The startup Boston Metal has raised a $75 million funding round to produce critical metals, MIT Technology Review can exclusively report.  

The company has been known largely for its efforts to clean up steel production, an industry that's responsible for about 8% of global greenhouse emissions today. With the additional money, the new focus could help it survive at a time when support for industrial decarbonization has been waning in the US.

In addition to steel, Boston Metal has also worked to use its technology with other metals, and a subsidiary (Boston Metal do Brasil) is setting up a commercial facility in Brazil to produce niobium, tantalum, and tin. The funding will help support that facility’s operation as well as future efforts to produce critical metals like vanadium, nickel, and chromium, says CEO Tadeu Carneiro. The funding comes after the company faced cash-flow problems following an industrial accident at the Brazil facility earlier this year.

Boston Metal’s core technology is called molten oxide electrolysis (MOE). It involves running electric current through a reactor filled with ore dissolved in a molten electrolyte. The electricity heats everything up to about 1,600 °C (3,000 °F) and drives chemical reactions that separate the desired metal (or metals) from the ore. The metal gathers at the bottom of the reactor, where it can be siphoned off.

In early 2025, Boston Metal completed the largest run of its pilot industrial cell in Woburn, Massachusetts, producing about a ton of steel.

But the focus is currently on making other metals, which are more valuable and can command a higher price. The company’s Brazilian subsidiary is working to test and start up an industrial-scale plant that takes in a low-grade material and makes a mixture of critical metals. Niobium, for example, is used in some steel alloys, as well as in alloys used to make jet engines and the superconducting magnets of MRI scanners. Tantalum is used in aerospace applications like rocket nozzles and turbine blades, as well as medical devices and electronics.

Construction on the Brazil plant kicked off in 2024 and took about 18 months, but the company ran into some challenges that delayed official startup.

In January there was an issue with the plant’s refractory system, the equipment that insulates the reactor and prevents corrosion. That caused electrolyte to leak. Operators shut down the system and removed the metal, and there weren’t any injuries or environmental issues, Carneiro says.

But the leak did interfere with the timeline for the plant’s opening, which meant the company missed a milestone and lost out on funding that had been committed. It restructured and laid off 71 employees in April.

This new funding will help support the plant moving forward. “Because of this delay, we had a big stress in our cash flow, so the investors came very strong to support us,” Carneiro says. Boston Metal is repairing the facility in Brazil now, and it should be ready to start up in September 2026, he adds.  

The funding will also help support other critical metals projects, Carneiro says. The company plans to eventually deploy a US plant to produce chromium, a metal the country imports nearly all its supply of today. 

Boston Metal has now raised over $500 million in total. The latest round of funding includes support from existing investors and from the massive Indian steel company Tata Steel Limited.

Making a higher-value critical metal now could help Boston Metal prove its technology and pave the way for future steel projects, says Seaver Wang, director of climate and energy at the Breakthrough Institute. “Nobody wants to pay a green premium for steel—hence niobium,” he adds.

Correction: An earlier version of this article incorrectly named an investor as Tata Steel Unlimited. The company is Tata Steel Limited.