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Rare Earth Metal Separation with Ionic Liquids

Final Report Summary - REMSIL (Rare Earth Metal Separation with Ionic Liquids)

Rare earth metals (REMs) shape the way we live and belong to the critical metals which are technologically important and are used in everyday green energy products such as hybrid cars, wind turbines, next generation solar cells, rechargeable batteries as well as energy saving LED lighting and flat screen displays. Rapidly increasing demand has strained supply of REMs, and there is growing concern that the world may soon face a serious shortage of the rare earths.
This project resulted in the development of novel, highly selective extractants for REM separation with ionic liquids, which have two orders of magnitude higher selectivity.
A new class of Multifunctional Amide Ionic Liquids (MAIL) that present a breakthrough in terms of their excellent extractability and very high separation factors for rare earth metal intra-group separation has been synthesised and tested. Better separation factors were achieved over current state of art and are fully satisfying the checklist of an ideal separation process. This extraction system has offered the possibility for a new, cost-efficient and environmentally benign process for the rare-earth metal intragroup separation, which has the potential to change the way these metals are processed.
Current REM mining and recycling technology is costly and has severe environmental issues due to the use of toxic chemicals and a high number of separation stages due. The currently used REM separation methods using liquid-liquid separations (hydrometallurgy) rely on the use of diluents, which are usually kerosene and n-heptane. These solvents are used to dissolve and dilute the organic extractants to reduce the viscosity of the extracted complexes, but most organic solvents are highly volatile and flammable. Therefore, strict standards due to the fire and explosion hazards are needed in the industrial processes. Due to the ionic nature of the MAIL system, our new MAIL extractants are non-volatile and non-flammable. As diluents, we can use cheap, available ionic liquids such as phosphonium ILs. Since our system works already at moderate pH conditions the use and consumption of strong acids is significantly reduced. We have demonstrated high recyclability of the extractants and low leaching / emulsification issues compared to other extractants.
The extractants developed within the project have the potential to drastically reduce the processing costs by reducing the number of separation stages by more than one order of magnitude (from >150 stages to 10-15 stages) and use non-toxic extractants to lower the environmental impact of the REM separation, which is a step-change impact of this invention. It has the potential to completely change the mining and recycling processes that are currently in use and there is a high demand for better performing, more environmentally benign, efficient alternative extractants.
Within this project, we have achieved separation factors of (depending on pH and rare earth element) 103-104 selectivity of separation in liquid-liquid batch separation experiments, which is a breakthrough in the selectivity of rare earth metal extractants. A patent has been filed on this new class of selective ionic liquid extractants. The development in this project has led to an industrial project with a scale-up to pilot scale of the separation process, in which we intend to design a process for these new extractants and set up a continuous-flow system for the separation of REMs to demonstrate the full commercial potential of the process.