Application of corn stalk waste in direct reduction of vanadium titanium magnetite: Phase composition, microstructure evolution, reduction behavior and mechanism analyses.

In order to facilitate low-carbon and green development in the steel industry and the resource utilization of agricultural waste, this study explored the possibility of biomass stalk recycling instead of fossil fuels in coal-based reduction of vanadium-titanium magnetite (VTM). The corn stalk hydrochar (CSH) was selected as the reducing agent and mixed with vanadium-titanium magnetite to fabricate pellets. The evolution behavior of slag in initial pellets was simulated by Factsage7.2 thermodynamic software. The effects of basicity (R) and C/O ratio on pellet reduction behavior, mineral composition, micromorphology, mechanical and physicochemical properties were investigated and discussed using SEM, XRD, LSCM, mechanical force measuring machine and Image J software. Besides, the reduction mechanism of CSH participating in the carbon-containing pellet reduction process was revealed. The results indicated that appropriate R could promote the reduction of carbon-containing pellets and facilitate the formation of liquid phase. Nevertheless, excessive R would generate dicalcium silicate, causing cracks in the pellets during cooling, which led to a decrease in compressive strength. Similarly, increasing the C/O ratio could promote the reduction reaction to some extent, but continuous addition would also cause a large amount of saturated CSH to volatilize and escape, resulting in malignant expansion of pellets. Therefore, the optimal reduction process conditions are R = 1.0 and C/O = 1.3, and the metallization rate of the metalized pellets is above 92 %. The CSH is considered as a potential reducing agent to replace anthracite for direct reduction of iron ore, which will contributes to the high-value utilization of biomass and the sustainable development of steel metallurgy.