Unconventional critical mineral solutions
Revisiting yesterday's waste for tomorrow's technology metals Critical Minerals Alliances - September 2021
Last updated 9/16/2021 at 9:24am
From electric vehicles plugged into renewable energy to smartphones connected to 5G networks, new technologies take advantage of the special properties of a suite of critical minerals and metals that are often rare and in short supply.
In addition to the rare earths, cobalt, lithium, and other technology metals that capture headline attention, this list includes even more obscure mined materials such as gallium, germanium, scandium, and tellurium.
While scarce, these critical elements are often found alongside more common minerals and metals such as aluminum, coal, copper, and zinc.
Recent work by government, academia, and innovative companies has shown that sifting through the ash left behind from more than a century of powering America with coal and digging into the tailings of yesterday's mines could offer unconventional supplies of these equally unconventional metals needed to build tomorrow's technologies.
U.S. Secretary of Energy Jennifer Granholm understands the need for these critical metals, and her department is investing in companies and universities at the leading edge of recovering these technology metals from unconventional sources.
"America is in a race against economic competitors like China to own the EV market – and the supply chains for critical materials like lithium and cobalt will determine whether we win or lose," she said. "If we want to achieve a 100% carbon-free economy by 2050, we have to create our own supply of these materials, including alternatives here at home in America."
American coal ash resources
A compelling source for the rare earths needed for EV motors, wind turbines, and an array of high-tech digital devices is the ash left behind by more than a century of burning coal to generate electricity in the United States.
Not quite as uncommon as their name suggests, rare earths are often found in the coal that has been burned to generate electricity in America for decades. While the coal itself typically does not have high enough REE concentrations to recover economically, the burning of this fuel works like a concentrator that leaves behind higher grades of this suite of critical minerals in the ash.
"Coal ash is rich in rare earth elements, as rich as some of the ore deposits," said Linda Wang, a professor of chemical engineering at Purdue University. "The United States produces about 129 million tons of coal ash every year."
While this annual production of ash is expected to wane as America transitions to lower-carbon energy sources, more than a century of coal-fired electrical generation has created billions of tons of this REE-enriched waste product.
American Resources Corp. recently acquired exclusive rights to potentially game-changing rare earth and critical elements separation and purification technologies developed in Wang's lab at Purdue.
Joe Pekny, a professor of chemical engineering at Purdue, believes these processes developed by Wang offer a sustainable and economical path for the U.S. to become less dependent on imports for rare earths.
"Linda's method replaces a very inefficient process and replaces it with an earth-friendly, safe extraction process," he said.
Over the past five years, American Resources has accumulated more than $370 million worth of coal assets and related infrastructure, primarily in Kentucky, that could provide domestic sources of ash and other materials enriched with rare earths and other critical minerals that could be recovered with this process.
American Rare Earth LLC, a subsidiary of American Resources, plans to use the exclusive patents and technologies developed at Purdue to advance environmentally sound rare earths and critical minerals supply chains in the U.S.
"We're excited about partnering with American Rare Earth and American Resources on the implementation of our research," said Wang. "We look forward to working with their team on the design of a pilot production facility and an eventual full-scale production plant."
Critical coal clays
Ash left behind at power plants is not the only coal-related resource rich in rare earths.
Materia USA, a company formed for the very purpose of producing critical minerals from unconventional sources, has found that layers of clay underlying Pennsylvania coal seams are particularly enriched in rare earths and other critical minerals such as gallium and lithium.
With funding from DOE's National Energy Technology Laboratory, Materia has been advancing conceptual designs for a facility to recover critical minerals from these alternative sources uncovered by previous coal mining.
In addition to a potential new domestic source of the rare earths that America is almost completely dependent on China for, this project has the potential to provide work for Pennsylvania coal miners that are looking for new jobs as the U.S. transitions to lower carbon-emitting energy sources, as well as reclaim legacy coal mines.
"I was proud to support Materia-USA's application to recover rare earth elements and critical minerals from Pennsylvania's coal fields," said Rep. Guy Reschenthaler, R-Pennsylvania. "By working to establish a reliable domestic supply of these resources through projects like this, we can support good-paying jobs and economic opportunities in our communities, eliminate significant sources of pollution such as acid mine drainage, and end our nation's dependence on China and other foreign countries."
With conceptual studies showing promise, earlier this year Materia launched the second phase of the DOE-supported effort to recover critical minerals from coal under-clays.
In partnership with Penn State University, Materia is developing a feasibility study that details the economic benefits of its conceptual design. This study will also provide information on the environmental impact of the design through a life cycle analysis of greenhouse gas emissions.
"This feasibility study is another critical step in our work towards a sustainable future for the coal industry in a post-fossil fuel age," said Materia USA CEO Rabbi Yechezkel "Zeke" Moskowitz. "The fact that the Biden administration is taking an active role in our work means that the administration understands that rare earth and critical mineral extraction via reclamation work is not only an option but also economically viable – it's truly exciting."
Transforming coal country
The Biden administration's interest in transforming coal country into new energy regions is further evidenced by the $19 million DOE awarded earlier this year to 13 projects in traditionally fossil fuel-producing communities from Appalachia to Alaska.
"The very same fossil fuel communities that have powered our nation for decades can be at the forefront of the clean energy economy by producing the critical minerals needed to build electric vehicles, wind turbines, and so much more," said Secretary Granholm. "By building clean energy products here at home, we're securing the supply chain for the innovative solutions needed to reach net-zero carbon emissions by 2050 – all while creating good-paying jobs in all parts of America."
Roughly $5.4 million of this funding went to universities researching techniques to extract and process the rare earth elements and critical minerals from coal, coal sediments, coal ash, coal mining waste, acid mine drainage, and other unconventional resources in the Appalachia coal mining region of eastern U.S.
Similar grants were awarded to universities in coal-producing regions across the U.S. – from Alabama to Montana, and even Alaska.
Sen. Joe Manchin, chairman of the Senate Energy and Natural Resources Committee, says these funds are helping to spur the economy of coal-producing areas like his home state of West Virginia while also creating innovative solutions for a cleaner energy future.
"The coal industry downturn has left many West Virginians without the good-paying jobs they once relied on, which has negatively impacted our state economy. I am pleased that DOE is investing in West Virginia University's Mid-Appalachian Carbon Ore, Rare Earth and Critical Minerals Initiative, which will work to expand and transition coal resources to other high-value products," said the Mountain State Democrat.
Liability to liquid asset
Penn State, which is among the universities to receive the coal country grants from DOE, has also developed a process that could transform acid mine drainage from an environmental liability that is costly to a liquid asset that produces rare earths and other valuable minerals.
"We are currently incurring costs just to treat the water, and in many cases, we are not even collecting all these minerals," said Sarma Pisupati, professor of energy and mineral engineering at Penn State. "Now we are able to turn what had been considered a waste product into a valuable resource."
Acid mine drainage occurs when mining exposes sulfide-containing minerals, which react to air and water to form sulfuric acid. While this process sometimes occurs naturally, it can be more pronounced after mining.
"Acid mine drainage has been a significant environmental concern for many decades," said Mohammad Rezaee, assistant professor of mining engineering in the College of Earth and Mineral Sciences at Penn State.
By their very nature, these acidic waters are laden with metals.
Rezaee and his colleagues have developed a two-stage treatment process that recovers more of the metals out of acid mine drainage, while using less chemicals than previous solutions to this environmental hazard.
"This research shows we can modify existing treatment processes in a way that not only addresses environmental concerns, but at the same time recovers valuable elements and actually decreases the cost of treatment," Rezaee added.
The traditional process Penn State is building on involves collecting acid mine drainage in ponds and using chemicals to neutralize the pH, which causes the dissolved metals to solidify and drop out of the water. The Penn State researchers said that about 70% of rare earths could be extracted as a sludge using this process.
By first injecting carbon dioxide into acid mine drainage, a process that produces a carbon mineral called carbonatites, the Penn State team found it could recover even more metals with less pH neutralizing. This is because rare earths and other metals latch onto the carbonatites and more readily settle out of the water.
With the CO2 technique, Penn State scientists were able to recover 90% of the contained aluminum at a pH of 5, which is still mildly acidic, and 85% of rare earths at pH 7, which is neutral.
To get the same recoveries with other methods would require raising the pH even higher, which translates to more chemicals and costs.
"With a simple modification of existing treatment processes, industry could use less chemicals and get more value out of AMD waste," Rezaee said. "This is the beauty of this research."
Phoenix arises from tailings
The tailings left behind from mining aluminum, copper, gold, silver, zinc, and other more common metals offer another potential unconventional source of critical minerals while also chalking up a win for the environment.
Mining is an energy-intensive industrial process that typically involves crushing massive quantities of rock dug from the earth into a sand- or silt-like consistency to extract the minerals and metals needed by society. The leftovers from this process, called tailings, are typically stored in a facility until the mine closes and then covered up and contoured during the mine reclamation process.
Critical minerals such as cobalt, germanium, rare earths, tellurium, and titanium are thrown out with the tailings. In the past, the market was not large enough to justify extracting most of these minor elements, or the cost of the extra steps was too great.
With modern solar panels, EVs, lithium-ion batteries, and other modern technologies creating new demand for these metals, companies are beginning to look at tailing storage facilities as critical mineral ore deposits – Phoenix Tailings is one such company.
"We want to get to the point where there is no such thing as 'waste' and there is only material waiting to be processed into new products," Mike Martin, an engineer, material scientist, and co-founder of Phoenix Tailings, told Jaclyn Severance at the University of Connecticut. "To put it another way, we want to show people tailings ponds are a huge untapped opportunity."
One of the advantages of tapping this opportunity is most of the hard work has already been done – the rock has been mined and crushed.
With these energy-intensive and costly steps out of the way, a company like Phoenix only has to focus on the most efficient and sustainable methods for recovering whatever critical minerals might be in the cast-off material.
Using three separate processes – hydrometallurgy, solvometallurgy, and electrometallurgy – Phoenix has the ability to tailor its extraction systems to the tailings and minerals being targeted.
Much like extracting critical minerals from coal ash and acid mine drainage, the re-mining of tailings offers the added benefit of leveraging liabilities at already industrialized sites to produce the unconventional metals needed to build a cleaner and greener future.