Reduction of CO2 emissions from steel plants by using steelmaking slags for production of marketable calcium carbonate

By carbon dioxide mineralization (i.e mineral carbonation), CO2 emissions can be stored safely and leakage-free for very long times. Due to their high calcium content, steelmaking slags are suitable for mineral carbonation. In a country like Finland, where there are no suitable geological formations for CO2 storage, steelmaking slag carbonation could offer means for reduction of CO2 emissions from steel plants. By extracting calcium from the slags prior to carbonation, a pure, and possibly marketable, calcium carbonate may be produced. This could replace some of the natural and synthetic CaCO3 used in industry, combining savings in natural resources with CO2 emissions reduction. Development work on the production of pure calcium carbonate from steelmaking slags by carbonation is presented in this study. Selective extraction of calcium from steelmaking slags was investigated using various solvents. Precipitation of CaCO3 from dissolved calcium at atmospheric pressure was also investigated. Amongst the various tested solvents ammonium salt solutions (NH4Cl, CH3COONH4, NH4NO3) were found to be the most promising solvents for selectively extracting calcium from the steel converter slag. These solvents dissolved calcium efficiently also from the desulphurization slag, while extraction of calcium from the two other types of slag, produced by the integrated process route (blast furnace slag and ladle slag), was poor. CaCO3 was successfully precipitated from the solution containing ammonium salt and steel converter slag.