Teaching limestone to capture carbon faster.

A rock with another working life

Limestone is already a store of carbon. Heirloom’s proposition is to make it work another shift: release its carbon dioxide under controlled conditions, prepare the remaining material to absorb CO₂ from ordinary air, and repeat. Instead of inventing an exotic substance to catch carbon, the company is trying to turn a familiar mineral into reusable industrial equipment.

The distinction matters because direct air capture has to do something unusually demanding. It collects carbon dioxide after it has dispersed into the atmosphere, rather than intercepting a concentrated stream at a factory. Heirloom combines that task with mineral chemistry, using heat, water and carefully managed exposure to air. The intended product is not the limestone itself but a measured service: removing atmospheric carbon and putting it somewhere durable.

That makes the company an experiment in industrial repetition. A mineral reaction must become a dependable cycle, and the cycle must become a business whose customers pay for a climate outcome they cannot see. The interesting question is not whether limestone can bind carbon. It is whether that chemistry can be organized into affordable, verifiable removal at a meaningful scale.

Speeding up the return to stone

Heirloom describes a process that begins by heating limestone powder in a kiln powered by renewable energy. This releases CO₂ and leaves calcium oxide, which is hydrated to make calcium hydroxide. The material then takes up carbon dioxide from the air as it returns toward its carbonate state. Heirloom says its technology reduces that absorption time from years to less than three days.

The company spreads the prepared material across vertically stacked trays and treats it to improve uptake. Once carbonated, the material returns to the kiln, releasing captured CO₂ for storage and starting another cycle. Heirloom identifies underground storage and incorporation into concrete as destinations for the separated gas. The trays and repeated handling are as central to the proposition as the chemical reaction.

Abundant feedstock is an attractive starting point, not a complete cost calculation. Heating material, moving it repeatedly and arranging permanent storage still require infrastructure and energy. Nor is every molecule released from newly introduced limestone a new atmospheric removal. The meaningful climate measure must distinguish the mineral’s original carbon from subsequent atmospheric uptake and account for emissions incurred along the way.

The founder behind the mineral loop

Heirloom’s investor Lowercarbon Capital dates the company to 2020 and identifies Shashank Samala and Noah McQueen as co-founders. Their backgrounds connected two different parts of the problem: Samala had co-founded electronics manufacturing company Tempo Automation, while McQueen brought chemical-engineering research and co-invention of the technology. Building a removal company required both a scientific mechanism and a way to turn it into repeatable operations.

In a 2021 MCJ podcast profile, Samala’s motivation is linked to growing up in southeast India and seeing the effects of climate change on people there. Before Heirloom, he was an entrepreneur in residence at the carbon-removal policy organization Carbon180. That history places the company’s origin somewhere more specific than a generic interest in sustainability: an encounter with climate vulnerability followed by work on how atmospheric carbon might actually be removed.

The pairing also helps explain the company’s choice of problem. This is neither simply a materials discovery nor simply a manufacturing exercise. It asks whether an established mineral reaction can survive the practical demands of plant design, equipment, financing and customers. The founders’ respective experiences meet at that boundary, where a promising laboratory process has to become an operating system.

What Tracy actually established

In November 2023, Heirloom unveiled its direct air capture facility in Tracy, California. Its announcement gave a capture capacity of up to 1,000 metric tons of CO₂ a year, with captured carbon destined for storage in concrete. The company’s projects page identifies CarbonCure as its partner in incorporating the captured CO₂ into concrete used in buildings and structures.

Tracy gives the story a physical anchor: a facility rather than only a process diagram. It connects air capture to a storage route and to commercial removal purchases. Yet the wording of the capacity figure matters. Up to 1,000 tons a year is a design capability, not evidence that the facility has delivered that quantity in a particular operating year. The cited announcement does not supply a year-by-year record of net removals.

The achievement should therefore be read at its actual scale. Tracy demonstrates deployment of Heirloom’s approach and a concrete destination for its captured carbon. It does not, by itself, establish the economics of a much larger plant. The next industrial test is whether repeated cycles and expanded equipment can produce reliable output without an equally rapid expansion in cost and resource demand.

Louisiana, and the changing federal bargain

Project Cypress moved Heirloom into a different scale of ambition. In March 2024, the US Department of Energy announced more than $50 million for the hub’s initial phase, covering planning, design, and community and labor engagement. Battelle manages the project, with Heirloom and Climeworks providing distinct capture technologies. That initial award was not a payment of the full potential hub allocation to Heirloom.

Heirloom’s published Louisiana plan places two facilities at the Port of Caddo-Bossier near Shreveport. It describes an initial 17,000-ton annual-capacity facility targeted for 2026, followed by a separate Project Cypress facility with 100,000 tons targeted for 2027 and another 200,000 in subsequent years. Those are company development targets, not confirmation that the capacity has entered service. The company describes the hub as eligible for up to $600 million in federal funding.

The federal position subsequently became uncertain. MIT Technology Review reported in October 2025 that an internal DOE list marked initial Cypress funding for termination; DOE said no final decision had been made. In April 2026, Heatmap reported that Cypress and the South Texas hub had passed the department’s review and could proceed. It also reported that the companies had never received termination letters and that funding amounts and possible modifications remained unclear. This is a story of threatened withdrawal and renewed permission to advance, not a verified cancellation followed by a fully funded restart.

Capital is not the same as removal

Heirloom announced a $150 million Series B financing in December 2024, co-led by Future Positive and Lowercarbon Capital. Participants included companies associated with aviation, shipping and manufacturing, among them Japan Airlines, Mitsui & Co. and Siemens Financial Services. The financing shows that investors were prepared to fund further development; it does not establish a profitable removal price or guarantee future plant performance.

The business has several separate milestones that can easily be collapsed into one optimistic narrative. Raising equity finances a company. Securing public support helps develop infrastructure. Selling removal services creates an obligation to customers. Operating a plant and documenting durable net removal fulfills a different task again. Heirloom’s progress is more intelligible when those milestones are kept separate rather than treated as interchangeable evidence of scale.

The same discipline applies to the low-cost argument. Limestone’s availability may help, but the finished service includes energy, plant operations and storage. Heirloom’s financing announcement emphasizes affordability as the condition for expansion. That is a statement of commercial strategy, not a disclosed, independently demonstrated cost per net ton at its planned Louisiana scale.

Why Global58 noticed them

Global58 noticed Heirloom because it makes an abstract climate proposition unusually tangible. A familiar rock, prepared and circulated through industrial equipment, becomes a way to ask whether society can retrieve some of what it has already emitted. The editorial interest lies in that meeting of ordinary material and demanding infrastructure, rather than in a claim that one company has solved atmospheric cleanup.

This classification is not a ranking or endorsement. Heirloom is worth examining because its work exposes the real conditions of carbon removal: useful chemistry, energy requirements, storage arrangements, patient capital and public decisions. Tracy provides an operating foothold; Louisiana shows how much more must align before a small facility becomes a larger industrial system. Neither makes the remaining uncertainties disappear.

The limit is also the point

The International Energy Agency places direct air capture within a portfolio of responses to climate change, including ways to balance residual emissions and address historical pollution. It explicitly says carbon removal is not an alternative to cutting emissions or a reason to delay action. That boundary is essential to understanding Heirloom: removing yesterday’s carbon cannot become permission to keep adding avoidable emissions today.

What to watch next is consequently more demanding than another capacity announcement. Evidence of sustained operation, measured net removal, durable storage and the practical cost of expansion would say more than a rendering of a future facility. In Louisiana, the questions include how renewed federal permission translates into funding, project design and delivery. The published dates remain targets until operating evidence catches up.

Heirloom matters because it is trying to give a slow natural process an industrial cadence. Whether that becomes a durable business depends on much more than making limestone absorb carbon faster. It depends on proving that the entire chain, from electricity and mineral handling to storage and accounting, produces a credible climate benefit worth paying for. That is both a narrower promise than undoing climate change and a substantial undertaking in its own right.