Cerium-group earths, separation

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... 

Double sulphate precipitation is one of the most common methods used in industry for the separation of cerium group from yttrium group rare earths. Various other precipitants such as chromates, double chromates, ferrocyanides, phosphates etc. have been tried. 

The organic amine extractants are the most commonly used anion exchangers. Secondary amines have been used to recover uranium from leach liquors (GlO) secondary and tertiary amines to recover molybdenum from uranium mill circuits (L13) a primary amine, diethylenetriamine-penta-acetic acid (DTPA) to extract cerium group lanthanides (B6) tri-,V-butylamine-3-methyl-2-butanonc to separate yttrium and rare earth nitrates (G13) tricaprylyl amine (Alamine 336) and methyltrioctyl-ammonium salt (Aliquat 336) to recover vanadium from acidic solutions (A3) and Aliquat 336 to extract vanadium from slightly acidic or alkaline leach liquor (S36). 

If the material is to be separated into the cerium and yttrium groups of rare earths by precipitation of the double sulfates of the former, removal of the last trace of cerium is unnecessary since it does not seriously interfere in the fractionation of the cerium group double magnesium nitrates. It is important, however, that there be no ceriuni in a bromate series,... 

Yttrium-group earths, containing samarium, separation from mona-zite by magnesium nitrate, 2 56 separation by fractional crystallization of bromates, 2 56, 62 separation from cerium earths by double-sulfate method, 2 44, 46... 

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. 

The separation of light rare earths (cerium group) sulfates obtained from bastnasite by primary amine with or without an aqueous phase chelating reagent was studied by Bauer et al. (1968). Kerosene was used as the diluent. The pH of the lanthanide-amine system affects the molecular species present in both the aqueous and organic phases. The extraction of rare earths at high acid concentrations is inhibited due to the formation of stable amine bisulfate... 

R-M-(M )P compounds with cerium-group rare earths are listed in table 23. Pavlov et al. (1991) studied the isothermal section of the system La-Mn-P at 1873 K and found two separate phases to exist in the liquid state at the temperatures investigated. Samples with 35 at.% of lanthanum contain two liquid phases and solid LaP. 

The element cerium is inseparably connected with the rare earth group, and it is generally customary to discuss it with the members of Group III. But it differs from the other rare earth elements in forming a well defined series of quadrivalent compounds, resembling thorium quite closely. Because of this relationship, as well as its greater abundance and commercial importance, it seems best to discuss certain phases of the chemistry of cerium with Group IV. The history, occurrence, extraction, and separations are discussed in Chapter VI. 

Thus, Mosander s activities led to the originally two-element division into a six-element division. The cerium compounds are yellow at the higher oxidation level and colourless at the lower oxidation level, lanthanum compounds are white, didymium compounds are red, yttrium and erbium compounds are white, terbium compounds are pink. Chemists existed, of course, who disputed the existence of these elements. Unequivocal identification of elements was, however, possible in later times only. In the period in question, the main characteristics on the basis of which a substance could be qualified as a new element were separability, colour, crystal shape and reactivity. Even atomic mass determinations were largely uncertain, particularly in the group of the rare earth elements, it will be seen in the... 

In the comprehensive studies of the radioactive species produced in the fission of uranium it has been found that over thirty are members of the rare earth family (isotopes of yttrium and the group lanthanum through europium). The chemical and physical identification of these was an important part of the research program of the Manhattan Project. Standard oxidative separations and fractional precipitations and the use of radiochemical methods based on chain relations served to distinguish the activities of yttrium, lanthanum, cerium, and some of praseodymium, and those of samarium and europium. The characterization of the sequence praseodymium, neodymium, and element 61 presented very difficult problems that were solved only with the intensification of ion exchange methods originally developed by Boyd and co-workers and applied to the rare earth field by Cohn and co-workers. (Marinsky et al. 1947)... 

The rare earth elements (REE) include lanthanum and the f-block elements, cerium through lutetium. Scandium and yttrium are included in this group as they have ionic radii similar to the lighter f-block elements and are found together in the same ores. The chemical similarities of the 17 REE make diem unique in comparison to the other metals in the periodic table where two adjacent elements in a period typically have significantly different chemical properties. This makes the REE relatively difficult to separate from one another, although there are minerals where the lighter (La Eu) and heavier (Y and Gd Lu) REE are concentrated. REE research has benefited from this similarity, however, as compounds and materials formed with one REE can often be replicated with one or more of the other REE. 

Ever since his arrival in Florence, Rolla conducted research on the group of rare earths with the specific intention of isolating the element possessing atomic number 61. He smdied new methods of fractional crystallization, the method of choice for separating rare earth elements. He worked first with small, then with immense quantities of material so that in the 1930s the Instimte possessed, as its Director declared with great pride, the richest and purest collection of cerium oxides in the world [147]. ... 

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