Everything in the earth's crust is present in coal, and combustion by-products, including coal ashes, have long been of interest for potential recovery of valuable metals and trace elements. The National Energy Technology Laboratory's Research and Innovation Center recently initiated research for the recovery of rare earths from abundant domestic coal and coal by-products. The coal burning power plants are a domestic treasure chest for the trace elements, including economically important ones like the rare earths, and ash can be considered a low-grade ore for valuable metals. Most of the common inorganic lanthanide compounds, such as the phosphates found in coal, have very high melting, boiling, and thermal decomposition temperatures, allowing them to concentrate in combustion by-products such as bottom ash and fly ash. Approximately seven hundred eighty six million tons of coal were mined in the United States in 2017, with most burned to generate electricity. With an average concentration of 62 ppm, it is estimated that 45,000 tons of lanthanide elements are present within the coals burned each year in US power plants. The partitioning of the rare earths across US coal power stations is being investigated through a collaborative research effort between the Electric Power Research Institute and the Department of Energy. Early results suggest the lanthanides mainly partition to the bottom ash and the fly ash. A brief overview of recent results for the determination and recovery of rare earths in various solid samples obtained across different points within coal-burning plants will be presented, and future research will be discussed. This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.
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