Electrochemical co-reduction of praseodymium and bismuth from 1-butyl-1-methylpyrrolidinium bis(fluorosulfonyl)imide ionic liquid

Electrochemical reduction of rare-earth elements is an important industrial process in the separation and puri-fication of naturally occurring ore mixtures and concentrates. Due to the extremely low reduction potential, high-temperature molten salt mixtures are generally used for this process, which is very energy intensive. As an alternative, room-temperature ionic liquids can be used to achieve the same goals at lower environmental cost. For this to become viable on an industrial scale, further research is required to understand the electrochemical reduction process of single rare-earth elements and how different external factors influence the electrochemical deposition process. For this purpose, praseodymium was chosen as an example of a rare-earth element to study electrochemical deposition from an ionic liquid. It was found that Pr alone cannot be reduced at an Au electrode surface in significant quantities, likely due to the formation of a blocking layer on the electrode surface. The addition of a small concentration of a bismuth salt significantly enhances the deposition rate and is highly beneficial for the deposition and separation of Pr from the ionic liquid.