Phosphoric acid phosphate rock used

Chemistry ndProperties. The chemistry of phosphoric acid manufacture and purification is highly complex, largely because of the presence of impurities in the rock. The main chemical reaction in the acidulation of phosphate rock using sulfuric acid to produce phosphoric acid is... 

Hydroxyapatite, Ca2Q(PO (OH)2, may be regarded as the parent member of a whole series of stmcturaHy related calcium phosphates that can be represented by the formula M2q(ZO X2, where M is a metal or H O" Z is P, As, Si, Ga, S, or Cr and X is OH, F, Cl, Br, 1/2 CO, etc. The apatite compounds all exhibit the same type of hexagonal crystal stmcture. Included are a series of naturally occurring minerals, synthetic salts, and precipitated hydroxyapatites. Highly substituted apatites such as FrancoHte, Ca2Q(PO (C02) (F,0H)2, are the principal component of phosphate rock used for the production of both wet-process and furnace-process phosphoric acid. 

Dorr One of the two wet processes for making phosphoric acid by the acidulation of phosphate rock the other is the Haifa process. The Dorr process uses sulfuric acid. Phosphate rock is primarily apatite, Ca5(P04)3F. The calcium phosphate portion generates orthophos-phoric acid and calcium sulfate ... 

On the other hand, defluorinated phosphate rock is utilized as an animal feed ingredient. Defluorinated phosphoric acid is mainly used in the production of animal foodstuffs and hquid fertilizers. Finally, sodium phosphates, produced from wet process acid as the raw material, are used as intermediates in the production of cleaning compounds. 

In some cases it may be economically desirable to obtain phosphoric acid from phosphate rock using hydrochloric acid instead of sulfuric acid,... 

Phosphoric acid intended for use in manufacturing fertilizers and other chemicals is obtained by treating phosphate rock with sulfuric acid (see Chapter 15) ... 

In the manufacture of fertilizers, sulfuric acid is used to digest phosphate rock (largely Ca3(P04)2 and Ca5(P04)3F) to make phosphoric acid or the calcium salts such as Ca(H2P04)2-Some of the phosphoric acid is also used to make ammonium phosphate. More details on the manufacture of fertilizer were presented in Chapter 13. 

Ammonium polyphosphate solutions are the most popular phosphatic solutions now in use. The usual grades are 10-34-0 and 11-37-0. One company that uses a rather pure rock to produce phosphoric acid, which is used in the production of polyphosphate solution, has found it can produce a 12-40-0 grade of good quality. These ammonium polyphosphate solutions are used for direct application or as phosphate sources for NPK solution and suspension mixtures. Ammonium polyphosphate solutions are to the solution mixture industry as DAP is to the granular bulk-blend industry. This solution is usually produced in re onal plants that sell to dealers. The dealer sells it to farmers who use it for direct application, or the dealer mixes it with nitrogen solution and pota to produce NPK fluids. 

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. 

High contents of toxic impurities in phosphate rock used (for example, cadmium compounds) may =en-der the resulting phosphoric acid unsuitable for fertilizer production. 

However, HCl-route phosphoric acid has some advantages over wet-process acid. Unlike wet-process acid, it contains no scale-forming components, and its composition and quality are practically independent of the type of phosphate rock used. Superphosphoric acid (70%r72% P2O5) can ea y be produced from HCI-route phosphoric acid. 

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). 

The only major bulk chemical not so far considered is phosphoric acid, which can be manufactured pure from phosphorus and in an impure form from phosphate rock. The latter process is the dominant one, the impure product being used mainly in the preparation of fertilizers. Phosphate rock is also the most common source of elemental phosphorus. It is extracted by open-cast mining. The thermal process for producing phosphoric acid from the element produces an acid which is about three times more expensive than that produced direct from phosphate rock using the so-called wet process. 

Because phosphate rock contains Cap2/ hydrofluoric acid is a by-product in the preparation of phosphoric acid. HF is used in aluminum production. 

Extraction of Nonmetallic Inorganic Compounds. Phosphoric acid is usually formed from phosphate rock by treatment with sulfuric acid, which forms sparingly soluble calcium sulfate from which the phosphoric acid is readily separated. However, in special circumstances it may be necessary to use hydrochloric acid ... 

Minerals. Supplementation of macrominerals to mminants is sometimes necessary. Calcium and phosphoms are the minerals most often supplemented in mminant diets. One or both may be deficient, and the level of one affects the utilization of the other. Limestone, 36% calcium, is commonly used as a source of supplemental calcium. Dolomite, 22% calcium oyster sheUs, 35% calcium and gypsum, 29% calcium, are sources of calcium. Bone meal, 29% calcium, 14% phosphoms dicalcium phosphate, 25—28% calcium, 18—21% phosphoms and defluorinated rock phosphate, 32% calcium, 18% phosphoms, are sources of both calcium and phosphoms. Diammonium phosphate, 25% phosphoms phosphoric acid, 32% phosphoms sodium phosphate, 22% phosphoms and sodium tripolyphosphate, 31% phosphoms, are additional sources of phosphoms (5). 

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. 

Triple (Concentrated) Superphosphate. The first important use of phosphoric acid in fertilizer processing was in the production of triple superphosphate (TSP), sometimes called concentrated superphosphate. Basically, the production process for this material is the same as that for normal superphosphate, except that the reactants are phosphate rock and phosphoric acid instead of phosphate rock and sulfuric acid. The phosphoric acid, like sulfuric acid, solubilizes the rock and, in addition, contributes its own content of soluble phosphoms. The result is triple superphosphate of 45—47% P2 s content as compared to 16—20% P2 5 normal superphosphate. Although triple superphosphate has been known almost as long as normal superphosphate, it did not reach commercial importance until the late 1940s, when commercial supply of acid became available. 

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. 

Wet-process acid is manufactured by the digestion of phosphate rock (calcium phosphate) with sulfuric acid. Depending on availabiHty, other acids such as hydrochloric may be used, but the sulfuric-based processes are by far the most prevalent. Phosphoric acid is separated from the resultant calcium sulfate slurry by filtration. To generate a filterable slurry and to enhance the P2O5 content of the acid, much of the acid filtrate is recycled to the reactor. 

Phosphorus [7723-14-0] is a nonmetaUic element having widespread occurrence in nature as phosphate compounds (see Phosphoric acid and phosphates). Fluorapatite [1306-03-4], Ca F(P0 2> is the primary mineral in phosphate rock ores from which useful phosphoms compounds (qv) ate produced. The recovery from the ore into commercial chemicals is accompHshed by two routes the electric furnace process, which yields elemental phosphoms and the wet acid process, which generates phosphoric acid. The former is discussed herein (see Furnaces, electric). Less than 10% of the phosphate rock mined in the world is processed in electric furnaces. Over 90% is processed by the wet process, used primarily to make fertilisers (qv). 

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. 

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... 

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 element phosphorus, like nitrogen, is essential to plant and animal life. Although phosphorus was not identified and isolated until 1669, phosphorus-containing materials have been used as fertilizers since ancient times, usually from bird droppings, fish, and bone. The first phosphoric acid was made by treating bone ashes with sulfuric acid. This marked the beginning of the commercial fertilizer industry. Eventually, mined phosphate rock, a poor fertilizer by itself, was substituted for bones as a raw material for phosphoric acid in the mid-1880s. 

Most of the sulfuric acid produced by the chemical industry is used to make fertilizers. Fertilizers are produced using phosphorous, an essential nutrient that plants need to grow well. Phosphate is found in rocks, and these rocks are more soluble, or more easily dissolved, in water when broken down with sulfuric acid. Treating phosphate rocks this way releases phosphorous in a form that plant roots can absorb. 

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