While the advancement of industrial technology drives societal progress, it also exacerbates atmospheric pollution, with sulfur dioxide (SO₂) emissions being particularly prominent (China’s annual SO₂ emissions reached 5.2908 million tons). To control industrial pollutants such as SO₂ and nitrogen oxides, flue gas desulfurization technologies have been rapidly promoted, and it is projected that China’s desulfurization equipment will reach 109,200 units by 2025. Currently, calcium-based desulfurization processes are widely adopted in industries such as power generation and steelmaking due to their cost-effectiveness. However, their by-products require differentiated treatment: desulfurization gypsum (composed of calcium sulfate dihydrate) generated from wet processes can be resourcefully utilized in fields like construction materials and agriculture. In contrast, calcium-based desulfurization ash (CDA) produced from dry and semi-dry processes, primarily composed of calcium sulfite, poses significant challenges due to its high chemical reactivity, hygroscopic nature, and poor volume stability. These properties lead to issues such as material cracking and strength degradation when directly applied in construction materials, severely limiting its resource utilization.

In this context, the Low-Carbon Ironmaking and Solid Waste Resource Utilization Team at Anhui University of Technology, building on a systematic summary of their related research achievements and integrating the latest advancements in CDA resource utilization, published a comprehensive review titled “Resource Utilization of Flue Gas Calcium-Based Desulfurization Ash: A Comprehensive Review” in the Journal of Iron and Steel Research International. This paper focuses on exploring the technological pathways and sustainable development strategies for the resource utilization of calcium-based desulfurization ash from industrial flue gas.

Article Information

Title: Resource utilization of flue gas calcium-based desulfurization ash: a comprehensive review

Author: Dongxiang Meng, Rufei Wei, Feihu Zhang, Hongming Long, Yuanyuan Zhang

Citation Format：D. Meng, R. Wei, F. Zhang, H. Long, and Y. Zhou, Resource utilization of flue gas calcium-based desulfurization ash: a comprehensive review. J. Iron Steel Res. Int. 30 (2023) 405-418.

Highlights of the Article

(1) Based on systematic research on the physicochemical properties of CDA produced by dry and semi-dry processes, the composition, morphology, and reactivity characteristics of CDA were clarified, and the key limiting factors for its direct application in construction materials were revealed.

(2) The modification technologies for CDA were systematically summarized, and it was proposed that hydrothermal oxidation technology combines the dual functions of oxidation and impurity removal, highlighting its efficiency and environmental benefits, thereby laying the foundation for large-scale application.

(3) The one-step preparation technology of calcium sulfate whiskers from CDA was introduced, further demonstrating its significance as a high-value-added utilization direction for CDA. This technology promotes the evolution of solid waste resource utilization in the metallurgical industry toward low-carbon and high-profit development, with clear market application prospects.

Content Resume

This paper begins with a detailed analysis of the physicochemical properties of calcium-based desulfurization ash. However, the high content of CaSO₃ in CDA poses a critical challenge that severely limits its direct application in the construction materials sector. Specifically, when used as a cement admixture, CaSO₃ reacts with cement minerals, leading to a linear reduction in the strength of the hardened paste; when employed as a retarder, CaSO₃ fails to form the core retarding phase, resulting in ineffective retardation; and when utilized as a cementitious material, it cannot establish a dense microstructure.

To achieve efficient resource utilization of CDA, current research primarily focuses on modification through high-temperature oxidation and wet oxidation methods (using liquid-phase oxidants to facilitate component transformation). Modified CDA can replace natural gypsum or slag, serving as a cementitious material admixture, wall material additive, and other applications in green building material production. In recent years, hydrothermal oxidation technology has garnered significant attention due to its unique advantages. Under high-temperature and high-pressure hydrothermal conditions, calcium sulfite in CDA can be deeply oxidized to calcium sulfate, while the hydrothermal reaction significantly removes harmful impurities such as Cl⁻ and F⁻, thereby simultaneously achieving the stabilization and detoxification of CDA.

Finally, this paper introduces the one-step preparation of calcium sulfate whiskers from CDA as eco-friendly rubber fillers, providing an innovative solution for the “waste-to-resource” transformation of industrial solid waste. This approach combines environmental benefits with economic value and offers a multi-dimensional outlook on the industrialization prospects of preparing calcium sulfate whiskers from CDA.

Graphic and Text Analysis

(Physicochemical Properties of Calcium-Based Desulfurization Ash）

(Preparation of calcium sulfate whiskers from CDA)

（Overview of resource utilization of CDA）