Carbon dioxide sequestration by slurry-phase carbonation of Waelz Slag

The alkaline waste residues seem to be appropriate resources for the application of mineral carbonation processes. Indeed, these solid wastes are characterized by having a high reactivity toward CO2 and an availability near to CO2 point-sources emissions. In this study, the aim was to apply the accelerated carbonation process on Waelz Slag, produced by metallurgical industry, assessing the influence of operating conditions such as particle size and liquid-to-solid ratio (L/S) on CO2 sequestration capacity. Several accelerated carbonation tests were performed on Waelz slag according to a slurry-phase route at two different particle size and under fixed operating conditions. Furthermore, release of metals before and after accelerated carbonation was evaluated and studied by means of geochemical modelling. The experimental results confirm that significant CO2 uptakes could be attained by appropriately selecting the operating parameters. The lower uptake of 1.79% was achieved for the coarser material at a L/S ratio of 2.5 l/kg, while the highest of 9.31% was obtained for the finer at a L/S = 10 l/kg. Hence, since huge amounts of slag are produced at Waelz plant, this residue could be considered a good candidate for the application of mineral carbonation. Results of geochemical modelling showed differences between the solubility-controlling minerals of Waelz slag before and after accelerated carbonation at different operating conditions. Accelerated carbonation likely lead to a decreased release of the alkaline earth metals due to the formation of carbonates, less soluble than the original alkaline minerals.