This article is part of a two-part reporting project on decarbonizing aluminum production. Read our story on Kentucky’s green smelter dreams here.

On a muggy summer day in an industrial stretch of Brooklyn, New York, Josefa Marín stood in a sea of empty aluminum cans, methodically sorting the tall green Heinekens from blue-and-silver Red Bulls and bright red Coca-Colas. She put the different brands into separate garbage bags, filling each one up with exactly 144 beverage containers. All around her, mountains of bags crackled in the glaring morning light.

Marín is one of the thousands of independent ​“canners” who comb through New York City’s detritus to salvage many millions of cans, plastic bottles, and glass containers every year. Canners earn 5 cents for every unit they redeem under the state’s bottle bill. For some people, collecting is a way to bring home extra cash. But for many like Marín and her husband, Pedro Romero, this is how they earn a living.

“I started doing this little by little, but then other work opportunities began drying up. Now I do this 100 percent of the time,” Marín told me in Spanish. We spoke in late June under the shade of a plywood awning at Sure We Can, the nonprofit recycling center where Marín organizes her cans for beverage companies to come pick up.

In cities across the country, informal waste pickers are filling in the big gaps left by formal recycling programs: Americans throw away an estimated $800 million worth of aluminum drink cans alone every year. Canners help to keep significant volumes out of landfills, in turn reducing the need to produce aluminum from scratch.

Marín, who is 54, moved to New York nearly 40 years ago from her home in Puebla, Mexico, and has been canning for the last two decades. She estimated that, on a very good weekend, she and Romero can collect some 20,000 containers, earning about $1,000 for the haul, plus a few hundred extra dollars for sorting and bagging the cans. 

“I’m not going to be rich,” she said, ​“but this gives us stability.”

Workers like Marín and Romero represent a crucial link in the complex supply chain for aluminum recycling — one that begins with hands-on collecting and extends all the way to multimillion-dollar factories, where old car doors and building beams are melted down into fresh material. This vast network plays an increasingly vital role in limiting the carbon dioxide emissions that come from making the ubiquitous metal. 

Aluminum is the second-most-used metal in the world after steel, found in everything from frying pans, kitchen foil, and smartphones, to airplanes, bridges, and buildings. The lightweight material is also a key component of the clean energy transition, used to make low-carbon technologies like electric vehicles and solar panels, as well as the power cables and electronics supporting the modern grid.

But making primary, or virgin, aluminum is extremely carbon-intensive. Giant smelters consume inordinate amounts of electricity — typically derived from fossil fuels — and they require blocks of actual carbon to transform raw, powdery alumina into shiny aluminum metal. 

The process is responsible for the vast majority of the aluminum sector’s climate footprint, which amounts to 2 percent of global greenhouse gas emissions every year.

Making secondary, or recycled, aluminum is a much cleaner operation by comparison. Gathering scrap, melting it down, and molding it into new products or parts uses only 5 percent of the energy needed to make primary aluminum, resulting in dramatically lower emissions for the repurposed material.

“Secondary aluminum production in and of itself is a decarbonization tool,” said Caroline Kim, a technical analyst on climate and energy for the Natural Resources Defense Council, or NRDC.

The United States produced about 3.3 million metric tons of secondary aluminum in 2023, representing about 80 percent of total U.S. aluminum production last year, according to the U.S. Geological Survey. The aluminum industry likes to tout the fact that, because so much of America’s aluminum is recycled, products made here are significantly less carbon-intensive than aluminum made in countries such as China, which relies heavily on smelters.

But recycling alone can’t address aluminum’s outsize climate impact. To start, there’s not enough scrap metal to satiate the world’s ever-growing appetite for aluminum. And secondary producers themselves need at least some amount of virgin material to achieve the right degree of strength and durability in their finished products. 

For those reasons, Kim and other experts argue that the highest priority in the U.S. and globally should be tackling emissions from primary aluminum smelters. The most meaningful way to do that is to decarbonize the world’s electricity grid, so that aluminum manufacturers can access renewable energy around the clock. 

Still, there’s plenty more the aluminum industry can do to drive down emissions through recycling — both by recovering more material, and by cleaning up the recycling process itself. And with global aluminum demand set to increase by up to 80 percent by 2050, producers need all the low-carbon solutions they can find to tackle the metal’s industrial emissions.

“We need to both decarbonize primary aluminum production and continue to increase and optimize secondary aluminum production as well,” said Christina Theodoridi, who manages NRDC’s industrial policy team.

A sprawling, low-slung factory rises from the flat farmland in Henderson, Kentucky, a city of some 28,000 people spread along the Ohio River. Malia Sellers met me at the building’s entrance on a sweltering morning in early August. Soon we were surveying heaps of gleaming metal strips and shredded bits piled up in a scrap yard.

Sellers is the managing director for Hydro Aluminum​’s recycling plant in Henderson. Hydro, a Norwegian company, is one of the largest aluminum recyclers in the United States. Its facility in western Kentucky produces some 90,000 metric tons of secondary aluminum every year by turning old window frames, doors, car parts, and factory trimmings into log-shaped billets. Other companies later form those aluminum billets into new products, including bumpers and crash-safety features for lightweight vehicles.

The Henderson plant gets an assortment of scrap from a variety of places. It’s Micah Hall’s job to figure out exactly what kinds of metallic elements, and what quantities, are mixed in with the aluminum.

Hall met Sellers and me at the scrap yard and ushered us into a small side room. He slipped on a heavy reflective jacket and a protective face shield, then dumped a paint bucket full of metal pieces into a kind of cauldron, out of which a viscous shimmering liquid dripped into a crucible. He held up a solid silvery puck in his gloved hand to take to the laboratory.

“This is the most critical part of our process,” Sellers told me from where we stood across the hot, musty room. 

Aluminum products, especially safety components like bumpers, have specific chemistry requirements. Using a spectrometer in the lab, Hall can count the particles of, say, manganese or chromium in each sample puck. Then, as if concocting a recipe, he determines which scrap material and alloys should go together in the melting furnace to achieve the desired qualities.

Once a load of scrap is prepared, a giant railcar pushes it into the furnace’s fiery-orange cavern. 

Sellers and I watched as a skim paddle resembling a huge garden hoe combed over an eerily bright, opaque lake of liquid aluminum, removing impurities. A buzzer in my pocket vibrated, letting me know that, in trying to get a closer look, I’d moved within 10 feet of an operating vehicle. 

The molten aluminum is later poured over a sprawling casting table, where cylindrical molds reach down hundreds of feet into an underground pit. A crane then lifts and lays the metal logs on a long conveyor belt. Hydro employee Kris Dunlap showed me how he checks for any cracks or imperfections: by squirting a glob of gel onto a log and scanning it with a handheld ultrasound device. 

From there, the aluminum billets are baked in large industrial ovens, then sawed into pieces and piled up in the loading yard. Finally, the material is trucked to customers across the Midwestern U.S.

Earlier this year, Hydro announced it was investing $85 million to expand its Henderson facility to meet the growing demand from automakers, which are using more lightweight aluminum to make electric vehicles in particular. When completed in 2026, Hydro’s new casting line will have the capacity to produce an additional 28,000 metric tons of high-quality aluminum — mostly using end-of-life metal — that will then be made into automotive suspension components

“The more post-consumer scrap you can use, the lower the carbon footprint of your input material,” Duncan Pitchford, the president of Hydro’s U.S. operations, told me by phone. ​“And thus, the lower the carbon footprint of the material that we’re delivering to our customer.”

Hydro claims its aluminum has a relatively tiny carbon footprint — ranging between 0.5 and 4 kilograms of CO2 equivalent per kilogram of aluminum, depending on how a particular product is made, compared to the global average of 15.1 kilograms of CO2 equivalent for primary aluminum. 

Even so, the company continues to look for ways to clean up its operations. At the Henderson plant, Hydro recently installed a giant enhanced air-filter system, called a baghouse, to capture harmful particles that come off of end-of-life scrap that has paint or other contaminants. Globally, the company is ​“pursuing multiple pathways” to reduce emissions from its natural-gas-fired furnaces, including by testing green hydrogen and plasma technology in its European facilities, Pitchford said.

Most aluminum recycling facilities burn fossil fuels to achieve the extremely high temperatures required to melt and process metal. In North America, which has more recycling plants than primary smelters, this represents a significant chunk of the industry’s climate impact. Electrifying gas furnaces or swapping in cleaner fuels — such as hydrogen made from renewables — could reduce carbon emissions by 23 percent within the region, according to the Aluminum Association, a trade group.

In March, the U.S. Department of Energy announced nearly $100 million in project awards to help reduce and replace natural gas consumption at two aluminum recycling facilities: a Constellium plant in West Virginia and Golden Aluminum​’s operation in Fort Lupton, Colorado. The funding is part of a $6.3 billion demonstration program aimed at curbing greenhouse gas emissions from heavy-industry sectors. 

The federal initiative also includes major funding for decarbonizing primary production. Century Aluminum, the largest U.S. primary aluminum producer, is slated to receive a DOE grant of up to $500 million to construct a $5 billion ​“green smelter,” potentially in northeastern Kentucky. The facility could emit 75 percent less CO2 than traditional smelters, thanks to its use of carbon-free energy and energy-efficient designs.

In Colorado, Golden Aluminum will use the new funding for its ​“mini-mill,” a type of recycling facility that consolidates steps that otherwise happen in separate locations, such as collecting, melting, casting, and rolling scrap metal to make aluminum sheets. Caroline Kim of NRDC said that building more mini-mills nationwide would help improve the energy efficiency of recycling aluminum and cut down on transportation-related emissions.

Kim added that, as recyclers work to modernize their facilities, similar efforts are needed to improve collection methods for post-consumer aluminum — much of which still winds up in landfills due to the difficulty of separating and cleaning dirty, jumbled-up material. Hydro, for its part, is partnering with U.S. recycling company Padnos to install laser-based sorting technology at a sorting hub in Granville, Michigan, that will ​“dig deeper into the scrap pile” to recover and repurpose more aluminum alloys. 

Another key way to boost the supply of post-consumer aluminum is to keep it from being thrown away in the first place. 

Ryan Castalia spends his days surrounded by the heaps of soda cans and beer bottles that New York City’s canners have rescued from dumpsters and trash bins. Castalia is the executive director of Sure We Can, the nonprofit recycling center in Brooklyn where I first met Josefa Marín. Just inside the entrance, colorful murals were splashed across stacks of shipping containers, which overflowed with empty White Claws and Sprites.

In the U.S., some 1.9 million tons of aluminum containers and packaging wound up as waste in 2018, according to the most recent data from the U.S. Environmental Protection Agency. That’s equal to nearly half of all the aluminum the United States produced in 2023.

Castalia has pushed for years to improve recycling policy in New York state, advocating to expand the state’s 42-year-old program for redeeming beverage containers. When we met in late June, he seemed weary. A couple of weeks earlier, New York legislators had declined to advance legislation to raise the state’s deposit return fee from 5 cents to 10 cents a bottle. It also would have raised the handling fee that recycling centers like Sure We Can receive from 3.5 cents to 5 cents.

“The deposit was created as an incentive for folks to participate in the system, to actually bring back material to be recycled,” he said as we cooled off inside his cramped office trailer. ​“But the cost of living has gone up considerably in the last 40 years, and the incentive just isn’t what it used to be. It means that more containers get littered or end up in landfills and waterways. It also makes the situation for canners even harder.”

Around 150 redemption centers across New York state have closed their doors in the last two years, owing to rising rent and operational costs. As a nonprofit outfit, Sure We Can has been able to keep its doors open thanks to grants and tax breaks, Castalia said. Along with providing space to store and sort containers, the center offers a place where people can unwind and find community in an otherwise isolating and physically demanding job.

“You need faith to operate in this context,” Castalia said of the center’s work. ​“You have to envision that it will all make a difference.”

New York is one of 10 states with bottle bills, which vary by deposit value and the types of beverages they include. While these states make up 27 percent of the total U.S. population, they account for nearly half of all packaging that gets recycled, according to a 2023 industry report. Oregon — one of three states that refund 10 cents per container, instead of the more typical 5 cents —has the highest return rate of any state, with consumers turning in 87 percent of eligible beverage containers.

At the federal level, U.S. Senator Jeff Merkley (D-Oregon) is leading the push for a nationwide bottle bill to improve recycling efforts. But, as in New York, skeptics of the program have raised concerns that it would disrupt existing recycling systems, including by undermining the businesses that recover high-value materials from curbside collection.

The Aluminum Association says a variety of policies are needed to reverse a worrying trend: in recent years, the recycling rate for aluminum cans has dipped below the 20-year average of around 50 percent.

The trade group supports container deposit programs, which deliver a disproportionate amount of the high-quality and high-volume aluminum scrap that the secondary industry relies upon. It has also called for initiatives that effectively penalize people and companies for tossing out aluminum, including landfill tipping fees and ​“pay-as-you-throw” residential programs that charge people based on the weight of their garbage.

“The one thing that can move the needle on decarbonizing the industry, more than anything else in North America, is recycling policy,” said Chuck Johnson, CEO of the Aluminum Association. ​“We just have to have more aggressive recycling policies to get this material back at its end of life.”

In the meantime, places like New York City will continue to rely on informal waste collectors to pick up the slack and salvage the material that other people disregard, Castalia said.

Standing beneath the plywood awning, Pedro Romero said that, when he first started working alongside Marín, he never imagined they’d be paying their bills this way. ​“She’s my teacher,” he said as his wife sorted through countless cans, wearing a blue apron wrapped around her waist and a T-shirt proclaiming ​“No Stopping New York.”

For Marín, the best part of the work is staying active and meeting people at the center. ​“I like the coexistence here,” she said.