Producing vaterite by CO2 sequestration in the waste solution of chemical treatment of recycled concrete aggregates

A recent study showed that the properties of recycled concrete aggregates (RCAs) can be significantly improved by acetic acid treatment. This study demonstrates that a useful product, vaterite, a metastable polymorph of calcium carbonate, can be produced from the waste solution of this treatment through an improved pH swing method. The salient feature of this improved method is that ethanol is added into the waste solution to not only prohibit the phase transformation of vaterite, but also to suppress the ionization of the regenerated acetic acid. This method allows not only more vaterite to be produced, but also more acetic acid to be regenerated from the waste solution through a CO2 bubbling method. Meanwhile, CO2 can be permanently stored in the produced vaterite to achieve sustainable CO2 sequestration. Experimental results confirm that near-pure vaterite can be produced from the waste solution by adding 20% ethanol into the waste solution. 1 kg RCAs can be used to produce about 76.6 g vaterite and permanently store 33.7 g CO2 by using this new method. The potential application of the produced vaterite as an internal curing agent for high performance concrete has also been demonstrated.