Leaching of lanthanide and yttrium from a Central Appalachian coal and the ashes obtained at 550–950 °C

In this work, we investigated leaching of lanthanide and yttrium (REY) from a Central Appalachian coal and its ashes obtained at 550–950 °C with the main purpose of understanding the impact of ashing temperature on REY leachability in water, ammonium sulfate, and hydrochloric acid. It is found that the coal contains a negligible amount of water-soluble REY, less than 1% ion-exchangeable REY, and about 28% of HCl-soluble REY. Ashing leads to dramatic changes in REY leachability in both ammonium sulfate and hydrochloric acid solutions, which is believed to be related to transformation and redistribution of organically-associated REY in coal during the ashing process. Ashing temperature significantly affects REY leaching from coal ashes; higher ashing temperature results in lower REY leachability in both solutions. Clay minerals may play a significant role in changing the leachability of REY after ashing. In addition, the results also suggest that the organic matter in the coal is relatively enriched in heavy REY. During the ashing process, rare earth elements will likely transfer from raw coal to ash in three different ways. REY-bearing minerals will remain in the ash and REY chemically bound to organic matters will likely either be adsorbed by existing minerals such as clays or transform to new REY compounds. [Display omitted] •Ashing led to dramatic changes in REY leachability.•Ashing temperature had a significant impact on REY leaching from coal ashes.•The organic matter in coal was relatively enriched in heavy REY.