Study: Appalachian coal ash high in coveted rare earth elements
Energy Daily, The
Holly, Chris
In what could lead to a potential gold mine for U.S. electric utilities facing political and financial headaches over coal ash disposal, researchers for the first time have quantified the amount of rare earth elements that can be recovered in coal fly ash using common industrial techniques, with ash from Appalachian coal having the highest percentage of the metals coveted for a raft of clean energy and high-tech applications.
However, rare earths are more readily extracted from ash derived from Powder River Basin coal using current industrial processing technology, according to the research, which was published online Thursday in the journal Environmental Science and Technology by a team from Duke University and the University of Kentucky
The study measured the amount of rare earth elements in samples of ash from every major coal source in the United States, and determined how much of the elements could be extracted using a common industrial technique.
The team found that ash from coal mined in Appalachia contains the most rare earth elements, which are a group of 15 chemically similar metals, including gallium, germanium, indium, scandium, tellurium and yttrium. Their unique properties make them essential in the manufacture of wind turbines, solar panels and electric vehicle components, including batteries, and in guidance and precision instrument systems for the defense and aerospace industries, as well other high-tech industries.
Currently China controls about 95 percent of global rare earth element production, and holds at least half the world’s reserves of these metals, according to U.S. government figures. China has held those strategic reserves tightly, but in January 2015 was forced drop a long-standing export limit on rare earth elements after losing a trade case at the World Trade Organization brought by the United States and a host of other industrial nations.
Finding low-cost methods for extracting the commodities from coal ash would give the United States a valuable new source of rare earth elements--as well as provide an unexpected revenue stream for U.S. utilities struggling to manage the roughly 100 million metric tons of coal fly ash produced each year. Much of the ash is now stored in aging storage ponds—many of which have been documented as leaking toxic metals such as arsenic, iron, lead and selenium into groundwater and surface waters.
That coal and coal fly ash contain rare earth metals has been understood for decades but is now being pursued by the Energy Department because demand for those exotic materials is fast outstripping supply in a host of booming high-tech and clean energy sectors. At the same time, experts believe improved processes for extracting rare earths from certain coals and fly ash may be cost-competitive with large-scale mining operations for those metals.
DOE’s National Energy Technology Laboratory (NETL) has launched an initiative to better understand the potential to extract those resources. The December 2015 budget agreement for fiscal year 2016 gave NETL $15 million to pursue technologies for the extraction and recovery of rare earth elements and minerals from U.S. coal and coal byproduct sources.
The Duke and University of Kentucky team constitutes the first comprehensive study to calculate the amounts of rare earth metals in different kinds of U.S. coal ash.
The researchers got their results by taking coal ash samples from power plants mostly located in the Midwest that burn coal sourced from all over the country, including the three largest sources: the Appalachian Mountains, southern and western Illinois, and the Powder River Basin in Wyoming and Montana.
They then tested extraction of rare earth elements from ash using hydrochloric acid, which is much stronger and more efficient than typical industrial extraction methods but is too hazardous for use on a large scale.
They found that ash from Appalachian coal has the highest amount of rare earth elements at 591 parts per million (ppm), while ash from Illinois and the Powder River Basin contains 403 ppm and 337 ppm, respectively.
The team then used a common industrial extraction technique employing nitric acid to see how much rare earth elements could be recovered. Appalachian ash had the lowest extraction percentages, while Powder River Basin ash had the highest. The study said this might be because the rare earth elements in the Appalachian ash are encapsulated within a glassy matrix of aluminum silicates, which nitric acid does not dissolve well.
“One reason to pick coal ash from the Appalachian Mountains would be for its high rare earth element content, but you’d have to use a recovery method other than nitric acid,” said Hsu-Kim, an associate professor of civil and environmental engineering at Duke who also holds an appointment in Duke’s Nicholas School of the Environment.
“For any future venture to begin an extraction program, the recovery method will need to be tailored to the specific chemistry of the coal ash being used.”
The researchers tried “roasting” the ash with an alkali agent before dissolving it with nitric acid, and while this process hadn’t been optimized for recovery purposes, the tests showed a marked improvement in extraction efficiency, they said.
“The reagents we used are probably too expensive to use on an industrial scale, but there are many similar chemicals,” Hsu-Kim said. “The trick will be exploring our options and developing technologies to drive the costs down. That way we can tap into this vast resource that is currently just sitting around in disposal ponds.”
http://www.theenergydaily.com/publi...igh-in-coveted-rare-earth-elements_14114.html
Energy Daily, The
Holly, Chris
In what could lead to a potential gold mine for U.S. electric utilities facing political and financial headaches over coal ash disposal, researchers for the first time have quantified the amount of rare earth elements that can be recovered in coal fly ash using common industrial techniques, with ash from Appalachian coal having the highest percentage of the metals coveted for a raft of clean energy and high-tech applications.
However, rare earths are more readily extracted from ash derived from Powder River Basin coal using current industrial processing technology, according to the research, which was published online Thursday in the journal Environmental Science and Technology by a team from Duke University and the University of Kentucky
The study measured the amount of rare earth elements in samples of ash from every major coal source in the United States, and determined how much of the elements could be extracted using a common industrial technique.
The team found that ash from coal mined in Appalachia contains the most rare earth elements, which are a group of 15 chemically similar metals, including gallium, germanium, indium, scandium, tellurium and yttrium. Their unique properties make them essential in the manufacture of wind turbines, solar panels and electric vehicle components, including batteries, and in guidance and precision instrument systems for the defense and aerospace industries, as well other high-tech industries.
Currently China controls about 95 percent of global rare earth element production, and holds at least half the world’s reserves of these metals, according to U.S. government figures. China has held those strategic reserves tightly, but in January 2015 was forced drop a long-standing export limit on rare earth elements after losing a trade case at the World Trade Organization brought by the United States and a host of other industrial nations.
Finding low-cost methods for extracting the commodities from coal ash would give the United States a valuable new source of rare earth elements--as well as provide an unexpected revenue stream for U.S. utilities struggling to manage the roughly 100 million metric tons of coal fly ash produced each year. Much of the ash is now stored in aging storage ponds—many of which have been documented as leaking toxic metals such as arsenic, iron, lead and selenium into groundwater and surface waters.
That coal and coal fly ash contain rare earth metals has been understood for decades but is now being pursued by the Energy Department because demand for those exotic materials is fast outstripping supply in a host of booming high-tech and clean energy sectors. At the same time, experts believe improved processes for extracting rare earths from certain coals and fly ash may be cost-competitive with large-scale mining operations for those metals.
DOE’s National Energy Technology Laboratory (NETL) has launched an initiative to better understand the potential to extract those resources. The December 2015 budget agreement for fiscal year 2016 gave NETL $15 million to pursue technologies for the extraction and recovery of rare earth elements and minerals from U.S. coal and coal byproduct sources.
The Duke and University of Kentucky team constitutes the first comprehensive study to calculate the amounts of rare earth metals in different kinds of U.S. coal ash.
The researchers got their results by taking coal ash samples from power plants mostly located in the Midwest that burn coal sourced from all over the country, including the three largest sources: the Appalachian Mountains, southern and western Illinois, and the Powder River Basin in Wyoming and Montana.
They then tested extraction of rare earth elements from ash using hydrochloric acid, which is much stronger and more efficient than typical industrial extraction methods but is too hazardous for use on a large scale.
They found that ash from Appalachian coal has the highest amount of rare earth elements at 591 parts per million (ppm), while ash from Illinois and the Powder River Basin contains 403 ppm and 337 ppm, respectively.
The team then used a common industrial extraction technique employing nitric acid to see how much rare earth elements could be recovered. Appalachian ash had the lowest extraction percentages, while Powder River Basin ash had the highest. The study said this might be because the rare earth elements in the Appalachian ash are encapsulated within a glassy matrix of aluminum silicates, which nitric acid does not dissolve well.
“One reason to pick coal ash from the Appalachian Mountains would be for its high rare earth element content, but you’d have to use a recovery method other than nitric acid,” said Hsu-Kim, an associate professor of civil and environmental engineering at Duke who also holds an appointment in Duke’s Nicholas School of the Environment.
“For any future venture to begin an extraction program, the recovery method will need to be tailored to the specific chemistry of the coal ash being used.”
The researchers tried “roasting” the ash with an alkali agent before dissolving it with nitric acid, and while this process hadn’t been optimized for recovery purposes, the tests showed a marked improvement in extraction efficiency, they said.
“The reagents we used are probably too expensive to use on an industrial scale, but there are many similar chemicals,” Hsu-Kim said. “The trick will be exploring our options and developing technologies to drive the costs down. That way we can tap into this vast resource that is currently just sitting around in disposal ponds.”
http://www.theenergydaily.com/publi...igh-in-coveted-rare-earth-elements_14114.html
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