SusChEM: Collaborative Research: Coal Ash Wastes as a Resource for Critical and Strategic Elements

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1510965(Hsu-Kim) & 1510861(Hower)This project aims to quantify and characterize critical elements in coal combustion residues from U.S. power plants and explore methods of extraction that could enable an alternative and more sustainable resource of high value materials, rare earth elements. Critical and strategic elements are those in which disruptions to the supply are a concern for the manufacturing of consumer products and for materials crucial to national welfare and defense. Collectively coal combustion residues represent one of the largest industrial waste streams in the country, with more than 100 million metric tons generated annually. Less than half of the total is currently used beneficially (mostly for construction, agriculture, and other sectors). This project will provide fundamental information that is necessary for the utilization of coal ash as a resource for these high value metals.The research will result in a comprehensive database of critical metals concentrations in ash from a broad array of U.S. power stations and coal sources. The results should also improve the understanding of the types of coal deposits and ashes that are enriched in these elements and the geochemical speciation of these elements in the ash. This project will systematically explore acid extraction and physical-chemical separation methods that will provide a basis for resource recovery. This project will investigate the potential for coal ash wastes to serve as an alternative resource for critical metals such as rare earth elements. Previous surveys have shown that some coal sources and their respective ash by-products are enriched in rare earth elements to levels that are similar to deposits at mining sites. Despite the intense interest in alternative rare earth elements sources, data is limited for coal and coal ash in the U.S. Specific objectives of the research are to: 1) Perform a survey of coal ash materials collected from a wide variety of coal sources and combustion conditions and develop a database that will include concentrations of rare earth elements, platinum group elements, germanium and other critical metals. The data will also include the origins and geochemical and physical properties of the ash. 2) Characterize the speciation of elements identified for resource recovery, and evaluate how they are bound in the coal ash material. 3) Evaluate how speciation, coal mineralogy and particle physical properties influences acid extraction efficiencies and explore separation methods to extract and purify critical elements from fly ash and bottom ash. Thus, this project will address a great need to diversify the supply market while also utilize a solid waste material (coal ash) for beneficial purposes. Partnerships with industry stakeholders will be leveraged to provide avenues for dissemination and feedback of this work. Educational activities will include mentorship and research opportunities for K-12 students and undergraduate students from underrepresented groups.