The pile of steel slag sitting outside a factory might look like refuse. But to a small team of metallurgists working from Vienna's Millennium Tower, it represents something closer to opportunity—a vessel for locking away carbon dioxide, possibly forever, while producing materials the construction industry actually wants.
sequestra, the Vienna-based startup behind that vision, has pulled together just over €3 million in a mix of equity and public grants. It's not a massive sum by venture standards, but it might be enough to prove whether their Accelerated Carbonation Technology—a process that mineralizes CO2 into industrial leftovers like steel slag, incineration ash, and demolition rubble—can work at commercial scale.
The funding arrives in pieces. A €1.1 million pre-seed round closed this past February, led by Carbon Drawdown Initiative, VSE Beteiligungs-GmbH, and Climate Founders. That came alongside a €1.9 million grant from Austria's FFG (Austrian Research Promotion Agency), announced late last year to support a two-year scaling project. An earlier FFG "Basisprogramm" grant of €1.2 million is also part of the total. All told, the company has secured roughly €4.2 million.
Permanent Storage, With a Regulatory Twist
What sets sequestra apart—at least according to its founders—is the claim of permanence. The company's process doesn't just capture CO2; it binds it chemically into solid materials: carbonated aggregates, cement constituents, bricks. And crucially, under recently updated EU Emissions Trading System rules, this kind of permanent carbon capture and utilization (CCU) qualifies for exemptions from surrender obligations. For heavy industrial emitters navigating compliance costs, that distinction matters.
The technology can sequester up to 300 kilograms of CO2 per ton of residue, depending on what you feed it. It's not a one-size-fits-all proposition. Different waste streams—steel slag versus ash from municipal incinerators—require different handling, which is why sequestra operates what it describes as an integrated platform: an analysis facility, empirical modeling tools, and in-house measurement and verification capabilities tailored to industrial carbonation plants.
By early this year, the team had aimed to complete its first rapid-testing automated analysis facility, though timelines in early-stage hardware ventures have a way of slipping.
The Race to One Ton Per Hour
The near-term target is straightforward, if ambitious: continuous processing capacity of one ton per hour within two years from early 2026. It's the kind of throughput that would signal a shift from pilot-scale tinkering to something industrially relevant—perhaps more than the founders initially expected when they first spun the company out of their shared studies in metallurgy and recycling at Montanuniversität Leoben.
DI Dr. Lukas Höber, DI Roberto Lerche, and DI Gero Schwarz—the three co-founders—grew the team from four to 15 employees over the course of last year. The headcount is overwhelmingly technical: 92 percent engineers and scientists, concentrated in one Vienna office. It's a composition that reflects both the complexity of the challenge and the early stage of the business.
A Crowded Field, With Room for Nuance
sequestra is hardly alone in chasing carbon mineralization. Swiss competitor neustark, which raised a hefty €64.3 million in mid-2024, now operates 19 plants across the DACH region. UK-based 44.01 pulled in €33.9 million around the same time for its peridotite mineralization approach. More recently, Finland's Carbonaide announced a fresh €3.7 million raise to scale CO2-cured concrete, while UK's O.C.O Technology secured a multi-year carbon credit investment from Rothschild & Co.
The field is getting crowded, in other words. But there's nuance beneath the competition. Each approach targets different waste streams, different chemistries, different end markets. sequestra's bet is that the regulatory environment—specifically, the EU's evolving stance on permanent CCU—will create demand among industrial operators who need compliance solutions that go beyond mere offsetting.
Whether that bet pays off depends on execution. The FFG project funding buys sequestra two years to optimize its process, automate its materials analysis, and hit that one-ton-per-hour benchmark. After that, the company will need to prove it can sell what it produces—and convince industrial emitters that mineralized waste is worth integrating into their compliance strategies.
For now, it's a small team with big ambitions and a modest war chest, working in a corner of the climate tech landscape where chemistry meets regulation, and where yesterday's industrial waste might—just might—become tomorrow's carbon sink.
