Nitrophosphate fertilizers

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. 

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. 

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. 

With minor exceptions, the commercial fertilizer, products are triple superphosphate (TSP), ammonium phosphates, and other compound fertilizers (some of the minor exceptions are potassium phosphates and magnesium ammonium phosphate [MgNH4P04]). Use of phosphoric acid in compound fertilizers will be described-under subject headings Compound Fertilizers" (Chapter 16), Liquid Fertilizers and Mtrogen Solutions" (Qiap-ter 10), and Nitrophosphate Fertilizers (Chapter 13). The present chapter wSi deal mainly wrath TSP and solid ammonium phosphates. 

Conradsen, A., and G. Kongshaug. 1993. Nitro-phosphate Technology and the Environment, An Overview of Potential Sources of Pollution From an Integrated Nitrophosphate Fertilizer Production Complex, IN Nitric Acid-Based Fertilizers and the Environment, International Workshop Proceedings, pp. 135-151, R. G. Lee (Ed.), SP-21, International Fertilizer Development Center, Muscle Shoals, AL, U.S.A. 

Dicalcium phosphate is a common constituent of nitrophosphate fertilizers and of compound fertilizers formed by ammoniation of siperphosphates. There is a relatively small but substantial production of straight dicaldum phosphate in Europe, diich is based on use of byproduct hydrochloric add. The process consists of dissolving phosphate rock in hydrochloric add and then precipitating dicalcium phosphate by stepwise addition... 

Soluble salts of copper, manganese, iron, and zinc are likely to become insoluble when Incorporated in ammonium phosphates or ammoniated mixed fertilizers. The reaction forms one of several metal ammoriiufrr phosphates such as ZnNH4P04. In general, the water solubility decreases with increase in pH of the fertilizer product. Loss of water solubility does not necessarily imply loss of effectiveness but may delay it. Sodium borate when incorporated in ammoniated fertilizers containing calcium may become partially or wholly insoluble presumably because of formation of calcium borate. The boron in calcium borate is insoluble in cold water but soluble in boiling water.) This effect has been noted with nitrophosphate fertilizers and may occur with other formulations. 

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. 

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. 

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. 

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. 

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. 

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. 

Wet processes may be dassified according to the acid used to decompose phosphate rock. Sulfuric, nitric, and hydrochloric acid are used in commercial processes. Processes using nitric acid will be described under Nitrophosphates (Chapter 13). Processes usinghydrb chloric acid are not competitive for fertilizer purposes, except under unusual conditions, and will be described briefly in this chapter. Processes using sulfuric acid are by far the most common means of producing phosphoric acid for fertilizer use (and sometimes for other uses) therefore, these processes will be described in more detail. However, the scope of this manual precludes extensive detail of even the most important processes. For more detail, readers should consult Phosphoric Acid, edited by A. V. Slack 12], and other references listed at the end of this chapter. 

Other important uses for phosphoric acid are covered in other chapters, i.e., for production of liquid fertilizers (Chapter 10) and for production of mixed-acid nitrophosphates (Chapter 13). 

After the invention of this principle in 1928, ErBng Johnsen transferred his patent to Norsk Hydro A.S., which developed it in the 1930s and introduced its own technology in 1938. Norsk Hydro was among the first to produce multinutrient fertilizers - NPs and NPKs -via the nitrophosphate route. 

World consumption of nitrophosphates increased from 3.46 million tonnes of P2O5 in 1975 to 3.9 million tonnes in 1988 this represents an increase of 13% in 13 years, and nitrophosphates supplied less than 10% of world fertilizer P2O5 in 1988 [18]. 

Under these influences, world consumption of nitrophosphates increased to 4.33 million tonnes of P2O5 in 1990 this represented 10.5% of world fertil-... 

With a reduction of 26%, nitrophosphates were more severely affected by the crisis than the average of fertilizers. The reason for this seems to be that their main market was in Europe, where the fertilizer market decreased more than the world average under the combined influences of fertilizer use restrictions in Western Europe and farm economy disturbances in Eastern Europe and Russia. 

The International Fertilizer Development Center conducts an annual survey of NPK granulation plants in the United States. By 1995 the number of operating plants decreased to only 25, from about 200 in 1965. No estimate has been made of the number of NPK granulation plants worldwide, but aImost-all-of-these-plants,-pIus-all nitrophosphate plants, incorporate secondary nutrients, primarily calcium and/or sulfur, in their products as the preferred, least expensive raw materials. Magnesium is different and is usually incorporated as a special additive. 

The warehouse or storage temperature is important with respect to caking tendency. Higher ambient temperatures lower the CRH of a fertilizer material and thereby increase its hygroscopicity. For example, the CRH of a 15-15-15 nitrophosphate is approximately 55% at 30°C, whereas it is approximately 45% at 40°C. Conversely, raising the temperature of existing warehouse air will reduce the relative humidity (RH). This method can be employed to lower the warehouse RH below the CRH of the fertilizer. 

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