Clean cement startup Brimstone can make another key material: alumina

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.

Tariffs, funding turbulence ensnare aluminum production

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.