Coal ash, acid drainage, and tailings for future green economy

As the world continues to prime itself for the global energy shift, academia, governments and the private sector are scrambling to extract the valuable minerals and metals necessary to power the low-carbon renewable future – resulting in some truly innovative and unconventional methods.

In addition to the rare earths, cobalt, lithium, and other technology metals that capture headline attention, this list often misses the 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.

The green transition is driving staggering new demand for these previously little used critical minerals and metals.

To combat a looming scarcity, groundbreaking technologies have begun to spring up to sift through the remnants left behind from more than a century of powering America with coal, the tailings of yesterday's metal mines, and the acid mine drainage created when water and air oxidize sulfide-rich rocks, offer potential unconventional domestic sources of the equally unconventional metals needed to build tomorrow's technologies.

Win-win in coal country

The Biden administration believes that extracting the critical minerals left behind by historical mining and coal-fired electricity generation offers multiple layers of benefits to the U.S. – new domestic sources of the minerals and metals vital to America's climate goals and technology industries; an opportunity to clean up legacy mine waste with modern technologies, and under modern environmental law; and the creation of new economic opportunities in regions that have traditionally delivered the coal that powered much of America's homes and industries for more than a century.

"Applying next-generation technology to convert legacy fossil fuel waste into a domestic source of critical minerals needed to strengthen our supply chains is a win-win – delivering a healthier environment and driving us forward to our clean energy goals," said U.S. Secretary of Energy Jennifer Granholm.

Toward this altruistic goal, the $1 trillion Infrastructure Investment and Jobs Act includes $140 million to support the design and development of a refinery to demonstrate the commercial viability of extracting rare earths and critical minerals from unconventional resources and separating and refining them into the metals being demanded by American industries.

"With the Bipartisan Infrastructure Law's investment in the build out of this first-of-its-kind critical minerals refinery, we are moving ideas from the lab to the commercial stage and demonstrating how America can compete for the global supply chain to meet the growing demand for clean energy technology," the Energy Secretary added.

To put the best ideas and technologies into this critical demonstration refinery, DOE invited input from industry, investors, developers, academia, research laboratories, government agencies, non-governmental organizations, and communities that potentially could be affected by the development of the critical minerals plant.

DOE sought feedback on demonstration facility features, supply chain considerations, research and development needs, business models, and potential societal impacts and benefits of the proposed critical minerals extraction and separation facility.

While the energy department encourages outside-of-the-box thinking when it comes to unconventional sources of critical minerals, it does not want to stray too far from convention when it comes to the technologies that will be used to extract and refine these technology metals.

The energy department envisions that this first-generation separation facility will use proven methods such as hydrometallurgy and solvent extraction for the separation of individual rare earth and critical mineral oxides, as well as the subsequent refining and alloying of metals.

"Further advanced technologies will be encouraged, but only if tested and ready to be applied at demonstration scale," DOE inked in its request for information.

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 often 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 innovative technologies creating new demand for these metals, companies are beginning to look at tailings 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 heavy lifting 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.

Geomega reduction in aluminum waste

While still wholly capable of recovering rare earths from recycled magnets and potential ore, Geomega Resources Inc.'s rare earths and critical minerals extraction technology may draw value from and reduce the environmental footprint of bauxite residues piling up at aluminum refineries.

Commonly referred to as red mud, a reference to the color and consistency of this waste material, bauxite residues are typically stored in large containment facilities. The large quantities of this ofttimes caustic red mud have led researchers and refiners to seek alternative uses for it.

Bauxite residue is a byproduct that is generated during the refining of alumina. Geomega's core project is based around its Innord's Separation of Rare Earths (ISR) technology, a proprietary, low-cost, and environmentally friendly way to tap into the C$1.5 billion global market to recycle magnet production waste and end-of-life magnets.

Innord, a subsidiary of Geomega, has been tasked with developing solutions to large industrial mine waste challenges with its technology to extract critical minerals. The process has the potential to significantly reduce the quantities of this red mud that would need to be stored at aluminum refineries.

Taking immediate interest in the potential to reduce the discarded waste piles, Rio Tinto, the largest aluminum producer in North America, along with Sustainable Development Technology Canada and the Quebec government, have invested a total of C$5 million to evaluate Innord's technology to potentially monetize the iron compounds produced by Innord's Bauxite Residues Technology (IBRT).

"Bauxite residue, the waste generated from aluminum production, requires significant management and monitoring from mining companies to avoid environmental impacts," said Sustainable Development Technology Canada CEO Leah Lawrence. "Innord Inc. is developing a process that reduces the volume of red mud by 70-90% while recovering valuable minerals from that waste."

This has the potential to create a new value stream for Rio Tinto, reduce the financial and environmental liabilities associated with storing the red mud, and extend the life of alumina operations without the need to build additional storage.

For Geomega, this offers a way to scale up and generate revenue from a technology with the potential to transform costly waste products into valuable metals.

With more than 4 billion metric tons of red mud stored in facilities around the world, there is no shortage of material for a commercial version of Innord's bauxite residue technology.

REEs from the ashes of coal mining

Aside from the obvious motivation of giant companies seeking to squeeze value from every stone it digs up, government research facilities, universities and private labs are inching along in the pursuit of clever and unique ways to tap into not only waste but new chemistries involving REE separation and recovery.

One such resource, a mainstay as the focal point of energy production before petroleum began to dominate, was coal.

A compelling source for the rare earths needed for electric vehicle 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 America.

"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 the US transitions to lower-carbon energy sources, more than 100 years of coal-fired electrical generation has created a glut of this REE-enriched waste product – billion of tons of it.

Best known for its contribution to advancing the Round Top rare earths and critical minerals mine project, Texas Mineral Resources Corp. has been leading a group targeting the development of a mine capable of recovering rare earths from Pennsylvania coal byproducts.

You can read about Round Top and Texas Mineral Resources at Making rare earths separation less rare in this edition of Critical Minerals Alliances.

The Texas-based mineral explorer teamed up with Penn State University; Jeddo Coal Company, a family-run mining company with an operation in Pennsylvania; and H22OS Consulting, an engineering and construction firm that specializes in mining.

With added support from the Department of Energy, the consortium hopes to use an advanced extraction method Penn State developed to extract rare earths from coal byproducts.

This advanced extraction method, which uses continuous ion exchange and continuous ion chromatography (CIX-CIC), is the same technology being developed to extract rare earths and other critical minerals from concentrates from a future mine at the Round Top project in Texas and is also the focus of Texas Mineral's funding partner, USA Rare Earth's pilot plant in Colorado.

Value from acid mine drainage

But coal is not the only waste product from mining that scientists are seeking to recycle. Once again, Pennsylvania State University focused its attention on another aspect that damages the environment and leaves miners scratching their heads – acid mine drainage.

Acid mine drainage occurs when mining exposes sulfide-containing minerals, which react with air and water to form sulfuric acid.

While this process sometimes occurs naturally, it can be more pronounced after mining if the exposed sulfides are not cut off from sources of water and air. The acidic runoff from such mines often carries excessive quantities of metals, many of which are toxic to plants and wildlife.

Hence, the university developed a process that could transform acid mine drainage from an environmental liability that is costly, to an asset that produces rare earths and other valuable minerals.

"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.

Thus, Rezaee and his colleagues have developed a two-stage treatment process that can recover more of the metals out of acid mine drainage while using fewer chemicals than earlier techniques.

"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 involves collecting acid mine drainage in ponds and adding 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 sludge using this process.

This could provide a valuable domestic source of these rare earths used in an increasing number of high-tech, renewable energy and other applications.

"This technique represents an efficient, low-cost and environmentally friendly method to extract these valuable minerals that are used in a wide variety of consumer and industrial products," said Pisupati, who is also director of the Center for Critical Minerals at Penn State.

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 more metals at higher pH values. This is because rare earths and other metals latch onto the carbonatites and more readily settle out of the water.

While transforming carbon dioxide into rocks is an emerging technique for removing carbon dioxide from the atmosphere, the Penn State research is the first time carbon dioxide mineralization has been applied to treating acid mine drainage.

"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."