Abstract
Manganese is a widely used element in the steel industry; its main source is a mineral named rhodochrosite (MnCO3). For industrial usage, rhodochrosite is reduced to different manganese oxides by means of nodulation furnaces. In this study, rhodochrosite was thermally analyzed at temperatures ranging from 100 °C to 1200 °C. XRD (Powder X-ray diffraction), XRF (X-ray fluorescence), AAS (Atomic Absorption Spectrometry), and FESEM-EDX (Field Emission Scanning Electron Microscopy-Energy Dispersive X-ray Spectrometry) were used to characterize the mineral and the residues were analyzed by XRD and FTIR (Fourier-transform infrared spectroscopy) to determine the stoichiometry of the thermal decomposition reactions. Three mass losses were observed, the first attributed to the transformation from carbonate to manganese (III) oxide, the second to the reduction to manganese tetroxide, and the third to the decomposition of calcium carbonate (CaCO3) present as a contaminant in the studied mineral. Thermal decomposition kinetics shows that the first mass loss required 17.91 kJ mol−1, indicating a control by mass transport-controlled process. For the second and third mass loss, the apparent activation energy of 112.41 kJ mol−1 and 64.69 kJ mol−1 was obtained respectively, indicating that both mass loss events were rate-controlled.
Highlights
Manganese occurs in natural environments in the 2+, 3+, and 4+ oxidation states.The higher the oxidation states, the stronger the tendency of this element to hydrolyze and precipitate
The manganese carbonate does not have high thermal stability, a slow mass transfer is sufficient for the transformation to manganese (III) oxide (Mn2O3), where manganese atoms are found at two different octahedral sites
An X-ray fluorescence (XRF) analysis of the rhodochrosite sample obtained from the mining district of Molango, Hidalgo, Mexico, indicates the presence of 86.89% manganese carbonate (MnCO3); this was verified with the X-ray diffraction (XRD) analysis
Summary
Manganese occurs in natural environments in the 2+, 3+, and 4+ oxidation states.The higher the oxidation states, the stronger the tendency of this element to hydrolyze and precipitate. Manganese occurs in natural environments in the 2+, 3+, and 4+ oxidation states. Manganese is a relatively abundant element on the Earth’s crust and most commonly occurs in a variety of oxides, oxyhydroxides, and carbonates such as pyrolusite (MnO2 ), manganite (MnO[OH]), rhodochrosite (MnCO3 ), and kutnahorite (CaMn[CO3 ]2 ) [2]. Manganesebased materials, especially those formed by manganese oxides, are important for their relevant physical and chemical properties, which enable their use in important technological applications, such as rechargeable batteries, sensors, and optical or magneto-electronic devices. Manganese-based solids with a spinel structure have attracted attention as effective catalysts in the reduction of dangerous gases, such as CO, NO, and N2 O, and several organic compounds [3]
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