A Toxic Pit Could Be a Gold Mine for Rare-Earth Elements

New York Times

13-05-2025

There's a tale told about a miner who found copper cans in his garbage dump in the early days of mining. Wastewater from copper mining had flowed through his land, he said, and turned steel cans into copper.
The story might be apocryphal, but the process is real, and it's called cementation. Montana Resources, the mining company that took over from the Anaconda Copper Company, still uses this alchemical trick in a process at its Continental Pit mine in Butte, Mont.
Next to the mine is the Berkeley Pit, which is filled with 50 billion gallons of a highly acidic, toxic brew. Montana Resources pipes liquid from the pit, enabling it to cascade onto piles of scrap iron. The iron becomes copper and is gathered for production.
While methods to remove metals from water have been around a long time, in recent years the global scramble for metals critical to manufacturing and technology advances has given birth to a new generation of extraction technologies and processes.
One of the mineral-rich sources researchers are focused on is wastewater, including the brine from desalination plants, oil and gas fracking water and wastewater from mining. Researchers at Oregon State University estimate the brine from desalination plants alone contains metals valued at about $2.2 trillion.
'Water is the ore body of the 21st century,' said Peter S. Fiske, director of the National Alliance for Water Innovation at the Department of Energy's Lawrence Berkeley National Lab California. 'Technology now is allowing us to pick through the garbage piles of wastewater and pick out the high-value items.'
Research on the extraction of rare earths, a set of metallic elements, from waste is widespread as the need for them increases significantly. Researchers at Indiana Geological and Water Survey at Indiana University, for example, are studying the potential for mining rare earths in coal waste, including fly ash and coal tailings. And researchers at University of Texas at Austin have created membranes that mimic natural ones to separate rare earths from waste.
Not only is mining wastewater more economical and faster than starting new mines, it is also cleaner.
Among the big waterborne prizes in the pit next to Butte are two light rare-earth elements (REEs), neodymium and praseodymium. They are vital for small, powerful magnets in electric vehicles, for medical technology and for defense purposes, such as precision-guided missiles and satellites. A single F-35 fighter jet uses 900 pounds of rare-earth metals.
'We're turning a giant liability into something that's contributing to defense,' said Mark Thompson, vice president for environmental affairs at Montana Resources. 'There's some high-level metallurgy going on here. Real egghead stuff.'
This is a critical time for research into domestic production of rare earths. Not only does the United States lag far behind China, but President Trump's trade war has spurred China to threaten to further restrict rare-earth mineral exports as a result of the Trump tariffs. Experts with the critical minerals security program at the Center for Strategic and International Studies say the large gap would enable China to expand its defense capabilities far more quickly than the United States could.
Both Greenland and Ukraine are the focus of the Trump administration's attention in large part because the countries have significant deposits of rare earths.
Mr. Trump also just ordered the government to move toward mining large portions of the ocean floor, including in international waters, for its mineral riches.
There are 17 types of metals known as rare earths, all of which have been found in the Berkeley Pit. They aren't rare in prevalence, but they are called that because they are often scattered in small concentrations.
Rare earths are sorted into two kinds: heavy and light. Heavy rare earths — such as dysprosium, terbium and yttrium — have a greater atomic weight and are typically more rare, meaning they sell in smaller quantities and are prone to shortages. Light metals, by contrast, have a lower atomic weight.
Acid mine drainage is a highly toxic pollutant created when sulfur-bearing pyrite in rock is exposed to oxygen and water during mining. The drainage then oxidizes and creates sulfuric acid and poisons waterways. It's one of the country's biggest environmental problems, and tens of thousands of abandoned mines have contaminated 12,000 miles of streams.
However, the acid also dissolves zinc, copper, rare earths and other minerals out of the rock and into the water, providing an opportunity for the right technology to extract them — which didn't exist until recently.
Paul Ziemkiewicz, director of the water research institute at West Virginia University, has researched the pit water in Butte for 25 years. He and a team of researchers from Virginia Tech and L3 Process Development, a chemical engineering firm, developed a method to extract critical metals from acid mine drainage in West Virginia's coal mines, the same process used in Butte. Large, densely woven plastic bags are filled with a mudlike sludge from the water treatment plant. The water slowly percolates out, leaving a preconcentrate of about 1 to 2 percent rare earths that need further refinement, with chemical processes. The final step in the patented process is an extraction with solvents that creates pure rare-earth elements.
'One of the nice things about acid mine drainage is the concentrates we get are particularly enriched in heavy rare earths,' Dr. Ziemkiewicz said. 'The light ones aren't as valuable.'
The Butte project is awaiting word on a Department of Defense grant of $75 million to build a concentrator, the last step needed to refine the preconcentrate to rare earths and begin full-scale production.
Zinc is also plentiful in the acid-mine-drainage mix here and, because it fetches a higher price, is important as a way to pay for the process. Nickel and cobalt are also extracted.
While rare-earth elements are much in demand, China produces a majority and manipulates prices to keep them low, which forces out competition. That's why the Defense Department is funding much of the work on rare-earth elements and other metals. The United States has just one operational rare-earths mine, in Mountain Pass, Calif., which produces around 15 percent of the global supply of rare earths.
The Berkeley Pit has been a festering sore since 1982, when, the Anaconda Copper Company closed the open-pit mine, turned off the pumps and let water fill it. The water is so acidic from acid mine drainage that when tens of thousands of snow geese flew over it on their migration in 2016, many landed on the surface and were quickly poisoned. About 3,000 birds died.
The Atlantic Richfield Company and Montana Resources are required to treat the pit water in perpetuity to keep it from reaching levels that could contaminate the area groundwater. (Montana Resources mines the Continental Pit, next to the Berkeley Pit.) The Clean Water Act requires that companies treat acid mine drainage, an expensive process. Adding another level of treatment to the Horseshoe Bend plant here is less costly than building a new one and can offset the costs of treatment or even turn a profit.
There have been dozens of research efforts to liberate the suspended metals from the water. Mr. Thompson displayed a map with lines radiating out from Butte, showing where water samples had been sent to research facilities across the country. But the metal-producing process that's going on now is the first one that's proven economical.
While the riches in the mineral soup here have been known for decades, a way to extract them was elusive, until Dr. Ziemkiewicz's team developed the new method. He has been producing rare earths at two coal mines in West Virginia where acid mine drainage is a problem. Each mine produces four tons of rare earths a year.
The Berkeley Pit, however, has a much richer concentration of rare earths in solution and a higher volume of water and is expected to produce 40 tons a year. Dr. Ziemkiewicz believes this process if used at other mines could eventually provide nearly all of the U.S. imports of rare-earth elements needed for defense purposes, which, he said, currently amount to about 1,400 tons.
But demand for rare earths could increase by as much as 600 percent in the coming decades, according to some estimates.
In the global effort to clean water and produce critical minerals, the lab at Lawrence Berkeley researches an array of water-filter-related technology, especially experiments to improve membranes. It operates a particle accelerator called Advanced Light Source, which creates very bright X-ray light that enables scientists to study various membranes at the atomic scale.
The lab has worked with outside researchers to create a new generation of filters, called nanosponges, that are designed to trap a single target molecule, such as lithium.
'It's an atomic catcher's mitt,' said Adam Uliana, the chief executive of ChemFinity, a Brooklyn company studying the use of nanosponges for cleaning many different types of waste. 'It catches one and only one type of metal.'
Lithium, cobalt and magnesium are critical minerals, in addition to rare earths, that have attracted considerable attention from researchers.
Ion exchange, a proven technique for removing metals and pollution from water, is gaining interest. Lilac Solutions, a start-up in Oakland, Calif., has developed the specialized resin beads needed to extract lithium from brine with ion exchange and plans to start its first production facility at the Great Salt Lake in Utah.
The company's technology pumps brine through ion exchange filters, extracts the mineral and returns the water to its source, a process David Snydacker, the company's president, said caused very little environmental disturbance. If it proves to work at scale, it could revolutionize lithium extraction and reduce or eliminate the need for underground mines and open pits.
Magrathea Metals is a start-up in Oakland that makes magnesium ingots from salty brines left over after seawater has been desalinated. The company allows the brines to dry, which leaves behind magnesium chloride salts. An electrical current — which can utilize off-peak renewable energy — heats the solution and separates the salts from the molten magnesium, which is cast into ingots.
Its chief executive, Alex Grant, said this process is extremely clean, though it has yet to be used to manufacture magnesium at a large scale. The Department of Defense has funded much of its work.
China produces 90 percent of the world's magnesium. The metal is smelted with something called the Pidgeon process — . heated with coal-fired kilns to around 2,000 degrees, which is highly polluting and carbon-intensive. Dr. Fiske expects a lot more innovation.
'Three vectors are converging,' he said. 'The value of some of these critical materials is going up. The cost of conventional mining and extraction is going up, and the security of international suppliers, especially Russia and China, is going down.'