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 N2 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.