3. Different rare earth chemistries

3.1 Salts

The salts used industrially are nitrates and chlorides of trivalent rare earths, which can be derived directly from separation processes. They come in the form of dried crystals or aqueous solutions at a few moles per liter. In the latter case, the solutions exhibit a slight free acidity (HCl or HNO ₃ ). The color of trivalent rare earth salts is related to their 4f-4f transitions: Nd(NO ₃ ) ₃ mauve, Pr(NO ₃ ) ₃ green, Dy(NO _...