedns nitrates hence, these pro-... 

Iron and aluminum oxides present no special problem within the range of occurrence in commercial phosphate rocks these oxides usually are dissolved in nitric acid and reprecipitated during ammoniation as citrate-soluble phosphates, TVA tested leached-zone" Florida phosphate containing a high percentage of aluminum phosphate minerals in a special nitrophosphate process... 

The two commercially important nitrophosphate processes differ in the way they solve the problem of phosphate water solubility caused by the presence of calcium nitrate in the slurry resulting from the reaction of phosphate rock vnth nitric acid. The first process, historically, is the Odda process wherein calcium nitrate is precipitated and separated. Tlie mixed acid process does not separate the calcium nitrate the phosphate water solubility is increased by adding phosphoric acid to decrease the CaO P205 ratio. 

Table 13.1. Process Requirements of the Odda Nitrophosphate Process... 

As a result of developments in recent years, the nitrophosphate process of today is more economically... 

R. Richmann. 1994. The BASF Nitrophosphate Process, IN Nitric Acid-Based Fertilizers and the Enuironment, Proceedings of an Inter-national Workshop, R. G. Lee (Ed.), pp. 203-210, SP-21, IFDC, Muscle Shoals, AL, U.S.A. 

NO2 emissions from the nitrophosphate process can be controlled by adding urea to the digestion... 

Norsk Hydro nitrophosphate process emissions treatment ... 

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