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Europium - Sinha S.P.

Sinha S.P. Europium - Springer-Verlag, 1967. - 88 p.
Download (direct link): europium1967.djvu
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Occurrence in Nature
The number of rare earth-containing minerals is amazingly high. Some 160 of them are tabulated in the Nouveau Traité de Chimie Minérale [21]. However, in the production of rare earths from their minerals the following factors must be considered for economical reasons : a) the concentration of the rare earths in a particular mineral b) the ease with which the mineral can be processed and the cost of processing c) the geographical location of the mineral deposite. The effort necessary to process rare earth minerals other than monazite has hardly been justifiable.
Some important rare earth containing minerals, together with then-physical properties and the geographical locations of their major deposit, are summarized in Table 2, and a few of them are discussed in some detail below.
Fergusonite.—This mineral is a niobate-tantalate of yttrium earths with variable amounts of uranium and thorium. The amounts of the cerium group (1—8%) and the yttrium group (22—40%) rare earths vary depending on the locality of its occurrence. It has been shown that fergusonite is amorphous at ordinary temperature, but on heating to 400° C it assumes a crystalline (tetragonal) form. On heating at 500—600° C about 1.5 ml. He per gram of the ore is liberated, and the density decreases from 5.62 to 5.38.
Oadolinite.—This classical mineralwas discovered by J. GADObENin 1794 and is a useful source of the heavy rare earths. Gadolinite is a silicate ore with probable chemical formula ВегРеУгвігОю, or Be2Fe(Y0)2(Si04)2. Beryllium is invariably associated with this mineral and up to an amount of 10%. Yttrium earth concentration varied from 35 to 48% and cerium earth from 2 to 23%. Natural gadolinite is opaque, and black or greenish in colour. Gadolinite crystallizes in a monoclinic structure but often prismatic crystals without cleavage and giving conchoidal fracture are encountered. They are found to be isotropic. Anisotropic crystals may, however, be obtained by heating the mineral to about 1000° C. Native crystals possess strong, positive birefringence and are pleochroic.
Table 2. Important rare earth minerals and their physical properties
6
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Occurrence in Nature
7
Monazite. — This mineral is the principal source of rare earths. It is a complex phosphate of cerium group rare earths, often containing as high as 70% cerium. A typical monazite contains 50—70% cerium group rare earths, 1—4% yttrium, 5—10% Th02, 1—2% Si02, and 22—30% P2O5, and also traces of uranium. The ratio of lanthanide to yttrium in monazite is approximately 55: 1. Table 3 records the amount of individual rare earth present in various samples of monazite of different origin. The presence of a radioactive constituent is well established. On examining
Table 3. Percentage of individual rare earths in monazites of different origin
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