Molten salt electrolysis

Also known as molten salt electrolysis, this method involves melting the salt of the metal to be extracted at high temperatures to form an electrolytic bath, and then depositing the metal on the cathode by electrolysis. Molten salt electrolysis is generally performed on metals that are electrochemically more base than hydrogen ions and have a small hydrogen ion overvoltage on the metal. However, the salt of the target metal often has a high melting point on its own, so the salt is generally mixed with a salt of a baser metal, known as a supporting salt, to form the electrolytic bath. Electrolytic baths include all-chloride systems, all-fluoride systems, chloride-fluoride systems, and these with oxides (Al ₂ O ₃ ) or sulfides (PbS) dissolved in them. Industrially, they are used to produce Al, Mg, alkali metals, etc., and in all cases the deposited metal is obtained in a molten state. However, the elements of interest in research are Be, V, Ti, Zr, Nb, Ta, most rare earth elements, U, Th, etc., which have high melting points and are highly reactive with gas. All of these elements deposit in solid form on the cathode, which necessitates the time and effort required to separate the deposit from the salt afterwards, and this is a major obstacle. Recently, there have been some attempts at alloy electrodeposition using molten salt electrolysis.

Source: Morikita Publishing "Chemical Dictionary (2nd Edition)" Information about the Chemical Dictionary 2nd Edition

融解塩電解ともいう．採取を目的とする金属の塩を，高温で融解状態にして電解浴とし，電解により陰極に金属を析出させる方法をいう．一般に，電気化学的にみて水素イオンより卑な金属イオンで，しかもその金属上での水素イオン過電圧の小さな金属を対象にして溶融塩電解が行われる．しかし，目的とする金属の塩単独では融点の高いことが多く，一般に支持塩といわれる卑な金属の塩を混合して電解浴として電解する．電解浴には全塩化物系，全フッ化物系，塩化物-フッ化物系，およびこれらに酸化物(Al₂O₃)または硫化物(PbS)を溶かしたものがある．工業的にはAl，Mg，アルカリ金属などの製造に用いられているが，これらはいずれも析出金属が溶融状態で得られる．しかし，研究上興味があるのは，高融点でガスとの反応性の大きいBe，V，Ti，Zr，Nb，Ta，希土類元素の大部分，U，Thなどであって，いずれも陰極には固体状として析出してくるので，析出物と塩を後で分離する手間がかかり，大きな障害になっている．最近，溶融塩電解で合金電着を試みている例がある．

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