A density less than 2000kg / m 3 noble metal in general. Main group of the Periodic Table â… comprising lithium, rubidium, cesium and beryllium 4 â…¡ main group elements.
Among them, cockroaches were first discovered in 1798, and metal bismuth was produced in 1829 after more than 30 years of discovery. Industrial production began in the 1920s, and by the 1980s, the world's consumption reached 500-600 tons. Lithium was discovered in 1817, and metal lithium was produced in the second year. Lithium began industrial production in the 1940s. In the 1980s, the world's lithium consumption reached 6,000-7000 tons.铷 and 铯 were discovered in 1861 and 1860 respectively, and the metal was produced in the same year, and the metal enamel was made in 1881 after 20 years of discovery. Both 铷 and 铯 found the application 60 years later. After the American research succeeded in extracting lanthanum and cerium from the mother liquor of lithium mica smelting in 1957, their production increased significantly. However, neither 铷 and 铯 have reached the level of complete industrial production. In the 1980s, the world's consumption was about 20 to 25 tons, and the consumption was less than 4 tons.
The content of rare light metals in the earth's crust is relatively high. Among them, the abundance of crust is the largest, 78×10 -4 %, which is tens to hundreds of times of abundance of copper , zinc and lead . Lithium has a crust abundance of 18 × 10 -4 %, exceeding lead and zinc. The crustal abundance of 铯 is 2.6×10 -4 %, and the enthalpy is 2.0×10 -4 %, both of which are larger than 锑 . However, they are dispersed in the crust, and the grade in the ore is low. For example, lithium concentrate generally contains only Li 2 O 4% to 8%, and niobium concentrate contains 10% to 12%.铯 can only produce a small amount of concentrate, and there is no independent mineral, but it is scattered in various types of brine and lithium minerals. It is difficult to extract, and its world production is less than one-millionth of copper production.铷 and 铯 are mainly recovered from lithium smelting by-products.
Rare light metals have large molar masses and weak metal bonds, and thus have the common characteristics of low density, low melting point and low hardness (see Table). In all non-ferrous metal and steel metals, lithium is the lightest metal, metal beryllium is most fragile. Metallic lithium, lanthanum and cerium are all soft metals, so soft that they can be cut with a knife. Strong chemical activity is a common feature of the chemical properties of rare light metals. Among them, niobium is the most active and positively charged metal among all metals. The outer electron orbitals of such metal atoms have 1 or 2 electrons, but the inner electron orbitals are saturated, so there is only one valence state, and the oxides and chlorides are stable and difficult to reduce.
Rare light metallurgy is generally divided into two stages. Firstly, the pure compound is prepared by the wet process using the concentrate as the 884 raw material, and the solvent extraction and separation technology is widely used in the process. Metal preparation mainly adopts molten salt electrolysis method and metal thermal reduction method. For example, industrially, lithium metal, lanthanum and cerium are electrolyzed by molten salt system such as LiCl-KCl, CsCl and BeCl 2 , and calcium is reduced by RbCl and CsCl. Helium, magnesium reduces BeF 2 to make bismuth, and so on.
Rare light metals have a wide range of uses in high technology and national economy sectors. In the nuclear industry, lithium-6 is the raw material for thermonuclear reactions (including hydrogen bombs), which are also heat carriers and moderators for atomic reactors. The neutron neutron has a large reflection cross section and a small absorption cross section, and is an ideal moderator and reflection material for the atomic reactor. Aerospace industry aluminum-lithium alloy, and beryllium metal compound is an excellent structural material properties, it is widely used in the manufacture of aircraft and spacecraft. The gyro is an inertial navigation tool. Since ruthenium and osmium are sensitive to light, they are used to manufacture photovoltaic cells, photomultiplier tubes, and television camera tubes. Tantalum and niobium are important raw materials for the manufacture of ion thermoelectric converters, ion engines and magnetic fluid generators. Magnetic fluid power generation is close to industrialization, and the use of lanthanum and cerium in this area will increase significantly.
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