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A mineral carbonation method based on steelmaking slags and ammonium salt solutions has been found to have economical and CO2 emission reduction potential. Although the aqueous solution of ammonium salt can be recycled, some of the solvent is likely to escape in a form of ammonia vapor within the outgoing gas flow during the carbonation step. In this study, the escape of ammonia vapor was investigated. The loss of NH3 was found to be quite insignificant and in addition, the total solution loss per step was very small. The CO2 content of the ingoing gas flow affected the rate of the CaCO3 precipitation; the smaller the CO2 content, the longer the duration of the carbonation reaction. However, the CO2 content did not seem to have a significant effect on the degree of CaCO3 precipitation, indicating that CO2 capture in a separate process step should not be needed. CaCO3 precipitated in a form of calcite, although two of the precipitates also contained aragonite. Furthermore, the precipitates were found to be of high quality with bright white color, and fine and powdery texture. Nonetheless, in order to obtain high‐quality CaCO3, the precipitate resulting from the carbonation step should be washed with an adequate amount of water. © 2011 Society of Chemical Industry and John Wiley & Sons, Ltd

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The slag2PCC concept aims at transforming steelmaking slag into precipitated calcium carbonate (PCC) with market value. This paper reports on R&D work on two features that impact the overall performance and costs of slag2PCC as a carbon capture and utilisation (CCU) technology. Operating near ambient conditions, calcium is selectively leached from steelmaking slag using aqueous ammonium salt solvent, followed by carbonation using a CO 2containing stream. Separators for removing spent slag and PCC connect two reactors for extraction and carbonation, respectively, between which the solvent solution is cycling. One requirement is effective conversion of the CO 2 fed to the system: while the dissolution of CO 2 is the rate-liming step it is essential minimise release of unreacted CO 2 . Mixing the solutions enhances mass transfer. High-speed video recordings were made around mixers located at various heights in a bubble column, analysing CO 2 bubble swarm dissolution. A second feature studied are losses of ammonia (NH 3 ) from the solution. An outlet for unreacted gas presents a risk of NH 3 vapour release, which lowers solution alkalinity while adding costs.Multicomponent mixture mass transfer analysis showed that diffusion of NH 3 into CO 2 bubbles may be significant at least during initial stages of dissolution. Experimental findings were verified.

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