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Since launching in 2019, the U.S. startup Brimstone has positioned itself as a pioneering producer of low-carbon cement. The company’s technology can make the essential material without using any limestone — the carbon-rich rock that, when heated up in fiery kilns, releases huge amounts of planet-warming gases into the air.
Now, Brimstone is looking to use its same process to supply another emissions-intensive industry: aluminum production.
The Oakland, California-based company sources carbon-free rocks that are widely available in the United States but are primarily used today as aggregate for building and road construction. Brimstone pulverizes those rocks and adds chemical agents to leach out valuable minerals. Certain compounds are then heated in a rotary kiln to make industry-standard cement.
Last month, Brimstone announced that its novel approach can also yield alumina, which is the main component of aluminum — the lightweight metal found in everything from household appliances and smartphones to buildings, bridges, and airplanes. Aluminum is also a key ingredient in many clean energy technologies, such as solar panels, heat pumps, power cables, and electric vehicles.
Alumina production today involves extracting and refining a reddish clay ore called bauxite from a handful of countries using environmentally destructive methods. The United States imports nearly all of the alumina it needs to feed its giant, energy-hungry smelters. Over half that supply comes from Brazil, with Australia, Jamaica, and Canada providing most of the rest.
Brimstone says its approach could reduce or supplant the need to scrape bauxite from overseas mines, a process that generates copious amounts of toxic waste. Instead, the company aims to supply U.S. aluminum smelters by sourcing common calcium silicate rocks from domestic quarries and by using chemicals that can be more efficiently recycled than bauxite.
The strategy might also help the six-year-old startup navigate the fraught early period that many newcomers face when trying to break into giant, incumbent industries. Cement is a fairly cheap and abundant material, and the construction sector is inherently wary of deviating from tried-and-true — if carbon-intensive — practices. But the U.S. makes relatively little smelter-grade alumina, despite the essential role it plays in the country’s economy.
“Alumina is a very high-value product that allows us to get into the market…and be very investable in the beginning,” Cody Finke, Brimstone’s co-founder and CEO, told Canary Media. He said that producing alumina could help his team “bridge that valley of death” as it works to scale low-carbon production of cement, which he described as a “larger but lower economic driving force” for the business.
The company, which has raised more than $60 million in venture funding, is slated to open a pilot plant in Oakland later this year that will produce alumina alongside Portland cement — the product that comprises the vast majority of cement made today — and supplementary cementitious materials. Brimstone also plans to build a $378 million commercial demonstration plant by the end of the decade, the site for which is still being decided.
Brimstone is expanding its scope during an especially dynamic period for the aluminum sector.
In recent decades, U.S. aluminum producers have significantly reduced domestic production in response to spiking energy prices and increased competition from China. That in turn has reduced alumina demand from U.S. smelters — which dissolve the alumina in a molten salt called cryolite, then heat and melt it to make aluminum metal. From 2019 to 2023, U.S. alumina imports fell by nearly 33% as manufacturers closed or curtailed their operations.
President Donald Trump has called for imposing fresh tariffs on U.S. aluminum, copper, and steel imports as a way to “bring production back to our country,” and his administration this week imposed or threatened duties on imports from Canada, Mexico, and China, a sweeping action that affects aluminum products. Industry analysts told Reuters that aluminum tariffs would result in higher costs for U.S. consumers, at least until domestic output ramps back up. The country-focused tariffs have already sparked volatility across commodities markets.
At the same time, however, Trump is trying to block federal investments that could boost domestic production of both aluminum and alumina.
Century Aluminum, for example, is set to receive up to $500 million from the U.S. Department of Energy to build the nation’s first new smelter in 45 years. The Biden administration finalized the award on January 15 as part of its larger initiative to slash emissions from industrial manufacturing. Century’s “green smelter” — the location of which hasn’t been announced — will purportedly emit 75% less carbon dioxide than traditional smelters, thanks to its use of carbon-free energy and energy-efficient designs.
The DOE award is currently entangled in Trump’s freeze on tens of billions of dollars in congressionally mandated climate and energy spending. Brimstone is also affected by the pause. In December, the DOE awarded Brimstone up to $189 million to cover half the cost of its planned commercial demonstration plant.
Brimstone declined to comment on the federal funding fracas, which remains in flux even though federal courts have ordered the flow of investment to resume.
Despite the policy uncertainty, there are still potential upsides to making alumina from alternatives to bauxite and within the United States.
Producing alumina using less environmentally intensive techniques — and supplying that material to smelters powered by clean energy — would help lower emissions across the U.S. supply chain and provide much-needed metal for domestic manufacturers. Lessening the country’s reliance on imports could also help insulate the United States from supply chain disruptions and national security risks, according to a 2018 report by the U.S. Department of Commerce.
“Aluminum is a linchpin of domestic aerospace, defense, and automotive applications,” Kevin Kramer, a former executive for U.S. aluminum maker Alcoa who is now a Brimstone senior advisor, said in a statement. “Establishing a new alumina source stateside is vital, and Brimstone’s 100% U.S.-based solution is exactly what the industry needs.”
Three U.S. states — Alabama, Arkansas, and Georgia — mine small amounts of bauxite for chemical and industrial applications. The nation’s single alumina refinery, located in Louisiana, uses imported bauxite to make alumina for aluminum smelting. But most of the world’s alumina production happens in other countries with much larger bauxite deposits.
Other types of minerals and clays also contain alumina, though the modern industry only deals with bauxite. That’s because of “the relatively straightforward nature of extracting bauxite, combined with its commercial abundance,” Adam Merrill, a mineral commodity specialist at the U.S. Geological Survey, said by email. Nearly all commercially produced alumina uses the Bayer process, which involves dissolving bauxite in a high-temperature caustic solution and filtering it to remove impurities.
“Today, the process is used much in the same way as when it was patented in 1888,” he added.
Merrill said that, aside from Brimstone, he isn’t aware of other current research efforts that involve using calcium silicate rocks for alumina production. Earlier studies in the mid-20th century pointed to the fact that silicates contain relatively tiny quantities of alumina — meaning producers would have to dig up substantially more rocks to match what they’d get from bauxite.
Finke said that Brimstone’s answer to this challenge is “co-production,” something he said the industry hasn’t tried before in a meaningful way.
“We’re not just taking the bit of alumina that’s in this and then throwing the rest out,” he said, holding up a small chunk of the silicate rock basalt. “We’re additionally making Portland cement and supplementary cementitious materials. That’s really what our insight was.”
Brimstone plans to mine rocks from existing surface quarries across the United States. At its future commercial demonstration plant, about 20% of its total product will be smelter-grade alumina, with the remaining materials turned into inputs for concrete.
“This would be the first time that alumina is produced from a rock quarry in the United States in a generation,” Finke said of the facility.
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