Direct dissolution of metal oxides in ionic liquids as a smart strategy for separations: Current status and prospective

The dissolution of metal oxide in ionic liquid (IL) medium is an important and challenging issue for the development of alternative solvent systems for carrying out non-aqueous chemistry operations of metal ions in the nuclear field where IL could be a potential alternative to the high-temperature molten salt for non-aqueous processing of metal ions. This review article emphasizes on the developments in the field of dissolution of metal oxides in IL medium particularly that of the of oxides of uranium and few other metal oxides including those of lanathanides which have relevance in the spent nuclear fuel (SNF) reprocessing. The dissolution of metal oxides in ILs is broadly divided on the basis of different factors affecting the dissolution. The chloroaluminate-based ILs although reported to have dissolved many oxides including inert oxides suffer from the air and moisture sensitivity issues whereas the dissolution of metal oxides in acid and water stable ILs are limited by the solubility of acid and water in the ILs. Task-specific ionic liquids (TSIL) containing Brønsted acid functional groups are reported to have dissolved many oxides depending on the pKa of the functional acid group and the complexing ability of the conjugate base. This review article will help the readers to understand the basic problem of dissolution of metal oxides in ILs and recent development in the field of dissolution.