The technology of extracting rare earth from fly ash has been developed in the United States.

It is reported that researchers at the Georgia Institute of Technology in the United States have invented a simple and easy process to use ionic liquids to extract rare earths from fly ash without producing toxic substances.

In a paper published in (Environmental Science & Technology), scientists explain that ionic liquids are environmentally friendly and reusable. In particular, bis-trifluoromethylsulfonimide betaine (betainium bisimide) or [Hbet] [Tf2N]) can selectively dissolve rare earth oxides rather than other metal oxides.

Scientists say that when heated, ionic liquids can dissolve in water and become two-phase after cooling. Knowing this, they began to test whether useful elements can be effectively and selectively separated from fly ash, and whether they can effectively clean and develop a safe process without causing major pollution.

For this reason, the research team pretreated and dried fly ash with alkaline solution. Then, the fly ash in water with [Hbet] [Tf2N] is heated to form a single phase. The solution is separated after cooling. Ionic liquids can extract more than 70% of rare earth elements from fresh fly ash, while the recovery of weathered fly ash, which has been stacked in tailing ponds for many years, is even higher (97%). The last step of the process is to extract rare earth elements from ionic liquids with dilute acid.

The researchers found that increasing betaine in the leaching process can increase the extraction amount of rare earth elements.

Recyclable rare earth elements include scandium, yttrium, lanthanum, cerium, neodymium and dysprosium.

Finally, the team also experimented with the reuse of ionic liquids, removed excess acid with cold water, and found that there was no change in extraction efficiency after three rounds of leaching cleaning.

"this low-emission method can produce solutions rich in rare earths and limited impurities, and can also be used to recover precious metals from fly ash in tailings ponds," scientists said at a media conference.

This method is important for coal-producing areas such as Wyoming. At a time when demand for fossil fuels is falling, they are seeking to reinvest in local industries.