This new method for extracting rare earth elements (REEs) from coal fly ash (CFA) not only reduces the environmental hazards and the amount of CFA going into landfills, but it can also produce enough REEs to meet 100 years of annual consumption in the U.S. Developed by researchers at Georgia Tech, this highly efficient method selectively extracts REEs from CFA using a two-phase leaching/stripping process. Following an alkaline pretreatment, the extraction uses a water-saturated hydrophobic ionic liquid and an aqueous salt solution, with REEs selectively leached into the ionic liquid phase. The stripping process then extracts the REEs back into the aqueous phase using a mildly acidic solution. REEs and select metals can be recovered from the acid solution by precipitation and calcination, electrochemical separation, etc. The ionic liquid can be recycled and used over multiple leaching/stripping cycles with no loss in efficiency.
- Treating a waste as a resource: With REE concentrations in CFA around 500 mg/kg, processing only new CFA produced annually in the U.S could supply over three times the U.S. domestic consumption for REEs. This method is also likely applicable to other wastes.
- Meeting U.S. REE demand: REE demand is expected to increase, as rare earths are essential for the green energy transition, playing critical roles in electric vehicle motors and wind turbines.
- Simplifies the process: Unlike other extraction processes, this method does not require coal ash to be digested prior to separating the REEs—REEs are directly extracted from the coal ash and separated from other elements in a single step. Furthermore, this novel process does not require complicated mechanical or electrochemical devices.
- Reduces CFA disposal and hazards: With over 50% of CFA currently being stored in landfills where they create environmental hazards, this innovation presents an opportunity for recycling and a significant reduction in CFA waste disposal.
- Environmentally friendly: The process operates at mild conditions and significantly reduces chemical consumption and waste production. The ionic liquid can be recycled and reused over multiple leaching/stripping cycles with no loss in efficiency.
- Improves efficiency: Compared to the parent coal, the concentrations of REE in CFA are enriched due to the combustion process, making extraction more efficient.
- Extraction of REEs for multiple applications in:
- Renewable energy technologies
- Mining processes and products
- Commercial products including permanent magnets, batteries, catalysts, and more
For more information about rare earth elements, please see the following infographics from the U.S. Department of Energy: