Modification and Utilisation of Dried Red Mud for Construction of Vegetation Cover

Bauxite Residue or Red mud is the waste generated during bauxite processing for production of alumina through Bayer process. Red mud is a highly alkaline material (pH about 10.5-12.5) because of digestion of bauxite ore in caustic soda solution at elevated temperatures. The high alkalinity also limits its use for various applications such as vegetation, construction material etc. Land disposal of these materials often has negative environmental impacts such as contamination of soil and groundwater, and consumes vast areas of land. Revegetation of dewatered red mud is not possible without addition of amendments because of the high pH, high salinity, and absence of nutrients and organic constituents. Red mud ponds can be rehabilitated and abandoned bauxite mine pits can be refilled by identifying suitable amenders to ameliorate the caustic properties of red mud so that vegetation cover can be developed. Red mud from an alumina refinery situated at the eastern coast of India has been modified by adding amenders/ modifiers/ neutralizers such as coal dust, superphosphate and gypsum and their effectiveness is studied by carrying out the pH studies. The effect of addition of these neutralizers has been very well seen as the pH of red mud slurry stabilizes to a value well below 8.5-9.0 as compared to the value of above 10.5 obtained without using them. Gypsum and a combination of superphosphate and coal dust are found to be very effective as amenders as they reduce the pH of red mud to a much lower value. To study the suitability of red mud for vegetation, shrubs have been planted in red mud mixed with amenders The survival of the plants in red mud mixed with neutralizers/ amenders and their proper growth in it show that bulk utilization of red mud can be carried out in the area of vegetation by growing suitable flora and fauna.