Blast furnace slag derived CaO for carbon capture

Blast furnace slag was used as the raw materials for CaO preparation. Acid treatment is required. Although good performance of the derived CaO was reported in terms of CO2 capture, this approach of CaO development might have challenges related to cost and environmental impacts.

“The blast furnace slag (BFS) used in this study was sampled from an integrated iron and steel plant in China. The fresh BFS sample was mechanically ground to a particle size of 0.05–0.1 mm before use. An acid extraction followed by precipitation approach [41] was employed in this study to transform the BFS sample into CaO-based CO2 sorbents. Accordingly, the BFS sample was mixed with a solution of acetic acid or nitric acid at a solid-to-liquid ratio of 1 g to 10 mL. Then, the mixture was shaken mechanically at a speed of 10 rpm at room temperature for a desired duration. The resulting slurry was centrifuged to separate the BFS leachate from the residues at 4 °C. The BFS leachate was dried overnight in a vacuum oven at 110 °C, and then calcined at 800 °C for 30 min to obtain the required CO2 sorbents. ” “In addition to the type of acid, other factors influencing the preparation of the BFS-derived, CaO-based CO2 sorbents included the concentration of acid and duration of shaking, which were investigated in the range of 1–5 mol/L and 30–150 min, respectively, in this study. For brevity, the nomenclature of Ax/Nx-y, where A and N denote the use of acetic acid and nitric acid, respectively; the subscript x denotes the concentration of acid, and y denotes the duration of shaking, was used to refer to the prepared sorbents.”

Fig. 6 depicts the cyclic CO2 capture performance of the BFS-derived sorbents. Among all sorbents, N3-120 presented the maximum uptake of CO2 (0.37 gCO2/gsorbent) in the first cycle, and A3-30, N3-30, as well as A3-120 followed with the CO2 uptake of nearly 0.3 gCO2/gsorbent, while N1-30 presented the lowest CO2 uptake of merely 0.15 gCO2/gsorbent. In fact, CO2 uptake of these sorbents in the first cycle was largely determined by the content of free CaO in the material, and the significant difference in the uptake of CO2 between N3-120 and N1-30 was likely associated with the different mass ratios of SiO2 to CaO in the sorbent. A higher SiO2/CaO ratio in N1-30 would result in the formation of the inert Ca2SiO4 phase (Fig. 4), limiting the availability of free CaO in the sorbent for CO2 capture. This could be evidenced by the results in Fig. 1, where a significantly higher Si/Ca ratio was observed in the BFS leachate for preparation of N1-30 than that for N3-120. Despite that all sorbents experienced a decay in the uptake of CO2 over the following cycles, the cyclic CO2 capture stability of these materials could be easily distinguished by comparing the average deactivation rate, calculated as the average percentage of decay in the CO2 uptake of a sorbent as compared to its CO2 uptake in the first cycle, over the 20 cycles performed in this study. N3-120 and N3-30 exhibited a lower deactivation rate of 2.3% and 2.6% per cycle, respectively, while other sorbents had an inferior stability for cyclic CO2 capture due to their higher deactivation rates of more than 3.5% per cycle. ”


Fig. 6. CO2 capture performance of the BFS-derived, CaO-based sorbents over repeated carbonation–calcination cycles.”


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