Open-pit mining at Kennecott Copper Mine, also called Bingham Canyon Mine, in Utah
Witold Skrypczak/Alamy
The leftover ore discarded by US mines is packed with key minerals – enough to provide virtually all of the raw material needed to build clean energy technologies. Recovering just a fraction of these minerals could meet the country’s growing demand for green energy without requiring imports or environmentally-damaging new mines – but getting them is easier said than done.
“We have to get better at using the material that we mine,” says Elizabeth Holley at the Colorado School of Mines.
Currently, most individual mines focus on extracting just a few types of minerals, such as copper or gold. That involves digging up ore, crushing it and then separating out the main product using various metallurgical processes. Everything left over is then disposed of as tailings. “Most of what we are mining is waste,” says Holley.
These leftovers often contain other useful materials, including dozens of critical minerals the US government has identified as essential to military and energy technologies, such as solar panels, wind turbines and batteries. But the supply chains for some of these minerals are controlled by China, sparking urgent concern among the US and its allies they could be wielded for geopolitical leverage. That has spurred a search for alternative mineral sources, including mining byproducts and tailings.
However, most mines don’t know exactly what they are tossing out. “Many of the elements we currently consider critical were not in much use in the past, so no one was analysing for them,” says Holley.
Holley and her colleagues looked at thousands of ore samples and production data representative of mines around the US. They used this information to estimate the volume of other minerals that could be extracted from 54 active hard rock metal mines if new refining steps were added.
For some minerals, they found extracting just 1 per cent of what is contained in mining byproducts could replace all current US imports. Other minerals required higher recovery rates, ranging from 10 to 90 per cent, to replace imports. And a few metals, including gold, platinum and palladium, would still have to be imported even if 100 per cent could be recovered from byproducts.
These numbers suggest the US could meet most of its rising demand for critical minerals without building new mines, says Holley. That would help secure supply chains, as well as reduce the environmental impacts of mining. “It would be better to get more out of what we already mine,” she says.
Brian McNulty at the University of British Columbia in Canada says this shows the “opportunity is vast” – but much more research is needed to translate estimates of the total quantity of minerals that are out there into actual recovery. “Hopefully it energizes people in government as well as industry to take a closer look at what we’re mining,” he says.
Just knowing where these minerals exist is hardly the only barrier. Current refining technology isn’t well-suited for these small, complicated waste streams, and deploying the necessary tech is too expensive for most US mines, says Megan O’Connor at Nth Cycle, a start-up focused on extracting critical minerals from unconventional sources.
Mines can also be hesitant to invest money in extracting new types of minerals when future demand is so uncertain, says McNulty. Whether it is electric vehicle batteries or solar panels, “the change in technology is happening exponentially faster than how we mine”, he says.
Despite its hostility towards renewable energy, the Trump Administration has made boosting US critical mineral production a key part of its agenda. Last week, the Department of Energy (DOE) announced nearly a billion dollars in funding for unconventional mining efforts, including $250 million focused on recovering minerals from mining byproducts.
A spokesperson for the DOE says these mine tailings are “an important domestic opportunity” and could help the US diversify its sources of critical minerals and materials.
However, this doesn’t preclude support for new mines, said the agency’s undersecretary P. Wells Griffith III during a workshop about the DOE’s strategy on 20 August. “We should never apologize for our modern way of life or our abundance of natural resources,” he said.
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