How one startup is recovering copper from old mines that were left for dead in the 1980s

In central Arizona, about 90 miles east of Phoenix, an old open-pit copper mine sits full of water. 

The mine closed in the 1980s, left to accumulate rain and groundwater. These “pit lakes,” as they’re called, are monitored so that they don’t contaminate the environment, but otherwise they just sit there, a new part of the landscape.

That water, though, is full of critical minerals like copper, and in a looming copper shortage, every bit counts. 

Now, a startup called SiTration, which spun out of the Massachusetts Institute of Technology, is launching a pilot to recover copper from that old mine. SiTration’s CEO, Brendan Smith, says the two-month pilot will be able to extract two tonnes of copper from that pit water. 

That’s a small amount when compared to what traditional copper mines can produce. But through the pilot, Smith hopes to validate the startup’s technology, and potentially “unlock a whole new source of copper that’s sitting there on the table for taking,” as he puts it.

Copper demand is surging

The demand for all sorts of critical minerals is surging. From lithium to cobalt to nickel, these materials are crucial for technologies like batteries, electric vehicles, drones, computer chips, and data centers. 

Copper in particular is in high demand. One hyperscale data center could need up to 50,000 tons of copper—or roughly the annual output of a whole copper mine, Smith says. 

Our electric grid also relies on copper, for transistors and transmission lines, for instance. By 2040, general demand for copper could grow by 50%.

At the same time, supply is dwindling. Experts estimate we’ll see a copper shortfall of 10 million metric tons by that same year.

One reason is that the grade of copper we’re mining has fallen nearly 50% since 1990, meaning we’re getting just half of the copper now that we would have gotten out of the same operation back then.

“That’s a pretty staggering decline in a very short amount of time, and that’s actually accelerating as we have gotten better at locating and leveraging all the best resources around the world,” Smith says. “And so nowadays, it’s even more important to get everything we can as efficiently as possible out of this rock and ore that we’re digging up.” 

Opening a new copper mine in North America could take up to 23 years, about half of which is due to the permitting process.

North America also lacks the resources to refine copper once it’s mined; more than 50% of copper refining happens in China. That makes getting the most out of the resources we already have here, like the pit water, especially important.

Unlocking the future of mining

The site in Arizona, called Copper Cities, began operating in the 1950s and produced nearly 400,000 tonnes of copper until it closed in the ‘80s. Copper mines have closed because their reserves were depleted or because of economic factors.

When pit mines close, though, they’re not filled in. They’re monitored and maintained to make sure they’re geologically stable and don’t contaminate the surrounding environments, but otherwise the holes in the ground stay open, filling with rain and groundwater.

Because that pit water, also called legacy mining water, touches the still mineral-rich walls of the old mine, it too becomes full of these minerals. But the concentrations are often very diluted, as little as 1 gram of copper per liter. 

SiTration says it has the technology to pull the copper out of that water. Using only electricity—no chemicals or heat—SiTration invented a type of electrode material that can extract the copper and plate it onto sheets measuring one square meter. 

From there it’s ready to go to market, no refining needed. “We’re collapsing the extraction and the refining into that single stage,” Smith says. 

The process uses five to six times less energy, Smith estimates, than the conventional process of digging ore out of the ground and refining it into copper. 

SiTration’s Arizona pilot is in partnership with BHP Copper, one of the largest mining companies in the world and an investor in SiTration. BHP manages all sorts of mining assets, including legacy assets like the Arizona site, and can help SiTration find locations to deploy its technology.

To Smith, this work is about “unlocking the future of mining,” as he puts it. “Can we recover all the minerals, all the resources that are on these asset sites, instead of leaving some behind?”

Critical minerals are trapped in mining waste

SiTration’s Arizona pilot is in two parts. First, in August, a month-long project will validate that SiTration’s technology works out in the natural environment, in the pit lakes, and not just inside its own facility. 

Then, beginning in the fall, SiTration will run a two-month, larger-scale deployment with the aim of producing two tonnes of commercial-scale copper cathodes. 

Smith admits that amount is a “drop in the bucket” compared to what traditional mines can do, and what the world demands. But as SiTration grows, he says, there’s opportunity for big impact.

There’s roughly $3.5 trillion worth of critical minerals trapped in mining waste, Smith says, and about half a trillion dollars worth in copper specifically. 

Those minerals aren’t just languishing in legacy pit water; they’re also stuck in rocks. Traditionally, mining operations tend to waste a lot of these crucial materials. 

What is in liquid today, and thus accessible to SiTration’s technology, is about $100 billion worth of copper globally, Smith says.

“We know the specific sites,” he adds. “There are these legacy assets and operating mine sites. . . . It’s very well catalogued.” Some $40 billion worth is likely in the U.S. Southwest alone.

There are other waste sources for copper, and new efforts to mine copper in general. A startup called Red Metals is working on what it calls “urban mining,” or extracting copper from old products and scrap.

Some companies, like Rio Tinto and Endolith, are using microbes to recover copper from rocks, rather than blasting the ore. Others inject acid underground to dissolve and then pump out the metal. Copper and other critical minerals are also increasingly recovered through recycling.

SiTration says its technology can work for other minerals, including gold, platinum, palladium, cobalt, and nickel. “It’s a whole slate of really critical and precious and high-value metals,” Smith says, “and so we can pull those out of really dynamic, diverse streams.”