Mineral carbonation technologies aim at permanently storing CO2 into materials rich in metal oxides. A multi-step mineralization process employing Ca-rich waste streams to precipitate calcium carbonate is investigated in this paper. Ground granulated blast furnace slag (GGBS), phosphorus slag (PS) and steel slag (SS) were employed as feeding materials for the process. Solid to liquid ratio (S/L) is an important factor which affects mineral carbonation and this study examines its effect on the carbonation efficiencies. The main phases present in the carbonated residues were identified using XRF, XRD and SEM-EDS analytical techniques. For the three materials investigated, the carbonation efficiency increased when the S/L ratio decreased (from 50 g/L to 25 g/L and then 15 g/L) because of the dilution effect. In a previous study, where an analog process was employed, efficiency using serpentine was found lower than that calculated here for GGBS and SS, and slightly above PS. This confirms that, in general, waste materials require less energy-intensive carbonation conditions, in comparison to mineral rocks. Finally, the structure of the carbonated particles is also discussed. (C) 2013 The Authors. Published by Elsevier Ltd. All rights reserved.