Enhancing the Quantification of Critical Elements in WTE and Coal Ash via Alkaline Fusion: Superiority of Lithium Metaborate (LiBO₂)

Ashes generated from coal combustion, as well as waste incineration, can be a potential source of critical elements necessary for the ongoing transition to electrification and greener energy technologies. For the quantification of critical elements, traditional methods such as acid digestion are time-intensive and can fail to dissolve critical elements in refractory minerals. One potential solution is to adopt alkaline fusion for faster, total digestion. However, the role of flux choice and the subsequent digestion efficiency (DE) is unknown. Here, we report a systematic investigation on the feasibility of alkaline fusion with lithium metaborate (LiBO2) and lithium tetraborate (Li2B4O7) as fluxes for the digestion of two standard reference materials (BCR 176R and SRM 1633c). Our findings suggest that LiBO2 yields higher DE values than Li2B4O7 for several critical REEs and volatiles, such as Pb and Cd. Specifically, for REEs in SRM 1633c, the DE values with LiBO2 are, on average, ∼16% higher than those with Li2B4O7. Similarly, for Pb and Cd in BCR 176R, the DE values with LiBO2 are ∼20% higher than with Li2B4O7. These results suggest that LiBO2 is a superior flux for rapid ash digestion.