Green steel startup Boston Metal is doubling down on critical metals

Boston Metal, a startup originally known for developing technology to decarbonize steel production, has raised $75 million to pivot its focus toward producing critical metals like niobium, tantalum, and nickel. The company’s molten oxide electrolysis (MOE) technology uses electric current to separate metals from ore, and a new commercial facility in Brazil will produce these higher-value metals, which are used in aerospace, medical devices, and electronics. The funding comes after a refractory system leak at the Brazil plant caused delays and cash-flow issues, leading to layoffs, but the company plans to restart operations by September 2026 and eventually produce metals like chromium in the U.S.

Green steel startup Boston Metal is doubling down on critical metals The company is focusing on metals like niobium, tantalum, and nickel rather than steel. 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 Unlimited. 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. Deep Dive Climate change and energy The snow gods: How a couple of ski bums built the internet’s best weather app “We were just trying to create something that made us happy.” The balcony solar boom is coming to the US Plug-in panels are getting popular—how do we make sure they’re safe? Is fake grass a bad idea? The AstroTurf wars are far from over. Around the country, heated debates are taking place over whether to install artificial turf, pitting neighbors against each other. The noise we make is hurting animals. Can we learn to shut up? The good news is it’s a problem we can solve if we want to. Stay connected Get the latest updates from MIT Technology Review Discover special offers, top stories, upcoming events, and more.