Separation of Rare Earth Elements using a Novel Antisolvent Crystallization Method

Background

To address the global issue of climate change and to meet the goals set in the Paris agreement, decarbonization of the energy sector is necessary. This includes among other things a significant transition in the source of energy from fossil-based to renewable. The electrification of the transport sector is also required. Vital to such green technologies and to other technological advancements are specialty metals like the rare earth elements (REEs). The world bank has projected scenarios where the need for neodymium (a REE) would increase from the current 7000 tons/year to 400 000 tons/year [1]. However, to meet these rising demands, more and more REE minerals would have to be mined out of the Earth’s crust. This is an unsustainable scenario, since mining can have adverse effects on the environment which could offset the benefits from the decarbonization or cause new environmental concerns. Therefore, it is important to increase the efficiency of extraction from mining waste, as well as develop methods for recycling of end-of-life products containing these valuable metals.

In a hydrometallurgical separation process, the metals are first leached by a suitable acid into an aqueous solution. Antisolvent crystallization can be an effective technique to separate REEs, as a group, from the other metals in the solution, like Fe or Co. It might even be possible to achieve some degree of separation between individual REEs using the antisolvent crystallization technique. A benefit is that the precipitates obtained using this technique can easily be dissolved in water and further separated in downstream process steps, e.g. using traditional solvent extraction or novel extraction chromatography. Thus antisolvent crystallization can act as an excellent complimentary separation process to other separation techniques.

The project

The REE salts, or sulphates in the current case, are soluble in water. By adding an antisolvent, e.g. ethanol, the solubility of the salt decreases, eventually causing it to precipitate as a result of the supersaturation generated. The yield, purity and product of this precipitation depends on the amount of antisolvent added and on the solubility of the salts at varying solvent composition. Thus, determination of the solubility of REEs in a mixture of antisolvent and water is a key requirement for the development of this method.

In this project, a separation method based on antisolvent crystallization will be developed, for the purpose of recycling REE-containing waste sources. The project will focus on the solubility studies, of the REEs and of impurities like Co and Fe, necessary for developing antisolvent crystallization as a separation technique for REEs. Thus, the project contributes to the solution of global energy problems and offers the opportunity to work with a powerful, novel separation technique. The project is supervised by Dr:s Meher Sanku, Michael Svärd and Kerstin Forsberg, and carried out in collaboration with both industrial and academic partners. Funded by Formas.

For questions or to express your interest, please contact:

Meher Sanku (mgsanku@kth.se) or Michael Svärd (micsva@kth.se)

References

[1] “The Growing Role of Minerals and Metals for a Low Carbon Future - World bank,” 2017. [Online]. Available: http://documents1.worldbank.org/curated/en/207371500386458722/pdf/117581-WP-P159838-PUBLIC-ClimateSmartMiningJuly.pdf.