Extraction of Rare Earth Elements from Brown Coals of the Sergeevskoe Deposit (Amur Region) According to Experimental Data

A series of experiments on the leaching of rare earth elements (REEs) from Miocene brown coals of the Sergeevskoe deposit with water and alkaline and acid solutions was carried out. Using a set of methods (ICP MS, XRD analysis, heavy concentrate analysis, SEM EDS, and IR spectrometry), it was revealed that acid leaching was the most effective: 72–99% of REEs was extracted with a 1 M solution of hydrochloric acid in 24–48 h. This fact indicates that most of the REEs in the brown coals of the Sergeevskoe deposit were associated with the organic matrix in the form of complexes with the carboxyl groups of humic and fulvic acids. The high percentage of REE extraction indicates the possibility of using coals from the Sergeevskoe deposit as an easily enriched source of REEs.