Magnitude 7 Metals plans to restart its aluminum smelter in southeast Missouri by the end of the year, reviving production at a facility that has been idle since 2024 and that’s been long scrutinized for its sulfur dioxide emissions.
The company announced it expects to resume operations in Marston before year's end, but it has not disclosed how it will power the energy-intensive facility or provided a more specific timeline.
Before the smelter shut down, air monitors showed the surrounding area exceeded the federal one-hour sulfur dioxide standard, prompting the Missouri Department of Natural Resources to develop an air quality plan to bring the area into compliance with the Clean Air Act. The state and the company reached an agreement in 2022, requiring pollution control measures and continued air monitoring.
Stephen Miller, manager of the Missouri Department of Natural Resources' Air Pollution Control Program, said the department will continue overseeing sulfur dioxide monitoring after the plant resumes operations.
"If there is a condition in an agreement that triggers some type of penalty, that may occur, but it depends on what the situation is in the future," Miller said. "Again, we do try to achieve compliance through assistance with companies."
According to the department, sulfur dioxide monitoring data for 2025 and 2026 has remained below the federal one-hour standard while the smelter has been idle. However, compliance with the standard is determined using a three-year average.
The 55-year-old smelter has changed ownership several times over the decades. Magnitude 7 Metals acquired the facility in 2018 after Noranda Aluminum filed for bankruptcy.
Environmental groups say the company should disclose how it plans to power the facility once it reopens. Jenn DeRose, Missouri strategist for the Sierra Club's Beyond Coal Campaign, said the electricity source will affect both the plant's operating costs and local air quality.
"We don't want to see people lose their jobs, but it's really important that people have clean air as well," DeRose said. "It's really important that, if they do indeed reopen the plant, they're powering it with clean energy to give the best possible outcome, both to the workers and to the community members."
Miller said the Department of Natural Resources does not know which power source or generating plant will supply electricity to the smelter. He said any Missouri power plant providing electricity would be required to operate under permits issued by the department's Air Pollution Control Program and comply with Clean Air Act requirements.
"We don't know which power plant specifically is going to provide power to this installation," Miller said. "As long as they're operating under that issued permit, they'll be in compliance with the standard."
The restart comes as the federal government has renewed its focus on expanding domestic aluminum production. The Trump administration has made rebuilding domestic manufacturing a priority, including an effort to expand U.S. aluminum production. Earlier this month, the administration announced support for a $4 billion aluminum smelter project in Oklahoma, coupled with tariff incentives, marking what officials say would be the first new primary aluminum smelter built in the United States in 45 years.
According to the U.S. Department of Energy, only four primary aluminum smelters are currently operating in the United States, down from dozens in previous decades as facilities closed because of high electricity costs, aging infrastructure and global competition.
