Rare earths, cerium separation from mixtures

Acid soluble rare earth salt solution after the removal of cerium may be subjected to ion exchange, fractional crystalhzation or solvent extraction processes to separate individual rare earths. Europium is obtained commercially from rare earths mixture by the McCoy process. Solution containing Eu3+ is treated with Zn in the presence of barium and sulfate ions. The triva-lent europium is reduced to divalent state whereby it coprecipitates as europium sulfate, EuS04 with isomorphous barium sulfate, BaS04. Mixed europium(ll) barium sulfate is treated with nitric acid or hydrogen peroxide to oxidize Eu(ll) to Eu(lll) salt which is soluble. This separates Eu3+ from barium. The process is repeated several times to concentrate and upgrade europium content to about 50% of the total rare earth oxides in the mixture. Treatment with concentrated hydrochloric acid precipitates europium(ll) chloride dihydrate, EuCb 2H2O with a yield over 99%. 

Praesodymium may be recovered from its minerals monazite and bastana-site. The didymia extract of rare earth minerals is a mixture of praesodymia and neodymia, primarily oxides of praesodymium and neodymium. Several methods are known for isolation of rare earths. These are applicable to all rare earths including praesodymium. They include solvent extractions, ion-exchange, and fractional crystallization. While the first two methods form easy and rapid separation of rare earth metals, fractional crystaUization is more tedious. Extractions and separations of rare earths have been discussed in detail earlier (see Neodymium and Cerium). 

From rare earth hydroxide or oxide mixtures in which cerium has been oxidized, the separation of cerium is usually accomplished by selective leaching away of the more soluble tervalent hydroxides with dilute acid, or by complete dissolution in a more concentrated acid followed by hydrolytic precipitation. 

Separation Processes. The product of ore digestion contains the rare earths in the same ratio as that in which they were originally present in the ore, with few exceptions, because of the similarity in chemical properties. The various processes for separating individual rare earth from naturally occurring rare-earth mixtures essentially utilize small differences in acidity resulting from the decrease in ionic radius from lanthanum to lutetium. The acidity differences influence the solubiUties of salts, the hydrolysis of cations, and the formation of complex species so as to allow separation by fractional crystallization, fractional precipitation, ion exchange, and solvent extraction. In addition, the existence of tetravalent and divalent species for cerium and europium, respectively, is useful because the chemical behavior of these ions is markedly different from that of the trivalent species. 

The discovery of samarium is credited to Boisbaudran, who in 1879 separated its oxide, samaria from Mosander s didymia, the mixture of rare earth oxides from which cerium and lanthanum were isolated earher. Demarcay in 1901 first identified samaria to be a mixture of samarium and europium oxides. The element got its name from its mineral, samarskite. The mineral, in turn, was named in honor of the Russian mine official Col. Samarki. 

Cement, laboratory, 1 189 Cerite, extraction of, 2 44 Cerium, phosphor containing strontium sulfide and, 3 23 separation of, from rare earth mixtures, 2 43, 47, 48 test for, 2 50 Cerium amalgam, 1 15 Cerium-group earths, separation of, from yttrium earths by doublesulfate method, 2 44, 46 Cerium (III) magnesium nitrate, 2Ce(N03)s-3Mg(N03)2-24H,0, separation of praseodymium from lanthanum by, 2 57 Cerium(III) nitrate, 2 51 Cerium (IV) nitrate, basic, 2 49 Cesium, cesium azide for preparation of, 1 79... 

Manganites, nomenclature of, 2 261 Marble, for use in separation of cerium from rare earth mixtures by bromate method, 2 49 Mercury, solubility of metals in,... 

THE SEPARATION OF CERIUM FROM RARE EARTH MIXTURES... 

Subsequent treatment depends on the intended use of the rare earths. For some applications, particularly the older ones, it is not necessary to achieve a separation of the elements. For example, a mixture of the cerium group metals, called mischmetal, has been used for decades for lighter flints. Thus from a bastnasite or monazite ore base, which contains predominantly the cerium group elements, little further separation work is necessary. However, for basic research into the properties of the elements and their compounds and in applications involving increasingly sophisticated technology the availability of the individual elements in a high purity form is essential. 

In 1839, Mosander who was working with cerium nitrate found it was possible to separate a soluble salt from this material, which he termed lanthana. Three years later, he separated this lanthana into didymia and the pure lanthana. Didymia was found later to be an impme element and was to be a mixture of two oxides which were inseparable using his procedures. In 1842, Mosander continued working on the pmification process and separated ytteria ore into three oxides pure ytteria, terbia and erbia. The oxide that provided pink salts was named terbium, and the other that gave a yellow peroxide he called eibium. Delafontaine and Berlin also had identical results, but alternatively named them eibium and terbium, respectively, as today. At this time there were six known rare earth elements yttrium, cerium, lanthanum, didymium, eibium and teibium. 

D. W. Bareis, a Continuous Fission Product Separation Process. I. Removal of the Rare Earths Lanthanum, Cerium, Praseodymium, and Neodymium) from a Typical Liquid Bismuth—Uranium Reactor Fuel by Contact with Fused LiCl-KCl Mixture, USAEC Report BNL-125, Brookhaven National Laboratory, 1951. 

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