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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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2 Sinha, Europium
18
Methods of Separation of Individual Rare Earth Elements
Fig. 3a. Gas chromatographic separation of several rare earth-THD complexes (reproduced from J. A. C. S. 87, 5254 (1965) with the kind permission of Journal of the American Chemical Society).
Fig. 3b. Variation of the retention times of M(THD)S complexes with ionic radii (reproduced from J. A. C. S. 87, 5254 (1965) with the kind permission of Journal of the American Chemical Society).
plexes are eluted without decomposition. The retention times for the rare earth tris-complexes as a function of the ionic radii (Fig. 3 b) exhibit the effect of lanthanide contraction (p. 30).
(v) Thin layer chromatography.—This technique is nowadays used in organic chemistry and biochemistry for separating small quantities of a mixture. Daneels et al. [126] have separated Sm, Eu, Gd and Tb by this technique using Silica gel H. Radioactive tracers were used to detect
Isolation of the Rare Earths Form Monazite
19
the rare earths. The Rf values for Sm, Eu, Gd and Tb are 0.54, 0.29,
0.73 and 1 respectively.
(vi) Electrophoresie. — Relative mobilities of rare earth ions in 0.05M lactic acid were estimated by Ptt6ab and Konard-Jakovac [127]. and proposals of electrophoretic separation of rare earth mixtures have been made. The cathodic mobility of rare earth ions decreases with increasing Z in the series. Theoretical calculations [128] of the electrophoretic process with the nitrilotriacetic acid (NTA) system show possibilities for the selection of the complex_ng a^ent in detecting and separating chemically similar elements including rare earths.
Separation based on valency change.—The easy oxidation of Ce3+ to Ce4+ permits its isolation from other rare earths. The separation of ceriu m is usually performed by selective leaching with acids, or by complete dissolution [129, 130] followed by hydrolys s. The solvent extraction behaviour of Ce(N0s)4 has boen extensively studied. Among the various extractants, alcohols, ethers», organic and inorganic acids, ketones etc.,
TBP proved to be most advantageous in laigo scale operations [131,132].
The classical method of McCoy [133] has been employed for the large scale recovery of Eu from materials containing as low as 0.05% of this element. Reduction of Eu3+ with zmc in HC1 solution followed by coprecipitation of Eu2+ with BaS(>4 is used on industrial scales [134].
The use of lithium amalgam electrodes allows better control of electrode potential than the potassium amalgam electrode. Separations of Sm from Gd, Eu from Sm, Sm from Eu and of IT) from heavy rare earths have been successfully carried out by Onstott [135—137].
Electrolytic reduction in the presence of 8-hydroxy-quinolinesul-phonic acid resulted in a selective precipitation of Eu2+-chelate [155] with only a very small amount of Sm.
Isolation of the Rare Earths Form Monaz ite
The crude mons zite sands are first concentrated by the general me-cJHamcal and physical treatments of mineral dressing. Brazilian monazite sands are processed mainly by the electromagnetic separation technique.
The Indian monazite industry is essentially based on the recovery of rutilc and ilmenite. Ilmenite has a magnetic susceptibility very close to that of monazite and thus direct electromagnetic separation cannot be applied to the In- an Travancore monazite sands.
The Travancore monazite is first reduced to convert leucoxene (ilmenite) into magnetite, thus changing the magnetic behaviour of the ilmenite [139]. The conductiv >y of monazite is not affected by the reduction process. Flotation processes have also been adopted to dress the Travancore monazite.
2*
.1
20
Methods of Separation of Individual Rare Earth Elements
After the primary concentration process, the monazite is broken down either by the traditional sulphuric acid treatment or by the more recent caustic soda method. Several books [21,140,141] and reviews [142—144] give the useful details of the treatment of monazite.
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 H2S04

Acid attack 200
Dilution ~ 30°
Filter
1
Filtrate Solid Residue
Na2S04
Filter
1 I
Filtrate Residue
Double Sulphates
NaOH
Boil
Rare Earth Hydroxides
Fig. 4. A schematic representation of the acid breakdown of monazite
The sand is slowly added to concentrated sulphuric acid and the temperature is maintained at —200° C. The reaction is highly exothermic, and helium and thoron are liberated. Barium sulphate is added as a collector for mesothorium. The reaction mixture is allowed to cool, and the product is carefully diluted with water, the temperature being kept below 30° C.
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