Fixation of CO₂ by carbonating calcium derived from blast furnace slag

Industrial waste materials, such as steelmaking slags, appear to be potential raw materials for reducing CO2 emissions by carbonation. The suitability of applying a carbonation route based on acetic acid leaching to produce carbonates from blast furnace slag is presented in this study. The effect of solution pH, temperature, and CO2 pressure on the precipitation of carbonates was experimentally studied. A simple thermodynamic model was used to verify our results. The feasibility of the process was also discussed, addressing energy input requirements and the consumption of chemicals. According to our experiments, the addition of NaOH, i.e. an increase in solution pH, is required for the adequate precipitation of calcium carbonate at temperatures of 30–70 °C and pressures of 1 or 30 bar. Preliminary process calculations showed that approximately 4.4 kg of blast furnace slag, 3.6 l of acetic acid, and 3.5 kg of NaOH would be required to bind 1 kg of CO2, resulting in 2.5 kg of 90% calcium carbonate. While the heat needed for the evaporation of the acetic acid could probably be acquired as waste heat by process integration with other processes, the electricity required for NaOH regeneration would make the process unsuitable for CO2 sequestration.