The removal of atmospheric CO 2 in agricultural land through the enhanced rock weathering of Ca-rich silicates (basalts and industrial by-products etc.) has been gaining attention as a novel method for reducing CO 2 emission. However, the calcium and carbon reaction process occurring in soil pore water due to pH changes remains unclear using industrial by-products. To elucidate this process, this study conducted tank leaching batch tests using steel slags with different properties (i.e., air-cooled blast furnace, converter, and granulated blast furnace slag) and performed atmospheric CO 2 removal experiments. The geochemical equilibrium calculation model PHREEQC was used to examine the calcium and carbon chemical reaction processes in the atmosphere and solution from steel slag dissolution. Batch test results revealed an increase in the steel slag carbon concentration with increasing additive amount. The solution pH was approximately 12 for converter slag and approximately 9 for air-cooled and granulated blast furnace slag. Thus, previous research indicates that increased carbon concentrations in solutions suggest atmospheric CO 2 removal. However, their removal efficiencies derived from carbon concentration were comparable. Calculations from PHREEQC showed that the carbon and calcium reacted readily in alkaline solutions (pH 8–13). The ionic species in the solution used for PHREEQC modeling and solution pH effectively expressed the differences in the atmospheric CO 2 removal effects of different steel slag types.
Nakamura et al. (Thu,) studied this question.