In the production of rare earth metals by molten sa1t electrolysis, there is the dissolution problem of cathodic deposited metal in an electrolyte such as metal fog. These behaviors are considered to lower cathodic current efficiency in molten sa1t electrolysis. In order to clarify this problem, saturated solubilities of metallic lanthanum. praseodymium. neodymium and ytterbium in LiF- REF₃ (RE :La, Pr, Nd, Yb) binary mo1ten salts have been examined in grahite crucible at the temperature range of 1213K to 1323K, and reaction compounds after dissolution have been also identified by X-ray diffraction method. Dissolution reactions oflanthanum, praseodymium, neodymium and ytterbium in rare earth fluoride melts containing lithium fluoride could be classified by following three forms. Saturated solubilty of metal such as dissoution of lanthanum decreased with an increase in rare earth fluoride concentration in melts. Saturated solubilities of metals such as dissolutions of praseodymium and neodymium were not dependent on rare earth fluoride concentration in melts. Futhermore, saturated solubilty of metal such as dissoution of ytterbium increased with an increase in rare earth fluoride concentration in melts. These dissolution behaviors can be considered to be caused by the differences of dissolution reactions in melts. Metallic lanthanum predominantly reacts with LiF in binary melt by the displacement reaction to form both compound of LaF₂ and LaF₃. Metallic praseodymium and neodymium respectively form PrF₃ and NdF₃ compounde by the displacement reaction with LiF in melt at the initial stage of dissolution, and also react with PrF₃ and NdF₃ itself in binary melt by the disproportionation reaction to form PrF₂，a nd NdF₂，compounds，respectively. On the other hand，Metallic ytterbium reacts with LiYbF，complex coumpound in melt at the initial stage of dissolution to YbF，compound，and also dissolves in melt by the displacement reaction with LiF in melt at the final stage of dissolution.
LiF-REF₃(RE : La, Pr, Nd, Yb) 2成分系溶融塩中における金属La, Pr, NdおよびYbの溶解挙動
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