Pennsylvania’s mine waste could play an important role in the nation’s green-energy future.
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Critical minerals, including rare earth metals, are vital components of our consumer goods, national defense, and emerging green-energy technologies, but the U.S is heavily dependent on imports for an adequate supply. Penn State researchers are looking for ways to tap Pennsylvania's coal mine waste as a domestic source for these materials and reduce environmental pollution at the same time.
Think of any technology that’s part of a clean-energy economy: electric vehicles, wind turbines, solar panels. Think of the devices we depend on for work and play: smart phones, computer hard drives, flat screen monitors, rechargeable batteries. Or the systems that undergird our national defense: lasers and missile guidance, radar and sonar.
All of these depend on critical minerals.
The U.S. Geological Survey (USGS) currently designates 50 minerals as critical to the U.S. economy or its national security or both. That number includes the so-called rare-earth elements — the 15 lanthanide metals at the bottom of the periodic table plus scandium and yttrium — along with the battery metals lithium, cobalt, nickel, and manganese, as well as platinum, aluminum, and graphite, among others.
With the accelerating shift toward renewable energy, need for these materials is rising sharply. By 2030, according to Bloomberg, demand for nickel and aluminum will increase 14-fold, with graphite and lithium not far behind.
Credit: Penn State.
“The problem is we are highly dependent on other countries for both production and processing,” said Sarma Pisupati, professor of energy and mineral engineering and director of the Center for Critical Minerals at Penn State. According to USGS, the U.S. imported almost all the rare earth elements it used in 2018, with 80% coming from China. Department of Energy figures show over 50% import reliance for the remaining critical minerals, and 100% reliance for 14 of them.
This dependence was a serious concern even before the COVID pandemic revealed major gaps in U.S. supply chains, and mineral-rich Russia’s invasion of Ukraine has only exacerbated the problem. The federal government has responded with executive orders directing increased efforts to find and develop domestic sources, but new mining poses steep environmental and political costs, and primary deposits of many of these minerals are limited in the U.S.
“There is a need for secondary resources,” said Pisupati. Fortunately, he added, “Pennsylvania is rich in these resources.” Pennsylvania’s legacy as a coal-mining state, he said, could be to turn a problem into an important part of the solution.
Joseph Cotruvo Jr., associate professor of chemistry at Penn State, holds a sample of a clay containing rare earths. His lab and their collaborators have previously developed a process to use a natural protein discovered by his group to recover rare earths from these types of sources. In a recent study, the team focused on separation of rare earths and discovered a new protein that can sort one rare earth from another. Credit: Patrick Mansell / Penn State. Creative Commons
Decades of industrial mining have left behind literal mountains of waste across the Commonwealth, Pisupati explained. Mine tailings, sludge ponds and acid mine drainage are an ongoing environmental concern. But locked inside those waste streams are significant quantities of rare earth elements and other critical minerals, he said. All we have to do is figure out how to safely and economically extract them.
“We already have to treat this stuff before releasing it into the environment,” Pisupati said. “By modifying existing treatment processes, we can address multiple problems: getting the material we need for national security and remediating long-standing environmental problems at the same time. If we do it right, we can create jobs and an economic boost for the communities coal has left behind.”
Penn State’s involvement in the state’s coal-mining industry traces back to the 19th century. The University established a mining engineering degree program in 1890, training graduates in mine mechanization and safety. Its programs in mining geology, mineral processing, and extractive metallurgy have long been recognized among the best in the world.
University experts were early to recognize the untapped potential in coal byproducts. In 1952, Edward Steidle, dean of what was then the College of Mineral Industries, wrote, “By the year 2000 we will not be wasting our coal ash, in which geochemists have shown there is a notable concentration of rare elements, such as germanium and rare earths. We will be recovering these elements.”
Today, Penn State’s research and teaching capabilities span the entire supply chain for critical minerals, from resource exploration and evaluation to raw material processing to extraction and refining of metals to the manufacturing of end products like lithium-ion batteries, magnets, and advanced carbon fibers. “No other university has that breadth,” said Pisupati.
The Center for Critical Materials that he directs was formed by the College of Earth and Mineral Sciences in 2019 to take full advantage of this expertise. Its research core now includes over 25 faculty from departments across Penn State, including geosciences, energy and mineral engineering, materials science and engineering, chemistry, chemical engineering and energy business and finance. A memorandum of understanding signed in 2020 with the Colorado School of Mines further expands that reach.
Last year Penn State was tapped by the U.S. Department of Energy to lead a regional consortium to assess and catalog critical mineral resources in Pennsylvania and surrounding states, to develop strategies to recover these materials, and to identify potential gaps in the supply chain. The Consortium to Assess Northern Appalachian Resource Yield, or CANARY, is part of a national effort to ramp up domestic production.
An acid-mine sludge pond in central Pennsylvania. A byproduct of coal-mining, such sites may be rich with critical minerals. Credit: Sarma Pisupati. All Rights Reserved.
“Critical mineral recovery from coal waste and its associated environmental remediation present a tremendous opportunity for the college, university, Commonwealth and nation,” says Lee Kump, dean of the College of Earth and Mineral Sciences. “Our research will guide the development of advanced green technologies that will ensure that this new industry will be a boon for the Appalachian economy and environment and create a domestic supply chain of minerals needed for energy transition to renewables, high-tech manufacturing, and national security.”
Much like other critical minerals, “Rare earths aren’t exactly rare,” said Barb Arnold, professor of practice in mining engineering and CANARY’s managing director. “But they’re rarely found in high concentrations, so mining for them often isn’t economically viable.”
In places like Pennsylvania, over the millions of years of coal’s formation, cations of various metals attached themselves to organic peat. “Some of the heavy stuff seems to have settled down into clays that were underlying the peat bogs,” Arnold said. “That’s why we have all these elements present in coals.”
Over decades of mining, these minerals were routinely tossed aside with the rest of the detritus. Now, however, coal’s waste streams hold enough potential value to be worth exploring. Acid mine drainage, the acidic runoff from abandoned mine lands, impacts over 5,500 miles of the state’s waterways. This literal waste stream, along with the acidic sludge held in treatment ponds, the vast piles of coal refuse, and the fly ash associated with coal-fired power plants, is a potential source of critical minerals.
The first step is assessing what’s out there. Arnold and the rest of the CANARY team, including Pete Rozelle, a doctoral alum and former project manager for the DOE who is now an adviser for the College of EMS, have begun the task of evaluating concentrations of cobalt, lithium, manganese, nickel, and rare earths likely to be present around the state. That means digging into the history of mining, scouring century-old government records and other publicly accessible databases as well as University archives. “We have a head start,” Rozelle said, “because Penn State was a leader in the U.S. in inventorying mine refuse in the 1960s.”
Coal mines are not the only object of interest. Mining for metals, including chromium, zinc, iron, and nickel, has been ongoing in Pennsylvania for 200 years, up until the 1980s. Waste dumps left behind by the metallurgical and metal-processing industries are another potential source of critical minerals.
Analyzing historical data brings special challenges, Arnold said. Assays relied on back in the day may not yield accurate results by today’s standards. “The USGS has qualified some of the numbers in its historical data,” she said. “In some cases, we have to go back and do our own assessment.”
Still, early results have been encouraging. In November 2021 the team released a preliminary estimate of the amounts of cobalt and manganese present in mine dumps and acid mine treatment ponds around the state. Both metals are essential ingredients in the lithium-ion batteries that power electric vehicles, and for both, the U.S. is highly dependent on imports from countries including the Democratic Republic of the Congo and China.
Pennsylvania once led the nation in cobalt production, Rozelle noted. “It was a byproduct of the steel industry.” So it was no surprise to find that there is as much of the stuff locked up in the state’s mine waste — some 52,000 metric tons — as exists in the entirety of U.S. primary reserves.
The same report estimates over half a million metric tons of manganese, with additional amounts of both metals leaking into waterways via acid mine drainage every year. Recovery and sale of these materials, Pisupati said, could not only provide a domestic source for the battery industry, but could help offset the costs of reclaiming abandoned mine lands and restoring polluted streams.
Accessing these dormant resources, however, will require bold advances in mineral processing — finding ways to make extraction and separation of the desired materials both environmentally friendly and economically feasible. It’s a tall order, which is why Pisupati and his colleagues are exploring every possible avenue.
“We’re looking at various approaches, and many different feedstocks,” he said. These include not only mine tailings, acid mine drainage and fly ash, but also waste piles associated with the Mercer Clay, a large clay deposit in central Pennsylvania that once supplied the refractory industry and may yet be a viable source of alumina and lithium. “We’re also looking at electronic waste recycling,” Pisupati said. “Our approach has been to try to recover multiple metals from a given waste stream in order to make the process economically feasible.”
He and Mohammad Rezaee, assistant professor of mining engineering, have already developed a process for extracting critical minerals from acid mine drainage via a modification of the method currently used for environmental treatment.
“Acid mine drainage is required to be neutralized before it is released into waterways,” Rezaee explained. “Generally, the practice is to add caustic soda to raise the pH. At neutral pH, the majority of toxic metals dissolved in the water will precipitate out of the solution as sludge.”
By substituting soda ash for the caustic soda or purging CO2, he and Pisupati found, they could cause iron, aluminum, and rare earth elements present in acid mine drainage to precipitate separately at pH values at or below those required for environmental compliance. “We also use a chemical-free process by purging ozone to recover cobalt and manganese,” Rezaee said. “This process produces multiple high-purity valuable products from these waste streams.”
Pisupati said he estimates that this simple modification can recover over 90% of the high-grade aluminum, cobalt, and manganese present in acid mine drainage and sludge ponds, as well as over 85% of the rare earth elements. “It also works for lithium-rich Mercer clay to pull out over 90% of lithium from the feedstock,” he said.
Across campus, Joey Cotruvo, associate professor of chemistry, is taking a different approach. As a bio-inorganic chemist, Cotruvo studies the important roles that metal ions play in the chemistry of life. “All organisms require certain metals to accomplish cellular processes,” he said. “They all have to figure out how to selectively bind the metals they need.”
In 2018, while studying this basic problem, he discovered a bacterial protein that binds extremely well to lanthanides, the class of rare earth metals, without appreciably binding other metals. He quickly realized that this protein, which he subsequently named lanmodulin (because its shape is modulated by lanthanides), might be useful for extracting rare earths from environmental sources.
Working with colleagues at Lawrence Livermore National Laboratory, Cotruvo and his team recently demonstrated a process that does exactly that: not only successfully extracting all the rare earth metals, and only the rare earths, from complex solutions but also separating the lighter rare earth metals present from the heavier ones. His team is currently fine-tuning the separations aspect to the point where it can isolate individual metals, in high enough purity to be sold. He said he believes this method will eventually be useful for recovering some of the most critical and valuable rare earths, like scandium, neodymium, dysprosium, and yttrium, from low-grade sources.
Meanwhile, Amir Sheikhi, assistant professor of chemical engineering and biomedical engineering, is applying nanotechnology to the problem. Sheikhi and his team engineer soft materials, mostly bio-based, for biomedical and environmental applications.
“One of the platforms that we are very excited about it is hairy cellulose nanocrystals, which are highly functional nanoparticles derived from a broad range of cellulose sources,” he said.
Hairy cellulose nanocrystals, he explained, have a crystalline core with amorphous regions of cellulose attached at either end. “Those regions we call hairs, and we can engineer them to perform critical chemical functions," said Sheikhi. Potential applications include removing residual drugs from the body after chemotherapy — and, it turns out, extracting critical minerals from the environment.
Recently Sheikhi and graduate student Patricia Wamea negatively charged their nanoparticles to attract and bind with positively charged ions of neodymium, effectively salvaging this highly sought-after rare earth element from samples of electronic waste. Unlike current recycling methods, the nanocrystals worked without the use of harsh chemicals or extreme pH levels.
“Using cellulose as the main agent is a sustainable, cost-effective, clean solution,” Sheikhi said. “And we can adapt it to extract other elements.” Sheikhi has filed provisional patent applications on the technology.
The goal of the Center for Critical Minerals, Pisupati said, is to act as a catalyst, integrating Penn State’s wide-ranging expertise and its world-class facilities in support of industry’s efforts to establish domestic production. A stakeholders’ group including representatives from industry and government meets regularly to discuss needs and priorities and share progress. At a recent workshop, held as part of Energy Days 2022 at University Park, attendees debated next steps.
“A lot more characterization is needed,” Pete Rozelle told the assembly, in order to get beyond broad estimates of how much resource is currently “lying on the ground.” Variability in quality is an issue, he said, and so is ease of access. Encouraging the private investment that will be necessary to develop these resources will require both sophisticated modeling and careful geological exploration.
In addition to the geoscience, center researchers are taking stock of existing infrastructure across the state, everything from manufacturing and processing capabilities to transportation logistics to the available workforce. “If we’re going to set up a new critical minerals industry in the U.S.,” Arnold said, “we’re going to have to rebuild the entire supply chain.”
At the same time, Pisupati said, the time is ripe to scale-up some of the novel extraction technologies that have shown such promise in the lab. The center has attracted $2.1 million in federal funding for a demonstration facility in University Park “to integrate all that we are learning and show potential investors that this can actually work,” he said. He and Arnold have begun working with partner companies on optimal designs for processing plants tailored for various feedstocks.
There are special challenges involved in dealing with secondary mineral sources, Pisupati acknowledged. One is the potentially complex legal issues associated with property rights pertaining to decades-old waste streams. But there is also strong precedent at Penn State for the kind of academic-industrial partnership that is now taking shape, he said.
In the 1980s, when the U.S. power industry was deregulated, Penn State research into fluidized-bed combustion technologies played a key role in the emergence of the independent power industry, Pisupati said, enabling the use of coal waste as fuel and thereby also effecting substantial environmental remediation across the state.
“We have had success at this scale,” he said. “We changed an industry. And we’re ready now to make that kind of impact in critical minerals.
“The need is urgent, and Penn State is ready and able to help.”
This story first appeared in the Fall 2022 issue of Research/Penn State magazine.