Rare earth elements are the 14 lanthanides on the periodic table, plus yttrium and scandium. These elements play a critical role in modern-day technologies such as liquid-crystal displays, GPS systems, and fiber optic cables. A majority of the mining of these elements is from China; however, due to decreasing reserves a need for alternative processes for extracting and processing rare earth elements (REEs) is becoming increasingly important. Special focus has been placed upon the identification of REEs within coal refuse, but the phase designation and speciation is not fully understood. This investigation focuses on the characterization, speciation, and morphology of REEs within fine and coarse coal refuse.
During this study, physical and chemical characterization was conducted on coal refuse samples to understand characteristics, which influence REE phase designation. Experimental methods were chosen to specifically evaluate REE content and speciation across four key characteristics: size distribution, density, seam location, and thermal decomposition. Characterization of the refuse material was conducted in two campaigns: (1) an exploratory campaign, which focused on size distribution, and physical imaging of REEs within fine refuse, and (2) a detailed campaign, which utilized sequential chemical extraction methods alongside calcination to understand the phases in which REEs are present in coarse refuse.
The results show that REEs within fine coal refuse are smaller than ten microns and found with phosphorus. In general, as size decreased REE content increased, likely due to increased clay content. Further conclusion could not be drawn from simple microscopic analysis. Consequently, detailed chemical characterization was conducted to fully understand REE speciation. The tests showed that a majority of REEs within coarse refuse were within insoluble species. A calcination treatment was found to greatly increase the recovery of REEs from the metal oxide fraction, thus increasing the overall soluble species contained within the coarse refuse material. / Master of Science / Due to increasing global demand and limited reserves, alternative sources for rare earth elements (REEs) have become an increasingly important research topic. REEs are a vital component of many modern technologies, including GPS systems, fiber optic cables, and LCD screens. Current mining of REEs is primarily from Chinese reserves which are becoming increasing depleted and are not strictly regulated for environmental impact. Due to these challenges, other resources of REEs are of increasing importance. Prior research has found coal and associated byproducts to have concentrations of REEs that could be economically exploited, reducing the rate of depletion of REE resources worldwide. To develop more efficient and cost-effective processing methods, fundamental information on the mineral composition of REE-bearing materials is needed. With this information, engineers can develop better processes that can specifically target REE-containing minerals while maximizing economic and environmental outcomes. This research seeks to overcome this knowledge gap through advanced material characterization and well-controlled laboratory process testing of coal refuse. The results show that REEs typically congregate in specific material fractions (e.g. fine size, moderate density), and these materials can be readily transformed through simple heat treatment. This transformation greatly improves the processability and provides a pathway for the economic recovery of REEs from coal wastes. The further development and deployment of these technologies can have societal benefits such as: more jobs, reduced reliance on foreign sources, and environmental cleanup of current coal waste deposits.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/112940 |
| Date | 24 June 2021 |
| Creators | Russell, Alexandra Dawn |
| Contributors | Mining Engineering, Noble, Christopher Aaron, Zhang, Wencai, Keles, Serhat |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Detected Language | English |
| Type | Thesis |
| Format | ETD, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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