Ammonium Phosphate Fertilisers

The relatively soluble ammonium phosphates (NH4)2HP04 and NH4H2PO4 both find considerable use as fertilisers (Table 12.3). 

Ammonium phosphate fertilisers have assumed a greatly increased importance in recent years and have now become the leading commercial product. Mixtures of the mono- and di-salt are obtained from direct reaction of ammonia with wet process phosphoric acid. Commercial production by this method started in the United States in 1917, and about half of the current world production of phosphoric acid is converted to ammonium salts. The tri-ammonium salt is not favoured in fertilisers because of the loss of ammonia on storage. 

The popularity of ammonium phosphate fertilisers arises from their high nutrient content of both P and N, high solubility and good storage and handling characteristics. They are easy to produce and compete economically with the longer-established calcium salts. Commercial products are available as solutions, solids or suspensions. 

Ammonium phosphate mixed with dicaldum phosphate and calcium sulphate ( ammoniated superphosphate ) can be prepared from superphosphate (12.1) by the action of ammonia on the monocalcium component (12.6). Excessive ammoniation should be avoided or the less-soluble tricalcium phosphate is obtained (12.7), (12.8). 

A wide variety of ammoniated phosphates are produced commercially. These may contain various combinations of ammonium phosphates with calcium phosphates, calcium nitrate, ammonium sulphate, and so on. 

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Vanadium leaches soil from a large number of diverse sources, including waste effluents from the iron and steel industries and chemical industries. Phosphate industries are also a major source of vanadium pollution because vanadium becomes soluble along with phosphoric acids when rock phosphates are leached with sulfuric acid. Vanadium is present in all subsequent phosphoric acid preparations, including ammonium phosphate fertilisers, and is released into the environment along with them. Other sources of vanadium pollution are fossil fuels, such as crude petroleum, coal and lignite. Burning these fuels releases vanadium into the air, which then settles in the soils. 

The production of ammonium phosphate fertilisers is an example of acidic and alkali media neutralisation under commercial plant conditions [1]. During the production of ammonium phosphate, at the liquid ammonium and phosphoric acid reaction stage, a six-section tubular turbulent reactor of diffuser-confusor design is used. The reactor maintains turbulence along its length, with a reactor diameter of 220 mm and confusor diameter of 105 mm the reactor operates in a normal mode at a... 

Ammonium phosphate fertilisers at the stage of interaction of liquid ammonia with phosphorous acid. 

Sodium nitrate is used as a fertiliser and in a number of industrial processes. In the period from 1880—1910 it accounted for 60% of the world fertiliser nitrogen production. In the 1990s sodium nitrate accounts for 0.1% of the world fertiliser nitrogen production, and is used for some specific crops and soil conditions. This decline has resulted from an enormous growth in fertiliser manufacture and an increased use of less expensive nitrogen fertilisers (qv) produced from synthetic ammonia (qv), such as urea (qv), ammonium nitrate, ammonium phosphates, ammonium sulfate, and ammonia itself (see Ammonium compounds). The commercial production of synthetic ammonia began in 1921, soon after the end of World War I. The main industrial market for sodium nitrate was at first the manufacture of nitric acid (qv) and explosives (see Explosives and propellants). As of the mid-1990s sodium nitrate was used in the production of some explosives and in a number of industrial areas. 

NH4N03), ammonium phosphate ((NH4)3P04) and potassium chloride (KC1) in varying proportions (Figure 11.19). Fertilisers have an important role in the nitrogen cycle (see below). 

Water is very good at dissolving substances. Thus, it is very unusual to find really pure water on this planet. As water falls through the atmosphere, on to and then through the surface of the Earth, it dissolves a tremendous variety of substances. Chemical fertilisers washed off surrounding land will add nitrate ions (N03 ) and phosphate ions (PC)43 ) to the water, owing to the use of artificial fertilisers such as ammonium nitrate and ammonium phosphate. 

By suitable combinations of the methods just described, mixtures of potassium and ammonium phosphates may be prepared. The preparation of very concentrated fertilisers containing potassium and ammonium phosphates has been described by Ross and Merz, 1916,1 Ross, Jones and Mehring, 1926.2... 

The System Lime and Phosphoric Acid —Solubility of Calcium Phosphates— Conditions of Formation of Basic and Acid Calcium Phosphates—Composition of Solutions Saturated with Calcium Hydrogen Phosphates—Equilibria between Solid Phases and Solutions at Various Temperatures—Changes during Neutralisation—The Acid Phosphates—Manufacture of Superphosphate—Retrogression—Treatment of Special Ores—Phosphoric Acid— Commercial Preparation and Extraction from Rook—The History and Technology of Superphosphate Manufacture—Mixed and Concentrated Phosphorio Fertilisers—Potassium Phosphates—Ammonium Phosphates. 

Apart from fertiliser ammonium phosphates, these salts, usually more expensive than those of sodium, are all produced commercially, but in much smaller quantities than the latter. 

Nitric phosphate is derived from phosphate rock using nitric acid instead of sulphuric (12.9) (sometimes nitric-sulphuric or nitric-phosphoric acid mixtures are used). The calcium nitrate by-product of this reaction must be removed, or the solid fertiliser would be hygroscopic. One method of achieving this is by crystallisation, and the other is by treatment with ammonia. In the latter instance, a mixture of ammonium phosphate, ammonium nitrate and dicalcium phosphate is obtained (12.10). Alternatively, the calcium nitrate can be converted and the product left in the mixture (12.11). 

Solid fertilisers are usually produced in granular rather than in powder form. Bulk blending of these by mechanical mixing is often practised to produce compound or mixed fertilisers with specific N P K ratios. The principal materials used in bulk blending are ammonium nitrate, ammonium sulphate, urea, superphosphate, ammonium phosphates and potassium chloride. Under EEC regulations, mixed fertilisers are required to have a minimum of 3% N, 5% P2O5 and 5% K2O with the sum of these not less than 20%. 

These fertihsers are non-pressurised solutions of the same raw materials that are used for sohd fertilisers. They should be distinguished from pressurised solutions, such as aqueous ammonia and anhydrous ammonia. At the time of writing, there is very little price differential in the kilogram cost of plant food in the solid or fluid form. Fluid compoimds are based on ammonium polyphosphate or ammonium phosphate, mea and potassimn chloride, whilst ammonium nitrate and ttrea are the main constituents for liquid nitrogen fertilisers. 

NPK compound fertilisers for farmers who want nitrogen, phosphoms, and potassium. These are usually a mixture of ammonium nitrate, ammonium phosphate, and potassium chloride. 

This is a product of utmost importance, the starting point of nitrogen chemistry for products such as nitric acid, fertilisers (luea, ammonium nitrate, ammonium sulphate, ammonium phosphate), amides, amines and nitriles. The annual world production is approximately 100 million tons, ranking it in fifth place among the chemical products. Ammonia is a gas that is easy to liquefy at ordinary temperatures (boiling point... 

Ammonium compounds are very important fertilisers. Nitrogen is removed from the soil as nitrates are absorbed through the roots when plants are growing. When crops are harvested by farmers the nitrogen is not replaced, as the plants do not die naturally and rot back into the soil. So farmers use ammonium compounds to replace this nitrogen in the soil. Common ammonium salts used in fertilisers include ammonium chloride, NH Cl, ammonium nitrate, NH NO, ammonium phosphate, (NH )3P0 > and ammonium sulfate, (NH )2SO. ... 

The ammonium nitrate solution is heated to evaporate off the water and melt the solid. The molten solid is then sprayed into a tower with air blown into it. This solidifies the ammonium nitrate into pellets, which makes it convenient for farmers to spread from tractors (Figure 13.6). Ammonium sulfate, (NH j SO, and ammonium phosphate, (NH jjPO, are other ammonium salts used in fertilisers. 

Markets. Industrial use of ammonia varies according to region. Eor example, industrial usage represents 20% of the ammonia production in the United States and Western Europe, 10% in the USSR, 1—10% in Asia, and 5% in Latin America and North Africa (79). Fertiliser ammonia consumed domestically in most countries is converted to straight or compound fertilisers such as urea, ammonium nitrate, diammonium phosphate, and various grades of mixed fertilisers. However, almost 29% of ammonia nitrogen in the United States is consumed as direct appHcation material. The use of nitrogen solution such as urea and ammonium nitrate (UAN) has also become popular in the United States and the USSR. 

Fertilisers For nitrates, non-molybdenum austenitic steels are satisfactory, but in the manufacture of ammonium sulphate some free acid is often present, so that evaporators and centrifugal dryer baskets in this case are generally made from molybdenum-bearing steels. For super-phosphates this has limited application. 

In nitrogenous fertiliser solutions of the NH4NOJ—NHj —HjO type corrosion of steel can be prevented by 500 p.p.m. of sulphur-containing inhibitors, e.g. mercaptobenzothiazole, thiourea and ammonium thiocyanate. However, these inhibitors are not so effective where most of the NHj is replaced by urea. For these solutions phosphate inhibitors such as (NH4>2HP04 and polyphosphates were more effective... 

Sulphuric acid is used to manufacture other nitrogen-containing fertilisers such as ammonium sulphate, (NH4)2S04. Phosphorus-containing fertilisers, derived from rock phosphates such as Ca3(P04)2, are also manufactured using sulphuric acid. 

The most important use of ammonia is in fertiliser production. Fertilisers are added to the soil to improve crop yields. A farmer has the choice of two fertilisers, ammonium nitrate, NH4NOj. or diammonium hydrogen phosphate, (NH4),HP04. 

In another process crude calcium acid phosphate is mixed with ammonium sulphate solution below 80° C., and the mixture concentrated and filtered, when (NH4)H2P04 crystallises. (NH4)2HP04 is made from ammonia, fumes of phosphoric acid and water.3 Or calcium phosphate is just dissolved in sulphuric acid, the calcium sulphate filtered off and the add solution treated with ammonia and carbon dioxide. The ammonium sulphate and phosphate form a good mixed fertiliser.4... 

USA commenced production of ammonium j4ios[4iate fertilisers Staudinger reaction - description of first ylide First mining of Moroccan phosphate deposits... 

Other fertiliser compounds which can satisfactorily provide phosphorus and nitrogen are urea phosphate, CO(NH2)2 H3PO4, ammonium polyphosphate, [(NH4)P03] and phosphazenes such as P3N3(NH2)g (Table 12.4). Red phosphorus is slowly oxidised in damp soil and has been considered as a possible fertiliser [32,33]. 

Commercial fertilisers are assigned an NPK value which is the % N, P2O5 and KjO by weight. Another specification is the BPL (bone phosphate of lime) value, which is the P content expressed as % Ca3(P04)2. Available phosphoric acid or APA is a measure of the P2O5 available to plants, as indicated by an empirical solubility test. Unavailable phosphoric acid is usually expressed as the portion of the fertiliser which is insoluble in neutral ammonium citrate. In the United States, available P = total P - citrate - insoluble P (Chapter 14.1). 

The cost of plant food per kilogram can be calculated from the cost of fertilisers which contain only one plant food such as nitrogen in ammonium nitrate, phosphate in triple superphosphate, and potash in muriate of potash. 

Ammonium and sodium phosphates are mainly used in fertilisers and washing powders. They are also used in cattle feed. 

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