Carved into a mountain range in Arizona’s Sonoran Desert, where temperatures often reach 118F (48C), a vast mining complex more than a century old is on the front lines of a race to unlock millions of tons of copper.
After 154 years of digging at Morenci, all the easily recoverable copper has been mined. Left behind are towering piles of waste rock that hold nearly 10 million tons of the metal seen as critical to global electrification. It’s a cache that could prove key to President Donald Trump’s ambition to boost US production of critical minerals.
Freeport-McMoRan Inc., which owns Morenci, is trying to develop technology that can burrow within those gigantic waste piles and extract low-grade copper that miners previously saw as too expensive and difficult to process. While the technology is still in its infancy, the US company is betting it can eventually retrieve the material in a way that’s cheaper, faster and greener than traditional mining.
The process, known as sulfide leaching, has been known to copper miners for decades, but the recent push to advance it comes as electrification and artificial intelligence are poised to drive global demand for the metal. BHP, the world’s largest miner, estimates that copper used for data centers will grow sixfold by 2050.
Trump’s focus on domestic copper output — “it’s time for copper to come home,” he declared in February — has revived optimism that operations in states like Arizona will have an advantage over rivals in Latin America, Africa and beyond. Copper prices have soared after Trump ordered the Commerce Department to investigate US imports of the metal, a likely precursor to tariffs that could come within weeks.
Copper futures on New York’s Comex exchange surged last week to a record high as traders priced in the prospect of hefty US import tariffs on the red metal. Such expectations helped fuel a 26% jump in US copper prices this year.
Sulfide leaching could, in some cases, be an alternative to building copper mines from scratch. High costs, slow permitting and local opposition often keep companies from pulling the trigger on major projects. Shareholders increasingly would prefer to see miners hunt for acquisitions or boost payouts to investors than greenlight new complexes.
Morenci is the largest copper mine in North America — about the size of Brooklyn. Between processing facilities and warehouses, lizards and organ-pipe cacti bask in blazing sunlight. The waste piles, each given their own name, are scattered around the site and shaped like giant cones. On a sweltering afternoon in September, a team of engineers, chemists and technicians experimented with heat, air pressure and chemicals to try to separate the copper from the waste.
“For a long time, we just didn’t think it was possible to recover any of this stuff,” said Robert Pollock, Morenci’s site manager, gazing up at a waste pile the size of a Manhattan office building. “But now, all this historical copper – we’re going after it.”
Other major copper producers including BHP Group, Antofagasta Plc and Rio Tinto Group — through its Nuton unit — are pushing to develop sulfide leaching technology as well. Some have outsourced the work to startups like Jetti Resources and Ceibo, which claim to have made strides with their own solutions. Because the geology of copper deposits varies, each company is developing slightly different technology to suit its mines.
The companies are focused on separating copper from a sulfide mineral called chalcopyrite, which is typically considered difficult to process, or “leach.” Jetti’s technology aims to leach those sulfides using little heating or grinding, which has typically driven up the cost of processing chalcopyrite to the point of being prohibitively expensive.
Ceibo, which is backed by BHP and recently partnered with Glencore Plc, uses a process that more quickly oxidizes chalcopyrite ores through electrochemical reactions, resulting in higher recovery rates in a shorter period of time. The startup claims it has recovered over 75% of copper from chalcopyrite through its technology — a significant increase relative to traditional leaching methods.
“For decades, miners have treated calcopyrite mineral to make copper,” said Corby Anderson, a professor at the Colorado School of Mines. “It’s not a magic box where copper’s been locked away. However, these technologies are focused on increasing the recovery of copper from calcopyrite, which isn’t always so easy to do.”
Freeport-McMoRan has used leaching methods at the Morenci mine to unlock lower-grade copper for years, but it’s now experimenting with chemical reagents to process previously inaccessible copper buried even deeper within its waste piles. The Phoenix-headquartered company has so far extracted 100,000 tons of copper using sulfide leaching. It aims to produce 400,000 tons by 2030, enough to wire more than 4.3 million electric vehicles.
“That’s the equivalent of a major copper mine anywhere,” chief executive officer Kathleen Quirk said last year.
The success of sulfide leaching, however, is no guarantee. The companies have struggled to prove their technology can function at scale, and few are willing to take the risk of being the first to invest heavily in the novel process. Behind the scenes, some miners have questioned the feasibility of some of the technology while haggling over ownership terms with partners.
At Escondida, a giant copper mine in Chile owned by BHP, the multinational mining company has been testing multiple technologies as it looks to offset declining copper quality that’s poised to send production sharply lower in the next few years. As part of that plan, BHP estimates it can produce as much as 55,000 tons of copper a year by leaching.
BHP is testing its own technology, as well as those of Nuton and Jetti. Yet each offers vastly different outcomes. Jetti is cheap to install, but only slightly increases recoveries. Nuton, which costs much more, greatly improves recoveries. BHP said it plans to make a final decision sometime after 2027.
Other miners have backed away from some of the technology after struggling to make it work. Freeport-McMoRan, an early investor in Jetti that partnered with the startup at its El Abra mine in Chile, said in an emailed response to questions that it’s no longer using the firm’s technology as it pursues its own.
“It’ll all come down to the economics,” said Anderson, who said he knows of previous efforts to boost copper recoveries through sulfide leaching that, while technically feasible, weren’t financially viable.
Freeport’s leaching push coincides with an ambition at the heart of Trump’s critical-minerals agenda: job creation.
The decline of American mining and mineral processing sent jobs overseas, to countries where the work could be done at far lower cost. For rural communities in the southwest, technological breakthroughs are critical to keeping aging mines alive.
Pollock, Morenci’s site manager, grew up in Clifton, 4 miles (6 kilometers) from Morenci in Arizona. The town was built to house the mine’s workers and their families in the late 1800s, back when mules hauled crates of ore up the mine’s dusty slopes. And like much of the surrounding economy, its prosperity became inextricably linked to the mine.
Today, Morenci is responsible for about 13,000 direct and indirect jobs and more than $1.5 billion in statewide economic benefits, according to Freeport.
“Seeing how the place has changed over the years is really impressive to me,” said Pollock. “Doing this work is how we make sure the mine stays here for the long term.”
(By Jacob Lorinc)
