Nitrophosphate fertilizers process

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. 

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. 

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... 

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. 

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. 

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. 

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. 

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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