Low-temperature hydrogen reduction of iron oxide by controlling the water potential using a CaH₂ drying agent

Lowering the reduction temperature of iron oxide is of great significance in applied engineering, but challenging to achieve in a hydrogen tube furnace as the partial pressure of hydrogen is limited to 1 ​atm. In this study CaH₂ was used as a drying agent to control the partial pressure of water vapor to lower the reduction potential of iron oxide. By comparing the extent of formation of the reduction product α-Fe in Fe₃O₄ reduced under hydrogen with and without CaH₂ at various temperatures, the presence of CaH₂ was shown to lower the temperature required for complete reduction from 400 ​°C to 300 ​°C accompanied by an increase in the H₂/H₂O ratio of the outlet gas. Thermodynamic calculations indicated that the addition of CaH₂ increases the reduction potential, causing a higher production ratio of α-Fe. These findings indicate that CaH₂ promotes reduction by efficiently absorbing the water vapor generated during reduction.