Simultaneous productions of high-purity CaCO (calcium carbonate) and amorphous nanosized SiO-rich (silica-rich) gel from waste concrete powder remain quite challenging, and thus the high-value added utilization of waste concrete powder is significantly limited. A novel technology involving a combination of alkaline treatment and carbonation, has been proposed for the greatly enhanced utilization of waste concrete powder. Through alkaline treatment, CaCO and SiO-rich gel formed during carbonation of concrete powder were transformed into Ca(OH) (calcium hydroxide) and NaSiO (sodium metasilicate), respectively. Subsequently, Ca(OH) and NaSiO were separated. As a result, CaCO with a high purity of 98.54% and amorphous nanosized SiO-rich gel were obtained via carbonation, and the recovery ratio of CaCO was 81.46%. Furthermore, the concrete powder exhibited a high CO (carbon dioxide) uptake efficiency of 0.24g CO/g. 30.31 Mt CaCO and 2.77 Mt SiO-rich gel productions as well as 38.54 Mt CO emission reduction could be realized via recycling a quarter of annually generated waste concrete powder worldwide.
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