Key Takeaways & Executive Findings
- •• • At 700 °C, fly ash achieved a peak dechlorination efficiency of 93.33%, outperforming red mud (88.61%), but both declined with temperature, dropping to 65.6% and 58.27% at 900 °C, respectively, indicating a temperature-dependent operational window. • • Alkali (NaOH) modification of fly ash significantly enhanced high-temperature performance: at 800 °C, efficiency rose from 71.9% (unmodified) to 94.98%, a 23.08% absolute improvement, enabling effective HCl capture at higher temperatures. • • The modification mechanism involved increased surface roughness and porosity, as confirmed by SEM, and disruption of Si-O-Si and Si-O-Al networks, which exposed active sites and increased contact area for HCl adsorption. • • Both fly ash and red mud demonstrated stable dechlorination across 600–900 °C, validating their feasibility as low-cost, abundant alternatives to conventional calcium-based agents, which suffer from severe efficiency losses above 700 °C.
Abstract
The escalating volume of municipal solid waste in China necessitates effective disposal strategies. Industrial kiln co-processing offers a promising route, but high-temperature decomposition of chlorinated components releases HCl and Cl2, causing severe equipment corrosion and operational issues. This study investigates the high-temperature dechlorination performance of fly ash and red mud, two abundant industrial solid wastes, as potential dechlorination agents. Using a high-temperature tube furnace system, dechlorination efficiencies were evaluated across 600–900 °C. At 700 °C, fly ash achieved a peak dechlorination efficiency of 93.33%, while red mud reached 88.61%. However, efficiencies declined with further temperature increase, dropping to 65.6% and 58.27% at 900 °C for fly ash and red mud, respectively. To enhance performance at higher temperatures, fly ash was modified via alkali (NaOH) treatment. The modification increased surface roughness and porosity, disrupted Si-O-Si and Si-O-Al networks, and exposed active sites. Consequently, the alkali-modified fly ash exhibited a peak dechlorination efficiency of 94.98% at 800 °C, a 23.08% improvement over unmodified fly ash (71.9%). These findings demonstrate the technical feasibility of utilizing solid wastes as dechlorination agents, offering a dual benefit of waste valorization and cost-effective high-temperature gas purification. The study provides a foundation for scaling up this approach in industrial kiln applications, contributing to sustainable waste management and reduced environmental impact.
1. Introduction
Industrial kiln co-processing of municipal solid waste is a promising strategy for waste reduction and energy recovery, yet it faces a critical bottleneck: the release of corrosive chlorinated gases (HCl, Cl2) during high-temperature combustion. These gases recirculate within the system, leading to accelerated equipment corrosion, increased maintenance costs, and reduced operational lifespan. Conventional wet scrubbing methods are effective but suffer from complexity, secondary wastewater, and incompatibility with high-temperature zones. Dry dechlorination using calcium-based sorbents (CaO, Ca(OH)2, CaCO3) is widely adopted due to low cost, but their efficiency drops sharply above 700 °C—for instance, CaO efficiency falls from a peak of 65.2% at 700 °C to a mere 3.11% at 1200 °C. This temperature limitation poses a significant challenge for industrial kilns that operate at higher temperatures, necessitating the development of alternative dechlorination agents that maintain activity under more severe thermal conditions.
This study addresses this bottleneck by exploring the use of fly ash and red mud—two abundant industrial solid wastes—as potential high-temperature dechlorination agents. Both materials contain alkali and alkaline-earth oxides that can react with HCl, and their porous structures may facilitate gas-solid contact. However, raw materials exhibit declining efficiency above 700 °C. To overcome this, the authors employed alkali modification (NaOH) to tailor the surface chemistry and porosity of fly ash. The modification disrupts the aluminosilicate network, increasing surface area and active sites, thereby enhancing HCl adsorption at higher temperatures. This approach not only offers a cost-effective solution for high-temperature dechlorination but also provides a new avenue for the resource utilization of solid wastes, aligning with circular economy principles.
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WANG Xuening, LI Hui, HU Yingying, GOU Yujin, CAO Taiyu, QI Yongle, ZHENG Wukui (2026). High-Temperature Dechlorination Performance of Solid Waste-Based Dechlorination Agents. Journal of Environmental Engineering Technology. https://doi.org/10.13205/j.hjgc.202606009
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Frequently Asked Questions
What are the specific dechlorination efficiencies of fly ash and red mud at 700 °C and 900 °C, and how do they compare to conventional calcium-based agents?
At 700 °C, fly ash achieves 93.33% dechlorination efficiency, while red mud reaches 88.61%. At 900 °C, efficiencies drop to 65.6% and 58.27%, respectively. In contrast, conventional CaO peaks at 65.2% at 700 °C and falls to 3.11% at 1200 °C, indicating that fly ash and red mud offer superior performance in the 700–900 °C range, though they also suffer from temperature-induced decline.
How does NaOH modification enhance the dechlorination performance of fly ash, and what is the underlying mechanism?
NaOH modification increases surface roughness and porosity, as evidenced by SEM, and disrupts the Si-O-Si and Si-O-Al networks. This disruption exposes active sites and increases the contact area for HCl adsorption. Consequently, the modified fly ash achieves a peak efficiency of 94.98% at 800 °C, a 23.08% improvement over unmodified fly ash (71.9%).
What is the optimal operating temperature range for these solid waste-based dechlorination agents, and what are the implications for industrial kiln design?
Both fly ash and red mud exhibit optimal performance at 700 °C, with efficiencies of 93.33% and 88.61%, respectively. However, alkali-modified fly ash extends the effective range to 800 °C, achieving 94.98%. This suggests that for processes operating above 700 °C, modification is necessary to maintain high efficiency, guiding kiln temperature control and sorbent selection.
What are the potential cost and scalability advantages of using fly ash and red mud compared to commercial dechlorination agents?
Fly ash and red mud are abundant industrial by-products with negligible raw material costs. Their use not only reduces waste disposal burdens but also provides a low-cost alternative to synthetic sorbents. The modification process using NaOH is relatively simple and scalable, though the additional chemical cost must be weighed against performance gains. Overall, the approach offers a cost-effective and sustainable solution for high-temperature dechlorination in industrial kilns.
What are the limitations of this study, and what further research is needed to translate these findings into industrial practice?
The study was conducted in a laboratory-scale tube furnace, and the dechlorination efficiency was measured under controlled conditions. Further research should investigate the performance under real flue gas compositions, long-term stability, and the impact of other acid gases (e.g., SO2) on dechlorination efficiency. Additionally, pilot-scale tests are necessary to assess the mechanical strength and attrition resistance of the sorbents in industrial reactors.
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