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![Alkali pretreatment effects on acid leaching recovery of rare earth elements from coal waste of the Western Kentucky No. 13 and Fire Clay seams](https://image.oaes.cc/020683d7-f854-43cd-b83e-bde768784680/4853.fig.1.jpg)
Figure 1. Leaching recoveries of TREEs, HREEs, and LREEs obtained from the alkali pretreatment of the (A-C) Western Kentucky No. 13 and (D-F) Fire Clay coal wastes with NaOH solutions of different concentrations. TREEs: Total rare earth elements; HREEs: heavy rare earth elements; LREEs: light rare earth elements.