Geologic CO₂ mineralization: Science, scale, and commercialization

Carbon capture and storage (CCS) is a key strategy for reducing CO₂ emissions and meeting decarbonization targets. Traditional CCS relies on injecting CO₂ into deep sedimentary formations. While proven effective, this approach typically takes decades for CO₂ to become fully trapped and limits storage to geologically suitable sedimentary basins.

Subsurface geologic CO₂ mineralization is an alternative approach that involves injection and precipitation of CO₂ as solid and stable carbonate minerals through reaction with in-place crystalline rocks like basalt. This process reduces the risk of CO₂ migration, may lower long-term monitoring requirements, and expands potential CO₂ storage options beyond sedimentary basins.¹

In this article, we will discuss the results of two mineralization projects – CarbFix in Iceland and Wallula in Washington – that have demonstrated feasibility and commercialization potential of mineralization. We will highlight current challenges and advantages of mineralization, including regulatory uncertainties, mineralization time scales, injection strategies, and geographic opportunities, with an emphasis on how these compare with traditional CCS strategies. Together this will highlight that mineralization offers developers a durable storage pathway and an early-mover advantage in an evolving market.

Mineralization is a geochemical process that permanently converts CO₂ injected into mafic and ultramafic igneous rocks (e.g., basalt, peridotite, serpentinite) into solid carbonate minerals. This occurs because these rock types contain high concentrations of reactive silicate minerals rich in magnesium (Mg), calcium (Ca), and iron (Fe), which readily bond with CO₂ to form stable carbonate minerals.^1–3 The diagram below provides an overview of the mineralization process.

The efficiency of the mineralization process depends on rock composition, temperature, pressure, fluid chemistry, and mineral surface area. Permeable formations – such as vesicular and fractured basalt – facilitate CO₂-rich fluid circulation, accelerating reactions.⁴ In some cases, carbonate mineral precipitation can induce microfracturing, further enhancing permeability and CO₂ uptake.³

Two projects are scaling up commercial-scale CO₂ storage via mineralization: CarbFix in Iceland and the Wallula Pilot Project in Washington, USA. As these commercial-scale operations expand, more feasibility studies and pilot tests are appearing worldwide, including 44.01 in Oman, Tamarack in Minnesota, and US DOE-funded feasibility studies in Virginia, Hawaii, and Arizona.

CarbFix: Dissolved CO₂ injection

CarbFix pioneered commercial mineralization-based CO₂ storage using dissolved CO₂ injection (Figure 1). The project sources CO₂ from a local power plant and from a direct air capture (DAC) plant operated by Climeworks. Dissolved CO₂ with co-captured H₂S is injected and stored into basalt at depths exceeding 1,640 feet. CarbFix has observed no permeability loss or reaction rate declines since operations began.¹

Following the success of its 4,000 tons per annum (0.004 million tons per annum, MTPA) Orca project, in 2024 CarbFix expanded with the Mammoth project, now injecting 36,000 tons per annum (0.036 MTPA).⁵ The company aims to reach gigaton-scale storage by 2050. However, challenges remain, particularly the large volumes of water required (~25 metric tons per ton of CO₂ stored), prompting ongoing research into seawater-based dissolution methods.¹

Wallula: Supercritical CO₂ injection

The Wallula Basalt Pilot Project demonstrated mineralization feasibility through supercritical CO₂ injection (Figure 1). The project injected 1,000 metric tons of supercritical CO₂ into permeable interflow zones of the Columbia River Basalt at depths of >2,717 feet over 25 days.^2,3,6 Reservoir simulations and core analyses indicate that 60% of CO₂ was mineralized within two years, filling 4% of the reservoir space.⁶ The Columbia River Basalts have a P50 estimated storage capacity of 304 gigatons.⁴

Building on Wallula’s success, the CarbonSafe HERO Basalt Project in Oregon aims to scale up mineralization-based storage to 50 million metric tons over 30 years.⁷ The project is currently conducting reservoir characterization and feasibility studies at a power plant as part of the DOE CarbonSAFE program.

Geologic CO₂ mineralization presents both challenges and advantages compared to conventional CCS. Regulatory uncertainty and lower injection rates have posed hurdles, but mineralization also expands storage opportunities beyond sedimentary basins while offering a rapid and highly secure CO₂ trapping mechanism.

Regulatory environment

Regulatory frameworks for carbon storage have largely been designed around conventional geologic storage, leaving mineralization with uncertainty around permitting and incentives despite its secure, permanent trapping mechanism

The 45Q tax credit remains one of the strongest incentives for CCS deployment in the US, providing up to $85 per metric ton for geological storage of CO₂ captured from power and industrial facilities and up to $180 per metric ton for CO₂ captured from DAC. However, the 45Q statute defines eligible storage as “secure geological storage” and explicitly lists deep saline formations, oil and gas reservoirs, and unmineable coal seams. Mineralization is not explicitly included, introducing some uncertainty on whether projects qualify, an ambiguity that future IRS guidance could clarify.

USEPA’s Class VI well regulations, established under the Safe Drinking Water Act’s Underground Injection Control (UIC) Program, were designed for CO₂ injection into porous sedimentary formations where fluid-phase trapping dominates. Mineralization, by contrast, involves conversion of CO₂ into solid carbonate minerals, and regulations do not fully account for this distinct storage mechanism. No Class VI permits have been submitted or approved for mineralization-dominant storage (Wallula was permitted as a Class V research well through the State of Washington). Ongoing regulatory discussions suggest that tailored permitting frameworks may be required for mineralization.

Regulatory uncertainty extends to monitoring, reporting, and verification (MRV) under USEPA’s Greenhouse Gas Reporting Program (GHGRP) – Subpart RR. These rules were developed for fluid-phase CO₂ storage, requiring plume tracking and long-term leakage monitoring. In mineralization, CO₂ is stored as solid carbonate minerals, and applying Subpart RR as currently written could require unsuitable monitoring protocols.

Despite these uncertainties, the rapid, stable nature CO₂ of mineralization trapping may alleviate certain regulatory requirements, offering economic advantages to developers. Because mineralized CO₂ no longer exists in a mobile phase, sites may qualify for reduced MRV requirements and shorter post-injection site care (PISC) periods, reducing long-term liability and financial assurance costs​. Additionally, community acceptance may be higher, as mineralization mitigates concerns about CO₂ migration into underground sources of drinking water.

Volumetric constraints

So far, CO₂ injection rates for mineralization remain lower than conventional geologic sequestration. The CarbFix Mammoth project, which began operations in 2024, currently injects 36,000 metric tons per year (~0.036 MTPA), though it is now expanding to 3 MTPA by 2032 at the Coda Terminal. The Wallula Basalt Pilot Project injected at approximately 0.014 MTPA, and the CarbonSafe HERO Basalt aims for 50 million metric tons of CO₂ storage over 30 years.^1,6,7

By contrast, saline aquifers and depleted oil and gas reservoirs have achieved much higher injection volumes. The Mount Simon Sandstone has reached injection rates of 1 MTPA per well under pressure-limited conditions, while commercial projects such as Sleipner and Quest have demonstrated injection rates of ~1 MTPA and Quest ~1.2 MTPA, respectively.

Lower injection rates for mineralization are driven by the geological properties of basalt. Unlike porous sedimentary rocks, basalts typically have low matrix permeability and porosity. While fractures and vesicles in basalt can enhance fluid circulation, the dense, crystalline interiors of basalts may limit large-scale injectivity, and near-wellbore clogging may diminish sustained injection rates. The core challenge for mineralization projects lies in balancing these injectivity and volumetric constraints with the storage security that mineralization provides.

Geographic opportunity

Mafic and ultramafic rock formations in the US present a largely untapped opportunity for CO₂ mineralization, particularly in the northwest (Figure 2). Unlike conventional geologic storage options, which are concentrated in sedimentary basins, mineralization targets exist in geologically distinct and diverse regions (Figure 2)⁸, broadening the storage landscape for CO₂ emitters. The common co-occurrence of mining districts and industrial corridors with mafic rocks presents opportunities to integrate CO₂ mineralization with stationary point-source capture (Figure 2).⁸

Large-scale formations with CO₂ reactivity include the Columbia River Basalt Group (Pacific Northwest), the Midcontinent Rift basalts (Upper Midwest), the Central Atlantic Magmatic Province basalts (Eastern US), the New Idria serpentinite (California) and the peridotite/serpentinite/basalt-rich belts of the Appalachians and southeastern US.