Conversion of different Brazilian manganese ores and residues into birnessite-like phyllomanganate

This work describes the first synthesis of birnessite-type manganese oxides, using manganese ores and residues at the old mining site from Serra do Navio (Amapá State, northern Brazil) and Carajás mine (Pará State, northern Brazil). The preparation method involved dissolution of Mn2O3 followed by reprecipitation of the layer phase. The product prepared was confirmed to be a single phase, birnessite, that is thermally stable up to 500°C. At 600°C, the layer structure synthesized from ores transforms to cryptomelane, a tunnel-type structure. The samples were investigated by using the following techniques: X-ray Powder Diffraction (XRD), Thermal Analysis (DTA-TG), NIR FT-Raman Spectroscopy (NIR FT-Raman), Scanning Electron Microscopy (SEM) and elemental analysis. •Manganese ores and residues•Synthesis of K-birnessite•Thermal stability up to 500°C•Transformation to cryptomelane•Raman spectroscopy