Phosphate rock occurrence

Phosphorus [7723-14-0] is a nonmetaUic element having widespread occurrence in nature as phosphate compounds (see Phosphoric acid and phosphates). Fluorapatite [1306-03-4], Ca F(P0 2> is the primary mineral in phosphate rock ores from which useful phosphoms compounds (qv) ate produced. The recovery from the ore into commercial chemicals is accompHshed by two routes the electric furnace process, which yields elemental phosphoms and the wet acid process, which generates phosphoric acid. The former is discussed herein (see Furnaces, electric). Less than 10% of the phosphate rock mined in the world is processed in electric furnaces. Over 90% is processed by the wet process, used primarily to make fertilisers (qv). 

Stow, S.H., 1969. The occurrence of arsenic and the color-causing components in Florida land-pebble phosphate rock. Econ. Geol., 64 667—671. 

Occurrence Occurs in nature in phosphate rock [impure Ca,(P04)2], apatite [Ca5(P04)3F], bones, teeth, organic compounds of living tissue, and as phosphorite nodules on the ocean floor. 

Iron and aluminum oxides present no special problem within the range of occurrence in commercial phosphate rocks these oxides usually are dissolved in nitric acid and reprecipitated during ammoniation as citrate-soluble phosphates, TVA tested leached-zone" Florida phosphate containing a high percentage of aluminum phosphate minerals in a special nitrophosphate process... 

By far the most important ores of iron come from Precambrian banded iron formations (BIF), which are essentially chemical sediments of alternating siliceous and iron-rich bands. The most notable occurrences are those at Hamersley in Australia, Lake Superior in USA and Canada, Transvaal in South Africa, and Bihar and Karnataka in India. The important manganese deposits of the world are associated with sedimentary deposits the manganese nodules on the ocean floor are also chemically precipitated from solutions. Phosphorites, the main source of phosphates, are special types of sedimentary deposits formed under marine conditions. Bedded iron sulfide deposits are formed by sulfate reducing bacteria in sedimentary environments. Similarly uranium-vanadium in sandstone-type uranium deposits and stratiform lead and zinc concentrations associated with carbonate rocks owe their origin to syngenetic chemical precipitation. 

The mining of massive sulfur deposits and the exposure of the element to air and water permits the development of populations of sulfur-oxidizing bacteria, with concomitant formation of acidity and sulfate ions. The occurrence of T. thiooxidans and T. thioparus in the Rozdol deposit in Russia has been described by Karavaiko (1959 1961). Similar events can occur during the industrial uss e of elemental sulfur and the amenability of sulfur to bacterial oxidation has been widely exploited agriculturally for modification of soil acidity, supply of sulfate ion and for in situ solubilisation of rock phosphate (Starkey, 1950 Gleen and Quastel, 1953 Vitolins and Swaby, 1969). While most attention has been focussed on chemolitho-trophic thiobacilli, such as T. thiooxidans and T. thioparus, an ability to oxidise elemental sulfur has been shown to be possessed by a number of heterotrophs such as the 35 species of Streptomyces examined by Yagi et al. (1971) and Arthrobacter (Ehrlich, 1962). 

Phosphorus occurrence in the lithosphere is predominantly as phosphates, P04 , although a rare iron-nickel phosphide, schreibersite ((Fe, Ni)3P)g is also known in nature [1]. For this reason, phosphates are the primary source of elemental phosphorus for chemical process requirements. Only 0.20-0.27% phosphate (0.15-0.20% as P2O5 0.07-0.09% as P) is present in ordinary crustal rocks. 

Apatite, monazite, and xenotime are found in rocks of nearly every metamorphic grade and, apparently, have wide P-T stability ranges. Despite their widespread occurrence, surprisingly few studies on the prograde metamorphic evolution of phosphates have been published. Kapustin (1987) reported on apatite compositions as a function of metamorphic grade (e.g., Fig. lb). 

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