Carbon mineralization is a technology that fixes CO2 permanently into solid carbonates via the reaction between
CO2 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 CO2 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 CO2 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.