Mineralization is the family of carbon dioxide removal (CDR) approaches that convert CO₂ into solid carbonate minerals — the same calcium and magnesium carbonates that make up limestone and dolomite. Once CO₂ is bonded into a carbonate lattice, it is thermodynamically stable on geological timescales, which is why mineralization sits at the durable end of the CDR spectrum alongside geologic injection. The pathway matters because it offers storage that does not depend on monitored plumes, biological uptake, or intact ecosystems — and because the reactive feedstocks (basalt, peridotite, olivine, steel slag, cement kiln dust, mine tailings, alkaline ash) are already abundant, often as waste streams.

How it works

The underlying chemistry is silicate weathering, the same process that has regulated Earth’s climate over million-year timescales by acting as a geological thermostat. Divalent cations — chiefly Ca²⁺ and Mg²⁺ — released from silicate minerals react with dissolved CO₂ to precipitate carbonates. In nature this is slow; the engineering problem is acceleration.

Approaches split roughly into four groups:

  • In-situ injection. CO₂ dissolved in water is pumped into reactive host rock — basalt or peridotite — where it mineralizes within months to a few years. Field evidence from CarbFix in Iceland underpins commercial deployments in Oman and East Africa.
  • Ex-situ reaction. Crushed silicates (olivine, serpentine) or alkaline residues (steel slag, ash, cement fines) are reacted with CO₂ in reactors, producing carbonate powders or aggregates. Reaction kinetics of olivine in seawater and the role of basalt mineralogy in dissolution rate and nutrient release are active areas of characterisation.
  • Concrete and construction materials. CO₂ is bound during concrete curing, either injected directly into fresh mix, used to cure precast blocks, or embedded via supplementary cementitious materials produced from mineralized olivine or slag.
  • Enhanced weathering on land. Powdered silicates are spread on agricultural soils, where they dissolve and export bicarbonate to groundwater and eventually the ocean. Modelling for the United Kingdom suggests substantial national-scale drawdown potential, and ecosystem responses to powdered rock can compound the carbon effect via improved plant productivity, though the agronomic literature on remineralizing soils is older than the CDR framing.

Energy intensity, kinetics, and feedstock logistics — not chemistry — are what determine cost and net removal.

Who’s doing it

  • 44.01 (Oman, ~168 FTE) injects dissolved CO₂ into peridotite in the Hajar Mountains; probably the largest in-situ peridotite operator.
  • Cella Mineral Storage (US/Kenya) runs a comparable in-situ approach in Rift Valley basalts, partnered with several direct air capture (DAC) suppliers.
  • CarbonCure (Canada, ~81 FTE) is the most widely deployed concrete-injection licensor, retrofitted into hundreds of ready-mix plants.
  • Paebbl (Netherlands) reacts CO₂ with crushed olivine ex-situ to make a supplementary cementitious material — a bet that mineralization pays for itself via the cement market.
  • Neustark (Switzerland) captures biogenic CO₂ from biogas plants and mineralizes it into demolition concrete aggregate, coupling a biogenic source to a waste-mineral sink.
  • Travertine (US) uses an electrochemical process on sulfate wastes (phosphogypsum, tailings) that co-produces sulfuric acid; a Frontier pre-purchase recipient.
  • Arca (Canada) targets ultramafic mine tailings with churning rovers, aiming to slot into existing mining operations rather than build greenfield sites.
  • Andes (US, ~219 FTE) sits at the enhanced-weathering/soil-microbiome boundary, applying microorganisms with crop seeds to accelerate silicate weathering in the root zone — the most agronomic approach in the directory.

Smaller entrants such as Carbonaide, CarbiCrete, Blue Planet, C-Crete, and Anvil illustrate the range of feedstocks (slag, olivine, non-carbonate rocks, ores) and formats (blocks, aggregate, binder, direct air mineralization).

Durability and MRV

On paper, mineralization is the most durable CDR pathway: carbonate minerals are stable for >10,000 years absent strong acids or high temperatures. In practice, three durability questions matter.

Reaction completeness. Not all injected or reacted CO₂ mineralizes; some remains as dissolved bicarbonate or gaseous CO₂. Isotope tracing and post-injection coring are the current tools for in-situ work.

Feedstock lifecycle. Concrete-embedded CO₂ is durable so long as the concrete is not calcined; demolition and landfill are generally fine, but re-use pathways need tracking. For enhanced weathering, the carbon may reside as bicarbonate in soil water or riverine transport for centuries before final ocean sequestration — durable, but different from a solid carbonate.

Measurement. measurement, reporting, and verification (MRV) for in-situ mineralization relies on injectate mass balance, tracer chemistry, and reactive transport modelling. For enhanced weathering on soils, MRV is genuinely unsettled: cation flux, secondary mineral formation, and downstream reprecipitation all confound simple mass balance. Cross-pathway analysis of diverse CDR approaches and their energy–water–land tradeoffs is a useful backdrop for how buyers should weight these differences.

Open questions

  • Whether enhanced-weathering MRV protocols converge on a defensible field methodology, or whether registries continue to issue credits under materially different accounting assumptions.
  • Whether the ex-situ mineralized-SCM route (Paebbl, Co-reactive, Carbonaide) can compete on cost with unmodified Portland cement replacement, or requires a carbon-price floor to clear.
  • How much of the cost curve for in-situ injection is driven by CO₂ supply versus subsurface engineering — i.e., whether 44.01-style operations get cheaper on their own or wait on cheaper DAC.
  • Whether concrete-injection removals are counted as removal or as avoided emissions, an accounting boundary