Assessment of Critical Minerals including Rare Earth Elements in Coal
Introduction
Microbeam Technologies, Inc (MTI) has developed analytical and modeling tools to determine the abundance and associations of rare earth elements (REE) and selected critical minerals (CM) in coal. These tools are particularly useful in helping clients to identify coal feedstocks with high levels of REE-CM.
Background
Figure 1. Rare earth elements highlighted in the periodic table.
Rare earth elements (REEs) are a group of elements with atomic numbers from 57-71. Besides the lanthanide series, yttrium (Y) and scandium (Sc) are often included in this group because of their similar properties (Figure 1). Their unique properties make REEs a crucial material for advancing modern technology and meeting current energy demands.
REEs, as well as other critical minerals (CM) such as germanium (Ge) and gallium (Ga), are becoming scarce and expensive as their resources in conventional ores are exhausted. Thus, there is a need for exploring new sources of these critical elements. One promising source is coal and coal fly ash. The concentrations of REE-CM in some coals are comparable to, or even higher than, those found in conventional ores.
Case Study: Understanding REE Associations in Coal
Microbeam uses a combination of morphological analysis and long-form computer-controlled scanning electron microscopy (CCSEM) analysis to determine the associations of trace elements such as REE and CM in fuel samples. Extended point dwell times and high X-ray counts were used to detect low levels of trace elements in mineral particles in samples of lignite coal. Advanced visualization techniques including ternary diagrams (Figure 2), distribution plots (Figure 3), and correlation matrices (Figure 4) were used to determine the distribution of different elements in the coals and their associations.
REEs were found to be present as REE phosphates.
Ternary diagrams suggest that REE-CM may be associated with kaolinite (1:1 Si/Al ratio).
High-REE particles were associated with high Al and Si, moderately high P, and low-moderate Fe.
Ge and Ga were associated with each other and with transition metals such as Fe, Cu and Zn based on correlation analysis.
Lanthanum (La) and Neodymium (Nd) showed a strong correlation with heavy transition metals and Ge/Ga.
Figure 2. Ternary diagram showing Si vs. Al vs. (La, Ce, Ga, Ge).
Figure 3. Distribution of elements in mineral particles from a lignite coal sample.
Summary
Using our expertise in REE-CM, MTI has pioneered analytical and modeling tools to determine REE-CM associations in coal. This allows our clients to accurately identify high-REE-CM coal feedstocks, advance American investment in domestic resources, and increase the availability of these elements required for commercial and national defense products.
Figure 4. Correlation matrix between elements for mineral particles in a lignite coal sample.