For promoting the absorption of atmospheric CO
2 into the ocean, the use of electrolysis treatment of seawater to produce calcium carbonate (CaCO
3) and decrease the concentration of carbonate ion in a superficial seawater was studied. Through an experiment using a continuous flow electrolytic cell with a porous separating membrane, a large amount of H
2 gas and CaCO
3 particle were produced at the cathode, and a small amount of O
2 gas was produced at the anode. CO
2 gas was not entirely emitted during the electrolysis treatment, and the mixture of catholyte seawater, after the separation of CaCO
3, and anolyte seawater was alkalined at pH 8.3-8.7 compared to the raw seawater of pH 8.1. A precipitate produced by the electrolysis treatment was composed of aragonite-CaCO
3 and brucite-Mg(OH)
2, and the amount, chemical composition and crystal shape were changed by the electrolysis conditions. Based on the fact that the excess atmospheric CO
2 could be stably isolated from the biosphere as solid CaCO
3 submerged on a sea floor, and alkalined seawater should have a potential to promote the absorption of atmospheric CO
2 without seawater acidification by the direct CO
2 discharge, the proposed method might become a solution for global warming.
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