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

By carbon dioxide mineralization, CO₂ can be stored safely and leakage-free for very long times. Owing to their high calcium content, steelmaking slags are suitable for mineral carbonatlon. In a country like Finland, where no suitable geological formations for CO₂ storage seem to exist, steelmaking slag carbonation offers an important CO₂ emissions reduction option for steel plants. If calcium could be extracted selectively 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, CH ₃COONH₄, NH₄NO₃) were found to be the most promising for selectively extracting calcium from steel converter slag. These solvents dissolved calcium efficiently also from desulphurization slag, while extraction of calcium from two other types of slag was poor. CaCO ₃ was successfully precipitated from the solution containing ammonium salt and dissolved steel converter slag.