Rare Earth Elements: What and Where They Are
REE are often misunderstood, beginning from the grouping of the relevant elements to the etymological misconception, that REE are rare or the fact that REE are ‘more abundant than gold’. Thus REE can get the impetus of being very abundant, which is only p
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Rare Earth Elements: What and Where They Are
2.1 Definitions REE are often misunderstood, beginning from the grouping of the relevant elements to the etymological misconception, that REE are rare or the fact that REE are ‘more abundant than gold’. Thus REE can get the impetus of being very abundant, which is only part of the truth. As well the allegation ‘‘The term rare earth is actually a misnomer’’ [1, p. 3] shows a cursory view of these metals. This view is for most purposes probably good enough, like the need for a 5min-overview of the REE. The problem here lies in a possible wrong perception which finally gets to a seemingly hard fact because ‘everybody says so’. In order to get a scientific plausible picture, several definitions are given at the beginning.
2.1.1 The Group of the REE The Rare Earth Elements (REE), also simply called Rare Earths (RE) or Rare Earth Metals (REM), are a group of 17 elements—according to the International Union of Pure and Applied Chemistry (IUPAC) [2, p. 51]. The 17 REE therefore consist of the elements scandium (Sc), yttrium (Y) and the 15 so called lanthanoids (Ln) which are the elements lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Th), ytterbium (Yb) and lutetium (Lu) [2]. Mortimer and Müller [22] in their chemistry and Meschede [3] in the physics both group the lanthanoids and rare earths synonymously and count 14 elements from Cerium to lutetium, i.e. without lanthanum itself [4, 3, p. 849]. Often the name lanthanides is used instead of lanthanoids. The ending—id however indicates a certain chemical structure like a sulphide whereas the ending—oid means that something is similar, looks or behaves the like. So the word lanthanoids would be the correct one to use as the REE are not derivations
V. Zepf, Rare Earth Elements, Springer Theses, DOI: 10.1007/978-3-642-35458-8_2, Springer-Verlag Berlin Heidelberg 2013
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2 Rare Earth Elements: What and Where They Are
from lanthanum but they are similar to lanthanum. Even though that would preclude lanthanum itself from the group, the inclusion of lanthanum has become common use [2].
2.1.2 The Terms ‘Rare’ and ‘Earth’ The name ‘Rare Earths’ is misleading as the name itself implies an earthen material which is not ubiquitous. To start with the easy part, the word ‘earth’ was a common denomination for an oxidic material, usually a metal oxide, i.e. a compound of an element with oxygen. In the German language there is another cause for error as the German word for earth, ‘Erden’, can be misunderstood with the expression ‘Steine und Erden’, which in the German language stands for materials from pit and quarry industry. Of course the ‘Steine und Erden’ have nothing to do with RE. The more difficult part is the adjective ‘rare’. Reiners [5] suggests that ‘rare’ has more of an etymological background, as ‘rare’ was used from the late 15th century onwards in the sense of something s
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