Ultrasound‐Assisted Capture of CO ₂ From Flue Gas Using Steel Slag Leachate and Synthesis of Vaterite‐Type CaCO ₃

ABSTRACT This study investigated the sequestration of CO 2 from flue gas using a Ca‐rich leachate obtained by leaching steel slag with CH 3 COOH. Ultrasound was used to accelerate the fixation of low‐concentration CO 2 in the leachate and to induce the transformation of CaCO 3 crystals into the vaterite form with a uniform particle distribution. Ultrasound‐induced cavitation bubbles in ethanol reduced the nucleation barrier and prevented clustering by maintaining a uniform dispersion of vaterite CaCO 3 crystals, which impeded their conversion to other CaCO 3 polymorphs. Experimental results revealed that ultrasonic action could effectively fix low‐concentration CO 2 in the leachate reaction system. Moreover, the addition of ethanol as a surfactant yielded vaterite CaCO 3 with an average particle size of 3.2 μm and uniform granularity of 1.4–5.6 μm. This product meets the industrial standards for light CaCO 3 micropowder, which makes it suitable for various applications as a filling material. The proposed method presents a sustainable approach for the valorization of steel slag and low‐concentration CO 2 from flue gas, and it highlights the potential of ultrasonic technology to improve the chemical processes required for Carbon Capture, Utilization, and Storage technologies.