Enrichment with rare earths

Table IL Neutron Capture Product Enrichment with Rare Earths...

Elderfield and Greaves [629] have described a method for the mass spectromet-ric isotope dilution analysis of rare earth elements in seawater. In this method, the rare earth elements are concentrated from seawater by coprecipitation with ferric hydroxide and separated from other elements and into groups for analysis by anion exchange [630-635] using mixed solvents. Results for synthetic mixtures and standards show that the method is accurate and precise to 1% and blanks are low (e.g., 1() 12 moles La and 10 14 moles Eu). The method has been applied to the determination of nine rare earth elements in a variety of oceanographic samples. Results for North Atlantic Ocean water below the mixed layer are (in 10 12 mol/kg) 13.0 La, 16.8 Ce, 12.8 Nd, 2.67 Sm, 0.644 Eu, 3.41 Gd, 4.78 Dy, 407 Er, and 3.55 Yb, with enrichment of rare earth elements in deep ocean water by a factor of 2 for the light rare earth elements, and a factor of 1.3 for the heavy rare earth elements. 

Fig. 5. A growth model of a nanocapsule partially filled with a crystallite of rare-earth carbide (RCj for R = Y, La,. . . , Lu R,C4 for R = Sc) (a) R-C alloy particles, which may be in a liquid or quasi-liquid phase, are formed on the surface of a cathode (b) solidification (graphitizalion) begins from the surface of a particle, and R-enriched liquid is left inside (c) graphite cage outside equilibrates with RCj (or R3C4 for R = Sc) inside.

The REE pattern for fresh volcanic rocks in the Kuroko mine area studied by Dudas et al. (1983) is shown in Fig. 1.47 which shows no negative Ce and no positive Eu anomalies and FREE (Light Rare Earth Element) are not enriched compared with HREE... 

Apatite exploration takes place in various regions of the World, and the most known are Kola Peninsula (Russia) and northwest Africa (Morocco). In both places, the apatite ores contain not only phosphorus as a main element but also many heavy metals, which are toxic for humans and animals. The given elements are F, As, Y, some rare earth species, Sr, Pb, Cd, Sn. The underground waters in these regions are enriched by F, Fi, Nb, some rare earth species with alkaline reaction that facilitates the migration of many ore elements. Some phosphorus containing ores are radioactive owing to the mixtures of uranium and thorium. 

Trace metals, such as copper, nickel, cobalt, zinc, and various rare earth elements, tend to coprecipitate with or adsorb onto Fe-Mn oxides. As shown in Table 18.1, this causes these elements to be highly enriched in the hydrogenous deposits as compared to their concentrations in seawater. The degree of enrichment is dependent on various environmental factors, such as the redox history of the underlying sediments and hydrothermal activity. This makes the composition of the oxides geographically variable. 

Ondov, J. M W. R. Kelly, J. Z. Holland, Z. C. Lin, and S. A. Wight, Tracing Fly Ash Emitted from a Coal-Fired Power Plant with Enriched Rare-Earth Isotopes An Urban Scale Test, Atmos. Environ., 26B, 453-462 (1992). 

This paper describes a new reaction which may yield useful amounts of the product isotope following neutron capture by lanthanide or actinide elements. The trivalent target ion is exchanged into Linde X or Y zeolite, fixed in the structure by appropriate heat treatment, and irradiated in a nuclear realtor. The (n, y) product isotope, one mass unit heavier than the target, is ejected from its exchange site location by y recoil. It may then be selectively eluted from the zeolite. The reaction has been demonstrated with several rare earths, and with americium and curium. Products typically contain about 50% of the neutron capture isotope, accompanied by about 1% of the target isotope. The effect of experimental variables on enrichment is discussed. 

Cs are more depleted in western coals. Silicon is also depleted in coal, probably because of the presence of clay minerals. Most lithophile elements (i.e., those normally associated with the earth s crust) have EF values near one, but it is interesting that the rare earth elements show slightly, but consistently higher enrichments in eastern coal. The apparent depletion of Ta is probably not real, but an artifact resulting from Wedepohl s use of too large a crustal abundance for it (14). 

Tarzia, M., Lima, A., De Vivo, B., and Belkin, H. E. (1999). Uranium, zirconium and rare earth element enrichment in alkali syenite nodules from the Breccia Museo deposit, Naples, Italy. Geol. Soc. Amer. Annual Meeeting, Abstracts with Programs, Vol. 31, n. 7, p. A-69. 

It now seems clear that after vanadium is deposited onto the catalyst it may be mobile in an atmosphere of steam and oxygen (from air). Mobile vanadia species migrate into the particles but may be enriched at the surface segment of low surface area particles such as our inert clay microspheres or old sintered equihbrium catalyst. Surface vanadyl groups are transferred to other FCC particles and migrate through them as well. Migration ceases when a reaction occurs with catalyst moieties, such as A1 or rare earth, to form stable vanadates (17). 

Separating rare earths by converting them to volatilie chelates, usually dpm complexes, followed by fractional codistillation was described. The mixture of chelates can be fractionally distilled with a codistillant to collect enriched fractions of the chelates, from... 

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