ANNOUNCEMENTS
Wastes originating from various industries are high in metal and metal oxide content and therefore have a potential to be used as low cost catalysts. Simple physical and/or chemical treatments may be employed to enhance the activity of the material without adding extra cost. Catalytic conversions of certain environmental pollutants such as hydrocarbons and volatile organic compounds are carried out over the oxides of transition metals like copper, iron and chromium. Red mud is one such waste generated as a by-product of the aluminium industry which is high in metal oxide content. It is highly alkaline and requires special disposal techniques to limit the hazardous impact it can have on the environment. Various studies have been conducted to look for suitable applications for red mud and are mostly based on ‘high volume’ utilization.
The present work focused on a ‘high value’ utilization of red mud by investigating its activity for oxidation and decomposition reactions. A detailed characterization of the study material collected from different locations in India was undertaken employing techniques such as inductively coupled plasma optical emission spectroscopy (ICP-OES), X-ray diffraction (XRD), BET surface area, scanning electron microscopy (SEM), transmission electron microscopy (TEM), CHN analysis, thermal analysis such as TGA/DTA, fourier transform infrared spectroscopy (FTIR) and temperature programmed reduction (TPR). The physical and chemical properties of red mud were modified by employing various treatments such as thermal treatment (CRM), acid activation (ARM), simple acid treatment (TRM), sulphatation (SRM), mechanical mixing of red mud with tannery shavings in different ratios (RMTS) and different loadings of red mud with metals extracted from electroplating sludge (MRM).
The reaction studies were carried out in fixed bed quartz tube reactor. Methane decomposition, carbon monoxide oxidation and total oxidation of propane were used for the study and were tested with as-received and treated red mud at different temperatures. Post reaction characterization was also carried out.
Red mud was found to be a complex mixture of different metal oxides and hydroxides. Of these iron compounds hematite (Fe2O3) and goethite (FeOOH) were dominant. Hydrogen and carbon were the main reaction products obtained in the methane decomposition reaction where red mud was used as a pre-catalyst. The maximum conversion obtained was 18.8% with a corresponding hydrogen formation rate of 3.8 x 10-5 mol H2 g-1 s-1. The post reaction samples showed formation of carbon nanostructures such as carbon nanotubes (CNT) and carbon nanospheres (CNS). The end product was magnetic in nature due to the presence of Fe and Fe3C and possessed a high surface area. In case of carbon monoxide oxidation the main reaction product was carbon dioxide. Simple acid treatment without calcination (TRM) was found to increase the activity of the material higher than the acid treatment with calcination (ARM). One of the TRM samples gave a 98% conversion at 320 0C and conversion on another TRM sample reached >90%; 100 0C lower than the corresponding ARM sample. In total oxidation of propane the main reaction products were carbon dioxide and water. In this case > 90% conversion was obtained at 400 ï‚°C and the high ratio red mud and tannery shavings mixture was found to give the highest activity of 98% at 350 ï‚°C
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