Production of lightweight aggregate ceramsite from red mud and municipal solid waste incineration bottom ash: Mechanism and optimization

Red mud (RM) and municipal solid waste incineration bottom ash (MSWIBA) are continually generated in large amounts all over the world. In this study, RM and MSWIBA were made into pellets by a disc pelletizer and then transformed to lightweight aggregate ceramsites by high-temperature sintering. The sintering mechanism and optimal production process were revealed from evaluation of the performance of ceramsites produced under different production processes. The results showed that as the proportion of RM increased, the required sintering temperature increased at least by 7.34%, while the apparent density, bulk density, strength, porosity, proportion of macropores and pH of ceramsites reduced up to 9.46%, 9.45%, 68.56%, 77.36%, 93.75% and 3.43%, respectively. On the other hand, with the increase in sintering temperature, the apparent density and bulk density of ceramsites made from calcium-rich red mud (CRM) generally increased while the water absorption and pH generally decreased. The strength, however, first increased up to 27.11 MPa and then decreased to 17.48 MPa. When the ratio of MSWIBA and CRM was 1:1 and the sintering temperature was 1070 °C, the ceramsites produced could achieve the best performance with a bulk density of 1046.73 Kg/m³, an apparent density of 1783.44 Kg/m³, a particle strength of 27.11 MPa, a 1-hour water absorption rate of 0.8%, and a pH of 8.9. The ceramsites, for use as lightweight aggregates, can be a promising construction material in particular counting the benefits of waste recycling.