Rare earth elements and yttrium in Oligocene coals of Makum coalfield, Assam (North-east India)

Rare earth elements and yttrium have attracted considerable attention in recent decade due to their crucial roles in modern technology, particularly in the production of electronics, magnets, and batteries. These elements are of particular importance for developed and developing countries, as they play a significant role in clean energy as well as their growth and development. The concentration, distribution, and modes of occurrence of rare earth elements and yttrium in coal from the Oligocene formation in the Makum coalfield were investigated in this study. The study found that the coal samples from the Makum coalfield have a low ash and high sulfur content. Furthermore, the study revealed that the total concentration of rare earth elements and yttrium in the coal samples ranged from 1.48 to 77.61 ppm, with an average of 27.49 ppm. Based on the analysis of the coal samples. Average concentration of rare earth elements and yttrium in the Makum coalfield, as observed in this study, is lower than the concentration found in world average coals. it was observed that the 60ft coal seam had a higher average LREE/HREE ratio compared to the 20ft and 8ft coal seams. This indicates variations in the distribution patterns of rare earth elements and yttrium within the different coal seams. Coals from this region show a positive europium anomaly and have a weak negative cerium anomaly, indicating a significant marine influence during their formation. The sequential leaching used in this study provided valuable insights into the modes of occurrence of rare earth elements and yttrium in the coal samples from the Makum coalfield. Having a comprehensive understanding of the proportions of rare earth elements and yttrium in different forms, such as organic, silicate-aluminate, acid soluble, ion-exchangeable, and water soluble, is crucial for the development of effective methods and technologies for the extraction of these critical elements from coal.