(117x) Environmental Impacts of Direct Carbonation and Indirect Carbonation in Calcium Carbonation Manufacturing Using Slag

The mineral carbonation is a technology that converts mineral resources into carbonate salts by directly or indirectly reacting with carbon dioxide [1]. However, the mineral carbonation process has problems that are difficult to widely apply due to crushing of raw materials, slow reaction speed, and distance from carbon dioxide emission sources [2]. Nevertheless, the mineral carbonation is a promising technology in the field of Carbon Capture, Utilization, and Sequestration (CCUS) because it can treat a large amount of carbon dioxide and can be a permanent carbon dioxide reduction technology [3]. Various industrial by-products such as steelmaking slag, cement kiln dust, waste ash and paper mill waste can be used as raw materials for the mineral carbonation [4]. Among them, steel slag generates more than tens of millions of tons every year and is used as an aggregate for mounding or concrete, but slag containing a large amount of alkali can be used as a raw material for mineral carbonation reactions [1]. In this study, we manufactured the calcium carbonate through direct and indirect carbonation reactions using slag, and compared the environmental impacts of two processes by Life Cycle Assessment (LCA).

The direct carbonation reaction produced calcium carbonate with a purity of 40% by reacting exhaust gas generated during the incineration process of municipal waste. In the indirect carbonation process, exhaust gas generated during the incineration of sewage sludge was used as a carbon dioxide raw material, and only calcium ions contained in slag were selectively separated to react with exhaust gas to produce calcium carbonate with a purity of 95%. Exhaust gas generated during the incineration of municipal waste and sewage sludge contains 9-10% carbon dioxide concentration. The direct carbonation facilities can produce 36 tons of calcium carbonate per day and the indirect carbonation facilities can produce 4 tons of calcium carbonate per day because of the addition of a process of extracting calcium ions in slag.

The scope of research to evaluate the environmental impact of direct carbonation and indirect carbonation reactions included from the process of slag entering the carbonation facility to the production of calcium carbonate. The functional unit is the manufacture of 1 kg of calcium carbonate, and input and output data collected the production of calcium carbonate for two months from June to July 2022. The environmental impact on the disposal of unreacted slag was excluded. LCA is a widely used method when evaluating the environmental impact of a product, and the program used in this study was SimaPro 9.2 version, and the methodology applied is IPCC 2013 GWP 100a.

The direct carbonation process not only has a small environmental impact on plant operation but also produces a large amount of calcium carbonate and sells it in bulk as a concrete material. However, indirect carbonation generates a large amount of carbon dioxide during plant operation because only calcium ions in slag must be selectively used in the reaction. However, it has the advantage of high economic feasibility because of the high price of calcium carbonate.

Acknowledgements

This work was supported by the Regulation-Free Special Zone (P0017177) and the Technology Development Program (S3025882) funded by the Ministry of SMEs and Startups (MSS, Korea) and Industrial Strategic Technology Development Program (00154970) funded By the Ministry of Trade, Industry & Energy (MOTIE, Korea) and the Korea Institute of Industrial Technology (KITECH, EH-23-0020)

References

1. Minah Son, Gookhee Kim, Kunwoo Han, Min Woo Lee, Jun Taek Lim, Development status and research direction in the mineral carbonation technology using steel slag, Korean Chem. Eng. Res., 55(2), 141-155, 2017
2. Sanna, A., Uibu, M., Caramanna, G., Kuusik, R., Maroto Valer, M., A review of mineral carbonation technologies to sequester CO₂, Chem. Soc. Rev, 43, 8049-8080, 2014
3. Lackner, K. S., A guide to CO₂ sequestration, Science, 300, 2003
4. Li-Shan Xiao, Run Wang, Pen-Chi Chiang, Shu-Yuan Pan, Qing-Hai Guo, E. E. Chang, Comparative life cycle assessment (LCA) of accelerated carbonation processes using steelmaking slag for CO₂ fixation, Aerosol and Air Quality Research, 14, 892-904, 2014