Synthesis of acicular aragonite via indirect carbonation of argon oxygen decarburization slag: Efficient calcium extraction and crystallization behavior

• Outlined the AOD slag application in CO 2 sequestration. • Ca leaching strategy in indirect carbonization route was studied. • Crystallization behavior of acicular aragonite under indirect-carbonation. • The acicular aragonite with maximum aspect ratio of 25.46 was prepared. • The total conversion ratio of Ca from AOD slag reached 83.96 %. The argon oxygen decarburization (AOD) stainless steel slag, a calcium-rich industrial byproduct, offers significant potential for CO 2 sequestration and high-value calcium carbonate production. This study developed an integrated indirect carbonation route to synthesize acicular aragonite from AOD slag while addressing critical challenges in selective leaching and crystallization control. Through systematic optimization, over 90.51 % of Ca was efficiently extracted via HCl leaching (1.5 M, 85 °C, 50 mL·g -1 liquid-solid ratio), overcoming silica gel encapsulation through intensified mass transfer. Impurity removal (>99 % Fe, Al, Si) was achieved by pH adjustment (7.5), enabling subsequent Mg 2+ -mediated aragonite growth. Under optimal carbonation conditions (80 °C, Mg/Ca=2, 6 mL min -1 CO₂ flow, 30 % leachate concentration), acicular aragonite crystals with 98.65 % purity, 55 μm length, and 25.46 aspect ratio were obtained. The hierarchical regulation of leaching-carbonation processes achieved 83.96 % overall Ca conversion, demonstrating a closed-loop strategy for steel slag valorization. This work provides both technical insights into aragonite crystallization kinetics and practical pathways for industrial synergy between CO 2 mineralization and high-performance material synthesis, with potential reductions in carbon emissions and landfilling costs.