Kinetic insights into measurable marine carbon dioxide removal via carbonation of electrolytically alkalinized seawater

[Geoengineering News]

https://www.sciencedirect.com/science/article/abs/pii/S1385894726028561

Authors: Trinh Thao My Nguyen, Arnaud Boussonnie, Aaron Sabin, Naga Boppana, Thomas Traynor, Fabian Rosner, Dante Simonetti, Gaurav Sant, Erika La Plante

https://doi.org/10.1016/j.cej.2026.175396

19 March 2026

Highlights

•Compared direct and sequential carbonation of alkalinized seawater for CO2 removal, achieving near-stoichiometric capture efficiency dominated by nesquehonite formation.

•Identified gas flowrate-to-volume ratio as a key control parameter governing CO2 dissolution kinetics, enabling efficient carbonation under ambient air conditions.

•Quantified the critical saturation index for hydrated magnesium carbonate precipitation, providing design insights for scalable reactor configurations and rate-optimization strategies.

Abstract

The rising levels of atmospheric carbon dioxide (CO2) necessitate solutions for effective mitigation strategies, such as marine CO2 removal (mCDR). This study investigates the kinetics of aqueous carbonation of seawater that has been alkalinized. Such alkalinization is effected via the Equatic process, an electrolysis-driven method designed to enhance the precipitation of calcium carbonate and magnesium hydroxide for CO2 removal. Carbonation was conducted using two approaches: direct (i.e., carbonation of the entire catholyte, including both solids and liquids) and sequential (i.e., carbonation of the catholyte liquid, followed by further carbonation after filtered solids are added back). These methods were employed to examine the dissolution behavior of CO2 and brucite (Mg(OH)2), as well as the transformation of brucite into various hydrated magnesium carbonate phases. Analyses of dissolved inorganic carbon (DIC), divalent cation concentrations, and X-ray diffraction data show that both approaches effectively sequester CO2 at similar rates and extent (3.50–3.56 g CO2/L of catholyte), achieving 96–98% CO2 removal efficiency. Trends in brucite carbonation were successfully fitted using kinetic models that describe both brucite dissolution and CO2 dissolution. The study also emphasizes the significance of optimizing the gas flow rate-to-reactor volume ratio, here quantified to be 0.45 s−1, and the role of surface properties in influencing carbonation products. Overall, the findings evaluate different means to effect carbonation via electrolytic mCDR processes within the framework of an engineered system (i.e., via so-called ISBL: Inside-the-battery-limit, carbonation within an engineered facility).

Source: ScienceDirect