According to the structure and physico-chemical properties of the rare-earth atomic electron layers and their different ionic radii in minerals, they can produce different characteristics. Seventeen kinds of rare earth elements are usually divided into two groups:
Rare earth and materials
Light rare earths include: lanthanum, cerium, praseodymium, neodymium, acenaphthene, samarium, europium, gadolinium.
Heavy rare earths include: terbium, dysprosium, holmium, erbium, gallium, ytterbium, gallium, scandium, yttrium.
Classified by mineral features:
Group of cerium (light rare earth) - lanthanum, cerium, praseodymium, neodymium, acenaphthene, samarium and europium;
Yttrium group (heavy rare earth) - gadolinium, terbium, dysprosium, holmium, erbium, acenaphthene, ytterbium, gallium and scandium.
Separation by Extraction Category: rare earth elements in the periodic table position
Light rare earth (P204 weak acidity extraction) - Lanthanum, Cerium, Praseodymium, Neodymium;
Medium rare earth (P204 low acidity extraction) - samarium, europium, gadolinium, terbium and dysprosium;
Heavy rare earth (acidity extraction in P204) - holmium, erbium, gallium, ytterbium, gallium, yttrium.