H ₂ adaptation in ironmaking: a review with focus on suspension smelting and its reaction mechanisms

Suspension smelting technology is emerging as a promising alternative in ironmaking to conventional hydrogen-based direct reduction (H-DRI) for low-carbon ironmaking. Unlike the slower solid-state reduction reactions in DRI processes, suspension smelting uses rapid in-flight reduction of fine iron ore particles. Within seconds, the ore fines undergo several process steps like heating up, phase transformation, reduction and partially melting, due to the high temperatures. This review explores hydrogen adaptation in suspension smelting technologies such as the flash ironmaking technology (FIT) and the HIsarna ^® process. The key reaction mechanisms, thermal decomposition and gas reduction with H ₂ /CO, are examined through thermodynamic and kinetic analyses. A comparison of reduction kinetics between classical DRI processes and suspension smelting is provided, highlighting the significantly faster reaction rates of suspension smelting. Finally, the influence of the water–gas shift reaction and its potential negative impact on the reduction behaviour is analysed.