Publisher Summary This chapter discusses recent progress in means of isolating individual lanthanides and yttrium. The chapter discusses well-developed processes for the preliminary treatment of rare earth mixtures. The lanthanides comprise a series of inner-transition elements in which the number of 4-f electrons increases from 1 to 14. The main effect of increasing the number of electrons in this internal energy sublevel, as the nuclear charge increases, is to gradually decrease the cationic radius of consecutive Ln3+ ions, so that they range in size from that of La3+ to that of Sc3+. Because of the remarkable similarities in their cationic charge and their radii, lanthanons form many isomorphic series of compounds, and are always found as complex mixtures (not always of exactly the same composition) in rocks and minerals that comprise the earth's crust. The problem of separating them by reactions in aqueous media is aggravated further by the fact that increased charge density, which accompanies lanthanide contraction, promotes a greater overall degree of aquation and renders individual hydrated cationic radii even more similar.
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