Triple superphosphate production

Triple superphosphate production—Triple superphosphate (TSP) is a fertilizer material with a phosphorus content of over 40%, measured as phosphorus pentoxide (P2O5). 

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. 

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. 

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. 

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. 

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. 

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... 

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

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. 

Thus all three formula Ca atoms are converted to dihydrogen phosphate, and the product is therefore called triple superphosphate (approximately 46% or 20% P). 

In recent years the production of SSP, to a large extent, has given way to the production of the higher-analysis triple superphosphate and ammonium phosphates. SSP retains greater importance in some countries. For example, SSP remains popular in Australia, at least in part because its sulfur content is particularly needed there. 

Poorly crystalline or amorphous Phosphorite sediments made from the hard remains of marine organisms are the principal commercial source of phosphates, although Apatites are also mined. Treatment of phosphate minerals with sulfuric acid yields superphosphate fertilizer, a mixture of Ca(H2P04)2, H3PO4 and CaS04. Phosphoric acid treatment gives triple superphosphate , rich in Ca(H2P04)2. Other soluble fertilizers such as ammonium phosphates are obtained from these products. 

The production of triple superpho.sphate with a P2O5-content greater than 40% and biologically more available phosphorus reached a peak in 1984 and has declined 30% since then. The worldwide capacity for triple superphosphate is considerably underutilized. Part of the spare capacity can be utilized for the manufacture of ammonium phosphate. The world production by region in 1990 is given in Table 2.5-5. 

Most of the phosphoric acid production in the U.S., about 85%, is consumed by fertilizer manufacturers, mostly for preparation of ammonium phosphates and triple superphosphate (Chap. 11). This consumption picture may be slightly distorted since the U.S. is also a substantial exporter of phosphoric acid. 

This is the reason for the commercial reference to this material as triple superphosphate . This product too may be ammoniated, or mixed with other nitrogen-containing constituents such as urea or ammonium nitrate nitrogen to provide both nitrogen and phosphorus for plant growth. 

Calcium dihydrogen phosphate, which is used in the production of triple superphosphate fertilizers, can be formed from the reaction of apatite, Ca5(P04)3F, with phosphoric acid. How many grams of calcium dihydrogen phosphate can be formed from 6.78 g of Ca5(P04)3F ... 

Note The products obtained from commercial processes are not pure monobasic calcium phosphate. The superphosphate obtained from the HjS04 treatment is about 30% CaH4(P04)).H20, 10% CaHP04, 45% CaS04, 10% iron oxide, silica, alumina, etc. and 5% water it contains 18-21% available P2Os. The triple superphosphate obtained from the H2POt treatment contains from 43 to 50% available P205. 

By far the most important use of phosphoric acid is in the production of fertilizers. At least four major types of fertilizers are made from phosphoric acid diammonium phosphate ((NH4)2HP04 DAP), monoammonium phosphate (NH4H2P04 MAP), granulated triple superphosphate (GTSP), and superphosphoric acid, the only liquid among the group. An additional 5 percent of the phosphoric acid produced is used as an animal feed supplement. 

Triple-superphosphate is made by using phosphoric( acid in place of sulphuric acid the product contains 45-50% available P2O5 ... 

The history of production of concentrated or triple superphosphate is associated with the production of phosphoric acid. The first known commercial production occurred in the 1870s in Germany where the... 

Triple superphosphate did not become an important fertilizer until the 1950s. In contrast with ordinary su perphosphate, triple superphosphate has a higher content of phosphate than the phosphate rock from which it is made thus, it should be produced near the source of the rock in large plants, with shipment of the product to local mixing plants or to farmers. 

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. 

A higher grade of fertiliser known as triple superphosphate is made by the action of wet process phosphoric acid on ground phosphate rock. The reaction may be summarised by Equation 12.3. The product contains a higher proportion of available phosphate than ordinary superphosphate, and its manufacture and use has become more economic than the latter, over the past two decades. On the industrial scale, reactions such as (12.1) and (12.3) do not go to completion immediately, and reaction periods up to 30 days may be required under some conditions. 

---