Initiator rare earth elements

Another widely used solution is for an instantaneous planeAine/point source (such as spill of a toxic pollutant, or diffusion of rare Earth elements from a tiny inclusion of monazite or xenotime into a garnet host) to diffuse away in either one dimension, two dimensions, or three dimensions (Figure l-6b). If the source is initially in a plane, which may be defined as x = 0 (note that x = 0 represents a plane in three-dimensional space), then diffusion is one dimensional. If the source is initially a line, which may be defined as x = 0 and y=0, then diffusion is... 

Rare earth element complexation by PAA and HA is fast (5). However, most of the initial interactions are labile or weak stronger interactions take over as the metal reside longer on the polyelectrolyte. Weak and strong interactions are indicated by both ion exchange and ligand exchange dissociation experiments. It is difficult to infer site binding versus counterion condensation from these methods, and such a distinction must await methods that probe more directly the molecular character of the different interactions. 

Extraction of columbate-tantalates, titanocolumbates, and titanosilicates may also be initiated by treatment of the mineral with hydrofluoric acid. The procedure has the advantage that columbium, tantalum, uranium(VI), scandium, titanium, zirconium, and hafnium are dissolved, while silica is volatilized as silicon tetrafluoride and the rare earth elements, together with thorium and uranium(IV), remain as slightly soluble fluorides. The residue is then heated with concentrated sulfuric acid to remove hydrogen fluoride and to oxidize uranium (IV), the thorium is separated by precipitation of the phosphate (synthesis 12), and the rare earths are precipitated as oxalates. 

The correlations of major-elements with initial Sr/ Sr ratios are positive for SiO and TiO, and negative for AljOj, MgO, and CaO. In addition, the concentrations of the light rare earth elements and strontium show excellent positive correlations with initial Sr/ Sr ratios. Nevertheless, Kyle et al. (1983) argued that the initial Sr/ Sr ratio of the Ferrar magmas was about 0.709 and that the addition of crustal strontium raised the value only incrementally to 0.7115. However, the evidence that sills of Ferrar Dolerite have a distinctive crustal character compelled Kyle et al. (1983) to conclude ... 

Fig. 7.4. Interlayer turn angle data vs. the de Gennes factor for the heavy lanthanide metals and binary alloys as determined from single crystal neutron diffraction experiments. o>i is the initial turn angle (just below Tn) [after Koehler (1972)]. Legend pure rare earth elements A Er-Dy alloys Er-Tb alloys V Er-Gd alloys O Ho-Dy alloys A Ho-Tb alloys.

A rather interesting plot (see fig. 9.6a) is the initial melting slope dT/dP of the rare earth elements versus atomic number. In this plot the divalent and trivalent lines are well established from the slopes of Eu and Yb and from La, Gd and Lu respectively. The quadrivalent line drawn parallel to these is perhaps not unreasonable. The deviations of the data points from the trivalent line, of Sm... 

The initial motivation for the study of self-diffusion in the bcc phases of the rare earth elements is connected to the problem of so-called anomalous diffusion in bcc metals. Any discussion of self-diffusion in the bcc rare earth metals must be viewed against the background of this anomalous diffusion. This subject has received extensive coverage and has been summarized by Le Claire (1965), Lazarus (1965), Peterson (1968) and Seeger (1972). 

The important raw material for cerium, monazite, is also the most important mineral source for thorium. As this metal was desirable it initially supported and accelerated the extraction of rare earth elements from monazite. TTie radioactivity of thorium has, however, created environmental problems for monazite. Nowadays, minerals free from radioactive components are favored for the extraction of REMs. 

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