Rivalia Chemical Co.,
Keywords: rare earth elements, coal fly ash, resource recovery, hydrometallurgy
Summary:Recent work found that valuable rare-earth elements (REEs) can be recovered from coal fly ash (CFA), a waste product from coal combustion, using the ionic liquid (IL) betainium bis(trifluoromethylsulfonyl)imide ([Hbet][Tf₂N]). Based on its unique thermomorphic properties, this IL/water mixture preferentially extracts REEs from CFA solids and shows strong separation of REEs from bulk elements (Si, Al, Ca, and Fe). To better understand the behaviors of various metals in CFAs, this study investigated 18 additional elements (and confirmed good selectivity of this new process, yielding low leaching of bulk elements, minimal leaching of trace elements, and minimal to no leaching of thorium and uranium. The study also identified several operational optimizations in pH, temperature, and duration, which confirmed that only moderate conditions are required for successful leaching. The process is compared with several other methods of CFA solid extraction and leachate separation for REE recovery to place the new method in context with existing literature. Finally, several process sustainability advancements are identified and currently under exploration, including beneficial uses of the residual solids.