Electrolytic Seawater Mineralization and the Mass Balances That Demonstrate Carbon Dioxide Removal

Erika Callagon La Plante; Xin Chen; Steven Bustillos; Arnaud Bouissonnie; Thomas Traynor; David Jassby; Lorenzo Corsini; Dante A Simonetti; Gaurav N Sant

doi:10.1021/acsestengg.3c00004

Electrolytic Seawater Mineralization and the Mass Balances That Demonstrate Carbon Dioxide Removal

ACS ES T Eng. 2023 Apr 27;3(7):955-968. doi: 10.1021/acsestengg.3c00004. eCollection 2023 Jul 14.

Authors

Erika Callagon La Plante^{1

2

3

4}, Xin Chen^{2

4

5}, Steven Bustillos^{2

5

6}, Arnaud Bouissonnie^{2

5}, Thomas Traynor^{2

4}, David Jassby^{2

4

5}, Lorenzo Corsini⁴, Dante A Simonetti^{2

4

6}, Gaurav N Sant^{2

4

5

7

8}

Affiliations

¹ Department of Materials Science and Engineering, University of Texas at Arlington, Arlington, Texas 76019, United States.
² Institute for Carbon Management, University of California, Los Angeles, Los Angeles, California 90024, United States.
³ Center for Advanced Construction Materials, University of Texas at Arlington, Arlington, Texas 76019, United States.
⁴ Equatic Inc., Los Angeles, California 90024, United States.
⁵ Department of Civil and Environmental Engineering, University of California, Los Angeles, Los Angeles, California 90024, United States.
⁶ Department of Chemical and Biomolecular Engineering, University of California, Los Angeles, Los Angeles, California 90024, United States.
⁷ California Nanosystems Institute, University of California, Los Angeles, Los Angeles, California 90024, United States.
⁸ Department of Materials Science and Engineering, University of California, Los Angeles, Los Angeles, California 90024, United States.

Abstract

We present the mass balances associated with carbon dioxide (CO₂) removal (CDR) using seawater as both the source of reactants and as the reaction medium via electrolysis following the "Equatic" (formerly known as "SeaChange") process. This process, extensively detailed in La Plante E.C.; ACS Sustain. Chem. Eng.2021, 9, ( (3), ), 1073-1089, involves the application of an electric overpotential that splits water to form H⁺ and OH^- ions, producing acidity and alkalinity, i.e., in addition to gaseous coproducts, at the anode and cathode, respectively. The alkalinity that results, i.e., via the "continuous electrolytic pH pump" results in the instantaneous precipitation of calcium carbonate (CaCO₃), hydrated magnesium carbonates (e.g., nesquehonite: MgCO₃·3H₂O, hydromagnesite: Mg₅(CO₃)₄(OH)₂·4H₂O, etc.), and/or magnesium hydroxide (Mg(OH)₂) depending on the CO₃^2- ion-activity in solution. This results in the trapping and, hence, durable and permanent (at least ∼10 000-100 000 years) immobilization of CO₂ that was originally dissolved in water, and that is additionally drawn down from the atmosphere within: (a) mineral carbonates, and/or (b) as solvated bicarbonate (HCO₃^-) and carbonate (CO₃^2-) ions (i.e., due to the absorption of atmospheric CO₂ into seawater having enhanced alkalinity). Taken together, these actions result in the net removal of ∼4.6 kg of CO₂ per m³ of seawater catholyte processed. Geochemical simulations quantify the extents of net CO₂ removal including the dependencies on the process configuration. It is furthermore indicated that the efficiency of realkalinization of the acidic anolyte using alkaline solids depends on their acid neutralization capacity and dissolution reactivity. We also assess changes in seawater chemistry resulting from Mg(OH)₂ dissolution with emphasis on the change in seawater alkalinity and saturation state. Overall, this analysis provides direct quantifications of the ability of the Equatic process to serve as a means for technological CDR to mitigate the worst effects of accelerating climate change.