Alkalinity Generation Constraints on Basalt Carbonation for Carbon Dioxide Removal at the Gigaton-per-Year Scale

Abstract

The world adds about 51 Gt of greenhouse gases to the atmosphere each year, which will yield dire global consequences without aggressive action in the form of carbon dioxide removal (CDR) and other technologies. A suggested guideline requires that proposed CDR technologies be capable of removing at least 1% of current annual emissions, about half a gigaton, from the atmosphere each year once fully implemented for them to be worthy of pursuit. Basalt carbonation coupled to direct air capture (DAC) can exceed this baseline, but it is likely that implementation at the gigaton-per-year scale will require increasing per-well CO2 injection rates to a point where CO2 forms a persistent, free-phase CO2 plume in the basaltic subsurface. Here, we use a series of thermodynamic calculations and basalt dissolution simulations to show that the development of a persistent plume will reduce carbonation efficiency (i.e., the amount of CO2 mineralized per kilogram of basalt dissolved) relative to existing field projects and experimental studies. We show that variations in carbonation efficiency are directly related to carbonate mineral solubility, which is a function of solution alkalinity and pH/CO2 fugacity. The simulations demonstrate the sensitivity of carbonation efficiency to solution alkalinity and caution against directly extrapolating carbonation efficiencies inferred from laboratory studies and small-injection-rate field studies conducted under elevated alkalinity and/or pH conditions to gigaton-per-year scale basalt carbonation. Nevertheless, all simulations demonstrate significant carbonate mineralization and thus imply that significant mineral carbonation can be expected even at the gigaton-per-year scale if basalts are given time to react.

Exotic Carbonate Mineralization Recovered from a Deep Basalt Carbon Storage Demonstration

“…Both efforts have highlighted the potential of reactive basalt reservoirs as efficient and permanent sinks for anthropogenic CO 2 . Understanding the geochemistry and carbon mineralization outcomes for aqueous and scCO 2 is critical for enhancing storage capacity in basaltic reservoirs . The Wallula Basalt Pilot Project − is the only geologic carbon storage site that has ever reported recovery and characterization of unambiguously anthropogenic carbonate minerals precipitated in rock pores .…”

Creep of CarbFix basalt: influence of rock–fluid interaction

“…Such large volumes can practically be stored in the subsurface. Geological carbon sequestration (GCS) by in situ carbon mineralization is recognized as one of the most secure, long-term storage solutions (Gislason and Oelkers, 2014;Kelemen and Matter, 2008;Lackner et al, 1995;Mani et al, 2008;Seifritz, 1990;Snaebjörnsdóttir et al, 2020;Tutolo et al, 2021). To date, several pilot projects have been launched to study GCS in basalt reservoirs, including the CarbFix program in Iceland (Callow et al, 2018;Gislason et al, 2010;Oelkers et al, 2008;Snaebjörnsdóttir et al, 2018) and the Wallula basalt (part of Columbia River Basalt Group) sequestration project in Washington, USA (McGrail et al, 2006(McGrail et al, , 2011(McGrail et al, , 2017Zakharova et al, 2012).…”

Geochemical Negative Emissions Technologies: Part I. Review

“…In 2021, the world's first DAC-mineralization plant (Project Orca) went live as a collaboration between CarbFix and the company Climeworks, with the goal to annually remove 4 kt CO 2 . Modeling studies indicate that basalt carbonation may be limited by alkalinity constraints and lead to the existence of unreacted free-phase CO 2 (Tutolo et al, 2021). However, recent field-scale three-dimensional transport models of the CarbFix injection site indicate mineralization rates remain high even after many years of injection and that 300 Mt CO 2 can be stored using just 10% of the rock pore space (Ratouis et al, 2022).…”