Xenotime

For instance, Forster (1998a, b) list compositional variations of xenotimes and monazites from the German Erzgebirge/Fichtelgebirge, showing that xenotime 

3 Xenotime, Madagascar. From the collection of Naturalis Biodiversity Center, Leiden, The Netherlands, Sample RGM412055. Photograph Naturalis. Used with permission 

In Table 2.1 examples of typical compositions of monazite, xenotime and bastnaesite are given. 

With respect to the actinides, monazite tends to concentrate thorium, whereas xenotime tends to concentrate uranium, but can take up also appreciable amounts of thorium. According to Deer et al. (2013), common varieties of monazite have 4-12 mol% of Th02, whereas uranium occurs in minor amounts. Van Emden et al. (1997) mention Th02 contents in monazite ranging 1.2-21.9 wt%, whereas UO2 contents are from detection limit up to 0.75 wt%. Xenotime analyses show UO2 contents ranging from detection limit to 5.82 wt%, while Th02 varies from detection limit to 8.44 wt%. Watt (1995) lists monazite compositions showing wt% of Th to vary from 5.17-21.41 wt%, and UO2 from 0.22-3.17 wt%. 

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Ytterby, a village in Sweden) Discovered by Mosander in 1843. Terbium is a member of the lanthanide or "rare earth" group of elements. It is found in cerite, gadolinite, and other minerals along with other rare earths. It is recovered commercially from monazite in which it is present to the extent of 0.03%, from xenotime, and from euxenite, a complex oxide containing 1% or more of terbia. 

The heavy mineral sand concentrates are scmbbed to remove any surface coatings, dried, and separated into magnetic and nonmagnetic fractions (see Separation, magnetic). Each of these fractions is further spHt into conducting and nonconducting fractions in an electrostatic separator to yield individual concentrates of ilmenite, leucoxene, monazite, mtile, xenotime, and zircon. Commercially pure zircon sand typically contains 64% zirconium oxide, 34% siUcon oxide, 1.2% hafnium oxide, and 0.8% other oxides including aluminum, iron, titanium, yttrium, lanthanides, uranium, thorium, phosphoms, scandium, and calcium. 

A limited number of rare-earth minerals are mined for large-scale rare-earth production mona2ite, bastnaesite, loparite [12173-83-OJ, xenotime [13817-22-6]. In addition, siace the 1980s rare-earth-containing clays called ionic ore are mined ia China. Table 4 shows the rare-earth composition of typical mineral concentrates. 

Rare earth Bastnaesite Loparite Mona2ite Xenotime... 

Xenotime, like mona2ite, is a rare-earth phosphate. Up to 60% of its rare-earth content is yttria [1314-36-9], Xenotime has a higher... 

Separation and Recovery of Rare-Earth Elements. Because rare-earth oxalates have low solubihty in acidic solutions, oxaUc acid is used for the separation and recovery of rare-earth elements (65). For the decomposition of rare-earth phosphate ores, such as mona ite and xenotime, a wet process using sulfuric acid has been widely employed. There is also a calcination process using alkaLine-earth compounds as a decomposition aid (66). In either process, rare-earth elements are recovered by the precipitation of oxalates, which are then converted to the corresponding oxides. 

Scandium is very widely but thinly distributed and its only rich mineral is the rare thortveitite, Sc2Si20v (p. 348), found in Norway, but since scandium has only small-scale commercial use, and can be obtained as a byproduct in the extraction of other materials, this is not a critical problem. Yttrium and lanthanum are invariably associated with lanthanide elements, the former (Y) with the heavier or Yttrium group lanthanides in minerals such as xenotime, M "P04 and gadolinite, M M SijOio (M = Fe, Be), and the latter (La) with the lighter or cerium group lanthanides in minerals such as monazite, M P04 and bastnaesite, M C03F. This association of similar metals is a reflection of their ionic radii. While La is similar in size to the early lanthanides which immediately follow it in the periodic table, Y , because of the steady fall in ionic radius along the lanthanide series (p. 1234), is more akin to the later lanthanides. 

Xenon, absorption b r, in counter, 45 Xenotime distinguished from zircon, 136 X-ray absorptiometer with a radioactive isotope, 133... 

Linares C, Louat A, Blanchard M (1977) Rare-Earth Oxygen Bonding in the LnM04 Xenotime Structure. 33 179-207... 

Nearly all transition metals are oxidized readily, so most ores are compounds in which the metals have positive oxidation numbers. Examples include oxides (Ti02, mtile Fc2 O3, hematite C112 O, cuprite), sulfides (ZnS, sphalerite M0S2, molybdenite), phosphates (CeP04, monazite YPO4, xenotime both found mixed with other rare earth metal phosphates), and carbonates (FeC03, siderite). Other minerals contain oxoanions (MnW04, wolframite) and even more complex stmctures such as camotite, K2 (002)2 ( 4)2 2 O ... 

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-... 

Table 1.17 Analysis of bastnasite, monazite, and xenotime from different locations3 (Percent of total rare Earth oxide).

Rare Earth Bastnasite (REFC03 Monazite (RE,Y,ThPOJ Xenotime (YREPOJ... 

Xenotime Epidote (3.5) Zircon Ilmenite Ilmenite Columbite- Copper (8.9)... 

Nuryono, Huber, C. G., and Kleboth, K., Ion-exchange chromatography with an oxalic acid-alpha-hydroxyisobutyric acid eluent for the separation and quantitation of rare-earth elements in monazite and xenotime, Chromatograph-ia, 48, 407, 1998. 

Euxenite is a titanotantalum/niobium-containing mineral and has a complex formula (Table 24.1) with variable chemical composition. It is usually found in sand deposits together with monazite, xenotime, zircon, beryl, columbite and other minerals. 

Linar s, C., Louat, A., Blanchard, M. Rare-Earth Oxygen Bonding in the LnMOj Xenotime Structure. Vol. 33, pp. 179—207. 

Several different flow sheets have been developed around DEHPA, which, as discussed earlier, vary according to the precise composition of the feed material. A typical process using a nitric acid leach of a xenotime ore follows as an example. 

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