Influence of Alkali Metals on Metallurgical Properties of Blast Furnace Burden

The effects of alkali metals (K, Na) on blast furnace burden performance were systematically investigated through metallurgical testing and microstructural analysis. Sinter and pellet samples with varying alkali loads (0.75–13.33 kg/tHM) were evaluated for reducibility (RI), low-temperature reduction degradation (RDI), and strength. Results demonstrate that alkali enrichment enhances reducibility but deteriorates structural integrity, evidenced by elevated RDI and reduced post-reduction strength. Potassium exhibits stronger catalytic activity than sodium, accelerating FeO reduction via lattice infiltration, thereby inducing interfacial stress and crack propagation. Microstructural analysis reveals alkali-driven phase evolution: sinter porosity increases, while pellets develop porous, glass-phase-rich structures with iron whiskers, exacerbating swelling. Elemental mapping confirms heterogeneous alkali distribution, influenced by interactions with Ca, Si, and Al. This study elucidates alkali-metal-induced degradation mechanisms, offering critical insights for optimizing blast furnace operations and advancing sustainable ironmaking under “Dual Carbon” objectives.