The word rare earth is a name left over from history. Rare earth elements were discovered at the end of 18. At that time, people often called water-insoluble solid oxides soil. Rare earth is generally separated in oxide state, which is relatively rare, so it is named rare earth. Lanthanum, cerium, praseodymium, neodymium, promethium, samarium and europium are usually called light rare earth or cerium group rare earth; Gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium and lutetium yttrium are called heavy rare earths or yttrium rare earths. According to the similarity and difference of physical and chemical properties of rare earth elements, some of them are divided into three groups (some are classified as sparse elements), that is, the light rare earth groups are lanthanum, cerium, praseodymium, neodymium and promethium; The medium rare earth group is samarium, europium, gadolinium, terbium and dysprosium; The heavy rare earth groups are holmium, erbium, thulium, ytterbium, lutetium and yttrium.

At present, the common raw materials for producing rare earth metals are their chlorides and fluorides.

(1) molten salt electrolysis method is generally used for batch production of mixed rare earth metals in industry. In this method, a rare earth compound such as rare earth chloride is heated and melted, and then electrolyzed to precipitate a rare earth metal on a cathode. There are two kinds of electrolysis methods: chloride electrolysis and oxide electrolysis. The preparation method of single rare earth metal varies with different elements. Samarium, europium, ytterbium and thulium have high vapor pressures and are not suitable for electrolytic preparation, so the reduction distillation method is adopted. Other elements can be prepared by electrolysis or metal thermal reduction.

Chloride electrolysis is the most commonly used method to produce metals, especially mixed rare earth metals, with simple process, low cost and small investment, but the biggest disadvantage is that chlorine gas is released and the environment is polluted.

Oxide electrolysis does not emit harmful gases, but the cost is slightly higher. Generally, the single rare earth with higher production price, such as neodymium and praseodymium, is electrolyzed by oxides.

(2) Vacuum thermal reduction electrolysis can only prepare general industrial grade rare earth metals. If you want to prepare metals with low impurities and high purity, vacuum thermal reduction is generally used. Generally, rare earth oxides are first made into rare earth fluorides, and then the crude metal is obtained by reduction with metal calcium in a vacuum induction furnace, and then the purified metal is obtained by remelting and distillation. All single rare earth metals can be produced by this method, but samarium, europium, ytterbium and thulium cannot be produced by this method. The redox potentials of samarium, europium, ytterbium, thulium and calcium only partially reduce rare earth fluoride. Generally speaking, these metals are made by using the principle that the vapor pressure of these metals is high and the vapor pressure of lanthanum metal is low, mixing and briquetting the oxides of these four rare earths with fragments of lanthanum metal, and reducing them in a vacuum furnace. Lanthanum is relatively active, and samarium, europium, ytterbium and thulium are reduced to metals by lanthanum, which are collected during condensation and easily separated from slag.

Rare earth is a chemical element. . .