Production of Precipitated Calcium Carbonate from Steel Converter Slag and Other Calcium-Containing Industrial Wastes and Residues

Abstract Precipitated calcium carbonate, a widely used filler material, is nowadays mainly produced by the so-called carbonation process. Natural limestone is first calcined and then contacted with carbon dioxide to precipitate particles of a controlled purity, size, and morphology. In the production process, an amount of carbon dioxide equal to or larger than what is later bound to the actual product is released. For climate change mitigation, it would be possible to reduce carbon dioxide emissions by capturing CO 2 from flue gases, if the required calcium could be obtained from another source than the natural rocks. Industrial alkaline by-product and waste streams such as slags and ashes contain calcium often in a readily soluble form. Recently, several processes have been developed to apply these materials for carbon dioxide capture, utilization, and storage, while simultaneously producing materials with market value. Since the chemistry of calcium carbonate precipitation is relatively complex, the levels of impurities should be maintained low in the carbonation process. In case of utilizing a solid waste stream, this requires efficient separation of the residual waste material from the calcium-rich solution after extracting the soluble calcium from the solids. Aspects related to a two-step aqueous process for steel converter slag carbonation are discussed in more detail, since a continuous laboratory-scale setup has been constructed and is currently under further development at Finnish universities. Even though the current issues related to product quality can be resolved, the process is still in such a small scale that it mainly serves the demonstration purposes for mineral carbonation technologies.