Brimstone plans to expand beyond cement with low-carbon aluminium production

Since its launch in 2019, the U.S. startup Brimstone has emerged as a trailblazer in low-carbon cement production. Now, Brimstone is planning to expand its approach to tackle another high-emissions industry: aluminium production. Its innovative technology eliminates the need for limestone—a carbon-heavy rock that emits significant greenhouse gases when heated in kilns.

Based in Oakland, California, Brimstone sources carbon-free rocks that are abundant in the United States but are mostly used today as aggregate for roads and buildings. The company pulverizes these rocks and applies chemical agents to extract valuable minerals. Certain compounds are then heated in a rotary kiln to produce industry-standard cement.

"Alumina is a very high-value product that allows us to get into the market…and be very investable in the beginning," said Cody Finke, co-founder and CEO of Brimstone, in an interview with Canary Media. He explained that alumina production could help his team "bridge that valley of death" while scaling up low-carbon cement manufacturing, which he described as a "larger but less economically driven" aspect of the business.

Last month, Brimstone announced that its innovative process could also generate alumina—the primary ingredient in aluminium, a lightweight metal used in everything from household appliances and smartphones to buildings, bridges, and aeroplanes. Aluminum also plays a crucial role in clean energy technologies, including solar panels, heat pumps, power cables, and electric vehicles.

Brimstone's sustainable alternative

Today, alumina production relies on extracting and refining bauxite, a reddish clay ore mined in just a few countries, through environmentally harmful methods. The United States imports nearly all of its alumina to sustain its massive, energy-intensive smelters, with over half coming from Brazil and the rest primarily sourced from Australia, Jamaica, and Canada.

Brimstone proposes a more sustainable alternative, potentially reducing or eliminating the need to mine bauxite abroad—a process that generates large volumes of toxic waste. Instead, the company plans to supply U.S. aluminium smelters using abundant calcium silicate rocks from domestic quarries and employing chemicals that can be recycled more efficiently than those used in traditional bauxite refining.

This strategy could also help the six-year-old startup navigate the challenging early phase that many newcomers face when entering large, established industries. Cement is inexpensive and widely available, and the construction sector tends to resist straying from traditional—albeit carbon-intensive—methods. However, despite its critical role in the nation's economy, the U.S. produces relatively little smelter-grade alumina, presenting Brimstone with a unique opportunity to fill this gap.

Despite policy uncertainty, there are clear advantages to producing alumina from non-bauxite sources within the United States. Using less environmentally intensive methods—and supplying alumina to smelters powered by clean energy—could significantly reduce U.S. emissions while providing essential metal for domestic manufacturers. Additionally, decreasing reliance on imports would help shield the country from supply chain disruptions and national security risks, as highlighted in a 2018 U.S. Department of Commerce report.

Three U.S. states—Alabama, Arkansas, and Georgia—mine small amounts of bauxite for chemical and industrial applications. The country's only alumina refinery in Louisiana relies on imported bauxite to produce alumina for aluminium smelting. However, the vast majority of global alumina production takes place in countries with significantly larger bauxite reserves.

A new plant in Oakland

Backed by over $60 million in venture funding, Brimstone is set to launch a pilot plant in Oakland later this year, producing both alumina and Portland cement—the dominant form of cement used today—along with supplementary cementitious materials. The company also plans to construct a $378 million commercial demonstration plant by the end of the decade, though the location has yet to be determined.

Brimstone plans to source rocks from existing surface quarries throughout the United States. At its future commercial demonstration plant, approximately 20 per cent of the total output will be smelter-grade alumina, while the remaining materials will be used as inputs for concrete production.