In the recent years, a study of CO2 capture and storage(CCS) technologies has gained great attention, because CO2 in the atmosphere causes a global warming. CCS technologies are classified as underground storage technologies and mineral carbonation technologies. This study focuses on mineral carbonation technologies with waste cement generated from waste concrete. Waste cement is a good source for mineral carbonation. For this study, we made consolidated cement with water/cement ratio of 6:4 and cured for 28 days in water bath. The cement paste was pulverized, and into a fine powder less than 0.15 mm. In order to improve efficiency of mineral carbonation technologies with cement paste, chloride additives were used in this study. Seawater has many cations and is abundant all over the world, so we also used seawater in an additive for mineral carbonation. In order to apply chloride(1 M NaCl, 0.25 M MgCl2, seawater) as additives, aqueous carbonation experiments was conducted by injecting pure CO2 gas (99.9 %) at the flow rate of 20 ml/min for mineral carbonation with cement paste. The mineral compositions and morphology who identified by XRD, SEM/EDS analysis.

The mineral carbonation with cement paste was divided into 4 groups: (1) no additive solution, (2) 1 M NaCl solution, (3) 0.25 M MgCl2 solution, (4) 1 M NaCl + 0.25 M MgCl2 solution. No additive solution and 1 M NaCl solution predominantly generated calcite, but 0.25 M MgCl2 solution and 1 M NaCl + 0.25 M MgCl2 solution predominantly generated aragonite than calcite. Aqueous carbonation experiments were conducted by control pH of solution to identify conditions for the type of carbonate mineral. If 0.25 M MgCl2 was added as an additive, calcite is predominantly formed in a high pH environment and aragonite is predominantly formed in a low pH environment because of Mg ion. If 0.25 M MgCl2 was not added as an additive, vaterite is predominantly formed in a high pH environment and calcite is predominantly formed in a low pH environment. vaterite is replaced with calcite because vaterite is unstable mineral at low pH condition. We conducted indirect aqueous carbonation experiment and direct aqueous carbonation experiment with seawater as a additive. Indirect aqueous carbonation experiment was predominantly generated calcite, but direct aqueous carbonation experiment was generated calcite, aragonite, vaterite together. To generate pure calcite, indirect aqueous carbonation experiment with seawater is more efficiently than indirect aqueous carbonation experiment with NaCl or MgCl2·6H2O as additives.