This study introduces an innovative strategy to mitigate global carbon emissions by integrating carbon dioxide (CO₂) absorption and sequestration through the carbonation of recycled concrete aggregate (RCA). This approach not only promotes the recycling of concrete waste but also alleviates the demand for new natural resources, addressing both environmental impact and geographical challenges associated with mining. The integrated process utilizes ammonia to capture flue gas emissions from natural gas combined cycle (NGCC) power plants, employing the captured solution to carbonate RCA for effective CO₂ sequestration and to enhance the quality of RCA. The study comprehensively assesses the process’s viability, considering capture performance, energy penalty, compliance with ammonia emissions standards, and capital costs. A techno-economic analysis (TEA) highlights the potential and economic feasibility of the proposed approach. Bench-scale experiments, conducted at low CO₂ concentrations (3~5%), focused on optimizing the carbonation process. The concentration of carbonated ammonia solution and its ratio to RCA were investigated to enhance the yield of carbonated RCA, resulting in an approximate 10% CO₂ capacity when using a 5% carbonated ammonia solution with a 0.25 ratio. The design of a large-scale plant, with an annual carbonated RCA production capacity of around 150 ktonnes, was formulated, and TEA calculations using Aspen Plus® V14 indicated a cost of approximately SGD 13 per tonne of carbonated product. These findings underscore the promising potential of the proposed process in efficiently reducing carbon emissions while providing economic viability at a larger scale.

The increasing generation of incineration bottom residues poses environmental risks due to heavy metal leaching, while carbonation is one of the effective methods to immobilize heavy metals. This study introduces a novel approach to mitigate heavy metal leaching from incineration bottom ash (IBA) by accelerated carbonation with ammonium carbonate solution. The effect of ammonium carbonate concentration on carbonation efficiency and inhibition of heavy metal leaching was systematically investigated. X-ray fluorescence was used to analyze the composition of IBA, and thermogravimetric analysis (TGA) and inductively coupled plasma optical emission spectroscopy/mass spectrometry were used to determine carbonation capacity and heavy metal leaching, respectively. Results showed that maximum carbonation capacity was achieved at 8 wt% ammonium carbonate concentration at a solid/liquid ratio of 1:5 for 1 h, but the increase in carbonation efficiency slowed down when the concentration exceeded 4 wt%. Ammonium carbonate accelerated carbonation effectively inhibited heavy metal leaching, particularly copper, with an 89% inhibition rate at 10 wt% ammonium carbonate, while diminished effects were observed with chromiun. The effect of the ammonium carbonate concentration on heavy metal inhibition became less significant above 4 wt%, revealing a nuanced relationship between carbonation and heavy metal leaching inhibition. TGA and X-ray diffraction analyses confirmed the formation of insoluble CaCO3 during carbonation, elucidating neomineralization processes that immobilize trace heavy metals. In addition, the study explored the impact of carbonation on leachate pH, emphasizing the interplay between pH reduction and heavy metal leaching inhibition.