Around the world, smelters use massive amounts of electricity — often generated by fossil fuels — to turn raw materials into aluminum. As more carbon-free energy comes onto the grid, these power-hungry facilities will get progressively cleaner. But smelters will never be entirely emissions-free until producers can solve a much trickier technical problem.
That’s because modern aluminum plants rely on a 19th-century process that uses big blocks of carbon, which account for almost one-sixth of the greenhouse gases associated with producing new aluminum globally. Replacing the blocks is crucial to decarbonizing this key industrial process.
Now the industry may be one step closer to reaching that goal.
Earlier this month, the Canadian firm Elysis said it hit a major milestone when it deployed an industrial-size, carbon-free anode inside an existing smelter in Alma, Quebec. Elysis is a joint venture of the U.S. aluminum giant Alcoa and global mining company Rio Tinto, both of which produce aluminum in the Canadian province.
“This is really a first for the aluminum industry, and a worldwide first as well,” François Perras, president and CEO of Elysis, told Canary Media.
Elysis installed its “inert,” or chemically inactive, anode technology in a 450-kiloampere (kA) cell, the same amount of electric current used in many large, modern smelters. The full-scale prototype is a significant step up from the company’s 100 kA pilot unit, which has produced low-carbon aluminum used in certain Apple laptops and iPhones, Michelob Ultra beer cans, and the wheels for Audi’s electric sports car.
Elysis launched in 2018 and has raised over 650 million Canadian dollars ($460 million) in investment for the effort, including from the governments of Canada and Quebec. The 450 kA cell will undergo several more years of testing as the company works to measure and validate how the larger unit performs inside a commercial smelter.
Rio Tinto, meanwhile, has already licensed the inert-anode technology from Elysis. The manufacturer plans to build a demonstration plant with 10 of the 100 kA cells at its existing Arvida smelter in Quebec, possibly by 2027, through a joint venture with the provincial government.
“We’re trying to replace a process that has been used for close to 140 years,” Perras said of the initiatives.
Smelting involves dissolving powdery alumina in a molten salt, which is heated to over 1,700 degrees Fahrenheit. Large carbon anodes are lowered into the highly corrosive bath, and electrical currents run through the entire structure. Aluminum then deposits at the bottom as oxygen combines with carbon in the blocks, creating CO2 as a by-product. It also releases perfluorochemicals (PFCs) — long-lasting greenhouse gases — as well as harmful sulfur dioxide pollution.
The anodes themselves are made using petroleum coke, a rocklike by-product of oil refining.
The Hall–Héroult process was revolutionary, but it is extremely energy-intensive. Most of the emissions associated with producing aluminum are tied to electricity production. In the United States, more than 70% of CO2 pollution from six operating smelters came from the power supply in 2021, according to the Environmental Integrity Project. (The U.S. now has four smelters left, three of which rely on fossil-fuel power.)
Another 20% of U.S. smelters’ carbon emissions were directly from the electrochemical process, the EIP study found. Smelting was also responsible for virtually all the PFCs reported by metal producers to the Environmental Protection Agency that year.
The solution to reducing electricity-related emissions is relatively straightforward: Deploy vast amounts of wind, solar, battery storage, and other clean energy sources. But completely eliminating emissions from the smelting process requires redesigning how the anodes and cells work — and researchers are only just beginning to develop alternatives.