Phosphate rock mineralogy

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. 

According to a literature survey conducted by Shahalam [28], the contents of various chemicals found in the natural mined phosphate rocks vary widely, depending on location, as shown in Table 1. For instance, the mineralogical and chemical analyses of low-grade hard phosphate from the different mined beds of phosphate rock in the Rusaifa area of Jordan indicate that the phosphates are of three main types carbonate, siliceous, and silicate-carbonate. Phosphate deposits in this area exist in four distinct layers, of which the two deepest - first and second (the thickness of bed is about 3 and 3.5 m, respectively, and depth varies from about 20 to 30 m) - appear to be suitable for a currently cost-effective mining operation. A summary of the data from chemical analyses of the ores is shown in Table 2 [28]. 

Frondel, C., 1943. Mineralogy of the calcium phosphates in insular phosphate rock. Am. Mineral., 28 215-232. 

Chemical Factors - In spite of the known physical, mineralogical, and chemical differences that exist among various types of phosphate rocks, grade is typically the primary criterion used to differentiate phosphate rocks and is often expressed in terms of tricalcium phosphate [Ca3(P04)2]. The trade name for tricalcium phosphate is bone phosphate of lime or BPL. Early workers believed that tricalcium phosphate was the chief constituent of commercial phosphate rock. Later studies have shown that bones and phosphate rock consist of varieties of apatite. Because these commercial terms are widely used, the following conversion factors are included for reference purposes ... 

Van Kauwenbergh, S. J. 1995. Mineralogy and Characterization of Phosphate Rock, IN Direct App/ication of Phosphate Rock and Appropriate Technology Fertilizers in Asia — What Hinders Acceptance and Growth, pp. 29-47, K. Dahanayake, S. J. Van Kauwenbergh, and D. T. 

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.. ... 

A complete chemical and mineralogical analysis of a phosphate rock is helpful in evaluating its usefulness for making phosphoric acid. However, this information is not sufficient in itself trial runs in a plant or pilot plant are needed for a reliable evaluation unless the rock is one that has been used extensively in other similar plants with known results [10]. 

Several hundred phosphate minerals (see Mineralogy) are known, virtually aU of which are orthophosphates An exception is Canaphite, CaNa2P20y dHyO. The important mineral Apatite, Cas(P04)3X is found in igneous pegmatite rocks and hydrothermal veins. Fluoro-, Chloro-, and Hydroxyapatites are found (X = F, Cl, OH, respectively) as well as many substituted varieties. 

Insular phosphates of two different types exist, depending on whether guano interacts with igneous rocks of intermediate or basic types, or whether such action is confined to calcareous accumulation — such as coral. The first type, which will now be discussed, has more diversified mineralogical compositions. Rock phosphates of magnesium, aluminium and iron comprise less extensive deposits than phosphorites and, consequently, are of less economic importance. 

Fluorine is common in terrestrial environment and is always present in plants, soils and phosphatic fertilizers. As a rule of thumb, the F concentrations in these materials are on the order of 3 x 10°, 3 x 10 and 3 x 10 ppm for plants, soils and phosphatic fertilizers, respectively. Fluorine is a common constituent of rocks and soils. Very common soil minerals, such as biotite, muscovite, and hornblende, may contain as such as several percent of F and, therefore, would seem to be the main source of F in soils. It appears, therefore, that the F content of soils is largely dependent on the mineralogical composition of the soil s inorganic fraction. Phosphatic fertilizers, especially the superphosphates, are perhaps the single most important source of F in agricultural lands. 

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