Preparation of Ultrafine Iron Powder by Direct Ferric Oxide Reduction with Ammonia Gas

Currently, the industrial production of reduced iron powder emits a lot of greenhouse gases. It is urgent to achieve the decarbonization of the iron powder-making industry. Ammonia (NH3), as a hydrogen (H2) carrier, is widely used as a potential zero-carbon energy source. Thus, this study proposes the direct preparation of ultrafine iron powder by reducing iron oxide (Fe2O3) using NH3. The research found that after a 900 °C/26 min heat treatment in a stream of 40% NH3 + 60% argon (Ar) at a gas flow rate of 100 mL/min, the iron oxide was reduced to extremely fine iron powder with a size of about 1.5 μm. The study of the reaction process shows that the ammonia-based reduction of iron oxide proceeds through an autocatalytic reaction, which is kinetically similar to the hydrogen-based direct reduction and is suitable for industrial applications with existing technologies. More importantly, the byproducts of ammonia reduction of iron oxide are nitrogen (N2) and water (H2O), which have no direct harm to the environment, and the collection of nitrogen can further reduce production costs. We conclude that the reduction of iron oxide by NH3 has a positive significance for the sustainable development of the iron powder industry.