SPECIATION OF RARE EARTH ELEMENTS IN SPRINGFIELD, HERRIN, AND BAKER COAL FORMATIONS IN SOUTHERN PARTS OF THE ILLINOIS BASIN

The Eastern Interior (Illinois) Basin is a cratonic basin that extends across most of Illinois, the western part of Kentucky and the southwestern part of Indiana. Although he Pennsylvanian part of the basin includes more than 50 named coal beds only three, the Springfield, Herrin and Baker, are currently mined. This study was designed to examine the occurrence and abundance of rare earth elements (REEs) in these coal beds.

Intact column samples of the Springfield, Herrin, and Baker coal beds, and associated rocks, were collected from 24 locations in the southern part of the Eastern Interior (Illinois) Basin. The sampling area includes the western Kentucky coal field, southern Illinois, and southwest Indiana. The columns, obtained from exploration drill cores and active coal mines, were further subdivided into numerous individual samples to assess any vertical and lateral trends in REE abundance that might be present in the study area. To assess the variation of REEs with ash yield, several float sink and flotation separations were performed at different density fractions. Moreover, individual samples from six coal preparation plants and some geological phenomena were collected and studied. In total, over 600 samples were retrieved and prepared in this study and were analyzed for REEs. Results indicate the highest total REE concentrations to occur in the Baker coal in Kentucky and a part of the Springfield coal in Indiana. Results also indicate that most of the REEs are associated with the inorganic (ash) fraction of the coal, and that coal-associated rocks generally have the highest REE concentrations. Although REE contents on a whole material (coal and rock) basis increases with the ash yield, the heavy-to-light REE ratio decreases when determined on an ash basis. In addition, while the fractionation of individual REEs in high-ash samples always follows the crustal pattern, most of the cleaner coal samples behave differently. This suggests various mechanisms of chelation and deposition events during the evolution of the coal.