<p>The continuous increase in the concentration of CO₂ in the atmosphere has become a key factor influencing global climate change, and effective emission reduction strategies need to be adopted urgently. The steel industry, as one of the largest sources of industrial CO₂ emissions, is facing increasingly severe pressure for carbon reduction. Steel slag carbonation is an effective way to reduce carbon dioxide emissions and promote green and low-carbon development. Three main ways of direct carbonation of steel slag are introduced systematically in this paper: direct solid-phase carbonation of steel slag, direct aqueous-phase carbonation of steel slag, and carbonation of steel slag concrete system. The reaction mechanism, main influencing factors (such as temperature, pressure, CO₂ concentration, particle size, liquid–solid ratio), and optimization strategy of each route were discussed in detail. The analysis shows that the reaction process is generally subject to kinetic constraints, including the mineral encapsulation and diffusion control through product/ash layers. Direct gas–solid carbonation provides process simplicity and the ability to directly treat low concentrations of flue gas; direct aqueous-phase carbonation achieves faster reaction rates and higher carbonation efficiency despite relatively high energy consumption; and incorporation of steel slag into concrete followed by carbonation curing can synergize CO₂ sequestration and enhance building material performance. Despite challenges such as power limitations and energy consumption, through multi-path development and process optimization, steel slag direct carbonation technology has shown considerable application prospects in supporting the low-carbon transformation of the steel industry and resource utilization of solid waste.</p> Graphical Abstract <p></p>