fig3
![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.3.jpg)
Figure 3. The Eh-pH diagrams of (A) La-H2O, (B) Y-H2O, and (C) Sc-H2O systems at 90 °C under atmospheric pressure with 5 × 10-6 M of REEs. (Note: The REE concentration was estimated based on the REE contents of the coal wastes). REEs: Rare earth elements.