Fertilizer phosphate

White phosphorus may be made by several methods. By one process, tri-calcium phosphate, the essential ingredient of phosphate rock, is heated in the presence of carbon and silica in an electric furnace or fuel-fired furnace. Elementary phosphorus is liberated as vapor and may be collected under phosphoric acid, an important compound in making super-phosphate fertilizers. 

Sulfur is a component of black gunpowder, and is used in the vulcanization of natural rubber and a fungicide. It is also used extensively in making phosphatic fertilizers. A tremendous tonnage is used to produce sulfuric acid, the most important manufactured chemical. 

The routes by which mineral phosphates are processed into finished fertilizers are outlined in Eigure 7. World and U.S. trends in the types of products produced are shown in Eigures 8 and 9, respectively. Most notable in both instances is the large, steady increase in the importance of monoammonium and diammonium phosphates as finished phosphate fertilizers at the expense of ordinary superphosphate, and to some extent at the expense of triple superphosphate. In the United States, about 65% of the total phosphate appHed is now in the form of granular ammonium phosphates, and additional amounts of ammonium phosphates are appHed as integral parts of granulated mixtures and fluid fertilizers. 

Fig. 8. World trends in types of phosphate fertilizers consumed, where (—) represents ammonium phosphates and multinutrient compounds (— normal superphosphate ( ), triple superphosphate and (— —), basic slag and raw rock.

Normal Superphosphate. From its beginning as the first commercial phosphate fertilizer, normal superphosphate (NSP), also called ordinary or single superphosphate, has continued among the top fertilizers of the world (Fig. 8). Use of normal superphosphate decreased steadily on a percentage basis because of growing production of more concentrated materials, but grew on a P2 s basis to a maximum of 6.7 x 10 t... 

The sustained world popularity of NSP results from simplicity of production and high agronomic quaHty as a carrier of available P2O5, calcium, sulfur, and usually some incidental micronutrients. In terms of agronomic value for large numbers of crops, no phosphate fertilizer has been shown to be superior to NSP. It is likely to remain in strong demand in parts of the world where simplicity of production or sulfur fertilization has high priority and where transportation costs are not prohibitive. 

Wet-Process Phosphoric Acid. As indicated in Figure 7, over 95% of the phosphate fertilizer used in the United States is made by processes that require an initial conversion of all or part of the phosphate ore to phosphoric acid. On a worldwide basis also, the proportion of phosphate fertilizer made with phosphoric acid is very high. Thus processes for production of phosphoric acid are of great importance to the fertilizer industry (see PHOSPHORIC ACID AND THE PHOSPHATES). 

Worldwide, triple superphosphate, over the period 1955 to 1980, maintained about a 15% share of the phosphate fertilizer market (Fig. 8). World consumption for the year ended June 30, 1991 (9) was equivalent to 3.6 x 10 t of P20, which was about 10% of world fertilizer P2O5 consumption. In the United States, consumption for the year ended June 30, 1990 (Fig. 7) was equivalent to about 240 x 10 t of P20, which represented only 6% of U.S. fertilizer P2O5 consumption. 

Since about 1968, triple superphosphate has been far outdistanced by diammonium phosphate as the principal phosphate fertilizer, both in the United States and worldwide. However, production of triple superphosphate is expected to persist at a moderate level for two reasons (/) at the location of a phosphoric acid—diammonium phosphate complex, production of triple superphosphate is a convenient way of using sludge acid that is too impure for diammonium phosphate production and (2) the absence of nitrogen in triple superphosphate makes it the preferred source of phosphoms for the no-nitrogen bulk-blend fertilizers that frequendy are prescribed for leguminous crops such as soy beans, alfalfa, and clover. 

Monoammonium Phosphate. Monoammonium phosphate [7722-76-1] (MAP), NH4H2PO4, has become second only to diammonium phosphate as a phosphate fertilizer material of trade. During the year ended June 30, 1990, monoammonium phosphate used ia the United States furnished 985 thousand t of P2O5 as compared to 1.5 million t furnished by diammonium phosphate and 240 thousand t by triple superphosphate (Fig. 7). Monoammonium phosphate furnished 25% of total P2O5 consumption. 

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. 

Resources of Sulfur. In most of the technologies employed to convert phosphate rock to phosphate fertilizer, sulfur, in the form of sulfuric acid, is vital. Treatment of rock with sulfuric acid is the procedure for producing ordinary superphosphate fertilizer, and treatment of rock using a higher proportion of sulfuric acid is the first step in the production of phosphoric acid, a production intermediate for most other phosphate fertilizers. Over 1.8 tons of sulfur is consumed by the world fertilizer industry for each ton of fertilizer phosphoms produced, ie, 0.8 t of sulfur for each ton of total 13.7 X 10 t of sulfur consumed in the United States for all purposes in 1991, 60% was for the production of phosphate fertilizers (109). Worldwide the percentage was probably even higher. 

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. 

Environmentally sound phosphate fertilizer plants recover as much of the fluoride value as H2SiFg as possible. Sales for production of AIF. -3H20 is one of the most important markets (see Fertilizers Phosphoric acid and the phosphates). 

Monoammonium and diammonium phosphates are produced on a large scale as fertilizers. During the 1970s, these materials, produced from economical wet-process phosphoric acid, became the world s leading phosphate fertilizers. 

An alternative route of manufacture is from siUcon tetrafluoride that is generated ia large quantities as a by-product of the production of phosphate fertilizers. The reaction is... 

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 decrease ia wodd sulfur iaveatories eaded ia the period 1990—1992. From 1991 to 1992, sulfur iaveatories remaiaed relatively stable. However, wodd sulfur iaveatories ia 1993 iacreased sharply, to an estimated 11.8 million metric tons. This iacrease was caused by a sharp fall ia wodd demand for phosphate fertilizers, which, because of market conditions, led to a large iacrease ia vattiag sulfur, especially ia Canada. Figure 3 shows wodd sulfur iaventory levels ia the maia produciag couatries or regioas from 1980 through 1994. 

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). 

Sulfuric acid is the most important sulfur-containing intermediate product. More than 85% of the sulfur consumed in the world is either converted to sulfuric acid or produced direcdy as such (see Sulfuric acid and sulfur trioxide). Worldwide, well over half of the sulfuric acid is used in the manufacture of phosphatic fertilizers and ammonium sulfate for fertilizers. The sulfur source may be voluntary elemental, such as from the Frasch process recovered elemental from natural gas or petroleum or sulfur dioxide from smelter operations. 

Agriculture is the largest industry for sulfur consumption. Historically, the production of phosphate fertilizers has driven the sulfur market. Phosphate fertilizers account for approximately 60% of the sulfur consumed globally. Thus, although sulfur is an important plant nutrient in itself, its greatest use in the fertilizer industry is as sulfuric acid, which is needed to break down the chemical and physical stmcture of phosphate rock to make the phosphate content more available to plant life. Other mineral acids, as well as high temperatures, also have the abiUty to achieve this result. Because of market price and availabiUty, sulfuric acid is the most economic method. About 90% of sulfur used in the fertilizer industry is for the production of phosphate fertilizers. Based on this technology, the phosphate fertilizer industry is expected to continue to depend on sulfur and sulfuric acid as a raw material. 

The need for acid concentrators exists because many uses of sulfuric acid do not lead to its consumption. Instead, the acid is diluted and partially degraded and contaminated. In the past, large amounts of acid were disposed of either by usiag it ia the phosphate fertilizer iadustry to dissolve phosphate rock or by neutralization and subsequent discharge to waterways. 

Historically, consumption of sulfuric acid has been a good measure of a country s degree of iadustrialization and also a good iadicator of general busiaess conditions. This is far less vaUd ia the 1990s, because of the heavy sulfuric acid usage by the phosphate fertilizer iadustry. Of total U.S. sulfuric acid consumption ia 1994 of 42.5 x 10 metric tons, over 70% went iato phosphate fertilizers as compared to 45% ia 1970 and 64% ia 1980 (144). Uses other than fertilizer have grown only slowly or declined. This trend is expected to continue. Production and consumption trends ia the United States are shown ia Tables 9 and 10. 

As of 1993—1994, over 70% of sulfuric acid production was not sold as such, but used captively to make other materials. At almost all large fertilizer plants, sulfuric acid is made on site, and by-product steam from these sulfur-burning plants is generally used for concentrating phosphoric acid ia evaporators. Most of the fertilizer plants are located ia Florida, Georgia, Idaho, Louisiana, and North Carolina. In the production of phosphate fertilizers, the primary role of sulfuric acid is to convert phosphate rock to phosphoric acid and soHd calcium sulfates, which are removed by filtration. 

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. 

Phosphates. The primary constituent of phosphate rock is fluorapatite, Ca3FP2022- Industrial phosphates including phosphate fertilizers (qv), phosphoric acid, and calcium phosphates (11) (see Phosphoric acid and the phosphates) are obtained from the large deposits of fluorapatite found in Florida in the United States, and in Morocco. Because phosphate rock is too insoluble to be useful as a fertilizer, it is converted to superphosphate [12431 -88-8] Ca(H2P0 2 CaSO, by H2SO and to triple superphosphate [7758-23-8] by H PO (l )- Phosphoric acid may also be... 

Primary Lead Smelters Primary Aluminum Reduction Plants Phosphate Fertilizer Industry Wet-Process Phosphoric Acid Plants... 

Phosphate Fertilizer Industry Superphosphoric Acid Plants... 

Phosphate Fertilizer Industry Diammonium Phosphate Plants... 

Phosphate Fertilizer Industry Triple Superphosphate Plants... 

Phosphate Fertilizer Industry Granular Triple Superphosphate Storage Facilities Goal Preparation Plants Ferroalloy Production Facilities Steel Plants Electric Arc Furnaces Constructed after October 21, 1974, and on or before August 17,1983... 

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