Author ORCID Identifier

Year of Publication


Degree Name

Doctor of Philosophy (PhD)

Document Type

Doctoral Dissertation




Mining Engineering

First Advisor

Dr. John G. Groppo


The purpose of this study is to characterize the distribution and occurrence of rare earth elements (REEs) in the coal and coal-related material from the Illinois Basin. For characterizing the distribution of REEs, 17 core samples were investigated from various parts in the basin. Also, several individual samples from coal preparation plants and isolated geological occurrences were included in the study. In result, the average REE concentrations were calculated on a bed-to-bed basis, although the distribution of REEs in the coal beds was found laterally and vertically heterogeneous. A number of trends were found that describe the variations. Most importantly, it was found that where samples of the Springfield and Herrin coal beds are away from syndepositional paleochannels, they have a higher ratio of heavy to light REEs; whereas nearer to contemporaneous channels, the ratio is lower. However, the total REE concentration was found to be higher near the channels. A similar trend was not observed in the Baker coal bed.

Samples representing the Springfield and Herrin coal beds at places near to, and away from, the syndepositional paleochannels were prepared. The samples were subjected to leaching studies, both in raw and roasted forms. It was found that the near-channel samples are more desirable for REE leaching. Leaching was also done on a coal refuse sample originated from the Baker coal bed. The sample contained the highest concentration of REEs among the coal preparation plant samples. Approximately 55% of the REE concentration was released in the test—the highest recovery in the leaching studies. The Anna shale was found to contain the highest concentration of REEs between the roof rocks. Leaching an Anna shale sample resulted in a leachate with the same level of REEs as the Baker refuse, but with a higher concentration of heavy REEs. Another leachate with a high level of heavy REEs was produced through leaching of a clean coal product of a coal preparation plant. The concentration of Ce in the leachate was below detection limits and other light REEs were at a minimum.

A sample representing the Baker coal bed was investigated by a chemical sequential extraction study. The study showed that most of the REEs can only get mobilized by complete digestion of the sample. The fraction the REEs that were mobilized were mostly heavy REEs, which increased in the mineral matter of the low-ash coals. Despite the obtained information, sequential extraction was found inefficient for assessing REE-mineral associations due to the highly interlocked minerals. A novel characterization method was developed for investigating the REE-mineral associations. The method is based on creating a mineralogical array by dividing the sample into several subsamples and investigating the way the REEs vary respectively to the mineralogical array. The method was applied to the same Baker coal sample and showed that 65% of the sample’s REE content is associated with clay minerals, and 25% with calcite.

Digital Object Identifier (DOI)