Preparation and characterization of foam ceramics from red mud and fly ash using sodium silicate as foaming agent

Fly ash from the thermal power plant and red mud from aluminium industry were regarded as hazardous industry waste all over the world. In order to effectively utilize these industrial wastes, a new foam ceramics was synthesized successfully by conventional ceramic sintering process using fly ash and red mud as the main raw material, with a small amount of sodium borate as fluxing agent and sodium silicate as foaming agent. An objective of this research was to investigate the influences of the amounts of red mud/fly ash and sodium borate as well as of the sintering temperature on the porosity, mechanical strength, bulk density, water absorption, microstructure and crystalline phase. The results showed that homogeneous microstructures of large pores could be obtained by adding about 40–50 wt% red mud, 26.25–40 wt% fly ash, 15–20 wt% sodium borate, 5 wt% sodium silicate, and using low sintering temperature (900 °C, 2 h), leading to foams presenting porosity, compressive strength, flexural strength, bulk density, and water absorption values of about 64.14–74.15%, 4.04–10.63 MPa, 2.31–8.52 MPa, 0.51–0.64 g/cm3, and 2.31–6.02%, respectively. Good correlations among mechanical strength, water absorption and microstructure (pore size and distribution) were observed.