Fertilizers production

Two of the previously mentioned accidents and the Oklahoma City bombing showed the explosive potential of nitrogen fertilizer so this is a good place to stan. 

The seventh element in order of abundance in the Earth s crust is potassium - about the same as sfjdium with similar properties. While sodium is readily available from the ocean, potassium is found and extracted from many mineral formations. About 90 percent of the potassium that is extracted goes to the production of fertilizers. Other purposes for it are ceramics and fire extinguishers for which potassium bicarbonate is better than sodium bicarbonate. 

By far the largest source of phosphorus is phosphate rock, with some use of phosphatic iron ore, from which phosphorus is obtained as a by-product from the slag. Phosphate rock consists of the insoluble tricalcium phosphate and other materials. For use as a fertilizer, phosphate must be converted to the water soluble form, phosphoric acid (H3PO4) which has three hydrogen atoms, all of which are replaceable by a metal. Tricalcium phosphate, is converted to soluble monocalcium phosphate and to superphosphate, A fertilizer factory, typically, a large installation, characterized by large silos produces year round, but peaks with the demands of the growing season. Phosphorus has many uses other than for fertilizer. 

The weight of the superphosphate can be reduced by replacing sulfuric acid with phosphoric acid (obtained by sulfuric acid acting on phosphate rock followed by product separation, or by the 

Instead of using sulfuric or phosphoric acid, nitric acid can be used to treat the phosphate lock to produce calcium nitrate fertilizer. Instead of neutralizing phosphoric acid with calcium which is useless, ammonia can be used to give ammonium phosphate, hence, two fertilizing elements. 

With a world population that has reached six billion, the production of food represents a monumental problem. Without the use of effective fertilizers, it would be impossible to meet this demand. For the most part, the fertilizers that are needed in such huge quantities are inorganic materials. 

Enormous quantities of phosphorus compounds are used in the production of fertilizers. Calcium phosphate is found in many regions of the world, but its direct use as a fertilizer is not very effective because of its low solubility. As was mentioned in Chapter 1, sulfuric acid plays an important role in fertilizer production and approximately 65% of the sulfuric acid manufactured (more than 80 billion pounds annually) is used for this purpose. 

When pulverized calcium phosphate is treated with sulfuric acid (the least expensive strong acid), the reaction is 

Approximately 100 billion pounds of phosphate rock are processed annually, primarily to produce fertilizers. This reaction occurs because the P043- is the conjugate base of a weak acid and it is easily protonated. The mixture of calcium dihydrogen phosphate and calcium sulfate (gypsum) is called superphosphate of lime, and it contains a higher percentage of phosphorus than does calcium phosphate, Ca3(P04)2. Moreover, it contains the phosphate in a soluble form, Ca(H2P04)2. Note that the latter compound contains a +2 cation and two -1 anions, whereas the former contains +2 cations and -3 anions. The 

Some fluoroapatite, Ca5(P04)3F, is often found along with Ca3(P04)2. Fluoroapatite reacts with sulfuric acid according to the following equation  

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KCl —NaCl —MgS04) and in many brines. Separated by fractional crystallization, soluble water and lower alcohols. Used in fertilizer production and to produce other potassium salts. 

Fertilizer industry Fertilizer products Fertilizer requirements Fertilizers... 

Ammonia from coal gasification has been used for fertilizer production at Sasol since the beginning of operations in 1955. In 1964 a dedicated coal-based ammonia synthesis plant was brought on stream. This plant has now been deactivated, and is being replaced with a new faciUty with three times the production capacity. Nitric acid is produced by oxidation and is converted with additional ammonia into ammonium nitrate fertilizers. The products are marketed either as a Hquid or in a soHd form known as Limestone Ammonium Nitrate. Also, two types of explosives are produced from ammonium nitrate. The first is a mixture of fuel oil and porous ammonium nitrate granules. The second type is produced by emulsifying small droplets of ammonium nitrate solution in oil. 

To determine the feasibiUty of, or need for, fertilization requires knowing (/) which of the required elements, if any, are deficient in the soil (2) what chemical forms of the deficient elements are assimilable by the plants and thus suitable as fertilizers (5) what quantity of fertilizer material is required to meet the needs of the crop and (4) whether the crop yield increase resulting from fertilizer appHcation would warrant the cost of the fertilizer production and appHcation. 

Physical Properties. The physical form and stabiUty of a fertilizer product is of an importance almost equal to that of its chemical content. Commercial fertilizers of importance include not only soHds, but also fluids, both solutions and suspensions, and even a gas (anhydrous ammonia). 

There are numerous variations of the wet process, but all involve an initial step in which the ore is solubilized in sulfuric acid, or, in a few special instances, in some other acid. Because of this requirement for sulfuric acid, it is obvious that sulfur is a raw material of considerable importance to the fertilizer industry. The acid—rock reaction results in formation of phosphoric acid and the precipitation of calcium sulfate. The second principal step in the wet processes is filtration to separate the phosphoric acid from the precipitated calcium sulfate. Wet-process phosphoric acid (WPA) is much less pure than electric furnace acid, but for most fertilizer production the impurities, such as iron, aluminum, and magnesium, are not objectionable and actually contribute to improved physical condition of the finished fertilizer (35). Impurities also furnish some micronutrient fertilizer elements. 

Filter acid from a dihydrate process contains 28—32% P2 5 usually concentrated to 40—45% P2 s when used at the site for fertilizer production. For shipping, the acid is concentrated to 52—54% P2 5 these concentrations the product is orthophosphoric acid [7664-38-2] ... 

Numerous purification processes have been developed for appHcation to wet-process acid (43—49) but these are not appHed to most acid used in fertilizer production. 

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. 

Secondary and Micronutrients in Fertilizers The great majority of farm fertilizers are produced, marketed, and appHed with regard only to the primary plant nutrient content. The natural supply of secondary and micronutrients in the majority of soils is usually sufficient for optimum growth of most principal crops. There are, however, many identified geographical areas and crop—soil combinations for which soil appHcation of secondary and/or micronutrient sources is beneficial or even essential. The fertilizer industry accepts the responsibiHty for providing these secondary and micronutrients, most often as an additive or adjunct to primary nutrient fertilizers. However, the source chemicals used to provide the secondary and micronutrient elements are usually procured from outside the fertilizer industry, for example from mineral processors. The responsibiHties of the fertilizer producer include procurement of an acceptable source material and incorporation in a manner that does not decrease the chemical or physical acceptabiHty of the fertilizer product and provides uniform appHcation of the added elements on the field. 

Because use of micronuttient fertilizers is expected to become increasingly important, their effective use requires cooperation between soil chemists and agronomists to identify and quantify needs, and fertilizer production technologists for effective incorporation. 

The 1993 prices and values of fertilizer products consumed in the United States are summarized in Table 16. The prices given are fob production sites or principal terminals thus costs to farmers are greater by virtue of shipping and handling costs and local dealer profits. 

Table 16. Prices and Value of Important Fertilizer Products Consumed in the United States...

Slow-Release Fertilizers. Products containing urea—formaldehyde are used to manufacture slow-release fertilisers. These products can be either soHds, Hquid concentrates, orHquid solutions. This market consumes almost 6% of the formaldehyde produced (115) (see Controlled release TECHNOLOGY, AGRICULTURAL). 

Ammonia is also the primary building block for downstream manufacturing of a wide range of fertilizer products. Table 18 gives the relative amounts of ammonia used for the manufacture of these nitrogen products. 

Nitrogen solutions consist of fertilizer product combinations, eg, ammonium nitrate —ammonia, urea—ammonium nitrate—ammonia, urea—ammonium nitrate, and urea—ammonia solutions. Mixed fertilizers cover a broad range and can be loosely defined as fertilizers which contain chemically mixed nitrogen, phosphoms, and potassium (N—P—K). Examples are ammonium phosphate—potash mixtures and ammonium phosphate nitrates. 

Although tetrafluorosilane can be readily produced by the action of hydrogen fluoride on sihca, its production is a by-product of HF production by the reaction of fluorospar and sulfuric acid and as a by-product from phosphate fertilizer production by the treatment of fluoroapatite with sulfuric acid (171). The most significant U.S. production is by IMC-Agrico at Uncle Sam, Louisiana. 

The wodd s largest sulfur iaveatories are stiH ia Canada. By the end of 1994, after significant vattiag, stocks iacreased by approximately 2.2 x 10 to 7.8 X 10 t. The United States, which had 4.2 million metric tons of sulfur inventories in 1982, reduced sulfur inventories to the lowest levels in a decade during 1992, a record year for phosphate fertilizer exports. This changed during 1993—1994, when phosphate fertilizer production eased and sulfur stocks increased to 1.1 million metric tons. Sulfur inventories in Poland and West Asia have also declined slightly (33). 

Because sulfuric acid has its greatest use in fertilizers, trends in that industry have a significant effect on the sulfuric acid business. Owing to a weak U.S. doUar in the early 1990s and high demand for fertilizer abroad, a considerable portion of U.S. phosphate fertilizer production was exported. High fertilizer exports are expected to continue until Thkd World countries can meet thek own demands. 

Metallurgical (smelter) plants and spent acid decomposition plants usually produce acid of good (low) color because the SO2 feed gases ate extensively purified prior to use. In some cases, however, and particularly at lead smelters, sufficient amounts of organic flotation agents are volatilized from sulfide ores to form brown or black acid. Such acid can be used in many applications, particularly for fertilizer production, without significant problems arising. 

The Osmocote product line is based on coating prilled N—P—K fertilizers. Product longevities range from 5 to 16 months, depending on the temperature. The Osmocote line also kicludes a coated N—P—K miniprill which lasts 2—3 months. 

Ammonia is shipped as a liquefied gas under its own vapour pressure of 114 psig (7.9 bar) at 21°C. Uses are to be found in refrigeration, fertilizer production, metal industries, the petroleum, chemical and rubber industries, domestic cleaning agents and water purification. Aqueous solutions of ammonia are common alkaline laboratory reagents ca 0.88 solution is the strongest available. Ammonia gas is expelled on warming. 

Excess fertilizer and combustion processes also can increase nitrous oxide (NnO) and nitrogen oxides (NOx) in the atmosphere. Nitrous oxide is a powerful greenhouse gas, and nitrogen oxides lead to smog and acid rain. The production of fertilizers requires a great deal of energy. The use of fossil fuels to supply the thermal requirements for fertilizer production further increases emission of nitrogen compounds to the atmosphere. 

The oxoacids and oxoanions of phosphorus are among the most heavily manufactured chemicals. Phosphate fertilizer production consumes two-thirds of all the sulfuric acid produced in the United States. 

Emissions of NOj due to fossil fuel combustion emissions (Tg N/yr) Fertilizer production and usage (TgN/yr) ... 

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