Nitrophosphate

Nitric acid acidulation of phosphate rock produces phosphoric acid, together with dissolved calcium nitrate. Separation of the phosphoric acid for use as an intermediate in other fertilizer processes has not been developed commercially. Solvent extraction is less effective in the phosphoric—nitric system than in the phosphoric—hydrochloric system. Instead, the nitric acid acidulate is processed to produce nitrophosphate fertilizers. 

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. 

Nitrophosphates are made by acidulating phosphate rock with nitric acid followed by ammoniation, addition of potash as desired, and granulation or prilling of the slurry. The acidulate, prior to ammoniation, contains calcium nitrate and phosphoric acid or monocalcium phosphate according to the foUowiag equations ... 

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. 

Nitrophosphate fertilizer is made by digesting phosphate rock with nitric acid. This is the nitrophosphate route leading to NPK fertilizers as in the mixed-acid route, potassium and other salts are added during the process. The resulting solution is cooled to precipitate calcium nitrate, which is removed by filtration methods. The filtrate is neutralized with ammonia, and the solution is evaporated to reduce the water content. The process of prilling may follow. The calcium nitrate filter cake can be further treated to produce a calcium nitrate fertilizer, pure calcium nitrate, or ammonium nitrate and calcium carbonate. 

European Fertilizer Manufacturers Association. 1995a. "Production of NPK Fertilizers by the Nitrophosphate Route." Booklet 7 of 8. Brussels, and 1995b. "Production of NPK Fertilizers by the Mixed Acid Route." Booklet 8 of 8. Brussels. 

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

Nitrophosphates mainly in Western Europe (capacity 2 10 t/a P2O5) and Eastern Europe (capacity l.l 10 t/a P2O5)... 

Nitrophosphates, made by treating PR with nitric acid, are produced in significant quantities in Europe, but to a much lesser extent in the U.S.A. 

Establishments primarily engaged in manufacturing phosphatic fertilizer materials, or mixed fertilizers from phosphatic materials produced in the same establishment. Included are phosphoric acid normal, enriched, and concentrated superphosphates ammonium phosphates nitrophosphates and calcium metaphosphates. 

Even when the material purchased meets all of the buyer s bid specifications, the material or product may not be well suited for its intended use. This is especially Traerifpht hate rock. Phrosphate rock is quite variable in phosphate content from deport to deposit and in quantities of impurities that drastically affect the rock s performance in production of nitrophosphates, phosphoric acid, superphosphates, and ammonium phosphates. Thus, the material purchased may not be what was initially wanted. Even though this material may meet all the stated specifications, it is possible for unspecified contaminants or impurities to affect the performance of the materials in subsequent processing or the crop response in finished fertilizers. 

Development of nitrophosphate fertilizer was started in Europe in the 1930s. Several processes were developed, and subsequent improvements have added to their efficiency and improved the quality of the producte. The jopularityTJ nitrophospfiaf m Europe has continued, and several plants have been built in other continents. Many of the plants are quite large and produce 1,500 or more tonnes of product per day. 

SulGdes- Sulfides can release H2S, which is a toxic gas, during acidulation. Sulfides produce reducing conditions, increase corrosion rates in phosphoric acid manufacture, and give NO release in nitrophosphate manufacture. 

The first patent on ammonia oxidation wras issued to Khulman in 1839 in this case platinum was used as a catalyst to oxidize ammonia with air. The ammonia-oxidation method using a platinum catalyst qn a commercial scale, developed by Oswald and Brauer and first operated in Germany about 1908, is at present the principal industrial method of nitric acid producticxi. The main use for nitric acid is in fertiDzer production, mainly for ammonium nitrate as such or in compound fertilizers, nitrogen solutions, or mixed salts. About 75% of total nitric acid production is consumed for nitrate fertilizers, mainly as 509 5% concentration acid. Smaller fertilizer uses are for calcium and potassium nitrates. A primary use is in addulation of phosphate rock for production of nitrophosphates. Plant capacities for weak nitric acid i Bed for fertilizer production are in the range of 35 to 1,380 tpd althoi h capacities of 2,000 tpd have been designed. 

CAN is produced by mixing concentrated ammonium nitrate solution with ground calcitic or dolomitic limestone, chalk marl, or precipitated calcium carbonate from nitrophosphate production. The mixing should be done quickly to avoid deccxnpoation of the ammonium nitrate ... 

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