Physico-chemical investigations on the sintering behaviour of red mud - flue dust composites

Abstract

Two industrial waste products namely red mud and flue dust have been utilised to form composites and their sintering behaviour was investigated in this study. It has been observed that red mud alone can be sintered around 1250°C. Addition of flue dust can reduce the sintering temperature and bring it in the range of 1150 - 1200°C depending on the extent of flue dust addition (10-30%). The sintering kinetics initially follows the Johnson - Mehl model of nucleation and grain growth and subsequently beyond fractional conversion of 0.7. follows the three dimensional contracting geometry model. XRD studies reveal that there are at least 6-8 phases in the sintered product. Some of these are Fe,O, Ca,Fe,Si,Ofz, SiO,. NaAlSiO4, FeT(O,, 710, and Na,Si,O, EPMA studies show that apart from the above phases, smaller amounts of ZrSiO, and a few other rare earth compounds were also present in the sintered product. The silicate phases are essentially present in the grain boundaries of other non-silicate phases and these phases are responsible for reduction in the sintering temperature. These glassy phases are also responsible for inter-particle bonding in the composites. This conclusion has also been verified through scanning electron microscopy (SEM). The sintering temperature and fraction of the flue dust in the composites have been optimised at 1200°C and 20% respectively.