Monazite rare-earth content

Rare Earths are produced primarily from three ores, monazite, xenotime, and bastnasite. Monazite is a phosphate mineral of essentially the cerium subgroup metals and thorium -(light rare Earths, Th) P04. The composition of monazite is reasonably constant throughout the world, with almost 50% of its rare Earth content as cerium and most of the remaining 50% as the other members of the cerium subgroup. Xenotime, like monazite, is a rare Earth orthophosphate but contains up to 63% yttrium oxide and also a markedly higher propor-... 

Xenotime, like monazite, is a rare-earth phosphate. Up to 60% of its rare-earth content is yttria [1314-36-9], Y203. Xenotime has a higher proportion of heavy rare earths than does monazite. Xenotime occurs with monazite in beach sand deposits. A second source of xenotime is that of cassiterite (tin ore) deposits. 

The average rare earth content of the three major minerals namely, monazite, bastnasite and xenotime is given in Table 1.11. 

Monazite is usually a minor constituent of deposits of other minerals, all of which must be separated and processed for a profitable venture. As an example, the mineral constituents of beach sands in Travancore, India, which are dredged for their zirconium, titanium, thorium, and rare-earth content, are as follows ... 

Monazite, the principal source of both thorium and rare earths, is readily available as the pure mineral, This consists essentially of the rare earth phosphates in which a few per cent of the rare earth content has been replaced by thorium. High-temperature chlorination of the ore with carbon has been suggested as a breakdown technique, 7 but it is not known to be operated commercially for either thorium or rare earth elements. The reaction (for thorium) may be represented apparently as ... 

Nei Monggol Autonomous Region) and the United States deposits (Mountain Pass, CA) are primarily bastnasite. This latter deposit is of the highest grade yet discovered and is the only one mined principally for its rare earth content. Most economic monazite and xenotime deposits are in the form of beach sands in which wave action has concentrated the minerals. Such sands contain the Indian reserves and most of the remaining world reserves. 

Lanthanum is most commonly obtained from the two naturally occurring rate-earth minerals, monazite and bastnasite. Monazite is a rare earth-thorium phosphate that typically contains lanthanum between 15 to 25%. Bastnasite is a rare earth-fluocarbonate-type mineral in which lanthanum content may vary, usually between 8 to 38%. The recovery of the metal from either of its ores involves three major steps (i) extraction of all rare-earths combined together from the non-rare-earth components of the mineral, (ii) separation or isolation of lanthanum from other lanthanide elements present... 

Samarium occurs in nature widely distributed but in trace quantities, always associated with other rare earth metals. The two most important minerals are (i) monazite, which is an orthophosphate of thorium and the rare earths and (ii) bastanasite, which is a rare earth fluocarbonate. The samarium content of these ores is about 2%, as oxide. It also is found in precambri-an granite rocks, shales, and certain minerals, such as xenotime and basalt. Its abundance in the earth s crust is estimated to be 7.05 mg/kg. 

Origins. Since the 1890 S, monazite, the first commercial rare earth ore, was mined from black beach sands in Brazil and shipped to Austria for its 5 to 10% thorium oxide content. Carl Freiherr Auer von Welsbach spent 20 years of research work developing a bright incandescent gas mantle he discovered in 1866 with... 

Acid breakdown of monazite. — Most monazite sands do not require grinding when they are treated with H2SO4. Their calcium content is often very low and is quite suitable for acid attack. There are many variations of this process and the trade secrecy of the commercial processes prevents an elaborate description of the methods. Fig. 4 presents a schematic picture of acid breakdown and the recovery of thorium and the rare earths. 

Monazite. The commercial digestion process for monazite uses caustic soda. The phosphate content of the ore is recovered as marketable trisodium phosphate and the rare earths as RE hydroxide (10). The usual industrial practice is to attack finely ground monazite using a 50% sodium hydroxide solution at 150°C or a 70% sodium hydroxide solution at 180°C. The resultant mixed rare-earth and thorium hydroxide cake is dissolved in hydrochloric or nitric acid, then processed to remove thorium and other nonrare-earth elements, and processed to recover the individual rare earths (see... 

Monazite (Ce,La,Y,Th)P04 A rare-earth phosphate. Most concentrates contain 55-65% REO including 2% Y2O3. Marketable REO content 55% (minimum)... 

From this table it is evident that all monazite contains much more ceria than thoria and since the mantle is mainly thoria a very large part of the ceria is not needed for mantle manufacture. The residue which remains after removal of the thoria contains about 45 per cent Ce02,25 per cent La203, and 15 per cent didymia, the remainder being yttrium earths, samaria, etc. The residue represents 60-65 per cent of the original monazite. Since the total world s consumption of monazite has been estimated as being about 88,000 tons up to 1918, it is evident that the supply of cerium material has been very large. Some firms have stored enormous quantities of these rare earth salts, and others have thrown them away. The residues are transformed to the chlorides, which are carefully dehydrated to prevent the formation of basic salts. The purity of the chlorides is not important, but the phosphorus and sulfur content must be low, and iron and aluminium should not be present in more than small amounts. A mixture of the... 

In the earth s crust thorium is almost four times more common than uranium, and the radioactive decay of thorium generates a considerable part of the geothermal energy. The primary source of thorium is monazite (Figure M25), a yellow or reddish-brown rare-earth phosphate. Seashore deposits at Travancore in India contain very big quantities of monazite. The mineral formula is (Ce,La,Nd,Th)PO and the thorium content in monazite ores is 5-10%. In 2001 the production of monazite concentrate in the world was 5710 tonnes [52.13], of which India accounted for 5000 toimes or 88%. Other producers were Brazil and Malaysia. 

Monazite is recovered mainly for its content of rare earth metals, and thorium has to be separated. This has led to an overproduction of thorium oxide. The excess is stored for potential use or disposed of as a radioactive waste. Most producers of rare earths have however switched to thorium-free raw materials due to the problems (and costs) of dealing with the radioactivity. This may change the situation for thorium supply. Other thorium minerals, besides monazite, are thorite ThSiO (Figure M24) and thorianite ThO. ... 

Monazite sample (1 g) was dissolved by heating with a mixture of H2SO4 and HF (1 1) with small content of HNO3. The solution was boiled until SO3 vapor appeared. The rare earth elements were separated from the matrix by extraction with 0.2 M diantipyrilmethane (a complex-forming reagent) solution in chloroform at pH 5 in the presence of 5.0M ammonium nitrate solution. The extraction was repeated and the combined extract was evaporated to dryness. The residue was dissolved in propanol saturated with NaCl and a 0.5 pi aliquot was spotted on TLC plate. After separation the rate earths were detected by spraying plates with a 0.1% arsenazo III solution (164). 

Uranium and thorium are widely distributed in the earth s crust, with average concentrations of 2 and 8 ppm, respectively (Grainger 1958 Boyle 1982 Frondel et al. 1967 Wills 1997). Over 100 different uranium-based minerals are known, but deposits of high-grade ore (hke uraninite and pitchblende, with as much as 70% uranium by weight) are rare. Most of the world s supply of recovered uranium has been extracted from ores with a uranium content of only about 0.2%. Conversely, the mineralogy of thorium is less varied, and deposits of its principal mineral, monazite, are fairly common. The thorium content of pure monazite is typically between 5% and 10%. 

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