Minerals phase transformation by hydrogen reduction technology: A new approach to recycle iron from refractory limonite for reducing carbon emissions

Abstract

Limonite is a potentially vital iron ore resource, but it is hard to be effectively utilized by conventional mineral processing methods due to the high aluminum, silicon and water content. This paper proposed the phase transformation by hydrogen reduction technology to treat refractory limonite ore. The optimal conditions were determined as a roasting temperature of 500 °C, the reducing gas concentration of 20 % (H2:CO = 3:1), roasting time of 25 min, grinding fineness of 85 % passing 0.038 mm, the magnetic field strength of 187.5 kA/m. Under the above conditions, the concentrate with an iron grade of 59.85 % and recovery of 98.47 % was obtained. X-ray diffraction, iron chemical phase analysis and Vibrating Sample Magnetometer showed that the phase transformation of iron oxide was goethite/hematite → magnetite. Thus, the magnetism was significantly enhanced, which was conducive to magnetic separation. Electron Probe Micro Analysis indicated that it was difficult to further improve the quality of iron concentrate due to the existence of aluminum in the form of extremely fine minerals and the isomorphic replacement between aluminum and iron.