The reactivity of iron oxides and hydroxide during low-temperature sulfation

Sulfation is a technique commonly applied to the extraction of mineral commodities, such as rare earths, lithium, nickel, and titanium, as a preparation stage for leaching. The behavior of iron compounds during sulfation/dissolution will directly impact acid consumption and downstream purification steps. This work shows the marked differences in the sulfation/dissolution of hematite (granular, specular, and one produced by pyrite roasting), goethite, and magnetite samples over increased temperature and time. At 80 degrees C, the solubilized iron fraction varies within 2% to 70% accordingly specular hematite < calcine hematite < granular hematite < magnetite < < goethite. Sulfation increases over time, from 5 to 15 min, when it reaches a plateau, ascribed to the formation of a ferric sulfate product layer. Increase in temperature from 80 degrees C to 160 degrees C increases the sulfation of magnetite (42.0 to 95.0%), calcine hematite (16.0 to 55.5%), and specular hematite (2.0 to 13.0%), with small or negative effect on goethite (70.0 to 76.0%) and granular hematite (33.0 to 25.0%). The influence of the crystalline structure, porosity, and phase transformation on the sulfation behavior of the different iron oxides and hydroxide, and the possible implications on the selective leaching of metals, are discussed in this article.