Worldwide phosphate fertilizers

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. 

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. 

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. 

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. 

Sulfur is used in a wide variety of industrial processes, however, its single most important use is as sulfuric acid in the production of phosphatic fertilizers. World demand for sulfur (in all forms) has traditionally grown at a fairly steady pace while world supply has been subjected to various sudden surges and shortfalls. The resulting interplay of supply/demand forces has led to an interesting price history for this commodity both worldwide and in North America. 

Over 300 million people worldwide now consume optimally fluoridated water. The U.S. Public Health Service has established recommended levels for fluoride concentrations in water supplies in accordance with mean annual temperatures. The daily intake of fluoride not only comes from drinking water but also from food consumed or prepared with fluoridated water. Also, crops are frequently fertilized with phosphate fertilizers of high soluble-fluoride content, and food products including bone in animal feeds contain fluoride. 

Table 2.1-6. Worldwide Production of Ammonium Phosphate Fertilizer in the Period 1980 to 1994 in 10 t/a P2O5.

Melt and sinter phosphates accounted for ca. 3% of the worldwide production of phosphate fertilizers in 1976, with its share decreasing relative to other types. 

The worldwide consumption of phosphate fertilizers in 1997/98 was >30x10 tons phosphate, with about 20x10 tons being used in developing countries. In comparison, 80x10 tons of nitrogen fertilizers were used worldwide. Asia has the highest production and also consumption of phos-... 

Metallurgical processing, discharge of phosphatic detergents, coal and petroleum burning, and phosphate fertilization emit molybdenum to the environment. Molybdenum is only partly recycled because its use is dissipative, and because there is an overproduction of molybdenum worldwide (Davis 1991, Barceloux 1999, Sebenik etal. 2002). 

In the last three decades, phosphoric acid has become the most significant source of phosphate fertilizer production, and this trend is expected to continue worldwide in the foreseeable future, Growth is particularly expected in southeast Asian countries, which are implementing national programs to become self-supporting in the production of fertilizers. 

Ammonium phosphates, particularly DAP, are the most popular phosphate fertilizers worldwide because of their high analysis and good physical properties. The compositions of the pure salts - monoammonium phosphate (MAP) and DAP - are given in Table 12.4. 

Sulfuric acid is a very important commodity chemical, and indeed, a nation s sulfuric acid production is a good indicator of its industrial strength. World production in 2001 was 165 million tons, with an approximate value of US 8 billion. The major use (60% of total production worldwide) for sulfuric acid is in the "wet method" for the production of phosphoric acid, used for manufacture of phosphate fertilizers as well as trisodium phosphate for detergents. In this method, phosphate rock is used, and more than 100 million tonnes are processed annually. This raw material is shown below as fluorapatite, though the exact composition may vary. This is treated with 93% sulfuric acid to produce calcium sulfate, hydrogen fluoride (HF) and phosphoric acid. The HF is removed as hydrofluoric acid. The overall process can be represented as ... 

Direct Application Rock. Finely ground phosphate rock has had limited use as a direct-appHcation fertilizer for many years. There have been widely varying results. Direct appHcation of phosphate rock worldwide amounts to about 8% of total fertilizer phosphate used, primarily in the former Soviet Union, France, Brazil, Sri Lanka, Malaysia, and Indonesia. The agronomic effectiveness of an apatitic rock depends not only on the fineness of the grind but also strongly on the innate reactivity of the rock and the acidity of the sod performance is better on more acid sods. Probably more than half of the potentially productive tropical sods are acidic, some with pH as low as 3.5—4.5. Certain phosphate rocks may thus become increasingly important as fertilizer in those areas. The International Fertilizer Development Center at Muscle Shoals, Alabama is active in researching this field (30). 

Sulfuric acid is the most heavily produced inorganic chemical worldwide, the annual production in the United States alone being more than 4 X 1(J10 kg. The low cost of sulfuric acid leads to its widespread use in industry, particularly for the production of fertilizers, petrochemicals, dyestuffs, and detergents. About two-thirds is used in the manufacture of phosphate and ammonium sulfate fertilizers (see Section 15.4). 

Crop yields can rise dramatically with the use of commercial fertilizers. For example, in 1800 an acre of land in the United States produced about 25 bushels of com. In the 1980s the same acre of land produced 110 bushels. Worldwide, approximately 4 billion acres of land are used to grow food crops. This would probably be enough land to feed the world s population if the entire acreage could be fertilized commercially. It has been estimated that world crop production would increase by about 50% if about 40 per acre were spent to apply modem chemical fertilizers. However, it would cost about 160 trillion to produce this additional food. Furthermore, the use of chemical fertilizers can lead to the contamination of streams, lakes, and bays with phosphates and nitrates. 

In addition to nitrate and other nitrogen compounds, guano contains phosphate and potassium, thus making it a good fertilizer. Deposits of guano were discovered and studied by Alexander von Humboldt in 1802 [11], This source of fertilizer had thus been known for some time before the development of the Haber process for producing ammonia. However, guano was and is limited and unsustainable as a source of fertilizer for crops, particularly on a worldwide basis. 

The demand for nitrogen in a chemically fixed form (as opposed to elemental nitrogen gas) drives a huge international industry that encompasses the production of seven key chemical nitrogen products ammonia, urea, nitric acid, ammonium nitrate, nitrogen solutions, ammonium sulfate and ammonium phosphates. Such nitrogen products had a total worldwide annual commercial value of about US 50 billion in 1996. The cornerstone of this industry is ammonia. Virtually all ammonia is produced in anhydrous form via the Haber process (as described in Chapter 2). Anhydrous ammonia is the basic raw material in a host of applications and in the manufacture of fertilizers, livestock feeds, commercial and military explosives, polymer intermediates, and miscellaneous chemicals35. 

Essentially all fertilizer phosphorus now is derived from mined ores. (The occurrence, mineral characteristics, mining, and benefici-ation of major phosphate ores were described in some detail in Chapter 23.) Worldwide, about 85 percent of the mined phosphate eventually finds its way into fertilizer.3 As mentioned earlier, the most conservative estimates indicate a sufficiency for hundreds of years at expected consumption levels. Supply problems of the immediate future will relate chiefly to exhaustion of the better ores, with the result that ores of lower grades and higher impurity contents will have to be processed. 

The ability of soils and soil microbes to neutralize excess fertilizers has limits. Nitrogen and phosphate draining from excessive fertilization of sugar cane fields favors cattail plants over native plants in the Florida Everglades. Nitrogen and phosphate from fertilizers and municipal wastewater are causing water problems worldwide. 

The phosphate concentrations of waters draining from soils usually are about 10-7 M. Worldwide, this amounts to a phosphate loss of 17 x 1010 moles yr-1 (10 mol ha-1 yr-1 or 1 kg ha-1 yr-1). Phosphate in eroded soil particles reaching the sea is estimated to be an additional 13 x 1010 mol yr-1. Fertilization affects the phosphate content of sediments eroded from surface soils, and increases the phosphate concentrations of drainage waters and groundwaters. Preventing erosion has the added benefit of reducing phosphate inputs to streams and lakes. 

The industrial separation of N2 is discussed in Section 14.4. Mining of phosphate rock takes place on a vast scale (in 2001, 126Mt was mined worldwide), with the majority destined for the production of fertilizers (see Box 14.11) and animal feed supplements. Elemental phosphorus is extracted from phosphate rock (which approximates in composition to Ca3(P04)2) by heating with sand and coke in an electric furnace (equation 14.1) phosphorus vapour... 

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