Proceedings of the 4th International Conference on Accelerated Carbonation for Environmental and Materials Engineering pages:127-139
ACEME 2013 location:Leuven, Belgium date:9-12 April 2013
Two approaches for the intensification of the mineral carbonation reaction are combined and studied in this work, namely: (i) the calcium leaching and aragonite promoting effects of magnesium chloride (MgCl2), and (ii) the passivating layer abrasion effect of sonication. The alkaline materials subjected to leaching and carbonation tests included lime, wollastonite, steel slags, and air pollution control (APC) residue. Batch leaching tests were conducted with varying concentrations of additives to determine extraction efficiency, and with varying solids-to-liquid ratios to determine solubility limits. Aqueous mineral carbonation tests, with and without the use of ultrasound, were conducted applying varying concentrations of magnesium chloride and varying durations to assess CO2 uptake improvement and characterize the formed carbonate phases. The leaching of calcium from lime with the use of MgCl2 was found to be atom-efficient (1 atom Ca extracted for every 1 atom Mg added), but the extraction efficiency for slags and APC residue reduced to 26–35 % due to mineralogical and microstructural limitations. The addition of MgCl2 notably improved AOD slag carbonation extent under sonication, where higher additive dosage resulted in higher CO2 uptake. Without ultrasound, however, carbonation extent was reduced with MgCl2 addition, possibly due to the reduction of CO2 solubility in saline solutions. The benefit of MgCl2 under sonication can be linked to the preferential formation of aragonite (85 wt% of formed carbonates), which precipitates on the slag particles in the form of acicular crystals with low packing density, thus becoming more susceptible to the surface erosion effect of sonication, as evidenced by the significantly reduced carbonated slag particle size.