Triple superphosphate

The manufacture of triple superphosphate proceeds according to the equation  

Its manufacture is very similar to that for superphosphate. Apatite with a P2O5 content 31% is ground to e.g. 70%  

74 im and wet-process acid with 52 to 54% P2O5 are used as starting materials. The molar ratio of CaO to P2O5 in the final product should be between 0.92 and 0.95 and the P2O5 content should be ca. 47%. The solidification of the reaction mixture occurs faster than in the manufacture of superphosphate. 

With minor exceptions, the commercial fertilizer, products are triple superphosphate (TSP), ammonium phosphates, and other compound fertilizers (some of the minor exceptions are potassium phosphates and magnesium ammonium phosphate [MgNH4P04]). Use of phosphoric acid in compound fertilizers will be described-under subject headings Compound Fertilizers (Chapter 16), Liquid Fertilizers and Mtrogen Solutions (Qiap-ter 10), and Nitrophosphate Fertilizers (Chapter 13). The present chapter wSi deal mainly wrath TSP and solid ammonium phosphates. 

In the period 1965-75, TSP sipplied approximately 15%r20% of the fertilizer phosphate used worldwide. This declined to 13.3% in 1988 and to 10.7% in 1992, primarily as a result of a continuous increase in the use of ammonium phosphates, mainly diammonium phosphate (DAP). 

The manufacture of TSP is quite similar to that of single superphosphate (SSP) and has the same advantages of simplicity, low technical skill requirement, and small capital investment. 

The reactivity of phosphate rock is of more importance in TSP production than in phosphoric acid production. Unreactive rocks may require unusually fine grinding or long reaction times or both. Even so, acceptable completion of reaction may be difficult to achieve with some igneous apatites. 

Rocks containing carbonates or carbonate substitutions in apatite release CO2 during reaction. The released gases result in a porous structure of the superphosphate made by den processes. This is considered desirable when the superphosphate is to be used in making compound fertilizers. When the rock contains very little carbonate, the superphosphate may be hard and dense, leading to granulation ckfhcuhies and poor ammoniation characteristics. 

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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.

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. 

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. 

Simplicity of production, high analysis, and excellent agronomic quaUty are reasons for the sustained high production and consumption of TSP. A contributing factor is that manufacture of the triple superphosphate has been an outlet for so-called sludge acid, the highly impure phosphoric acid obtained as a by-product of normal acid purification. 

Fig. 11. Dorr-Ohver type slurry process for manufacture of granular triple superphosphate. Courtesy of TVA.

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. 

Some commonly used primary nutrient fertilizers are incidentally also rich sources of calcium. Ordinary superphosphate contains monocalcium phosphate and gypsum in amounts equivalent to all of the calcium originally present in the phosphate rock. Triple superphosphate contains soluble monocalcium phosphate equivalent to essentially all the P2 5 product. Other fertilizers rich in calcium are calcium nitrate [10124-37-5] calcium ammonium nitrate [39368-85-9] and calcium cyanamide [156-62-7]. The popular ammonium phosphate-based fertilizers are essentially devoid of calcium, but, in view of the natural calcium content of soils, this does not appear to be a problem. 

Modem commercial wet-acid purification processes (see Fig. 4) are based on solvents such as C to Cg alcohols, ethers, ketones, amines, and phosphate esters (10—12). Organic-phase extraction of phosphoric acid is accompHshed in one or more extraction columns or, less frequently, in a series of countercurrent mixer—settlers. Generally, 60—75% of the feed acid P2 s content is extracted into the organic phase as H PO. The residual phosphoric acid phase (raffinate), containing 25—40% of the original P2O5 value, is typically used for fertilizer manufacture such as triple superphosphate. For this reason, wet-acid purification units are almost always located within or next to fertilizer complexes. 

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... 

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... 

A one-hoiir sampling period is generally required for both methods. Sampling periods are specified by the applicable standard e.g., standards applicable to triple-superphosphate plants require sampling of one hour or more. The standard may also specify a minimum sample volume that will dictate the minimum length of the sampling period. 

Superphosphoric acid, diammonium phosphate, triple superphosphate and granular triple superphosphate. 

Triple superphosphate, run of pile Sip4, HF Venturi or cyclonic scrubber... 

Triple superphosphate, granular SiF, HF, particulate matter Venturi or packed scrubber... 

The CaS04 or its hydrate (gypsum) acts only as an unwanted diluent. Its presence can he avoided by using H1PO4 instead of H1SO4 for the acidulation, thus giving rise to triple superphosphate ... 

Commercial triple superphosphate contains almost 3 tunes the amount of available (soluble) P2O5 as ordinary superphosphate hence its iianic (45-50wi% vs. 18-20wt %-). 

A great many phosphates are used in commercial fertilizers. Perhaps the most important of these is calcium dihydrogen phosphate, Ca(H2P04)2. In relatively pure form, this compound is known as triple superphosphate of lime. A 1 -2 mol mixture of Ca(H2PC>4)2 and gypsum, CaS04 2HzO, is commonly referred to as superphosphate of lime. ... 

The transfer of trace elements in phosphate rocks to P fertilizers is dependent upon the manufacturing processes. Triple superphosphate fertilizer contains 60-70% of the Cd present in phosphate rocks (Wakefield, 1980). The transfer coefficients may be similar for most other elements and heavy metals even though there are little data on the transfer of other elements from phosphate rocks to P fertilizers. In general, based on some long-term (> 50 years) soil fertility experiments in the U.S., annual Cd rates from the application of phosphate fertilizers are estimated to range from 0.3 to 1.2 g per ha. The addition of Cd to soils as a contaminant from P fertilizers... 

The product, Ca(H2P04)2, contains an even higher percent of phosphorus and it often referred to as triple superphosphate. 

LETS A process for making triple superphosphate (a calcium hydrogen phosphate). Developed by the J. R. Simplot Company in 1976. 

Solid phosphoric fertilizers are available as mono-ammonium phosphate, di-ammonium phosphate, triple superphosphate and single superphosphate additionally, high-grade liquid phosphoric acid is available. 

Triple-layer ODRs, 74 858-859 Triple point of water, 24 439-440 Triple-point temperature, 24 440 Triple porphyrin receptor, 76 787 Triple superphosphate, 77 119-120 Triplet multiplicity, 79 109 Triplet quenching additives, 74 703 Tripodal coelenterands, 24 45... 

The phosphate concentration in the tailings is upgraded to a level adequate for commercial exploitation through removal of the nonphosphate sand particles by flotation [32], in which the silica solids are selectively coated with an amine and floated off following a slurry dewatering and sulfuric acid treatment step. The commercial quality, kiln-dried phosphate rock product is sold directly as fertilizer, processed to normal superphosphate or triple superphosphate, or burned in electric furnaces to produce elemental phosphorus or phosphoric acid, as described in Section 9.2. 

The phosphate fertilizer industry is defined as eight separate processes phosphate rock grinding, wet process phosphoric acid, phosphoric acid concentration, phosphoric acid clarification, normal superphosphate, triple superphosphate, ammonium phosphate, and sulfuric acid. Practically all phosphate manufacturers combine the various effluents into a large recycle water system. It is only when the quantity of recycle water increases beyond the capacity to contain it that effluent treatment is necessary. 

Triple Superphosphate (TSP). Triple superphosphate is produced by the reaction between ground phosphate rock and phosphoric acid by one of two processes. One utilizes concentrated phosphoric acid and generates obnoxious gases. The dilute phosphoric acid process permits the ready collection of dusts and obnoxious gases generated. 

Triple superphosphate (TSP), made from phosphate rock and phosphoric acid, is mostly mono- and dicalcium phosphate. It is equivalent to a 48% P2O5 content. It led the market from 1965-1967. 

Reactions (1) and (2) are common for both normal and triple superphosphate. Reaction (3) is important in triple superphosphate because of the lack of large amounts of calcium sulfate. Reaction (5) is important... 

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