Phosphate rock reactivity

McClellan, G. H., and S. J. fen Kauwenbergh. 1990. Relationship of Mineralogy to Sedimentary Phosphate Rock Reactivity," IN Proceedings of the Workshop on Phosphate Sources for Acid Soils in the Humid Tropics of Asia, pp. 1-17, Malaysian Rubber Research Institute arxl Malaysian Society of Soil Science, Kuala Lumpur, Malaysia. 

Mineralogy of Sedimentary Apatites and the Relationship to Phosphate Rock Reactivity, Paper presented at the National Workshop on Fertilizer Efficiency. Cisarua, Indonesia, November 12-13, 1990.. ... 

Direct Application Rock. Finely ground phosphate rock has had limited use as a direct-appHcation fertilizer for many years. There have been widely varying results. Direct appHcation of phosphate rock worldwide amounts to about 8% of total fertilizer phosphate used, primarily in the former Soviet Union, France, Brazil, Sri Lanka, Malaysia, and Indonesia. The agronomic effectiveness of an apatitic rock depends not only on the fineness of the grind but also strongly on the innate reactivity of the rock and the acidity of the sod performance is better on more acid sods. Probably more than half of the potentially productive tropical sods are acidic, some with pH as low as 3.5—4.5. Certain phosphate rocks may thus become increasingly important as fertilizer in those areas. The International Fertilizer Development Center at Muscle Shoals, Alabama is active in researching this field (30). 

Total phosphorus content of phosphate rocks is relatively unimportant, since what really matters is its reactivity in the soil, which in turn depends on the soil itself, the rock mineralogy and the level of rock grinding. 

Dann, P.R., Derrick, J.W., Dumaresq, D.C. and Ryan, M.H. 1996. The response of organic and conventionally grown wheat to superphosphate and reactive phosphate rock. Australian Journal of Experimental Agriculture 36 71-78. 

Because of its high reactivity with oxygen in air, white phosphorus is generally stored under water. White phosphorus does not occur naturally. Industries produce it from naturally occurring phosphate rocks. 

Calcination. Phosphate rock normally is used as a dry rock or in slurry form. However, in some cases, particularly where the raw phosphate is high in carbonaceous matter or it is desirable to have a clean acid, the rock is calcined. Also, in a few cases, the phosphate rock is calcined, the product slaked, and free lime separated as a beneficiation step. Calcination is energy intensive and produces a less reactive rock and, in some cases, a less filterable gypsum. Therefore, the use of calcination is diminishing, and is being replaced by a wet oxidation step to produce green acid.16 In separating calcium carbonate, flotation, where it is successful, is favored over calcination because of its lower cost. 

Syers, J.K., Mackay, A.D., Brown, M.W., Currie, L.D., 1986. Chemical and physical characteristics of phosphate rock materials of varying reactivity. J. Sci. Food Agri. 37, 1057-1064. 

Phosphate rock preparation—Domestic phosphate rocks are essentially fluorapatite admixed with various proportions of other compounds of calcium, fluorine, iron, aluminum, and silicon. Phosphate rock preparation involves beneficiation to remove impurities, drying to remove moisture, and grinding to improve reactivity. Phosphate rock, when very finely pulverized, has limited direct use as a fertilizer. However, it is mainly used as a raw material for the manufacture of phosphate acid, superphosphate, phosphorus, and phosphorus compounds. 

Phosphate rocks can be applied directly to soils to furnish P, and they have been used for the past century. With their limited solubility, however, they are most beneficial on very acidic soils (pH below about 5.2). Most PR must be ground to a fairly fine state to improve its reactivity in soils, which make it less convenient to handle than granulated fertilizers. There are large differences in the reactivity of PRs, which increases with the amount of substitution of carbonate for phosphate in the apalMic mineral structure. Warm climates with adequate soil moisture and acidic soils have the potential for PR to be... 

Direct application of raw, finely ground phosphate rock has been practiced to a substantial extent in the United States, Russia, and China and to some extent in other countries. The practice has almost disappeared in the United States. However, recent information indicates that the value of raw phosphate varies widely, with variations in the character of the ore and the crop arid soil on which it is used. There are indications that reactive rocks may be useful sources for at least part of the phosphorus requirement of many crops grown on acid soils. 

Lehr and McClellan [17] studied a suite of sedimentary phosphate rocks and an igneous phosphate rock concentrate and concluded that carbonate substitution in apatite was the dominant factor influencing reactivity measurements. This study also concluded that reactivity... 

While determination of the type of apatite and reactivity of a phosphate rock may give an indication of the potential for direct application, many other factors are Involved. These factors include type of crop flong or short term), soil pH and other soil characteristics, and climatic factors. Agronomic testwork is needed to determine the potential for direct application under specific conditions or a range of conditions. 

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. 

Phosphate rocks vary widely in their reactivity hence their agronomic value varies. 

In the early part of the 20th century, several longterm experiments were, conducted in the United States with ground phosphate rocks in Tennessee, which is one of the less reactive sedimentary rocks. Hopldns has reported results from experiments in four states of the United States that show the increased value of crops... 

In tests with single-season crop results, the most reactive phosphate rocks have shown effectiveness nearly equal to superphosphate with some crops and soils. 

The use of bones and bone ash has already been mentioned above. Some varieties of finely ground phosphate rock (e.g. Tunisian Gafsa) are sufficiently reactive to be used as slow-release fertilisers. These are most effective in acid soils. Phosphorite with carbonate impurity has a somewhat higher water solubility than other varieties and is likely to be more suitable for fertiliser use, whereas Kola crystalline rock is quite unsuitable. 

These techniques are bas not only on the principle that lead-containing phosphates with the apatite structure are highly insoluble, but also that rapid reactions occur with apatite and lead ions at the sohd/aqueous solution interface [12, 13, 15, 20, 29, 48, 53, 56]. Removal of lead from aqueous solutions using synthetic hydroxyapatite gives aqueous lead concentrations below the maximum contamination level after Ih [12, 53]. Other workers [9] observed the formation of calcium-lead apatite solid-solutions after 3 mins contact between synthetic hydroxyapatite and aqueous solutions containing lead, and no lead was detected in the aqueous solution after 24 h contact. However, the efficiency of lead removal depends on the characteristics of the phosphate rock employed [15]. It has been shown that the composition and crystallinity of the phosphate influence the speed of the surface reactions [4, 44]. More highly crystalline solids have lower solubilities and dissolution rates, making the apatite less reactive [4]. The presence of fluoride in the hydroxyapatite structure decreases its solubility and dissolution rate, while the presence of carbonate decreases structural stability, and increases solubility and the dissolution rate [4, 35]. 

Phosphorus, shown in Figure 3.4c, is one of five solid nonmetals. Pure phosphorus is known in two common forms. Red phosphorus is a dark red powder that melts at 597°C. White phosphorus is a waxy solid that melts at 44°C. Because it ignites in air at room temperature, white phosphorus is stored under water. Phosphorus is too reactive to exist in pure form in nature. It is present in huge quantities in phosphate rock, where it is combined with oxygen and calcium. All living things contain phosphorus. 

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