A mineral carbonation method for using anthropogenic carbon dioxide emissions is discussed. In this method, steel manufacturing slags are carbonated with gaseous carbon dioxide at atmospheric pressure and temperature using an aqueous ammonium chloride solution. This lixiviant extracts calcium selectively from the slag material, after which the dissolved calcium is precipitated as calcium carbonate. A flue gas stream can be used as a CO2 source without pre-separation. The reactions occur pseudo-catalytically in one vessel, resulting in considerable savings regarding process capital costs and reagent usage compared to a previously developed two-step carbonation method (Slag2PCC). The one-step method uses steel slag more efficiently, potentially reducing the amount of landfilled slag while capturing significantly more carbon dioxide in the same amount of slag. The two-step method produces >95% pure calcium carbonate, which can be used, e.g., in papermaking, while the one-step method is capable of manufacturing 60-75% pure carbonates for reuse at the steel plant, thus decreasing the need of virgin raw materials, such as limestone. Direct recycling would also reduce the transportation and processing requirements, resulting in a better overall process economy.