Kinetic Studies of the Reduction of Limonitic Nickel Ore by Hydrogen

A sample of limonitic nickel ore was characterized by XRD, SEM-EDS, and ICP-OES techniques. The Rietveld refinement method showed that the main mineral constituent of this sample is goethite (55.8 pct). Thermal analysis experiments were performed and the determination of the goethite content in the sample could be confirmed by the mass loss associated to the dehydroxylation of this mineral at temperature of ≈ 150 °C. After thermal decomposition, the sample was reduced in a rotary kiln using hydrogen and subsequent characterization showed that for low temperatures (400 °C ≤ T < 550 °C) the main chemical reaction is the reduction of hematite to magnetite. At high temperatures (500 °C ≤ T < 800 °C), metallic iron could be identified in the solid product of the reaction by XRD technique and reduction of hematite to metallic iron was the main chemical reaction identified at this temperature. In addition to metallic iron, tetrataenite was identified and quantified in the reduced sample at high temperature (T > 600 °C) and the results suggest that most of the nickel is in this mineral phase. The shrinking core model was used for the kinetic studies of the reduction process and for the reduction of hematite to magnetite at low temperature (T ≤ 550 °C). The slow step was diffusion of reagent (H2) or product (H2O) through the reduced solid product layer on the particle surface, the apparent activation energy calculated for the reaction was 46.2 kJ. For the reduction of hematite to metallic iron at high temperature (T ≥ 550 °C), the slow step was the reaction of hydrogen with hematite at the reaction surface of the particle, and the apparent activation energy achieved by the chemical reaction was 29.5 kJ.