Research Progress on Formation Mechanism and Control Technology of Dioxins in Iron and Steel Sintering Flue Gas

The emission of dioxins (PCDD/Fs) from iron and steel sintering flue gas poses a serious threat to regional air quality and human health. The process is considered a major source of dioxins. Therefore, it is necessary to select a cost-effective, environmentally friendly, and efficient control technology for enterprises. To control the formation and emission of sintered dioxins, it is essential to clarify the formation mechanisms of dioxins during the sintering process. Additionally, understanding the formation and distribution of sintered dioxins and their homologues is crucial for regulating emissions at the source, during the process, and at the end-of-pipe. The complexity of the sintering process makes it difficult to study the formation mechanisms of sintered dioxins. However, current research indicates that the formation mechanisms of sintered dioxins mainly include the de novo synthesis mechanism and precursor synthesis mechanism. Since the sintering process meets the basic conditions for the de novo synthesis of dioxins: a carbon source, a chlorine source, and a metal catalyst, a consensus suggests that the primary formation mechanism of sintered dioxins is the de novo synthesis mechanism. Concerning the generation and distribution of PCDD/Fs and their homologues, researchers have sampled and analyzed iron and steel sintering plants worldwide. The results indicate that the products of sintered dioxins are primarily PCDFs, with a smaller proportion of PCDDs, which further supports the conclusion that the de novo synthesis mechanism is the dominant formation pathway for sintered dioxins. For the control of already-formed dioxins, strategies can be categorized into source control, process control, and end-of-pipe treatment. Source control is the most effective approach for reducing dioxin formation and includes measures such as raw material screening and the addition of inhibitors. Process control involves optimizing the sintering process, controlling the sintering temperature zone, and implementing synergistic solid waste treatment. Among these, the synergistic treatment of solid waste is a promising area for future research due to its significant potential. End-of-pipe treatments include high-efficiency dust removal systems, activated carbon adsorption technology, and selective catalytic oxidation technology. However, the application of high-efficiency dust removal and activated carbon adsorption technologies is limited due to economic limitations and technical constraints. Selective catalytic oxidation, on the other hand, has strong potential owning to its operational simplicity and lack of secondary pollution. The selection of an appropriate catalyst is crucial for the successful application of selective catalytic oxidation technology. Future research should focus on developing catalysts with high efficiency, stability, and cost-effectiveness, since no single solution is sufficient for dioxin control. Each control technology has its own limitations. Only by integrating multiple control technologies, methods, and processes adapted to specific conditions can optimal results be achieved. The control paradigm of waste treatment, solid waste co-treatment, and collaborative treatment is likely to become a major focus in future research on dioxin control in sintering processes.