"Due to abnormally cold weather, our operations have been severely impaired to the point where they cannot be restored while running," the Heartland News report cited the letter from Magnitude 7 Metals Llc as saying.

The letter added that Magnitude 7 would continue looking for fresh capital from potential investors to restart the smelter in the future.

The 263,000 tonne-a-year smelter in Missouri's New Madrid county restarted in mid-2018 after Swiss-based ARG International AG, led by former Glencore trader Matt Lucke, bought it out of bankruptcy from Noranda.

In an emailed response, Lucke refused to comment beyond confirming the curtailment decision.

The plant employs around 450 union workers, and according to a Reuters review of pollution monitor data for 2019, chemicals and soot pouring out of its smokestacks consistently produced the dirtiest air recorded in America.

Industrious Labs, a nonprofit working on the energy transition, said the main challenge for aluminum plants today is the high cost of electricity, which makes up around 40% of their total production costs.

"The announcement is yet another blow to the fragile primary aluminum industry in the United States and a clear signal that the Biden Administration must act swiftly to secure renewable affordable energy to retain this essential material for America's economy," said Annie Sartor, Aluminum Campaign Director for Industrious Labs.

The United States had 23 operating plants in 1998. It now has five, including Magnitude 7, with many of the lost smelters dismantled and sites reclaimed.

In March 2023, Alcoa (AA.N) announced the permanent closure of its 279,000 tonne-per-year Intalco aluminum smelter in Washington state to prepare the site for redevelopment.

In June 2022, Century Aluminum idled its Hawesville, Kentucky, smelter after the power cost to operate the plant more than tripled.