Sustainable valorization of industrial solid waste: Application of indirect carbonation and byproducts-derived activators

Abstract

As global CO₂ emissions and waste generation continue to rise, the demand for sustainable construction materials is becoming essential. In response, growing research efforts are focused on reducing dependence on conventional construction materials and promoting the practical application of alternative resources. Therefore, this thesis proposes innovative methods for carbon emission reduction through the upcycling of industrial by-products. In particular, this approach aims to enhance mechanical performance and address environmental challenges, with potential implications for seismic resilience, through the utilization of coal combustion residues and electronic waste. First, this study evaluated the potential of indirect carbonation using fluidized bed combustion (FBC) fly ash (HFA) and bottom ash (HBA) for CO₂ sequestration and high-purity CaCO₃ production. The calcium extraction was conducted using distilled water and NH₄Cl. A NH₄Cl achieved high calcium extraction efficiency, yielding 8.4 wt.% and 10.2 wt.% of CaCO₃ from HBA and HFA, respectively, corresponding to CO₂ capture capacities of 36.8 kg and 45.0 kg per ton of raw ash. XRD, SEM, and TGA analyses confirmed the formation of high-purity CaCO₃, and the formation of vaterite was observed under low pH conditions. Therefore, these findings indicate the potential to contribute to sustainable waste management and carbon capture, utilization, and storage (CCUS). Second, a novel method of synthesizing alkaline activators from coal bottom ash (CBA) was proposed. Instead of using CBA as a binder or filler, this study dissolves amorphous silica from CBA into a sodium hydroxide solution to produce an alkaline activator. The alkaline activator synthesized from CBA was successfully applied to the production of metakaolin- based geopolymer composites. The CBA-based activator exhibited improved mechanical performance compared to the use of the same amount of CBA as a binder. This suggests a novel utilization approach for CBA and contributes to expanding the methods for industrial by-product recycling. Third, this study proposed a sustainable method to utilize waste liquid crystal display (LCD) powder by synthesizing alternative alkaline activators. The LCD-derived activator provided approximately 35% of the silica content compared to silica fume and resulted in phase transformation of residual LCD into sodalite. Compared to direct binder replacement, the use of LCD-derived activators improved compressive strength and reduced porosity. These findings demonstrate that waste LCD powder can be effectively valorized through byproduct-derived activator synthesis, offering both environmental and mechanical benefits.