Phosphorites minerals

It has been recently demonstrated in shelf sediments of the highly productive upwelling area off the coast of Namibia that certain sulfur bacteria release very high concentrations of phosphate into the pore water near the sediment surface. This produces a stratified precipitation of phosphorite minerals (Schulz and Schulz 2005). The questions to be answered by modeling are as follows ... 

These varieties of carbonated apatite whose formulae may be represented as Cajo ,(P04)6 (C03) j (F,0H)2, where jc = 1, are often designated as Francolite (F OH) or Dahllite (OH F). Up to 25% replacement of PO4 by CO3 is, however, sometimes found, and replacement of up to 10% Ca by Mg can occur. A wide variety of other metals, including uranium are often incorporated in trace amounts. Common major impurities found with phosphorites are iron, alumina, quartz, montmorillonite and organic matter. Almost every element has been found, at least in trace amounts, in phosphorite minerals. Much of this arises from the remarkable nature of the Apatite crystal structure which allows substitution of the Ca ", and F by alternative cations and anions (Chapter 5.3). 

The ocean is host to a variety and quantity of inorganic raw materials equal to or surpassiag the resources of these materials available on land. Inorganic raw materials are defined here as any mineral deposit found ia the marine environment. The mineral resources are classified generally as iadustrial minerals, mineral sands, phosphorites, metalliferous oxides, metalliferous sulfides, and dissolved minerals and iaclude geothermal resources, precious corals, and some algae. The resources are mosdy unconsoHdated, consoHdated, or fluid materials which are chemically enriched ia certain elements and are found ia or upon the seabeds of the continental shelves and ocean basias. These may be classified according to the environment and form ia which they occur (Table 1) and with few exceptions are similar to traditional mineral deposits on land. 

Fig. 1. Global distribution of seabed mineral deposits, where x represents chromite + barite titanium, zirconium, hafnium, and thorium tin I gold, platinum, and silver 3 sand and gravel shell, calcium carbonate gems marine polymetaUic sulfides phosphorites Cl cobalt cmsts S sulfur and B...

Continental Shelf. Most consohdated mineral deposits found on the continental shelf are identical to those found on land and are only fortuitously submerged. Exceptions include those laid down in shallow marine seas or basins in earlier geochemical environments such as bedded ironstones, limestones, potash, and phosphorites. 

Phosphorus is the eleventh element in order of abundance in crustal rocks of the earth and it occurs there to the extent of 1120 ppm (cf. H 1520 ppm, Mn 1060 ppm). All its known terrestrial minerals are orthophosphates though the reduced phosphide mineral schrieber-site (Fe,Ni)3P occurs in most iron meteorites. Some 200 crystalline phosphate minerals have been described, but by far the major amount of P occurs in a single mineral family, the apatites, and these are the only ones of industrial importance, the others being rare curiosities. Apatites (p. 523) have the idealized general formula 3Ca3(P04)2.CaX2, that is Caio(P04)6X2, and common members are fluorapatite Ca5(P04)3p, chloroapatite Ca5(P04)3Cl, and hydroxyapatite Ca5(P04)3(0H). In addition, there are vast deposits of amorphous phosphate rock, phosphorite, which approximates in composition to fluoroapatite. " These deposits are widely... 

Each of these solid phases can be described in terms of their mineralogy. This classification scheme is based on crystal structure and chemical composition. The most common minerals found in marine sediments are listed in Table 13.2. Most are silicates in which Si and O form a repeating tetrahedral base unit. Other minerals common to marine sediments are carbonates, sulfates, and oxyhydroxides. Less common are the hydrogenous minerals as they form only in restricted settings. These include the evap-orite minerals (halides, borates, and sulfates), hydrothermal minerals (sulfides, oxides, and native elements, such as gold), and phosphorites. 

Phosphorite A hydrogenous mineral that forms in surficial sediments underlying surface waters of high biological productivity. It is composed primarily of calcium phosphate that is biogenic in origin. 

Tribasic calcium phosphate occurs in nature as minerals, oxydapatite, whitlockite, voelicherite, apatite, phosphorite. It has many industrial applications. Some are similar to the monobasic and dibasic salts. It is used in fertilizers, dental products, ceramics and pohshing powder. Some other important applications are in plastics as a stabdizer as an anticaking agent as a nutrient supplement in cattle food for clarifying sugar syrup as a mordant in dyeing textiles and as a buffer to control pH. 

X-ray excited steady-state luminescence has been checked as a distinctive feature for the phosphorites, Karatau (Gorobets et al. 1997a). Sedimentary apatite (francolite) is not luminescent under X-ray excitation and red Mn " luminescence of dolomite was employed. As a result, concentration of MgO in the accepted fraction was lowered from 5.0% to 2.4%. The use of this method is limited because in many cases the X-ray luminescence of dolomite is very low or non-existent. Besides that, other minerals without luminescence come together with the accepted phosphate fraction, including sihceous shale, which is harmful for the following deep beneficiation. Thus new methods have to be developed for detection and content evaluation of dolomite in Florida phosphates on moving belt conveyors. 

Minerals of economic importance within sedimentary formations include, hut are not limited to fluorite, barite, phosphorite, and oolitic hematite. Fluorite is utili/ed us a flux in steelniakiitg and when of high quality as lenses and prisms in the optical industry. Barite is an essential mineral used m gas- and oil-well drilling. Phosphorite, a product of chemical precipitation from seawater, when ircaled with sulfuric acid, produces superphosphate fertilizer, (.killtic hematite deposits of extensive size are important sources of iron ore. 

A topic of considerable controversy is the question of carbonate incorporation in the apatite lattice since carbonate apatite does not precipitate from aqueous solutions28, 395 398 Carbonate apatites (phosphorites) forming in marine environments134 are considered metasomatic alteration products of calcium carbonate, and as a result carbonate content decreases and phosphate content increases with time399. In biophosphates, the situation appears to be just reversed in that carbonate content increases with bone maturation and it was argued that the similarity between bone mineral and naturally occuring C03-apatite ends before it begins 397. ... 

Phosphorites are sedimentary rocks that contain at least 15-20 wt % P2O5 (Boggs, 1995), 266. The phosphate in phosphorites primarily occurs as apatite (Ca5(P04)3(F,Cl,0H)). Typically, phosphorites chemically precipitate in deep, cold marine waters. Due to chemical similarities, arsenate may partially substitute for phosphate and the arsenic concentrations of phosphorites may exceed 100 mg kg-1 ((Matschullat, 2000), 299 Table 3.23). However, arsenic concentrations in some phosphorites (e.g. southeast Jordan) are relatively low (7-9 mg kg-1) and the arsenic is mostly associated with clay and carbonate minerals rather than phosphates (Al-Hwaiti, Matheis and Saffarini, 2005). 

Phosphorite A sedimentary rock that is rich in phosphate (PO, 3-) minerals or other phosphate compounds. Phosphorylytic Cleavage or lysis of a phosphate group from a molecule. 

Biospheric cycles are known to last from dozens and hundreds to several thousands of years, and the geological cycle lasts for millions of years. During the history of the biosphere (3.5-3.8 billion years), as a result of the openness (95%-98%) of biogeochemical cycles, the oxygen and nitrogen in the atmosphere was formed as were the deposits of coals, oil shale, limestone, phosphorites, bauxites, and other minerals in the Earth s crust. 

It is an interesting fact that the two elements most necessary in the maintenance of soil fertility are the related elements nitrogen and phosphorus, which occupy adjacent positions in Group V of the periodic table. Phosphorus occurs in nature only in the combined form, chiefly as the mineral phosphorite [Ca3P04)2]. Impure calcium phosphate, known as phosphate rock, is mined extensively in Tennessee, Florida, Montana, and Idaho. Large deposits of this mineral are also found in Morocco and Tunisia in North Africa. 

Significant commercial deposits of sedimentary phosphate ore occur in the United States, the Former Soviet Union, Morocco, China, Jordan, and Tunisia, and lesser deposits are mined in many other countries. Although phosphorite ores generally are classified as having siliceous or carbonate gangue minerals, soluble salts and organic material are also of concern. The phosphate content of the ores,... 

Sources of Phosphates.—The most available and most exploited sources of phosphorus and its compounds at the present day are the phosphatic rocks, or phosphorites, which consist of tribasic calcium phosphate associated with calcium carbonate, alumina, magnesia, etc.1 Phosphates of alumina are also useful. The production of these secondary rocks from the older rocks has already been mentioned (p. 208). Although the apatites themselves, as pure minerals, contain a high proportion of phosphoric anhydride, they are difficult to decompose, and are admixed with other minerals of a still more refractory nature. 

Occurrence and Circulation op Phosphorus —-Mineral Phosphates—Assimilation by Plants—Sources of Phosphates—The Composition of Phosphorites —-The Distribution of Phosphatic Rooks—Ooeanio Deposits and Guanos—-The World s Production of Phosphate Rook. 

Solid phosphates constitnte many minerals, notably Apatites, which are also fonnd in living organisms as rigid components such as bones and teeth see Biomineralization). Amorphous Phosphorite deposits are important somces of phosphate fertihzers. 

Poorly crystalline or amorphous Phosphorite sediments made from the hard remains of marine organisms are the principal commercial source of phosphates, although Apatites are also mined. Treatment of phosphate minerals with sulfuric acid yields superphosphate fertilizer, a mixture of Ca(H2P04)2, H3PO4 and CaS04. Phosphoric acid treatment gives triple superphosphate , rich in Ca(H2P04)2. Other soluble fertilizers such as ammonium phosphates are obtained from these products. 

Precipitation of marine phosphate minerals is a significant exogenic sink for phosphorus (e.g., Froelich et al., 1982 Ruttenberg, 1993 Ruttenberg and Berner, 1993 Compton et al., 2000 Guidry et al., 2000). Marine phosphorites... 

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