Thermal behavior and evolution of the mineral phases of Brazilian red mud

This article studied the thermal behavior and the evolution of the crystalline phases with temperature of the red mud (bauxite tailing) from an aluminum industry at Maranho, North-Northwestern Brazil. The experiments were carried out by Field Emission Scanning Electron Microscopy (FE-SEM), Simultaneous Thermal Analysis (TG-DSC), Optical Dilatometry up to 1623 K, and X-ray diffraction (XRD) of previously heated samples between 523 and 1523 K. The crystalline phases and the amorphous contents were quantified on raw and heated samples (at 1523 K) according to the Rietveld Quantitative Analysis (RQA) method. The data obtained showed that the raw red mud is composed by a mixture of seven different phases (hematite, goethite, sodalite, anatase, gibbsite, calcite, and amorphous). Finally in the interval of 1023-1523 K the following crystalline phases: hematite, nepheline, sodalite, anatase, perovskite, and pseudobrookite have been observed.