Advanced ex-situ carbon stabilization technology using municipal solid waste incineration fly ash: A review
Research Background
Over the past decades, the pronounced increase in carbon emissions has drawn worldwide concern. In response, researchers have developed a variety of advanced chemical processes that capture and stabilize CO₂ by converting it into solid minerals, a strategy commonly referred to as carbon stabilization or carbon mineralization. Most efforts have focused on in-situ mineralization, in which fluid CO₂ is injected into calcium- or magnesium-rich silicate formations to promote geochemical reactions that form carbonate minerals. Nevertheless, pilot projects in this area face significant challenges: the reaction mechanisms are complex, mineralization kinetics are slow, and both storage capacity and its scalability are difficult to predict. Moreover, effective in-situ mineralization depends on specific geological conditions—such as adequate permeability, porosity and alkali-metal concentrations—that are absent in many countries.
Ex-situ carbon mineralization technology offers an alternative route that aims to permanently store CO₂ through controllable engineered processes while converting it into materials of practical value. Unlike in-situ approaches, ex-situ systems confine the feedstock in dedicated reactors, enabling precise control of reaction conditions and optimized kinetics. Moreover, replacing natural minerals with alkaline solid wastes—such as cement kiln dust, steel slag and municipal solid-waste incinerator fly ash (MSWIFA)—enhances sustainability. MSWIFA is produced in large quantities, exhibits high carbon-capture efficiency, and is intrinsically hazardous, requiring special treatment prior to landfilling or reuse; thus, it represents an ideal candidate feedstock for carbon stabilization.
In recent years, extensive research has focused on the mineralization of MSWIFA, covering CO₂ capture, heavy-metal immobilization, and the removal of chlorine and dioxins, as well as the reuse of the treated material in construction products. Several review papers have also summarized conventional MSWIFA disposal routes such as thermal separation and chemical stabilization.
Research motivation
To date, no review has specifically addressed the CO₂-capture capacity of MSWIFA. Moreover, the literature employs inconsistent calculation formulas, resulting in the absence of a universal metric for cross-comparing carbonation efficiencies. In addition, liquid-phase carbon mineralization technologies have not been systematically summarized or critically discussed.
Research Content
This study aims to summarize the latest progress in MSWIFA liquid-phase carbon mineralization, with a particular focus on its carbon capture capacity and its potential contribution to global carbon sequestration. Specifically, we analyzed 1,284 articles published over the past decade related to MSWIFA and its carbonation technology, combining large language models with manual screening. We conducted a standardized comparison of the carbonation efficiency and lead stabilization efficiency of different technologies to bridge the gap between existing research and the optimal selection of liquid-phase carbon mineralization technology. Additionally, we compared the optimal carbon sequestration technology of MSWIFA with other carbon capture schemes and engaged in an in-depth discussion on cost-effectiveness, environmental friendliness, and carbon capture capacity.
Conclusions:
1. MSWIFA is considered a highly potential material for ex-situ carbon mineralization due to its fine particle size, porous structure, and high content of alkali metals, and it can complement existing CCUS (Carbon Capture, Utilization, and Storage) schemes.
2. A unified formula for calculating the maximum theoretical CO₂ capacity (mCO₂,th) is proposed. Comparative studies have found that the carbonation efficiency is highest (close to 100%) using ammonia water washing (8% NH₄OH), which can also effectively reduce the risk of secondary pollution caused by heavy metal leaching.
3. Under the optimal ammonia water washing process conditions, the maximum carbon capture capacity of MSWIFA carbonation in 2024 is projected to reach 54 million tons per year, which is close to the current global total scale of carbon capture capacity.
4. MSWIFA carbonation is economically superior to other ex-situ carbonation methods because it avoids energy consumption from mineral grinding and raw material transportation. The cost of capturing CO₂ using MSWIFA is approximately $10 per ton when using CO₂-rich flue gas, or $20 per ton when using external CO₂ sources, which is significantly more favorable than technologies such as bioenergy and enhanced weathering. Moreover, recycling all carbonated MSWIFA and partially substituting it for cement can further reduce CO₂ emissions in the cement production process and promote the resource utilization of municipal solid waste.
In summary, MSWIFA carbonation is a low-cost, environmentally friendly, and highly promising carbon-reduction pathway that provides a feasible solution to the challenge of global warming. Future optimization directions for MSWIFA carbonation, especially in the combination of physical and chemical reagent methods, need to deepen the understanding of reaction mechanisms rather than being limited to the shrinking core model and surface coverage model. Moreover, the development of new MSWIFA treatment reactor systems is expected to achieve rapid numerical simulation and improve overall efficiency through the adoption of advanced computational technologies.
Source:https://mp.weixin.qq.com/s/gmzcA096fjggTd2CEm94HA