Preparation of rare earth metals

The production of rare earth metals is also called the production of rare earth pyrometallurgy. Rare earth metals are generally divided into mixed rare earth metals and single rare earth metals. The composition of mixed rare earth metals is similar to that of the original rare earth elements in ores. Using rare earth oxides (except oxides of samarium, europium, ytterbium and thulium) as raw materials, it is difficult to reduce to a single metal by general metallurgical methods because of its high heat of formation and high stability. Therefore, the common raw materials for the production of rare earth metals are their chlorides and fluorides.
(1) molten salt electrolysis
Mixed rare earth metals are usually produced by molten salt electrolysis in large quantities in industry. The process involves heating and melting rare earth compounds, such as rare earth chloride, and then electrolyzing them to separate rare earth metals at the cathode. Electrolysis includes chloride electrolysis and oxide electrolysis. The preparation methods of single rare earth metals vary with different elements. Due to high vapor pressure, reductive distillation was used instead of electrolytic preparation. Other elements can be prepared by electrolysis or metal thermal reduction.
Chloride electrolysis is the most common method to produce metals, especially the mixed rare earth metals.
Oxide electrolysis does not release harmful gases, but the cost is a little higher. Generally, the single rare earth with higher price, such as neodymium and praseodymium, are produced by oxide electrolysis.
(2) vacuum thermal reduction method
The electrolysis method can only prepare general industrial grade rare earth metals. If the metal with low impurity and high purity is to be prepared, it is generally prepared by vacuum thermal reduction method. In general, rare earth oxides are first made into rare earth fluoride, which is reduced with calcium metal in a vacuum induction furnace to produce crude metals, and then remelted and distilled to obtain more pure metals. All single rare earth metals can be produced by this method, but samarium, europium, ytterbium and thulium cannot be used in this way.
REDOX potentials of samarium, europium, ytterbium, thulium and calcium only partially reduced rare earth fluoride. General preparation of these metals, is the use of these metal high vapor pressure and the principle of lanthanum metal low vapor pressure, the four kinds of rare earth oxides and lanthanum metal debris mixed briquetting, reduction in vacuum furnace, lanthanum is lively, samarium, europium thulium, ytterbium, lanthanum reduction into a metal after collection in the condenser, and the residue is easy to separate.

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