Rare Earth Element Speciation in Miocene Brown Coals from the Sergeevskoe Deposit (Priamurie, Far East)

The concentration, speciation, and localization of rare earth elements in Miocene brown coals from the Sergeevskoe deposit (Amur oblast) have been studied. The total rare earth element content of the test coals (97.43 mg/kg) exceeds the clarke value by a factor of 1.5; the amount of light lanthanides (74.57 mg/kg) prevails over that of heavy ones (7.68 mg/kg). The main concentrators of lanthanides in Miocene brown coals are humic acids. The amount of rare earth elements in water-soluble, ion-exchange, silicate, and disulfide forms does not exceed 5% of the total content with the exception of scandium, 22% of which is associated with silicate minerals such as clays.