We have proposed a new type of mineral carbonation process, where CO2 is fixed as carbonates by the reaction with alkaline earth metals such as calcium or magnesium. The process is composed of four steps. (1) absorption of CO2 in the flue gas with an alkaline solution such as sodium hydroxide. (2) extraction of calcium or magnesium using an acid solution. (3) Precipitation of carbonates by mixing the calcium-leached solution and the alkaline carbonate solution. (4) Regeneration of an alkali-acid pair from the remained salt solution after precipitation with the bipolar membrane electrodialysis (BPED). In this study, we examined optimum conditions for the total process by using wollastonite as a calcium source and various kinds of acid in the view of the power consumption for the CO2 fixation. We focused on the extraction step because all the operation conditions for other steps were determined by performances of the extraction step. Table 1 shows the extraction conditions for each acid to show the highest calcium concentration and the highest calcium extraction ratio in the wollastonite after 24 h extraction for a fixed initial concentration of acids at 1.0 M. Among the acids used in this study, the highest calcium concentration as well as the calcium extraction ratio was obtained when nitric acid was used. In addition, the calcium selectivity in the extraction step was highest at 99.7. However, considering the electrodialysis process for the alkali-acid pair regeneration, the power consumption for the recovery of nitric acid was much higher and the recovery ratio was much lower than those for the cases with other weak acids. The power consumption and the recovery ratio were almost equivalent for these three weak acids; acetic acid should be the optimum acid for the extraction step.

New type of CO2 fixation process via mineral carbonation with electrodialysis

2019 Fall National Meeting

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