How Rocks Help Save the Climate: CO₂ Mineralization

Recently, increasing attention has been given to climate initiatives focused on the mineralization of carbon in soil and marine environments. Can this be considered a new direction in climate projects, or rather a well-forgotten approach that has been given a second life?

A climate project involving carbon mineralization belongs to a promising type of carbon removal projects (Carbon Dioxide Removal, CDR) and is one of the methods of carbon capture, utilization, and storage (Carbon Capture, Utilization and Storage, CCUS). The essence of mineralization is that carbon dioxide (CO_₂) reacts with other minerals and takes on a new stable form that is chemically durable and can store bound carbon for thousands or even millions of years. These include: mineralization into CaCO_₃ (calcite), MgCO_₃ (magnesite), CaMg(CO_₃)_₂ (dolomite), and others. Two types of mineralization are distinguished: belowground and aboveground.

Compiled based on: https://lot21.org/discover/solutions/understanding/carbon-mineralization and https://www.cdr.fyi

Subsurface mineralization (belowground), represented only by the in-situ method, involves the injection of CO_₂, where carbon dioxide reacts with elements found in underground soil layers (Ca, Mg, etc.), forming stable carbonate minerals (CaCO_₃, MgCO_₃, etc.).

Surface mineralization (aboveground) includes a broader range of methods, which either involve fully aboveground project implementation (ex-situ), or the involvement of shallow soil layers, shorelines, and oceans (surficial).

Ex-situ mineralization occurs on the surface, in special reactors or industrial installations. Carbon dioxide (CO_₂) interacts with crushed minerals, industrial waste, or specially prepared feedstock (such as mine tailings, industrial byproducts, or rocks) under high pressure and high temperature. As a result, carbonate minerals are produced and used in the production of low-carbon concrete. Startups implementing such climate projects include CarbonCure, O.C.O. Technology, and Neustark.

Surface mineralization involving shallow soil layers, shorelines, and the ocean (surficial) currently has several derivative forms. The most widespread mineralization method is Enhanced Rock Weathering (ERW), which is increasingly being recognized as a separate category of climate projects. ERW differs from conventional surface mineralization (surficial) in terms of scale, location, and mechanism: it is more scalable, involves the participation of shorelines and the ocean, and primarily leads to the formation of bicarbonates (HCO₃), which only later, in the ocean, transform into stable carbonate minerals (e.g., CaCO₃).

Another method of surface mineralization (surficial), which remains experimental, is microbial mineralization (microbial). Currently, there are two known startups that issue carbon credits using this method: Andes and Groundwork BioAg Ltd. Microbial mineralization involves the formation of stable carbonate minerals through the binding of CO_₂ with the participation of microorganisms (bacteria, algae), which catalyze chemical reactions between CO_₂ and minerals.

When evaluating these types of projects in terms of long-term carbon storage, scalability, and financial feasibility, no single method meets all these criteria simultaneously. Most CO_₂ mineralization technologies are either still relatively expensive, difficult to scale, or may carry negative environmental consequences—such as in the case of ocean mineralization. Thus, current mineralization methods each have their own advantages and disadvantages and are not yet widely adopted, requiring cooperation among business, scientific, and governmental actors to ensure reliable long-term carbon storage.

"Carbon mineralization and its various subtypes hold significant potential. However, despite the clear principle of CO_₂ absorption, it is essential to involve experts to minimize potential risks and unintended consequences," noted Varvara Gryaznova, Senior Specialist at the Department of Scientific and Methodological Support.