Modification of red mud by acid treatment and its application for CO removal

Activated red mud (ARM) samples were tested for carbon monoxide (CO) oxidation in the temperature range of 100-500°C. Conversion of >90% was obtained for temperatures above 400°C for all samples. In order to study the effect of hydroxylated phases of iron oxide in red mud on the removal of CO, 'as-received' red mud (RM) and acid digested and re-precipitated red mud (TRM) were also tested under similar conditions. It was found that TRM was more effective in removal of CO with the 50% conversion temperature (T50) 80°C lower than the ARM samples. The samples before and after reaction were characterized by inductively coupled plasma-optical emission spectroscopy (ICP-OES), BET N(2) adsorption, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), electron microscopy (SEM and TEM) and temperature programmed reduction (TPR). It was observed that TRM had iron in an amorphous form which then converted to iron oxide after heating. The higher activity of TRM was due to its higher surface area and presence of hydroxylated phase of iron oxide.

Carbon deposition and phase transformations in red mud on exposure to methane

A characterization study detailing the phase transformations and microstructural nature of the carbon deposited during methane decomposition over red mud has been undertaken. In situ XRD was carried out to study the phase transformation sequences of red mud during the reaction. Scanning electron microscopy, high resolution transmission electron microscopy, thermogravimetric analysis, BET surface area determination and CHN analysis were carried out to investigate the properties of the post-reaction samples. Exposure to methane with increasing temperature caused a stepwise reduction of iron oxides in red mud and promoted methane cracking leading to carbon deposition. The presence of carbon nanostructures was confirmed by HRTEM observations. The carbon formed was graphitic in nature and the spent red mud, rich in Fe and Fe(3)C formed as a result of the reduction of the iron oxide, was magnetic in nature. The surface area of the material was enhanced upon reaction. In addition, reactivity comparisons between goethite and red mud were carried out to study the formation of carbon oxides during reaction.