Efficient separation technology for ammonia phase transformation of hematite

Abstract

With the benefits of being inexpensive, easily compressible, storable, and transportable, ammonia is an effective reducing agent for turning weak magnetic minerals into strong magnetic minerals. Furthermore, there is no CO₂ emission in the reduction process, making it a new clean energy with broad application prospects. In this study, a novel ammonia phase transformation technology was proposed, and the ammonia reduction experiments were conducted using hematite as the research subject to investigate the impacts of reduction temperature, time, and ammonia concentration on the reduction products. The magnetic conversion, phase transformation, and microstructural changes during the mineral phase transformation process were systematically characterized. The optimal reduction conditions were determined to be a reduction temperature of 580 ℃, a reduction time of 17 min, and an ammonia concentration of 30 %. Under optimal conditions, an iron concentrate grade of 70.94 % and iron recovery of 98.06 % was obtained. Hematite was transformed into magnetite in ammonia atmosphere in the temperature range of 460 ℃ to 620 ℃. The microstructural changes indicated that micropores and cracks were gradually developed on the surface of the solid particles as the reaction proceeded, which was favorable for the inward diffusion of gases in the particle crevices and accelerated the reaction.