Superphosphate manufacture

The System Lime and Phosphoric Acid —Solubility of Calcium Phosphates— Conditions of Formation of Basic and Acid Calcium Phosphates—Composition of Solutions Saturated with Calcium Hydrogen Phosphates—Equilibria between Solid Phases and Solutions at Various Temperatures—Changes during Neutralisation—The Acid Phosphates—Manufacture of Superphosphate—Retrogression—Treatment of Special Ores—Phosphoric Acid— Commercial Preparation and Extraction from Rook—The History and Technology of Superphosphate Manufacture—Mixed and Concentrated Phosphorio Fertilisers—Potassium Phosphates—Ammonium Phosphates. 

Gray, A. N. 1930. Phosphates and Superphosphates, International Superphosphate Manufacturers Association, Paris, France. 

Fruhstorfer, A. 1961. Testir Granular Fertilizers for Hardness, Paper No. LE/61/58, The hi-ternational Superphosphate Manufacturers Association, Aflesbaden, Germany. 

In 1842, British patents for the mannfacture of superphosphate by the action of sulphuric acid on bones were taken out independently by J.B. Lowes and J. Murray [28-31]. This led to the world s first fertiliser factory at Deptford, Kent, England. A few years later superphosphate manufacture conunenced in the United States, but it was not until about 1855, however, that the work of Lowes... 

Liquid micronutrient compositions are made by dissolving metal salts such as CUSO4 and MnCl2 in phosphoric acid, and then neutralising with anunonia. A small amount of a phosphonate of type (12.13a) or (12.13b) may be added to complex and prevent any precipitation of the metallic salts. Commercial superphosphoric acid, when used for superphosphate manufacture, functions as a source of micronutrient elements. The add itself can be used for liquid fertilisers, since the small quantities of polyphosphates which are present will sequester the impurity metal ions present. 

The patent literature contains numerous recipes for constructional materials which utilise phosphogypsum, the waste material from superphosphate manufacture. Plaster of Paris and anhydrite plaster can be made from phosphogypsum (Chapter 4.1) [58]. 

The first example of imported chemical technology actually predated the period 1856-19L4, namely a sulphuric acid plant erected in 1834 under the supervision of a French factory master. Around 1850 two technologies were imported from England superphosphate manufacture, in 1851, and coal gas production, in 1853. Some of the first gas plants were built by an Anglo-Danish company with English equipment. 

Industrially. phosphoric(V) acid is manufactured by two processes. In one process phosphorus is burned in air and the phos-phorus(V) oxide produced is dissolved in water. It is also manufactured by the action of dilute sulphuric acid on bone-ash or phosphorite, i.e. calcium tetraoxophosphate(V). Ca3(P04)2 the insoluble calcium sulphate is filtered off and the remaining solution concentrated. In this reaction, the calcium phosphate may be treated to convert it to the more soluble dihydrogenphosphatc. CafHjPOjj. When mixed with the calcium sulphate this is used as a fertiliser under the name "superphosphate . 

Table 5. Process Variables in the Manufacture of Normal Superphosphate...

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.

Superphosphate Its Histoy, Chemistry, and Manufacture, U.S. Dept, of Agriculture and Tennessee VaUey Authority, Washington, D.C., Dec. 1964. 

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. 

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... 

Parrish, P. and OGILVIE, H. Calcium Superphosphates and Compound Fertilisers. Their Chemistry and Manufacture (Hutchison, 1939). 

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. 

The production of superphosphate is often combined with the manufacture of sodium fluorosilicate and then the amount of wastes is larger. 

All phosphorus fertilizers come from wet process phosphoric acid or directly from phosphate rock. Normal superphosphate, triple or concentrated superphosphate, and ammonium phosphate are the three common types used. Normal or ordinary superphosphate (NSP or OSP) is mostly monocalcium phosphate and calcium sulfate. It is made from phosphate rock and sulfuric acid and is equated to a 20% P2O5 content. It led the market until 1964. The production of normal superphosphate is similar to that for the manufacture of wet process phosphoric acid (Chapter 2, Section 3) except that there is only partial neutralization. Normal superphosphate is no longer used to any great extent. The following reaction is one example of an equation that represents this process. 

J. T. Meckstroth 22 showed that the largest use for phosphoric acid is in sugar defecation. It is also used in the manufacture of jellies, preserves, and soft drinks in pharmaceutical preparations and in the rust-proofing of iron. The chief phosphates in industry are the calcium hydrophosphates used in making baking-powder, and self-rising flour sodium phosphates used in making boiler compounds, in laundry work, etc. The superphosphates are used in fertilizers. Calcium orthophosphate is the form of bone ash extensively used in the manufacture of bone china. 

Sulfuric acid was also used in the manufacture of superphosphates, which were produced as fertilizers on a large scale by the mid-nineteenth century. By that time, a solution was found for the complex engineering problems that had hampered the use of the alternative process to produce soda... 

J.O. Hardesty, Granulation, Chapter 11 in Superphosphate Its History, Chemistry and Manufacture, U.S. Department of Agriculture, Washington, 1964. 

The major use of phosphate is to supply phosphorous, one of the three essential plant foods, nitrogen, phosphorus, and potassium. Phosphate rock extraction from its ore, and its subsequent conversion into fertilizer materials and industrial chemicals, is a relatively mature art. Single superphosphate, a mixture of monocalcium monohydrate and gypsum formed by the reaction of sulfuric acid with phosphate rock, has been used as a fertilizer since the mid-1800s. Phosphoric acid, derived by the treatment of phosphate rock with sulfuric acid so as to produce gypsum in a separable form, was manufactured in many locations by batch and countercurrent decantation methods in the 1920s. 

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