More than 140,000 abandoned, orphaned or otherwise inactive hard rock mines throughout the U.S. are a part of a legacy that is gaining new attention today. Though the precious metals originally mined are mostly depleted now, the waste piles left behind are gaining renewed attention because of the potential to reprocess the piles for critical minerals that are now essential to our modern day technologies and life.

These deposits are part of a whole new rush to remine, recycle, and repurpose dozens of abandoned and legacy sites for presently relevant critical minerals and metals. As the U.S. and most other developed nations transition away from fossil fuel-based sources of energy, minerals like lithium, cobalt, graphite and rare earth elements are among the dozens we’ve come to depend on — from the batteries in electric vehicles and magnets in wind turbines to night vision goggles and advanced weaponry needed by the military.

“More than a century ago, the U.S. was well known as a rich repository of precious metals and minerals that were needed for heavy industry,” says Dave McLane, mining manager at Burns & McDonnell. “Over time, shifts in supply chains and the emergence of new technologies allowed China and other Asian countries to jump into the lead as sources of critical minerals needed by advanced technology systems. Today, there is a renewed focus on bringing mining and processing back to the U.S. and other partner countries as a means to strengthen energy security, support military readiness and provide the minerals needed for the ongoing energy transition.”

The Way Forward

As governments and private industry increasingly focus on the technologies needed for decarbonization, it is becoming apparent that the billions of tons of waste piles left behind at mines that operated many decades ago could be rich sources of critical minerals.

Mines that originally produced precious metals or other types of metals needed for industry commonly left behind billions of tons of waste slag. Byproduct minerals within that waste had little economic value more than 100 years ago, but today often are among the 50 or so minerals that are considered essential to manufacturing and constructing the infrastructure needed for the future of energy.

For example, rare earth elements are present alongside more commonly mined substances like iron or nickel. Though rare earths themselves are relatively common chemical elements, what is rare is finding them in concentrations that make it economically viable to mine and process. In the past, companies may have only mined the iron or nickel, leaving the rare earths behind due to lack of need at the time. Now that more and more technology manufacturers need rare earths (key ingredients for manufacturing permanent magnets), they are revisiting these older sites to process the waste.

Assessing and evaluating the composition and volumes of these materials is a priority in the federal government. For example, the U.S. Geological Survey (USGS) has launched an ambitious program to identify and classify the minerals and materials left at abandoned mines. U.S. Earth MRI — a partnership between the USGS and state geological survey organizations — is part of a massive push to produce new geologic maps, geochemical sampling, and geophysical, topographic and hyperspectral surveys. Once these new data are available, the general public will be able to review these newly discovered datasets for economically viable mineral deposits itching to be remined.

Addressing Environmental Legacy

As momentum grows to produce a more complete understanding of America’s basic geologic framework and mineral resources, a legacy of environmental risk is becoming part of the conversation. Much of the waste left behind from now-closed mining operations contains various contaminants that will need to be addressed if recovery operations commence. It’s not surprising, therefore, that mining companies — including some new entrants — are taking a cautious approach about proceeding.

“There is a lot of push and pull between governments and the private sector when it comes to mapping waste at our abandoned mines,” says Danielle Woodring, geologist and geoscience policy leader at Burns & McDonnell. “We have seen some progress because nonprofits are approaching this effort as an academic exercise without any economic motivations. Still, there are some political and technological obstacles to overcome.”

There are a number of players — both established mining companies and new entrants — looking to clean up these old sites as they prepare to jump into this market. For example, Rio Tinto is mining battery-grade lithium from a mine in California that historically produced boron. Likewise, Perpetua Resources is cleaning up a legacy gold mine in Idaho in preparation to produce antimony trisulfide, a critical mineral needed for munitions that is now sourced primarily from Russia, China and Tajikistan. Another partnership between Australia-based Cobalt Blue Holdings and Regenerative Enterprises is deploying proprietary technology to mitigate environmental liabilities and extract metals and minerals from mine tailings, waste rock and water.

Until recently, companies and nonprofits alike could be held liable for huge expenses related to required environmental cleanup associated with approaching these old, mostly abandoned sites. However, in early December Congress passed the bipartisan Good Samaritan Remediation of Abandoned Hardrock Mines Act (HR. 7779, S.2781) to help remove most of the legal liabilities for those who undertake cleanup projects. The bill was sent to President Biden’s desk to sign in December. The bill creates a 15-project pilot program, administered by the EPA, allowing approved nonprofits, state agencies or industry groups without connections to the site to receive limited protection from litigation as they begin cleanup projects.

“The urgent need for critical minerals will help the mining industry resolve an unfortunate legacy of liability from hazardous materials that were left after earlier mining activities ended,” says Woodring. “The long-awaited passage of the Good Samaritan bill through the House and the Senate is a major milestone and will help the EPA establish a pilot program.”

Boosting Circular Economy

Another key strategy in transitioning to an era with minerals as building blocks will be recovering and recycling minerals used in the manufacturing of a number of end products. Lithium-ion batteries used by electric vehicles as well as in grid-scale energy storage facilities are obvious candidates.

Materials like lithium, nickel, cobalt and graphite contained in batteries can be recovered indefinitely through hydrometallurgical and pyrometallurgical processing methods. However, it is currently early in the 10-year life cycle of these batteries, with large-scale replacements or power supply augmentations not needed for many more years.

Until there is a surge in batteries that need to be replaced, the recycling industry exists in a kind of awkward waiting period, during which the timing of material supply is currently inadequately meeting the needs of demand. Although some recyclers are already working with major automative manufacturers in producing black mass — a material that is left when end-of-life batteries are shredded to extract lithium, nickel, manganese and cobalt — the U.S. recycling industry is still in its very early stages.

Addressing Energy Security

With the U.S. currently dependent on other countries — including some adversarial nations — for both raw materials and processing capacity, recalibrating trade relationships is becoming another key strategy.

For example, the U.S. now produces and processes only a small fraction of the rare earth elements neodymium and praseodymium, crucial magnetic components needed for products like EV batteries, wind turbine rotors, magnetic resonance imaging (MRI) equipment, robots, military drones and chips required by powerful new computers. Although one of the world’s largest rare earth mines is located in California, the vast majority of processing capacity is currently located in China.

Some good news may be on the way, however. According to recent announcements, significant deposits of economically viable rare earths have been found in Wyoming. Although some of the early estimates on the size of the deposits have been scaled back, it still is widely acknowledged as a significant find. Additionally, Lynas Rare Earths recently updated its contract with the U.S. Department of Defense for the construction of a commercial-scale rare earths processing facility in Texas.

Natural graphite is another critical mineral that is emerging as a concern. Though it is a crucial element needed for batteries and a wide range of other products, almost no natural graphite is mined in the U.S. China today controls nearly all the world’s natural graphite mining and processing, causing concern over supply chain security as demand for natural graphite increases.

These and other concerns over critical minerals supply chains are leading to increased urgency to solidify trading relationships with friendly partner nations with substantial reserves of these essential commodities along with adequate processing capacities.

The U.S. and Canada have recently taken steps forward with a bilateral commitment for increased U.S. investments in developing critical minerals mining and processing in return for easing of transit routes for imports of processed critical minerals and other materials. Canada has some of the world’s richest repositories of critical minerals, with large proven deposits in every province and territory.

Australia is another key U.S. trading partner with significant reserves of critical minerals as well as mature processing capacity. With a much greater share of its economy based on production of natural resources, Australia has long been a global leader in precious metals mining and corollary production of essential minerals and materials.

Role of Oil and Gas Producers

As the U.S. energy economy transitions toward lower carbon technologies, it is widely expected that the oil, gas and chemical sector also will play a significant role. Nearly all of the world’s major oil and gas companies have invested significant capital in leases and conducted extensive geological surveys for pinpoint accuracy in knowing where mineral resources are located.

For example, one promising pathway currently being developed is to extract lithium from brine left deep underground as oil and gas wells were depleted. Feasibility studies for major producers have demonstrated that significant volumes of lithium can be extracted from these wells on a scale to supply the needs for production of millions of new lithium-ion batteries. With the permitting cycle for a lithium injection well expected to take less than five years — compared to 20 years for a conventional lithium mine — this innovation is emerging as an exciting pathway that could help ease concerns over insecure supply chains.

“The oil, gas and chemical industry is actively pursuing a number of solutions to secure supplies and boost production capacity of critical minerals and materials,” says Meaghan McCaffrey, managing director, renewables and emerging markets at Burns & McDonnell. “Many sectors are coming together to secure the future of energy, helping our country and others make the transition to the critical minerals era.”

High environmental standards and sustainable practices will be national priorities as a new bonanza of critical minerals are produced on the very same sites where America’s historic mining legacy began.