Upcycling Construction and Demolition Waste into Calcium Carbonates: Characterization of Leaching Kinetics and Carbon Mineralization Conditions
Ning Zhang, Aaron Moment
Abstract
Carbon mineralization is a technology that fixes CO 2 permanently into solid carbonates via the reaction between CO 2 and alkaline substances. In our studies, we used Ca-bearing industrial waste (i.e., construction and demolition waste) as the feedstock to produce high-purity calcium carbonates. We aim to integrate valorization of solid wastes and CO 2 emission mitigation in our process. To achieve qualified products and fast kinetics, the reaction routes can be divided into two main processes: a dissolution process with acid followed by a two-step carbonation reaction. The advantages of this multistage process are obtaining products with high purity, tailored morphology, and narrowed particle size distribution. Conducting effective carbon mineralization requires a comprehensive understanding of the kinetics of the dissolution process, and it was found that the rate-limiting step is diffusion due to the intrinsic properties of the feedstock. In the subsequent carbonation process, impurities (Al, Fe, and Si) from the leachate were selectively removed as their oxides prior to the carbonation reaction, through pH swing, leveraging differential solubilities. Subsequent carbonation with bubbled CO 2 under controlled conditions produced calcium carbonate with tunable forms between vaterite, aragonite, and calcite. The variations of the particle size distribution and the shape of the solid were monitored in real time through a Blaze900 probe from BlazeMetrics Co., which provided optical information, facilitating a better understanding of the kinetics and mechanisms of the dissolution and crystallization processes. Thus, alkaline industrial waste can be efficiently and sustainably utilized through the carbon mineralization pathway.