Science

Can this MIT metallurgist clean up copper production?

ONE OF technology’s greatest inventions began with a dispute between two Italians over frog legs.

In 1800, scientists the world over were fascinated by electricity. Practical applications, however, were elusive, mainly because no one could figure out how to generate continuous current. At the time, physicist Alessandro Volta stood athwart Luigi Galvani, a physician-scientist who studied frogs—specifically, dissected legs still attached to their spinal cords and mounted on brass or iron hooks. Galvani noticed that when he touched a probe made of a different metal to the legs, they twitched. Convinced the muscles were generating the sensation, Galvani dubbed his find animal electricity.

Volta argued the amphibians’ legs were not generating the buzz but reacting to current produced by opposing metals. To prove it, he built a stack of alternating metal wafers (one early try tapped zinc and copper) separated by brine-soaked cloth to conduct current. When he touched a wire to each end of the tower, steady electricity flowed, no animal parts required. This Voltaic pile, as it was called, was the first electric battery. After Volta demonstrated the device in Paris, Napoleon was so impressed he even gave Volta a medal—and a pension.

Fast-forward to the 21st century, and one of Volta’s core elements, copper, is so much more than a means of disproving froggy hypotheses.

The red metal, which is also one of the world’s oldest, has formed the backbone of our lightbulb-loving lives since the Gilded Age. In its conductivity, it’s superior to all its elemental kin except silver. Unlike silver, though, it’s durable—and there’s no electrification without it. A new offshore wind turbine, for example, requires 21,000 pounds of copper. Meanwhile, each battery-powered vehicle uses 183 pounds of it, a full-on mile of the stuff. (Gas-powered cars tap, at most, 49 pounds.) The annual demand for EVs alone will be 3.6 million tons by 2030, according to CRU, a business intelligence firm with an eye on the metals market.

“It’s one of the key metals for decarbonization,” says Bernard Respaut, chief executive of the European branch of the International Copper Association, the nonprofit advocate for the global copper industry. “The more we electrify, the more copper we will need.”

Getting more of it, though, creates an environmental conundrum. Most of the 22.7 million tons of copper produced every year require roasting ore to purify the metal. Called pyrometallurgy, it’s a high-temperature process carried out in more than 120 smelting plants worldwide, including three in the US. Yet every ton of copper smelted emits 2 tons of carbon. While we need more copper, it’s unlikely additional smelting plants will come online in a more climate-conscious America, according to the Energy Security Leadership Council, a Washington, D.C.–based group whose goal is to reduce US oil dependence. “The industry recognizes that we need to decarbonize the process of producing copper,” Respaut adds.

This dilemma drew the attention of Antoine Allanore, a metallurgist and professor at the Massachusetts Institute of Technology. Allanore is one of a new wave of inventors trying to clean up metal production. He specializes in extracting materials from rock without burning fossil fuels like coal or gas. In February 2022, he completed work on his latest project, funded by the US Department of Energy: a reactor that employs a process called electrolysis, which uses current to separate copper from ore. In essence, while Volta deployed copper to funnel electricity, Allanore’s system uses electricity to make copper.

Allanore’s lab at MIT has shown that electrolysis can also extract nickel, cobalt, and manganese—three other minerals crucial for lithium-ion batteries. But copper is king.

According to Hal Stillman, who retired as director of technology development and transfer at the International Copper Association in 2020, Allanore’s contraption is a “big step,” as well as a scientific breakthrough. “This had never been done before, the electrolytic refining of copper,” he says.

Right now, Allanore’s device makes just a pound or two of copper every 24 hours, but it’s a demonstration of a larger principle. Meanwhile, the industry is also using other methods of purifying certain ores without the emissions of smelting. To succeed, Allanore will have to persuade producers that his tech is cleaner and more efficient. His next step? A version of the reactor that produces a ton of the element per day. “The electrification of metal production is groundbreaking,” he says. “It not only allows us to avoid certain fuels and carbon emissions, it opens the door to higher productivity.” If the world is going green, metal production can too.

ACROSS THE WORLD of metal-making, the idea of employing electricity as something more than what keeps the lights on at smelting plants has been gaining traction. It’s territory with which Allanore is already familiar: He was a research engineer for almost five years at ArcelorMittal, a major global steelmaker. While there, he helped design and construct the world’s largest reactor for refining iron via a technique called electrowinning, in which current separates metal suspended in an electrolyte solution. ArcelorMittal is constructing a pilot facility to put it into practice.

Like copper, steel begins as rock. Specifically, as iron ore, which is composed of tight bonds of iron and oxygen atoms. Pyrometallurgy is used to break those bonds, the first step in steel production. Massive blast furnaces burn coke, a processed form of coal, at up to 3,000 degrees Fahrenheit, the temperature at which the heated ore’s iron releases its clutch on oxygen. Carbon dioxide is a major byproduct. Globally the industry produces 2 billion tons of steel every year, but it throws off more than 3 billion tons of CO2—roughly 9 percent of the Earth’s total greenhouse emissions and a number directly in conflict with goals established by the United Nations’ Intergovernmental Panel on Climate Change.

After leaving ArcelorMittal in 2008, Allanore took a sabbatical at the French National Centre for Scientific Research and then joined MIT in 2010 to continue his work on electric steel. In 2012, he co-founded Boston Metal, a company spun out of MIT that uses current in place of coke to heat iron ore. His colleague and co-founder is Donald Sadoway, an MIT materials engineer whose own work on metal electrolysis dates back to the 1980s. “This is the future,” says Sadoway. “If you want to have zero emissions, you have to redesign all these heavy-duty, chemically intensive, energy-intensive, emissions-intensive processes.”

Copper certainly qualifies. More than two-thirds of it is processed through pyrometallurgy, which is most often fueled by gas and coal. According to data from the International Energy Agency, a typical smelting furnace consumes some 3,830 kilowatt-hours of energy to net 1 ton of copper—about what the average US household uses in four months—and churns out half a million tons a year. But the red metal also comes with its own challenges. Unlike steel, which contains some carbon in its final form, copper must be free of virtually all impurities to move electricity the way modern life demands. Its conductivity is directly proportional to its purity, Allanore points out. The wiring in a smartphone, for instance, is 99.9 percent perfect. Mined copper is nowhere close to that level.

Antoine Allanore’s reactor, seen here in his MIT lab, could replace noxious smelting as a means of purifying copper. Antoine Allanore

Fresh out of the ground, the ore consists of many elements, chief among them sulfur, the atom to which copper directly binds in the rock. At this stage, the raw material is usually less than 1 percent copper. Before it heads to a smelting plant, mining companies pulverize it into sandlike granules that they dump into a liquid froth to begin removing trace elements like lead and zinc. What’s left is called copper concentrate, which is only about 25 percent pure.

The concentrate goes to the smelter, which roasts it, using natural gas to generate temperatures as high as 2,300°F. That blast creates two things: slag, a waste product containing iron, silica, and other minerals; and matte, or liquefied copper, which still includes some iron and sulfide and is 60 percent pure. Molten matte travels to another furnace with similarly high temperatures—this one called a converter—where blown oxygen grabs hold of sulfur atoms, making sulfur dioxide. (Smelting plants capture most of the emitted sulfur dioxide and make it into the sulfuric acid they’ll need later in the process.) The setup spits out blister copper, which reaches a purity of 98 percent.

The conventional means of production does use electricity to forge the metal, but only at the end: Blister copper is poured into molds, which are then placed into an electrolyte solution partly made up of the captured sulfuric acid. The reaction that happens next is akin to the mechanisms within a battery. The slabs of blister copper, cooled and molded, act as anodes (the part of the cell that gives away electrons), and thin sheets of pure copper serve as cathodes (the part that receives electrons). When current is applied, only positively charged copper ions travel from the anodes over to the cathodes. Any leftover metals, like iron or lead, break loose from the anodes and fall to the bottom of the tank, leaving behind copper cathodes that are almost 100 percent pure.

AS EARLY AS 2013, Allanore began wondering if he could use electricity, instead of natural gas, to purify copper. “It’s the number one metal that mankind has been toying with, so it’s important,” he says.

The electrolysis method he proposed that year replaced all the steps in traditional smelting with just one, which both separated copper from sulfur and eliminated the iron that can make up as much as half of the ore. On paper, the plan was straightforward: The fundamental concept isn’t all that different from how Boston Metal uses current to liquefy iron ore, which forms into steel blocks as it cools.

In 2018, the Office of Energy Efficiency and Renewable Energy inside the US Department of Energy gave Allanore a $1.9 million grant to try it. “The DOE understood this link between more electrification, less energy consumption, and yet the need for more metals,” he recalls.

In Allanore’s lab at MIT, the copper-purifying contraption sits inside something resembling an oversize old-school phone booth. A ceramic vat with a cathode at the bottom and an anode at the top is filled with about two pounds of copper concentrate and an electrolyte stew made up in part of lanthanum sulfide, a chemically reactive element good at forming compounds with trace minerals that come bound up with copper ore.

The vat is then placed inside a small gas furnace that reaches a temperature of about 2,372°F. As the copper concentrate heats up and liquefies, current runs through the cathode. In a matter of minutes, copper starts to drop to the cathode while sulfur atoms travel upward to the anode. The metal that falls cools as purified copper, ready for shaping into wiring; the sulfur that emerges is inert, elemental sulfur, not toxic sulfur dioxide. The process still requires energy to produce extreme temperatures, but it takes only a single blast to create pure copper.

According to International Copper Association vet Stillman, Allanore’s use of lanthanum is a unique scientific insight. “You could not use an electrolytic reaction with copper to separate it before his step of adding lanthanum,” says Stillman, who now serves as senior adviser for a research group that works on the metals supply chain at the Argonne National Laboratory near Chicago. “That creates a situation where you can get separation of the copper ions from the other materials.”

Allanore’s lab has shown that electrolysis can also extract nickel, cobalt, and manganese—three other minerals crucial for lithium-ion batteries. But copper is king. The Energy Security Leadership Council suggests that we will need to produce the same amount of the metal in the next 25 years that we did in the previous 5,000 to meet the demand for electric vehicles alone. That’s not including their charging stations, which also need wiring.

Scaling the technology up so that it continuously produces 1 ton of copper a day (let alone many) is a major obstacle, Stillman allows—one it will take multiple steps to overcome. First there’s the cash Allanore will need to create a large-enough pilot reactor. He’ll have to get an engineering contractor with ties to the mining industry to manufacture an industrial-size reactor. Then he must demonstrate that, at that scale, using the reactor is more economical than the traditional smelting process.

“There’s always the question of who’s going to be funding,” Stillman says. “However, there are many copper miners who are interested in this kind of technology and its environmental benefits.”

Meanwhile, Respaut of the International Copper Association estimates that about 20 percent of global production already comes from mines that tap a process called hydrometallurgy. In this setup, water-based reagents dissolve copper from ore at ordinary temperatures to make a liquefied metal that can be purified through a method similar to the last step in use at smelting plants.

Hydrometallurgy, however, is suited only for oxide copper ore, which is less abundant than the sulfide copper ore that Allanore’s reactor could divert from traditional smelters. Moreover, hydrometallurgical processing still takes multiple steps to generate pure copper. When Allanore talks about the benefits of current-based metal processing, he means that in a single step, he can yield pure, liquid copper, ready to be shaped into wiring for electronics and battery-powered vehicles.

Still, his reactor is only a demo device capable of making just a couple of pounds of copper. Allanore wants to get it in front of several companies this year to demonstrate what high-quality, faster, more sustainable production looks like. After that, he hopes to conduct another round of testing, preferably in partnership with a smelting or mining site, to see if a larger reactor can reliably produce 1 ton of copper a day.

“We need to accelerate the way we can access high-purity copper,” he says. “And that’s really where novel technology and electrification has a key role.”

This story originally ran in the Summer 2022 Metal issue of PopSci, as the second piece in a three-part series about batteries. Read part one here, and keep a lookout for part three on our PopSci+ page.



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