Rare earth metals (rare earth metals), also known as a rare earth element, is a general term for a group ⅢB periodic table scandium, yttrium, lanthanides 17 elements, commonly represented by R or RE. Their names and chemical symbols are 钪 (Sc), 钇 (Y), 镧 (La), 铈 (Ce), 镨 (Pr), 钕 (Nd), 钷 (Pm), 钐 (Sm), 铕 (Eu ), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu). Their atomic numbers are 21 (Sc), 39 (Y), 57 (La) to 71 (Lu).
The term rare earth is the name left over from history. Rare earth elements were discovered from the end of the 18th century. At that time, solid oxides that were insoluble in water were often referred to as soil. Rare earths are generally separated by oxides and are rare, hence the name rare earth. Generally, lanthanum, cerium, lanthanum, cerium, lanthanum, cerium, lanthanum are called rare earth or lanthanum rare earth; lanthanum, cerium, lanthanum, cerium According to the similarity and difference of the physicochemical properties of rare earth elements, in addition to strontium (some of which are classified as sparse elements), they are divided into three groups, namely, light rare earth groups are 镧, 铈, 镨, 钕, 钷; The medium rare earth group is lanthanum, cerium, lanthanum, cerium and lanthanum;
The discovery of these rare earth elements, which was separated from the Finnish J. Gadolin in 1794 and the American Marinsky in 1947, lasted for more than 150 years. Most of these rare earth elements were discovered by some mineralogists, chemists, and metallurgists in Europe. The cockroaches were obtained by ion exchange of Americans Mariinsky, LEGlendenin, and CDCoryell, obtained from rare earth elements of uranium fission products. Promethium past that does not exist in nature, until 1965, a Finnish phosphate plant found traces of promethium in dealing with apatite.
Most rare earth metals exhibit paramagnetism.钆 is more ferromagnetic than iron at 0 °C. Niobium, tantalum, niobium and tantalum also exhibit ferromagnetism at low temperatures. The low melting point of niobium and tantalum and the high vapor pressure of niobium, tantalum and niobium show great differences in the physical properties of rare earth metals. The thermal neutron absorption cross sections of lanthanum, cerium and lanthanum are larger than those of cadmium and boron which are widely used in nuclear reactor control materials. Rare earth metals have plasticity, with lanthanum and cerium being the best. In addition to bismuth, the lanthanum group has higher hardness than the lanthanum group.
Rare earth metals has been widely used in electronic, petrochemical, metallurgy, machinery, energy, light industry, environmental protection, agriculture and so on. Application of rare earth to produce fluorescent materials, rare earth metal hydride battery materials, electric light source materials, permanent magnet materials, hydrogen storage materials, catalytic materials, precision ceramic materials, laser materials, superconducting materials, magnetostrictive materials, magnetic refrigeration materials, Magneto-optical storage materials, optical fiber materials, and the like.
China has abundant rare earth mineral resources and excellent ore-forming conditions. It is uniquely endowed with abundant proven reserves, which provides a solid foundation for the development of China's rare earth industry.
The average content of rare earth elements in the earth's crust is 165.35 × 10 -6 (Li Wei, 1976). In nature, rare earth elements exist mainly in the form of single minerals. At present, there are more than 250 kinds of rare earth minerals and rare earth-containing minerals found in the world, among which 50-65 kinds of rare earth content ΣREE>5.8% can be regarded as rare earth independence. Minerals. Important rare earth minerals are mainly fluorocarbonates and phosphates. The general characteristics of rare earth minerals: First, the lack of sulfides and sulfates (only very few), which means that rare earth elements have oxophilic properties; second, the silicates of rare earths are mainly islands, without layers, shelves and chains. The third structure is that some rare earth minerals (especially complex oxides and silicates) are amorphous; the fourth is the distribution of rare earth minerals, mainly composed of silicates and oxides in magmatic rocks and pegmatites. Fluorine carbonate and phosphate are mainly used in hydrothermal deposits and weathering crust deposits. Most of the rich minerals are distributed in granite rocks and their associated pegmatite, gas-forming hydrothermal deposits and hydrothermal deposits. Fifth, rare earth elements are often symbiotic due to their similar atomic structure, chemical and crystal chemical properties. Among the same minerals, the rare earth elements of the lanthanum and the lanthanum are often present in one mineral, but these elements do not coexist in equal amounts. Some minerals are mainly composed of lanthanum-containing rare earths, and some minerals are mainly steroids.
More than 250 kinds of rare earth minerals and rare earth-containing minerals have been discovered, and there are only 10 kinds of industrial minerals suitable for current smelting conditions:
1) Minerals containing lanthanum rare earths (lanthanum, cerium, lanthanum): fluorocarbon strontium ore, fluorocarbon strontium strontium, fluorocarbon strontium ore, bastnasite and monazite.
2) a mineral-enriched samarium and gadolinium: gadolinite, niobium xenotime, euxenite.
3) Minerals containing lanthanum rare earths (lanthanum, cerium, lanthanum, cerium, etc.): xenotime, fluorocarbon calcium strontium, strontium, brown sorghum, black gold ore.
