Characteristics study and process optimization of direct reduction of natural hematite with ammonia

The ironmaking process in the steel industry is characterized by high energy consumption and environmental pollution. To address these issues, this study explored direct reduction ironmaking technology utilizing ammonia (NH 3 ) as a hydrogen carrier. NH 3 surpassed H 2 in technical maturity for liquefaction and transport, offering significantly lower transportation costs. In this study, NH 3 served as a reducing agent in the treatment of natural hematite using a horizontal high-temperature heat treatment electric furnace. The study investigated the effects of reduction temperature, gas concentration, and reduction time on the reduction process. The experimental results indicated that NH 3 exhibited superior reducibility toward natural hematite under specific conditions. An elevation in temperature and an increase in NH 3 concentration substantially enhance the reduction efficacy of hematite. Higher temperatures facilitate the forward progression of the reaction and diminish the requisite critical NH 3 concentration. At 900°C, a flow rate of 500 mL·min −1 , and 30% ammonia concentration, complete reduction of hematite powder was achieved in 12 min. Scanning electron microscopy (SEM) characterization revealed gradual precipitation and coarsening of spherical iron (Fe) particles, forming a porous and loose structure.The ammonia reduction of iron oxide process is divided into three stages, sequentially controlled by surface chemical reactions, diffusion, and the shrinking core model. The third stage is the rate-controlling step with an activation energy of 69.67 kJ/mol.