Lanthanide mineral xenotime

Of all the 17 rare-earths in the lanthanide series, terbium is number 14 in abundance. Terbium can be separated from the minerals xenotime (YPO ) and euxenite, a mixmre of the following (Y, Ca, Er, La, Ce, Y, Th)(Nb, Ta, Ti O ). It is obtained in commercial amount from monazite sand by the ion-exchange process. Monazite may contain as much as 50% rare-earth elements, and about 0.03% of this is terbium. 

Thulium was discovered in 1879 by Cleve and named after Thule, the earliest name for Scandinavia. Its oxide thulia was isolated by James in 1911. Thulium is one of the least abundant lanthanide elements and is found in very small amounts with other rare earths. It occurs in the yttrium-rich minerals xenotime, euxenite, samarskite, gadolinite, loparite, fergusonite, and yttroparisite. Also, it occurs in trace quantities in minerals monazite and... 

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. 

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. 

Terbium is recovered from the minerals, monazite, xenotime, and euxenite. The recovery processes are quite similar to those of other lanthanide elements (See individual lanthanide elements). The metal is separated from other rare... 

Phosphates. The two major phosphate bearing ores are monazite and xenotime, the former being a source of light lanthanides and the latter a source of the heavy rare earths, see Table IV. Deposits in the form of heavy mineral sands are the major source of monazite. They are usually exploited as a byproduct of rutile, ilmenite, and zircon mining operations. 

Cations of the lanthanide elements also produce colours in some minerals through intra-electronic transitions within 4/orbitals (Adams, 1965 Bernstein, 1982). Absorption bands are usually sharp and weak, leading to pastel shades. Examples of such coloured minerals are monazite, bastnaesite, rhabdophane, xenotime, gadolinite, and certain apatites, calcites, scheelites and fluorites. As noted earlier, some rare earth-bearing minerals, notably fluorite and monazite, also display the alexandrite effect (Berstein, 1982 Schmetzer et al., 1980). 

Element 39, with 4d 5s2 electron configuration, is also similar to the lanthanides. It occurs with the lanthanides in minerals the best source is xenotime, YPO4. Yttrium has properties approximately midway between those of Sc and La its compounds also resemble those of the heavy earths dysprosium and holmium, the ionic radius (0.90 A) being similar. 

Apparently, formation of actinide (IV) compounds with more complex cationic and anionic compositions with the monazite or zircon (xenotime) structure types is possible. These compounds can be considered to be solid solutions. The possibility of forming this kind of compound is realized in the minerals mentioned above. These minerals are characterized by the complex cation compositions monazite - (La, Ce, other lanthanides, Y, Ca, Th)(P, Si)04, xenotime - (Y, lanthanides. Sc, Zr, Th, U)(Si, P)04 zircon - (Zr, Hf, Th, U, lanthanides, Ca, Fe, Nb, Ta)(Si,P)04 [71]. The ionic radii and cationic proportions, anionic sizes and synthesis conditions affect the formation of each type considered. 

Given the variety of important actinide oxidation states, what naturally occurring anion would best effect actinide mineralization The lanthanides, chemically analogous to the trivalent actinides, occur naturally in three commercially important forms monazite and xenotime, which are orthophosphate minerals, and bastnasite, which has the approximate composition LnFCOs. Uranium ores may be divided into... 

Occurrence Yttrium is a rare earth element and occurs in nearly all of the rare earth minerals. Rare earths are defined as a group of 17 elements, comprised of scandium, yttrium, and the lanthanides. The similar radii and oxidation states of the rare earths allows liberal substitution of the rare earths for one another into the crystal lattice sites of minerals. This substimtion accounts for their wide dispersion in the earth s crust and the characteristic occurrence as a group of elements within more than 100 minerals. The principal ores of the rare earths are basmasite, monazite, and xenotime. Several of the ores occur in unique geologic settings, whereas others are found in similar occurrences worldwide. 

There are three groups of minerals in which the REE are found. Minerals in the first group contain major quantities of lanthanides. All of these are associated with crystallizations from magmatic mother liquors of pegmatic character (Topp 1965). Important examples are the minerals monazite and xenotime. The second group includes minerals with the REE as minor constituents. Many calcium minerals, such as apatite, are members of this group. Minerals in the third group contain the REE in the bipositive state in small isolated distributions. These are not used as sources of rare earths. 

Placer deposits of potential future value as lanthanide ores invariably have the lanthanides present in common lanthanide or lanthanide-concentrating minerals (e.g., apatite, allanite, monazite, xenotime, zircon). Most pegmatites of potential value as ore have the lanthanides as common lanthanide-bearing minerals too (those previously mentioned plus fluorite). Alkalic rock complexes may produce commercially useful concentrations of common lanthanide-bearing minerals (e.g., apatite, perovskite) or rare ones (e.g., bastnaesite). 

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