Nitrophosphate fertilizers production

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. 

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. 

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. 

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. 

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. 

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. 

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. 

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. 

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. 

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). 

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. 

Nitric Phosphate. Fertilizers that are referred to as nitric phosphate or nitrophosphate are produced by acidulation of phosphate rock with nitric acid or with mixtures of nitric and sulfuric or phosphoric acids. As indicated in Fig. 11.5, there presently is no production, and little or no importation, of this type of fertilizer in the United States. 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. Also there are a number of plants in Central and South America and in Asia. In past years, there have been several U.S. ventures into production, but none has competed successfully with phosphoric acid-based processes. Production of nitric phosphates is complex. Simple substitution of nitric acid in a superphosphate-type acid-rock reaction is not... 

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