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Over the temperature range 700–1050°C, the following Arrhenius relations are obtained: Diffusion rates for the REE (and Y) are all quite similar, and faster than diffusion of Sr.This is in contrast to observations in other mineral systems (e.g., feldspars, zircon) where diffusion of more highly charged cations proceeds more slowly than that of cations with lower charge.The diffusion of Sr, Y and three rare earth elements (Nd, Dy and Yb) has been measured in natural fluorite under dry 1-atm conditions.Sources of diffusant consisted of mixtures of Sr, Y, or REE fluorides and Ca F powders, pre-reacted in vacuo in silica glass tubes.This paper reviews those metallogenetic belts and sets them in their geodynamic context.The most well-known of the REE belts are of Precambrian to Palaeozoic age and occur in Greenland and the Fennoscandian Shield.Review of Eleven Rare Earth Companies including Molycorp, Lynas, Arafura, Avalon, Rare Element Resources, Quest Rare Minerals, Greenland Minerals and Energy, Great Western Minerals, Commerce Resources and Medallion The companies reviewed below cover a variety of business models in the rare earths space.
Unfortunately these articles got much of it wrong, propagating inaccuracies that are particularly egregious when they keep appearing within various natural-resource media channels.
However, the ionic radius of Sr (1.019 Å) or the investigated REE (0.985–1.109 Å), suggesting that differences in cationic size may exert greater influence on diffusion rates in fluorite than do differences in cation charge.
This size dependence is weak, however, perhaps due to similarities in size between these cations and Ca, for which they likely substitute in the fluorite lattice, or as a consequence of the relatively flexible fluorite lattice.
IUPAC defines the rare-earth metals as the 15 lanthanoid elements (with atomic numbers of 57 through to 71) in addition to scandium (Sc) and yttrium (Y) .
The lanthanoid promethium (Pm) is radioactive, with no stable isotopes; it is thus present in the Earth’s crust in vanishingly small quantities and does not occur with the other REEs.