Phosphorites uranium

Phosphorite deposits, 17 688, 691 Phosphorite uranium deposits, 17 520 Phosphorochloridate synthesis, 19 28 Phosphorodithioate DNA, 17 630 Phosphorodithioates, 17 630 Phosphorothioates, 17 629-630 synthesis of, 17 630 Phosphorous acid, 19 52 Phosphorous donor ligands, thorium and, 24 768 Phosphors... 

Phosphorite Deposits. Sedimentary phosphorites contain low concentrations of uranium in fine-grained apatite. Uranium of this type is considered an unconventional resource. Significant examples of these uranium ore types include the U.S. deposits in Elorida, where uranium is recovered as a by-product, and the large deposits in North African and Middle Eastern countries (16). 

Domestic. Estimates of U.S. uranium resources for reasonably assured resources, estimated additional resources, and speculative resources at costs of 80, 130, and 260/kg of uranium are given in Table 1 (18). These estimates include only conventional uranium resources, which principally include sandstone deposits of the Colorado Plateaus, the Wyoming basins, and the Gulf Coastal Plain of Texas. Marine phosphorite deposits in central Elorida, the western United States, and other areas contain low grade uranium having 30—150 ppm U that can be recovered as a by-product from wet-process phosphoric acid. Because of relatively low uranium prices, on the order of 20.67/kg U (19), in situ leach and by-product plants accounted for 76% of total uranium production in 1992 (20). 

Owing to the stability of the uranyl carbonate complex, uranium is universally present in seawater at an average concentration of ca. 3.2/rgL with a daughter/parent activity ratio U) of 1.14. " In particulate matter and bottom sediments that are roughly 1 x 10 " years old, the ratio should approach unity (secular equilibrium). The principal source of dissolved uranium to the ocean is from physicochemical weathering on the continents and subsequent transport by rivers. Potentially significant oceanic U sinks include anoxic basins, organic rich sediments, phosphorites and oceanic basalts, metalliferous sediments, carbonate sediments, and saltwater marshes. " ... 

Kolodny Y, Kaplan IR (1970) Uranium isotopes in sea-floor phosphorites. Geochim Cosmochim Acta 34 3-24... 

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. 

Phosphorite Deposits in Florida, USA, and the large deposits in North African and Middle-eastern countries. Uranium is recovered as a by-product from Florida deposits. 

Spectrophotometric analysis following extraction with Aliquot 336 has been used to determine uranium in seawater [108]. Kim and Burnett [109] used X-ray spectrometry to determine the uranium series nucleides including 238uranium, 226radium and 210lead in marine phosphorites. 

Carbonate-fluor-apatite accommodates large quantities of trace elements, mainly uranium, which are potential luminescence centers. It has been proposed that uranium may occur in phosphorites in the following forms as a separate uraninite phase as an adsorbed or structurally incorporated uranyl ion as a dominantly replacement for Ca +, to be structurally incorporated... 

Burnett W. C. and Veeh H. H. (1977) Uranium-series disequihbrium studies in phosphorite nodules from the west coast of South America. Geochim. Cosmochim. Acta 41, 755-764. 

Reiterating, the phosphatic mineral of such phosphorites is essentially francolite, a carbonate fluorapatite of somewhat variable composition (McConnell, 1971 Rooney and Kerr, 1967). Although not proven to be contained within the apatitic phase through isomorphic substitution, some of the continental phosphorites are of considerable interest because of accumulations of uranium, thorium, yttrium, rare earths, scandium, and vanadium therein. These rarer components are thought to be related to diagenetic processes, in which case they were extracted from sea water during the early formative histories of the phosphorites. 

Christy AG, Alberius-Henning P, Lidin SA (2001) Computer modelling and description of nonstoichiometric apatites Cd5./2(V04)3li. and Cd5 /2(P04)3Bri as modified chimney-ladder stmctures with ladder-ladder and chimney-ladder couphng. J Sohd State Chem 156 88-100 Claike RS, Altschuler ZS (1958) Determination of the oxidation state of uranium in apatite and phosphorite deposits. Geochim Cosmochim Acta 13 127-142... 

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). 

Certain rare phosphate minerals such as Monazite, (Ce,Li,Th)P04 and Xenotime, YPO4, are important sources of rare earth elements which they frequently contain as impurities. Monazite, which is mined in Brazil, Travancore and Australia, is the most important commercial source of thorium (Chapter 3.5). One commercial source of lithium is Nalipoite, NaLi2P04, which is present in some natural brines. Phosphorite ore itself is a potentially valuable source of Uranium (Chapter 5). A few orthophosphate minerals are sometimes useful as gemstones (Table 5.23). 

Sedimentary marine phosphorites are composed principally of phosphatic minerals, and many contain significant amounts of disseminated uranium. These phosphorites have been classified as either miogeosynclinal or platform types. Four additional types that are low in uranium and of little economic importance are residual phosphorites, phosphatized rock, river pebble deposits and guano. 

Phosphorites that are richest and thickest and contain the most uranium are the miogeosynclinal type deposited on the outer parts of continental shelves where upwelling of deep marine waters has occurred. These waters were saturated with respect to phosphate and were probably the source of the phosphate in the phosphorites. These phosphorites are commonly present in thick miogeosynclinal sequences, where they are associated with carbonates, black shale, chert, carbonaceous mudstone and minor amounts of mudstone. " The Phosphoria Formation of the western U.S.A. is an example. 

Platform phosphorites are generally nodular, rather than bedded, and are associated with sandstone, limestone and glauconite. Most are low in uranium, but an exception is the Bone Valley Formation of the southeastern U.S.A. This unit has been reworked and enriched by re-exposure to sea water during a subsequent transgression. These phosphorites differ from shelf phosphorites in that they are near-shore sub-tidal and shoreline deposits, and they change facies oceanward to carbonate sediments. 

All niarine phosphorites consist mostly of microcrystalline apatite (carbonate fluorapatite) in the form of laminae, pellets, oolites, nodules and skeletal or shell debris. Uranium, considered syngenetic, may be present in carbonate fluorapatite as a substitute for calcium. Uranium in sea water was probably incorporated during or shortly after precipitation, and it is usually disseminated rather uniformly throughout a given bed or horizon. Primary uranium minerals are rarely present, but secondary uranium minerals (tyuyamunite, autunite, torber-nite) have been identified in a few localities. 

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