Seawater alkalinity enhancement with magnesium hydroxide and its implication for carbon dioxide removal

Abstract

For the first time we used lab and wind-wave tank experiments to prove the concept of using Mg(OH)2 for the ocean alkalinity enhancement and carbon dioxide removal approach (OAE-CDR). Experiment results showed up to 370 μmol kg−1 seawater total alkalinity (TA) increase without precipitation, stable enhanced TA, and OAE-CDR efficiency (ΔDIC/ΔTA) consistent with theoretical calculation. Based on the experimental results, we calculated the global Mg(OH)2 OAE-CDR efficiency and CO2 sink from this approach. The efficiency is in favor of lower initial DIC to TA ratio, lower temperature, and higher atmospheric CO2, and therefore is the lowest at the equator (0.7–0.8) and increases with latitude (1.0–1.2 above 70 N/S). However, factoring in the ocean's surface area, low latitude regions can absorb more atmospheric CO2. We conservatively estimate that 44. 4 × 109 ton of CO2 (∼ 3.3 times of current annual CO2 sink in the ocean) could be removed from the atmosphere with 175 μmol kg−1 Mg(OH)2 (equivalent to 350 μmol kg−1 of TA) added to the top 10 m of the ocean.