Geochemistry of the rare earths: determination and applications

The Earth was formed starting from a chemically homogeneous matter with specific mineralogical and chemical characteristics: nucleus, mantle and crust. About 90 % of the Earth, globally considered, is made up of iron, oxygen, silicon and magnesium. The main part of the iron is concentrated in the nucleus, it is to say, in the central layer. In the crust, the three more abundant elements that conform the external layer of the Earth are oxygen (46%) silicon (28%) and aluminium (8%). The mantle, located between the nucleus and the crust, is made up basically by silicon, magnesium and iron. There exist another elements, for instance, the lanthanides which can give a lot of information about the initial differentiation processes of the Earth. The rare earths or lanthanides are a group of 15 elements included in the atomic numbers 57 to 71 (from lanthanum to lutetium) of the periodic chart; their electronic configurations cause that the 15 elements present chemical characteristics quite similar. An important part of this article is dedicated to the analytical chemistry of the rare earths, presenting both nuclear and nonnuclear analytical methods. This paper is divided in the following sections: Geochemical and chemical properties, Applications to the study of terrestrial processes, and Analytical chemistry. (Author)