Yttrium chemical behavior

Also as a result of the lanthanide contraction, yttrium has an ionic radius comparable to that of the heavier REE species in the holmium-erbium region. If the effective ionic radius (Shannon 1976) of is plotted (0.90 A)., it plots in between element 67 (Ho) and 68 (Er). Scandium (effective ionic radius is 0.745 A), plots outside of the Lanthanide series. As also the outermost electronic arrangement of yttrium is similar to the heavy rare earths, the element behaves chemically like the heavy rare earths. It concentrates during (geo)chemical processes with the heavier REEs, and is difhcult to separate from the heavy REEs. Scandium, on the other hand, has a much smaller atomic radius, and the trivalent ionic size is much smaller than that of the heavy rare earths. Therefore, scandium does not occur in rare earth minerals, and in general has a chemical behavior that is significantiy different from the other rare earth elements (Gupta and Krishnamurthy 2005). 

Electronic Structures. Almost all the physical properties and chemical behavior of the rare earth elements find a logical explanation in terms of their electronic structures. Scandium, yttrium, lanthanum, and actinium are the first members, respectively, of the first, second, third, and fourth transition sequences of elements. In other words, each such element marks the beginning of an inner building where a stable group of 8 electrons is expanding to a completed (or more nearly complete) group of IS. This situation is illustrated for the first transition sequence. 

Scandium, yttrium, and the lanthanides represent 17% of all of the elements that can be obtained in coherent form. In view of their similar chemical behavior separation of these elements proved to be formidable (Szabadvary, 1988) but all of the metals have now been obtained in relatively high purity and, except for promethium, their thermodynamic properties have been measured with varying degrees of quality. Based on the interpolation of the properties of neighboring elements, it has also been possible to estimate the thermodynamic properties of promethium in order to complete this review. Because of the radioactive nature of this element and the fact that the most stable isotope has half-life of only 17.7 years, it is unlikely that further measurements will be carried out beyond the very basic properties which have already been determined. 

Monazite ubiquitously exhibits this type of behavior. Backscattered electron images and yttrium, thorium, and uranium X-ray maps nearly always reveal complex zonation (e.g., Parrish, 1990 DeWolf et al., 1993 Zhu et al., 1997 Zhu and O Nions, 1999 Williams et al., 1999 Pyle et al., 2001 Townsend et al., 2001 Williams and Jercinovic, 2002 see Figures 27 and 28), and several studies have demonstrated significant age differences between these chemically distinct domains (e.g., DeWolf et al., 1993 Zhu et al., 1997 Zhu and O Nions, 1999 Williams et al., 1999 Townsend et al., 2001 Figures 27 and 28). Extreme compositional and age heterogeneity implies that the analysis of a bulk mineral separate or even of a single grain is not very useful... 

From the geochemical point of view, the rare earths are dispersed elements, i.e., spread around among many common materials rather than concentrated into a select few. They are lithophile, i.e., when allowed to distribute themselves among common silicate, metal, and sulfide phases, they overwhelmingly enter the silicates. Geochemically, the term rare earth is best restricted to mean lanthanides plus yttrium. Yttrium behaves like the heavier lanthanides, although just which heavier lanthanide is dependent on the particular chemical environment. The geochemical behavior of scandium is substantially different from that of the rare earths and is less well characterized and understood. For these reasons, scandium is not further discussed here. 

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