According to the electronic shell structure and physical and chemical properties of rare earth elements, as well as their occurrence in minerals and the characteristics that different ionic radii can produce different properties, seventeen rare earth elements are usually divided into two groups. Light rare earth elements include lanthanum, cerium, praseodymium, neodymium, promethium, samarium and europium. Heavy rare earths include gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, scandium and yttrium.
physicochemical property
One is the lack of sulfide and sulfate (only a few), indicating that rare earth elements have oxygen affinity;
Second, the silicate of rare earth is mainly island-shaped, without layered, frame-shaped and chain-shaped structure;
Thirdly, some rare earth minerals (especially complex oxides and silicates) are amorphous;
Fourthly, the distribution of rare earth minerals is mainly silicate and oxide in magmatic rocks and pegmatite, and fluorocarbon and phosphate are mainly in hydrothermal deposits and weathered crust deposits. Most yttrium-rich minerals occur in granite, pegmatite and related gas-water hydrothermal deposits.
Fifth, rare earth elements are often born in the same mineral because of their similar atomic structure, chemistry and crystal chemistry, that is, cerium rare earth elements and yttrium rare earth elements often exist in the same mineral, but these elements do not exist in the same amount. Some minerals are mainly rare earths containing cerium, while others are mainly yttrium.
More than 250 kinds of rare earth minerals and minerals containing rare earth elements have been found, and only 10 kinds of industrial minerals are suitable for current smelting conditions.
Rare earth metals are generally divided into mixed rare earth metals and single rare earth metals. The composition of mixed rare earth metals is close to the original rare earth composition in the ore, and a single metal is a metal separated and refined from each rare earth. Rare earth oxides (except oxides of samarium, europium, ytterbium and thulium) have high heat of formation and high stability, so it is difficult to reduce them to a single metal by general metallurgical methods. Therefore, the common raw materials for producing rare earth metals today are their chlorides and fluorides.