Century Aluminum has restored another 50,000 metric tons of annual primary aluminum capacity at its 46-year-old Mount Holly smelter in South Carolina, lifting total U.S. primary production by nearly 10%. The restart, announced on an earnings call last week by CEO Jesse Gary, makes Mount Holly — still the youngest smelter in the country — one of only four operating U.S. primary aluminum plants.

The operating number matters because the market has none to spare. A global aluminum supply deficit is expected to worsen this year after damage to major Middle Eastern smelters and shipping disruptions in the Strait of Hormuz amid the U.S.-Iran conflict. At the same time, surging U.S. electricity consumption is pulling on aluminum demand as transformer, cable and grid-equipment manufacturers scale output.

"There is very little cushion left anywhere in the system," Gary said. "In a market with no slack, the value of secure domestic units goes up."

Built capacity vs. announced projects

The Mount Holly restart is real, operating capacity. Everything else in the U.S. pipeline remains announced. Century partially idled the plant in 2015 over high electricity costs — the structural problem that shadows every smelter, each of which requires hundreds of megawatts of continuous power. Last fall, Century signed a new long-term power agreement for Mount Holly with utility Santee Cooper, whose generation mix runs more than half coal and roughly a quarter natural gas and oil.

Two larger moves would reshape the domestic supply picture if they clear their gates.

In Inola, Oklahoma, Century and joint-venture partner Emirates Global Aluminium are developing Oklahoma Primary Aluminum, a proposed 750,000-metric-ton smelter that would more than double U.S. primary capacity. Gary said the venture could break ground by the end of this year and produce "first hot metal by the end of 2029." The project carries a $500 million Department of Energy grant Century won in 2024 under a Biden-era industrial decarbonization program, and Inola was chosen partly for the state's natural gas, wind and solar resources.

Construction cannot start without a power contract. The developers have spent more than a year negotiating with the Public Service Company of Oklahoma and have "advanced negotiations toward a final energy contract," according to Gary.

The project also faces mounting political and legal resistance. Members of the Muscogee (Creek) Nation and Cherokee Nation have raised concerns about environmental impacts, and Muscogee leaders adopted a bill opposing smelter construction and operation on the reservation. Oklahoma Attorney General Gentner Drummond, a Republican gubernatorial candidate, has objected to the project's foreign ownership and pollution risks; on Aug. 11 he filed a motion to block construction while his lawsuit against the project proceeds. Century and EGA say the Inola facility will use the latest version of EGA's smelter technology and run significantly cleaner than existing U.S. plants. "We're working very closely with the community in Inola and elsewhere in Oklahoma to better understand what their concerns are and to make sure that they have all the facts about our technology and process," Gary said.

New Madrid restart hinges on tariff math

Some 420 miles east, Magnitude 7 Metals plans to partially restart its idled New Madrid, Missouri smelter before the end of this year. The company shut the 263,000-metric-ton facility in 2024 and laid off more than 500 workers after low aluminum prices and high power costs took their toll, Bloomberg reported. At the time, the plant represented roughly 30% of U.S. aluminum production capacity and was Missouri's single largest energy consumer.

On July 1, Magnitude 7 Metals said it will restart about 75,000 metric tons of annual production, crediting the Trump administration's Section 232 aluminum tariffs, which raise the cost of imported metal for cars, cans and construction. The White House followed last month with a related tariff program designed to further incentivize investment in new U.S. primary capacity.

Whether tariffs can offset electricity costs remains the open question. Annie Sartor, senior campaigns director at Industrious Labs, flagged Missouri's "large load" electricity tariffs — adopted in 2025 to make major power users cover grid-infrastructure costs — as a potential roadblock. "The smelter would face the same electricity cost structure as a data center — even though that same smelter has already curtailed operations twice [in 2016 and 2024] because of skyrocketing power costs," Sartor said on LinkedIn. "The policy challenge is clear: a framework created to manage data center growth could unintentionally make it harder for manufacturers to operate, create jobs and support local economies."

Magnitude 7 Metals has not disclosed how it will power the partially reopened plant; the company did not respond to questions. Historically the smelter drew on the New Madrid coal plant, which in 2020 emitted more nitrogen oxides than any other power plant in the region and the country. A March survey by Industrious Labs found residents in southeastern Missouri back the restart but worry it will increase pollution unless the plant shifts off coal.

"Long-term economic investment will be more likely if this operation is powered by clean energy, especially solar and storage," Jenn DeRose, Sierra Club's Beyond Coal campaign strategist in Missouri, said in a July 1 statement. "Powering the smelter with clean energy will help ensure the smelter's long-term viability by leveraging affordable, fixed-cost energy, and cleaner air for everyone who lives in New Madrid County and beyond."

What decides what happens next

Three milestones now set the pace: a final energy contract between Oklahoma Primary Aluminum and the Public Service Company of Oklahoma before any groundbreaking; the outcome of Drummond's lawsuit and the Aug. 11 injunction motion; and whether Magnitude 7 Metals secures a workable power arrangement under Missouri's large-load tariff before year-end. Each one turns on electricity — the input that idled Mount Holly in 2015 and New Madrid in 2024, and the variable that will determine whether this recovery adds tonnage or stalls on paper.