Preparation of ultra-lightweight ceramsite from red mud and immobilization of hazardous elements

Red mud is a solid waste containing high alkaline nature and hazardous elements generated during the alumina production process, and its harmless utilization is of great significance to the environment. In this work, the sintering behavior and physical properties of ultra-lightweight ceramsite using red mud and waste sawdust were investigated when the sintering temperatures are between 1075 and 1175 ºC. The results reveal that the red mud is a suitable material to produce ultra-lightweight ceramsite, and the introduction of waste sawdust effectively enhances the expansion process. The bulk density of ceramsite decreases first and then increases with the increase of red mud and sawdust content. The pores are formed by the reduction reactions of Fe2O3 in red mud and the combustion of sawdust. When the red mud content is 50% and the mass ratio of sawdust to Fe2O3 is 0.3, the bulk density of ceramsite is in the range of 295–480 kg/cm3. Furthermore, the leaching concentrations of heavy metals in ceramsite are far below the permissible limit. This study is helpful to realize the harmless and large-scale utilization of red mud.