Review of rates, capacities and costs of carbon mineralization in peridotite

We review methods for carbon mineralization in peridotite to achieve carbon dioxide removal from air plus solid storage (CDR+SS), as well as using fluids with elevated CO2 contents to achieve CO2 solid storage (CSS). Peridotite tailings are the "low hanging fruit", and can achieve CDR+SS at costs much lower than manufactured air capture systems (as low as 10/ton CO2). However, the CO2 uptake capacity of mine tailings (existing, and produced annually) is low compared to human emissions. Mining and processing peridotite for CDR+SS may be cost and capacity competitive with manufactured air capture systems + storage, within uncertainties for both ( 100/ton). However, at rates of Gt CO2/yr, mining for CDR+SS might generate unacceptable volumes of tailings. CSS via in situ carbon mineralization in peridotite may be cost and capacity competitive with storage of supercritical CO2 fluid in pore space (10-20/ton). However, in low permeability formations, this depends on avoiding negative feedbacks due to "clogging" of pore space and armoring of reactive surfaces. Positive feedback regimes may exist, for example via "reaction-driven cracking" driven by stress due to solid volume change during carbonate crystallization. Subtle variations in surface energy, affecting "disjoining pressure" and "sorptivity", may be important in determining whether specific rock formations will be dominated by negative or positive feedbacks during carbon mineralization. This is a topic for continued, basic research. In situ CDR+SS is possible via production of Ca-rich alkaline water from peridotite hosted aquifers and precipitation of CaCO3 at the surface, and/or via circulation of surface water through subsurface peridotite. The size of peridotite-hosted alkaline aquifers is probably small compared to human emissions. Circulation of surface water through subsurface peridotite is less likely to generate clogging and passivation, compared to circulation of CO2-rich fluids, but may be ≤ 100 only where the geothermal gradient and permeability are sufficiently high for thermal convection. (Because CO2 concentration in water saturated in air is 100 ppm, 0.01 spent pumping a mass of water is equivalent to 100 for the same mass of CO2). Instead or in addition, combined CDR+SS and geothermal power generation is possible in some regions.