Upcycling Construction and Demolition Waste into Calcium Carbonates: Characterization of Leaching Kinetics and Carbon Mineralization Conditions

Abstract

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.

Directed synthesis of aragonite through semi-continuous seeded crystallization methods for CO2 utilization

“…10 Numerous studies have attempted to describe the ideal conditions for synthetic aragonite production from precursor salts such as calcium chloride or acetate and sodium carbonate, sodium bicarbonate, and ammonium carbonate. Aragonite is considered a more stable thermodynamic phase at higher temperatures in aqueous media, forming an apparent enantiotropic system with calcite; 11,28,29 generally, temperatures above 60 °C in the bulk are necessary to see appreciable amounts of aragonite. The kinetics of nucleation and growth of the carbonate phases are also temperature dependent, 11 leading to a rich landscape of phase behavior impacted by both kinetic and thermodynamic considerations.…”

“…The leachate was returned to the reactor and the pH was increased from 3 to 9 using ("pH-swing process") NaOH in an attempt to remove the ancillary ions of Si, Al, and Fe which are also extracted during the leaching of the HCP. 29 Fig. S1a † shows the leaching kinetics as measured by ICP-OES of the HCP over 60 minutes, yielding a 60% Ca extraction efficiency in a single batch-reactor pass.…”

“…Previous work has shown that 60 °C is the temperature at which appreciable amounts of aragonite precipitates in model salt systems; however, that number could be higher if Ca-sources with impurities are used. 12,29 Thus, seeding could prove especially useful to reduce the energetic barrier for aragonite synthesis, even at lower temperatures through the promotion of heterogenous nucleation. 52,58 Both semi-continuous and batch crystallizers produced similar aragonite phase compositions, with differences mainly relating to the agglomeration and growth of the new aragonite crystals as shown by SEM analysis in Fig.…”

Multiscale Process Intensification of Waste Valorization Reactions

“…The hydroxyl group for the neutralization of CO 2 bubbling can be supplied via chemical base addition or alkaline solid industrial wastes, such as steel slag, fly ash, demolition materials, etc. 25 In the search for approaches that are more energetically favorable than simply using a base for pH control, our group investigated three different processes that relied on the intensification of chemical reactions, optimized reactor design, and innovative nanoscale and nanoengineered additives. The integration of CO 2 mitigation technologies with brine utilization (often a waste product of desalination, oil and gas operations, and geological carbon sequestration) and with the production of valuable materials presents an attractive solution for industrial waste treatment and utilization.…”

“…However, as these are chloride- and sulfate-rich solutions, it is necessary to buffer the pH to enable carbonate precipitation. The hydroxyl group for the neutralization of CO 2 bubbling can be supplied via chemical base addition or alkaline solid industrial wastes, such as steel slag, fly ash, demolition materials, etc . In the search for approaches that are more energetically favorable than simply using a base for pH control, our group investigated three different processes that relied on the intensification of chemical reactions, optimized reactor design, and innovative nanoscale and nanoengineered additives.…”