Fertilization calcium

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. 

Because of its use in the manufacture of fertilizers, calcium phosphate is a compound of enormous importance. After being mined, it is converted into Ca(H2P04)2 by treating it with sulfuric acid. This converts the insoluble Ca3(P04)2 into a soluble, more efficient form (see Section 13.9). The reaction can be written as... 

Enormous quantities of phosphorus compounds are used in the production of fertilizers. Calcium phosphate is found in many regions of the world, but its direct use as a fertilizer is not very effective because of its low solubility. As was mentioned in Chapter 1, sulfuric acid plays an important role in fertilizer production and approximately 65% of the sulfuric acid manufactured (more than 80 billion pounds annually) is used for this purpose. 

The phosphoric acid salts in fertilizers (calcium hydrogen phosphate, ammonium phosphate and mixtures of different phosphoric acid salts) are dealt with in Section 2.1 Fertilizers. Of the phosphates industrially produced for non-fertilizer applications, the following are discussed below ... 

Other calcium compounds include calcium chloride (CaCl2), which can be spread on sidewalks and roads as a deicer in winter calcium hypochlorite (Ca(ClO)2), which is a form of powdered bleach calcium nitrate (Ca(N03)2), which is a fertilizer calcium carbide (CaC2), which is the primary ingredient used to produce acetylene in miners lamps and calcium sulfide (CaS), which is used sometimes as a hair remover. 

The second group (b) is of lower importance from the standpoint of the amounts and toxicity. Solid particles are emitted particularly during the production of mineral fertilizers, calcium carbide, soda, pigments and in other processes involving the handling and transport of loose substances [18, 19]. 

Although simple methods are available for producing calcium nitrate, its use as a fertilizer is offset by its extreme hygroscopicity. As a fertilizer, calcium nitrate has special advantages for use on saline soils becaise the calcium displaces the sodium that is absorbed by clay in... 

Write an equation to represent the reaction of gypsum, CaS04 2 H2O, with ammonium carbonate to produce ammonium sulfate (a fertilizer), calcium carbonate, and water. 

White phosphorus may be made by several methods. By one process, tri-calcium phosphate, the essential ingredient of phosphate rock, is heated in the presence of carbon and silica in an electric furnace or fuel-fired furnace. Elementary phosphorus is liberated as vapor and may be collected under phosphoric acid, an important compound in making super-phosphate fertilizers. 

The sustained world popularity of NSP results from simplicity of production and high agronomic quaHty as a carrier of available P2O5, calcium, sulfur, and usually some incidental micronutrients. In terms of agronomic value for large numbers of crops, no phosphate fertilizer has been shown to be superior to NSP. It is likely to remain in strong demand in parts of the world where simplicity of production or sulfur fertilization has high priority and where transportation costs are not prohibitive. 

There are numerous variations of the wet process, but all involve an initial step in which the ore is solubilized in sulfuric acid, or, in a few special instances, in some other acid. Because of this requirement for sulfuric acid, it is obvious that sulfur is a raw material of considerable importance to the fertilizer industry. The acid—rock reaction results in formation of phosphoric acid and the precipitation of calcium sulfate. The second principal step in the wet processes is filtration to separate the phosphoric acid from the precipitated calcium sulfate. Wet-process phosphoric acid (WPA) is much less pure than electric furnace acid, but for most fertilizer production the impurities, such as iron, aluminum, and magnesium, are not objectionable and actually contribute to improved physical condition of the finished fertilizer (35). Impurities also furnish some micronutrient fertilizer elements. 

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. 

Calcium. Soil minerals are a main source of calcium for plants, thus nutrient deficiency of this element in plants is rare. Calcium, in the form of pulverized limestone [1317-65-3] or dolomite [17069-72-6] frequendy is appHed to acidic soils to counteract the acidity and thus improve crop growth. Such liming incidentally ensures an adequate supply of available calcium for plant nutrition. Although pH correction is important for agriculture, and liming agents often are sold by fertilizer distributors, this function is not one of fertilizer manufacture. 

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. 

Some of the principal forms in which sulfur is intentionally incorporated in fertilizers are as sulfates of calcium, ammonium, potassium, magnesium, and as elemental sulfur. Ammonium sulfate [7783-20-2] normal superphosphate, and sulfuric acid frequendy are incorporated in ammoniation granulation processes. Ammonium phosphate—sulfate is an excellent sulfur-containing fertilizer, and its production seems likely to grow. Some common grades of this product are 12—48—0—5S, 12—12S, and 8—32—8—6.5S. 

Calcium. Calcium is the fifth most abundant element in the earth s cmst. There is no foreseeable lack of this resource as it is virtually unlimited. Primary sources of calcium are lime materials and gypsum, generally classified as soil amendments (see Calcium compounds). Among the more important calcium amendments are blast furnace slag, calcitic limestone, gypsum, hydrated lime, and precipitated lime. Fertilizers that carry calcium are calcium cyanamide, calcium nitrate, phosphate rock, and superphosphates. In addition, there are several organic carriers of calcium. Calcium is widely distributed in nature as calcium carbonate, chalk, marble, gypsum, fluorspar, phosphate rock, and other rocks and minerals. 

Two main categories of the wet process exist, depending on whether the calcium sulfate is precipitated as the dihydrate or the hemihydrate. Operation at 70—80°C and 30% P20 in the Hquid phase results in the precipitation of CaSO 2 filterable form 80—90°C and 40% P20 provide a filterable CaSO O.5H2O. Operation outside these conditions generally results in poor filtration rates. A typical analysis of wet-process acid is given in Table 4. For more detailed discussion of the wet-process acid, see Fertilizers. 

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. 

---