Partitioning Behavior of Lithium and Rare Earth Elements During Coal Preparation and Their Differences in Mode of Occurrence

Coal preparation technology is an important and widely useful way to achieve clean utilization of coal. Furthermore, it has a huge effect on the recovery of critical elements in coal, including lithium (Li) and rare earth elements (lanthanides and yttrium, REY). In this study, the migration of Li and REY during coal preparation was investigated from industrial practice and laboratory. After industrial separation, Li is significantly enriched in the coal gangue with high ash content, while REY mainly migrates to fine coal, clean coal, and coal slime. Results of screening and float-and-sink from the laboratory show that Li is enriched in the +3 mm particle size fraction and the +2.0 g/cm³ density fraction, while REY is greatly enriched in the −0.5 mm particle size fractions and the −1.8 g/cm³ density fractions. Modes of occurrence of Li and REY greatly affect their migration routes during separation. Results of sequential chemical extraction and oxidation decomposition reveal that more REY occurs in organic matter-bound form compared to Li. REY-bearing minerals (monazite and bastnaesite) in feed coal were found by SEM-EDS, but they are embedded in organic matter. In addition, oxidation decomposition experiments confirmed that REY can directly bind to organic matter in coal, especially heavy REY. These findings demonstrate that REY is closely associated with the organic fractions, while the majority of Li occurs in inorganic minerals for these coals. This research could give support to clarify the Li and REY migration during coal preparation and their extraction in the future.