POTENTIAL FOR CRITICAL MINERALS IN COAL MINING PRODUCTS, BYPRODUCTS, AND REJECTS, WITH SPECIAL EMPHASIS ON RARE EARTH ELEMENTS (REE)

Status Start Date End Date Locations
Active Sep 1, 2019 Jun 30, 2020 All Counties
Director: Maria Mastalerz
Other Researchers: Tracy Branam, Agnieszka Drobniak, LaBraun Hampton Phil Ames
Funding: Indiana University - Indiana Geological & Water Survey
Issue: Critical raw materials are driving some of the biggest advancements in technology and energy efficiency in the world today, and the demand for them is growing rapidly. For example, the demand for rare earth elements (REE) and yttrium (Y) has grown because they have wide applications in defense (jet engines), energy (land-based turbines, fuel cells), telecommunication and elec-tronics (hard disk drives, flat-panel displays), transportation (automotive components), and other fields (chemical catalysts, medical applications).However, as demand grows, these resources have become scarce and expensive as their availability from conventional ores is exhausted. In the last 10 years, the importance of REE has been universally recognized also because of changes in supply and demand. A limited number of sources have a monopoly on the supply of these rare earth metals. For example, China now controls approximately 85 percent of world REE production. The United States imports more than 20,000 tons of REE a year, of which more than 90 percent comes from China. These factors have initiated a global “treasure hunt” that has bolstered explo-ration for new sources, particularly for REE.
Objective: The overall objective of this project is to develop methodologies to identify potential targets for REE recov-ery from the coal value chain. To address this main objective, the more specific goals of this project are to: 1) Determine REE content in Indiana coals and identify coal beds that have highest REE concentrations. Although REE will be the critical elements of particular interest in this project, other elements such as aluminum, phosphorous, uranium, titanium, manganese, gallium, germanium, cobalt, and others will also be examined. These elements are included for bolstering our predictive tools such as principal component analysis, which will allow future explorations for REE to use less expensive methods to locate potential REE resources. 2) Evaluate the distribution of REE in various fractions generated by coal preparation plants: coarse re-fuse, fines, clean coal. The coarse refuse will be of special interest because REE concentrate in min-eral fractions. We expect that coarse refuse from coals having high REE contents as established in point 1 could be targets for REE recovery. 3) Investigate REE concentration in pulverized rejects from power plants and fly ash and bottom ash generated from Indiana coals. Because, as mentioned above, REE are dominantly associated with mineral fractions, they are concentrated in the mineral and glass phases of coal ashes. Special effort will be put into obtaining coal ash from the coals of increased REE concentrations, as established in point 1; 4) Assess REE potential in acid-mine drainage (AMD). AMD contains REEs in dissolved form, making them less expensive to process although concentrations are much lower than in raw coal material or coal combustion concentrates. Preliminary data suggest a strong correlation of REEs to aluminum and magnesium in AMD, indicative of a noncoal detrital clay association, which becomes soluble under acidic conditions. 5) Based on 1–4, identify set of geological/chemical attributes that can be used as proxies for “sweet spots” for REE. We will use selected statistical methods, for example, principal component analysis (PCA) to identify associations of REE with other elements, coal properties, geographic location, etc. These attributes will be used as a predictive tool for elevated occurrences of REE and ultimately will help to delineate best targets for future recovery.
Approach: Research materials for this study will consist of samples of coal from coal mines, various fractions from coal preparation plants, fly and bottom ash from coal-fired power plants, and water samples from AMD sites in Indiana. Being a coal-mining state for more than 200 years, Indiana has coal and coal utili-zation products that can be targeted in this study, and the PI and collaborating personnel have had long-term collaborations with coal mines and power plants. Therefore, collecting the samples in the field is an important first phase of the project. The solid samples collected will be analyzed at the Indiana Geological and Water Survey (IGWS) for elemental distribution (with a special emphasis on phos-phorous), total organic carbon (TOC), sulfur (S) content, porosimetry, and organic petrography. Analyses of REE will be performed at the Kentucky Geological Survey (KGS) in Lexington, Kentucky. Acid mine drainage water samples will be analyzed for conductivity and pH in the field, and the cations of calcium, magnesium, sodium, potassium, iron, manganese, aluminum, and the anion sulfate in the lab. Sulfate and iron will be determined at the IGWS laboratory; all other cations along with REE will be analyzed at the KGS.
Products: This study will provide not only preliminary data on REE distribution in the coal value chain, but also develop methodology to identify elevated concentration of REE for a potential recovery.
Benefits: The traditional sources of REE are alkaline- or carbonate-rich igneous rocks that crystallized at high tem-peratures deep within the Earth. These rocks are extracted in mines and ores, and the critical elements are then separated from the waste material. Because these conventional ores are scarce and are quickly becoming exhausted in response to the large demand, finding additional sources is critical; sedimentary rocks provide an attractive target for exploration. If found in sufficient quantities in “coal value chain” (coal mining products, byproducts, and rejects), extracting and utilizing critical elements would be extremely beneficial. Potential benefits include: 1) a steady supply of critical elements that would bolster national security; 2) a solution to the limitations of developing new conventional metalliferous mines, presently the main source of REE elements in the United States; and 3) identifying new domestic sources of critical minerals, making the country less dependent on foreign sup-plies and markets. However, to gain these benefits, elevated concentrations of critical elements must first be identified and the controls on their distribution need to be better understood.