CO2 storage and CaCO3 production using seawater and an alkali industrial by-product

Indirect carbonation is one of the typical carbon capture, utilization, and storage technologies. It is well known, however, that the technology is very difficult to achieve economic feasibility because expensive chemical solvents used account for most of the cost. To overcome this limitation, we performed an experimental study to secure the economic feasibility of the technology by replacing such chemical solvents with nearly costless seawater. For the study, we used cement kiln dust (CKD), which is an alkali industrial by-product, together with seawater. In this paper, we attained CO2 storage and CaCO3 yield despite the use of seawater, which is comparable in both quantitative and qualitative respects to the existing studies using chemical reagents. The CO2 storage and CaCO3 yield were 185 kg-CO2/ton-CKD and 419 kg-CaCO3/ton-CKD, respectively. With the addition of Mg into the seawater, moreover, the amounts could significantly increase to reach 271 kg-CO2/ton-CKD and 615 kg-CaCO3/ton-CKD, respectively. Despite using CKD and seawater containing many impurities, the purity of CaCO3 produced was as high as 99.4%. It was also found that Mg is one component, which can elute Ca from CKD, dissolved in seawater. The solid to liquid ratio was the most influential factor for the Ca elution efficiency, while the CO2 flow rate and NaOH dosage had significant effects on the carbonation efficiency.