Mineral carbonation has been recognized as a viable method of carbon capture and storage, utilization. CO2 is fixed as carbonates of alkaline earth metals such as calcium and magnesium. Calcium carbonate or magnesium carbonates are highly stable and can be utilized for a variety of industrial applications. Concrete sludge is a waste of fresh concrete including excess ready-mixed concrete or washing residue of fresh concrete, and can be a calcium source for mineral carbonation. Gaseous CO2 is bubbled into concrete sludge to proceed carbonation reaction with calcium ions in the concrete sludge. We proposed a new method of carbonization process of concrete sludge coupled with filtration to obtain calcium carbonate with high purity. The calcium concentration decreased with the number of the filtration from 934.6 ppm to 306 ppm after five times filtration, and the pH of the filtrate solution decreased from 12.44 to 11.98. The calcium concentration drastically decreased by starting bubbling, and reached almost zero after 15 min. The precipitation of white particles were observed upon starting the bubbling for all cases. The capturing of CO2 and the carbonation reaction were completed in 15-20 min and the equilibrium was attained. The average contents of calcium carbonate in all precipitants were about 96.8%, while that of the product for the direct bubbling method without filtration was about 6.5%. The overall conversion of calcium in the feed cement was about 9.9%, which is about double of the result for the direct bubbling method (4.8%). Thus, both the purity of the calcium carbonate and the conversion of calcium were significantly improved by the present method.

MIneral CO2 mineral carbonation using waste concrete

ACS Spring 2022

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