Phosphate Mineral Deposits

More than 300 different phosphate minerals are known [1-25]. Characterising optical and crystallographic data together with mineral location information are available in most cases [7,25]. However, only those minerals in the Apatite group occur in sufficient abundance and concentration to serve as commercial sources of the elanent 

Members of the Apatite group are common accessory minerals in almost aU igneous rocks and are also found in sedimentary and metamorphic rocks. They are the most abundant P-containing minerals. 

The commonest concentrated igneous apatite deposits consist mainly of fluorapatite, Ca,o(P04)6F2, but isomorphous chlorapatite, CamCPO igClj, and hydroxyapatite, Caio(P04)6(OH)2, are also found in close association or in solid solution (Chapter 5.1). Apatite occurs mostly as a sedimentary deposit with an approximate composition Caio(P04)6F2, which is named Phosphorite or phosphate rock. Collophane is a term sometimes used to describe varieties of cryptocrystalline phosphorite which are fine grained and optically isotropic. 

Most phosphorite is dirty white or greenish in colour and is believed to be of marine origin. It is mainly microcrystalline (10-100 A) or amorphous fluorapatite, and is almost always found associated with calcium carbonate and other impurities. 

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). 

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The dietary calcium/phosphorus ratio is important for the maintenance of kidney health. Where there is too much phosphate, mineral deposits may develop in the kidneys, in a process called nephiocalcinasis. Female rats are especially prone to nephiocalcinosis, which occurs when the calcium/phosphorus ratio is under 1/0.. For this reason, a recommended Ca/P ratio is 1.66 (the same as 1/0.6) Reeves, 1997). 

CNF Directing osteoblast alignment, enhancing cell adhesion, calcium phosphate mineral deposition on CNF/polymer composites [71,72]... 

Although urine remained the only source of the element for nearly 100 years after its discovery, it had been replaced by bones by the end of the eighteenth century. Supplies of the latter soon proved to be inadequate, but fortunately substantial phosphate mineral deposits were quickly found. This enabled serious commercial production of phosphorus compounds from these ores to commence in Europe about 1850, when wet process phosphoric acid became available. In 1888, a major development took place when Readman invented the electric furnace method for the continuous production of the element directly from phosphate ores. In 1890, the first industrial electric furnace came into use at Oldbury in England, and this was followed by similar production at Niagara Falls, USA. 

There are snbstantial reserves of oil-shale phosphorites in Israel, Jordan and the Eastern Mediterranean, bnt these are not economic to exploit with the present technology. While some of the known mineral phosphates (e.g. apatite) are widely distributed—in trace concentrations as well as in concentrated deposits, most others are quite rare and occm only in small veins or pockets, or as minor constituents of other commoner phosphate mineral deposits. 

The overall natural and artificial cycles involving phosphorus may be represented approximately as in Figure 2.6. Unlike other essential life elements H, C, N, O, no appreciable amounts of gaseous phosphorus compounds are involved, and the P cycles are restricted to the lithosphere and the hydrosphere. Rainwater contains 0.001 ppm P. Originally, it can be supposed that sufficient phosphorus became available for life processes through the slow solubilisation of phosphate mineral deposits. The resulting distribution of the element on land and in the seas then enabled the initiation and development of life to take place. Subsequent death and decay of these organisms ensured a return of phosphorus to the system. 

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... 

It is necessary to remember that as well as organic cross-links, elements such as boron, silicon and calcium cross-link all the major external proteins and saccharides even in the walls of prokaryotes. Many of the cross-linking binding sites are of oxidised side chains of biopolymers. As described in Section 8.10, certain of these elements form mineral deposits but now these minerals are frequently found inside the multi-cellular organisms. Here, we see a great difference between the chemo-types of plants and animals. The acidity of the extracellular fluids of plants differs from the neutral fluid of animals. It is not possible to precipitate calcium carbonates (shells) or phosphates (bones) in plants due to the weak acid character of these anions (see Table 8.12). Plants therefore precipitate silica and calcium... 

Contents of REE in massive sulfides from the BMC are strongly controlled by the abundance of and REE concentrations in phosphate minerals, specifically apatite, xenotime and monazite. Strong positive Eu anomalies in apatite, account for the anomalous Eu signatures of exhalative sulfides whereas REE in monazite masses are largely reflective of detrital sources and may mask hydrothermal signatures. Limited release of mobile trace elements (LREE and Eu) during green-schist facies metamorphism has partly modified REE profiles for VMS deposits of the BMC. 

The major sources of TT3PO4 traditionally have been mineral deposits of phosphate rock. Mining operations are extensive in a number of locations, including the United States (Florida), the Mediterranean area, and Russia, among others. The major constituent of most phosphate rocks is fluorapatite, 3Cai(P04)2 CaF>. The supply of high-grade phosphates,... 

As discussed in Chapters 5 and 7, the use of lime to precipitate calcium arsenates is a common method for removing inorganic As(V) from water or flue gases. Calcium arsenates were also once extensively used in pesticides (Chapter 5). The compositions of some calcium arsenates, such as johnbaumite (Ca5(As04)3(0H) Table 2.5), resemble the very common phosphate mineral, apatite (Ca5(P04)3(F,Cl,0H)), where arsenate replaces phosphate. Some lead arsenates, such as mimetite (Pb5(As04)3Cl Table 2.5), also have crystalline structures that are related to apatite. Mimetite may occur in oxidized lead-rich hydrothermal deposits. 

The only essential components of the mineral deposition mechanism that are fairly certain at this time relate to phosphate. Even for phosphate, alternative mechanisms are proposed, which are not mutually exclusive but probably function in parallel, in the regulation of different aspects of skeletal calcium transport, and to some extent provide redundancy that allows many mineral transport disorders to be survivable. Alkaline phosphatase activity is essential to produce phosphate. Its major substrate is pyrophosphate. In the absence of the alkaline phosphatase, normally highly expressed as an ectoenzyme by osteoblasts, there is little matrix mineralization... 

The deposition of limited quantities of hydroxyapatite in extracellular matrix has been observed without bounding cells. Cartilage calcification is such a case where local pH control and Ca2+ are dependent upon diffusion and the rate of mineral deposition is driven by phosphate presentation. Chondrocytes produce alkaline phosphatase that generates the required phosphate, but cartilage is not delimited by any cellular structures and transfer of Ca2+ and H+ is by diffusion from extracellular fluid. 

Lapis lazuli is a metamorphic rock composed of three minerals, blue lazu-rite, white calcite, and brassy pyrite. This stone was highly prized by some cultures, both ancient and modern, because of its intense blue color. Most good-quality lapis lazuli has been mined in Afghanistan and southern Russia, although small deposits have been found elsewhere in the world. Common imitations of lapis lazuli are glass, lazulite (a phosphate mineral), and sodalite (a tectosilicate mineral similar to lazurite). 

Another means of assessing the nature of the medium/solution from which the mineral forms is to analyse the very first mineral deposits precipitated. These must reflect the chemistry of the medium in which they formed. In most chiton teeth a poorly crystalline ferrihydrite is the first mineral deposited and it subsequently transforms into magnetite. In the anterior layer, amorphous calcium phosphate is first deposited, and only after several weeks does it begin... 

Crustacea exoskeleton, the carapace. The carapace of Crustacea strengthens their exoskeleton through mineral deposition (calcium carbonate or calcium phosphate) in, or on, a hbrous organic template. The hrst stage is the secretion... 

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