Coupling Electrochemical Alkalinization and Mineral Dissolution for Ambient Removal of Both Influent CO2 and Dissolved Nitrite in Seawater

Abstract

Marine carbon dioxide removal (mCDR) is increasingly recognized as a potential mitigation pathway to achieve the goals of the Paris Agreement. Among the scalable and cost-effective options for mCDR, ocean alkalinity enhancement (OAE) stands out as a potential eco-friendly option. Herein, a novel OAE strategy on the basis of coupled electrochemical alkalinization and CaCO₃ dissolution is developed for the removal of influent CO₂ in ambient conditions. The laboratory strategy also considers the additional benefit of converting dissolved nitrite, which can be toxic at high concentrations in seawater. The protons produced in the anodic sector are neutralized by timely dissolution of CaCO₃ powders, which converts an equivalent mole of dissolved inorganic carbon. The alkalinity generated in the cathodic sector reacts with influent CO₂ to form bicarbonate anions in seawater. As a result, the integrated OAE design produces increased total alkalinity and dissolved inorganic carbon in seawater with a relatively moderate energy consumption of 104.5 kJ/mol of CO₂ and high electron efficiency. In addition, the anodic reaction converts nitrite to nitrate. The proof-of-concept module thus provides an eco-beneficial pathway for mCDR. A potential environmental scenario could be the integration of OAE and wastewater treatment in intensive and recirculating marine aquaculture.