The abundant resources of steel slag make it an intriguing prospect for long-term CO₂ storage by mineral carbonation. Herein, the dissolution of steel slag in an acetic acid (HAc) solution and the fixation of CO₂ in the leachate of steel slag to synthesize high-value CaCO₃ were investigated. Results show that the microwave water bath condition is beneficial for improving the leaching rate of Ca and Mg elements in steel slag, while the low-concentration HAc solution displays high selectivity for Ca + Mg. In a water bath reaction enhanced by microwave, the leaching rate and selectivity of Ca + Mg can be increased by elevating the reaction temperature, extending the leaching time, lowering the concentration of HAc solution, and increasing the stirring rate. The kinetic parameters of the calcium element, including the apparent activation energy, were determined to be 14.51 kJ·mol⁻¹, suggesting control by surface chemical reactions. Finally, high-purity CaCO₃ crystal whiskers can be synthesized under 400 W ultrasonic conditions with a reaction temperature of 70 ℃, reaction time of 15 min, and a solution pH at 9.1 by introducing 20 % CO₂ into the leachate. This strategy facilitates the concurrent utilization of dilute CO₂ flue gas and voluminous solid steel slag waste, thereby improving the economic and environmental performance of the steel industry.