Engineered carbon mineralization in ultramafic rocks for carbon dioxide removal from air: Review and new insights

This paper based on studies conducted by Peter B. Kelemen and colleagues reviews carbon mineralization kinetics and the major pathways for carbon dioxide removal from air (CDR), combined with solid storage, via carbon mineralization, including estimates of rates, capacities and cost.

Carbon Dioxide removal from air (CDR) combined with permanent solid storage can be accomplished via carbon mineralization in ultramafic rocks in at least four ways:

Surficial CDR: Carbon dioxide -bearing air and surface waters are reacted with crushed and or ground mine tailings, alkaline industrial wastes, or sedimentary formations rich in reactive rock fragments, all with a high proportion of reactive surface area. This can be implemented at a low cost, but most proposed methods have a very large area footprint at the gigatonne scale.
In situ CDR: Carbon dioxide -bearing surface waters are circulated through rock formations at depth. These methods potentially have a cost similar to that of surficial carbon mineralization, and a giant storage capacity with reduced surface area requirements, but they involve uncertain feedbacks between permeability, reactive surface area, and reaction rate, providing a fascinating topic for fundamental research.
Combined partial enrichment of carbon dioxide using direct air capture with synthetic sorbents (DACSS) plus surficial carbon mineralization or in situ carbon mineralization
Energy requirements and total costs for partial enrichment of carbon dioxide are substantially lower than for enrichment to high purity. Carbon dioxide enriched air can be sparged through mine tailings at the surface, and/or through water to increase dissolved carbon concentrations prior to circulation through rock reactants.

Such combined or hybrid approaches have not been investigated thoroughly, and offer many avenues for optimization. New and revised cost estimates in this paper indicate that engineered carbon mineralization, and hybrid methods involving direct air capture with synthetic sorbents or solvents (DACSS) plus mineralization, are likely to be less expensive methods for CDR, per ton of carbon dioxide, compared to direct air capture alone.