Hydrogen-based pre-reduction of chromite: Reduction and consolidation mechanisms

Abstract

The pre-reduction of chromite plays a vital role in the production of ferrochrome, offering advantages such as reduced carbon consumption and improved production efficiency. In this study, the feasibility of a hydrogen-based pre-reduction process for chromite was examined, and the mechanisms of reduction and pellet consolidation were discussed. The results demonstrate that the degree of Fe metallization and the degree of iron oxide deoxidation increase with higher reduction temperatures, longer durations, and increased H2:CO ratios. Notably, the degree of Fe metallization reached a substantial value of 85.9% under pure H2 conditions at 1300 °C for 3 h. The strength of the pellets exhibits an initial increase followed by a decrease as the degree of Fe metallization increases and the Fe2+ degree decreases. This phenomenon is attributed to a decrease in the Fe2+ degree, leading to an increase in the melting point of the binder phases and subsequently resulting in a significant reduction in pellet strength. However, the average strength of pellets reduced at over 1200 °C is higher than 1000 N. The reduction process of chromite can be divided into four stages, metal Fe is primarily reduced from the Fe3+ site, followed by reduction from Fe2+ in the (Mg, Fe) (Cr, Fe, Al)2O4 structure. Only a small amount of Cr can be reduced, forming Fe–Cr metal. According to thermodynamic calculation, H2 offers a thermodynamic advantage over CO as a reducing agent. H2 exhibits higher reactivity and a greater affinity for oxygen compared to CO. These factors contribute to the superior performance of H2 in the reduction of chromite.