Carbon dioxide sequestration by accelarated carbonation of industrial residues

Alkaline industrial residues can be suitable materials for carbon dioxide sequestration through mineral carbonation and they can be used as alternative feedstock to natural minerals, due to their higher reactivity and the large quantity available close to CO2 point source emissions sites. In this study, the application of accelerated carbonation on Cement Kiln Dust and Waelz Slag, produced by the cement and metallurgical industry, is presented and discussed. Several accelerated carbonation tests were performed on the two selected residues according to direct aqueous routes, with the aim of assessing, comparing and optimizing the achievable CO2 sequestration. In a preliminary experimental phase, test were performed on both the materials at their original particle size and at wet-route conditions (L/S=0.4 L/kg). The assessed CO2 uptakes were low if compared with the maximum theoretical CO2 sequestration capacity of the two materials, indicating that the potential for CO2 sequestration was only partially exploited. In a view of process optimization, slurry-phase conditions were tested for CKD, whilst a pre-treatment stage based on particle size reduction was applied to Waelz Slag. At the new experimental conditions, the assessed CO2 uptakes raised up to 8.8 and 19% for CKD and Waelz Slag, respectively, with a conversion yield of 65.9 and 53.8%. This would result in the potential for sequestering 3.5% of the cement plant CO2 emissions and 16% of the Waelz plant CO2 emissions. Hence, both CKD and Waelz Slag could be considered good candidates for the application of mineral carbonation process, provided that optimal operating conditions are implemented