AbstractThe CO2 uptake and Ca‐to‐carbonate conversion yield attained by wet and slurry‐phase carbonation of stainless steel slag are reported. A maximum CO2 uptake of 180 g CO2/kg slag was achieved under wet conditions (50 °C, 3 bar CO2, 0.4 l/kg), corresponding to a Ca‐to‐carbonate conversion yield of 50%. The slurry‐phase process, even when adopting more energy‐intensive operating conditions, did not improve the CO2 uptake kinetics and conversion yield in comparison to the wet treatment. The mineralogy of the carbonated slag exhibited a decreased content of silicate phases (Ca2SiO4 in particular), a marked reduction of Ca and Mg oxides, and a noteworthy increase of calcite. © 2011 Society of Chemical Industry and John Wiley & Sons, Ltd