Na+-solidification behavior of SiO2-Al2O3-CaO-MgO (10 wt%) ceramics prepared from red mud

Abstract As an approach for reusing greater amounts of red mud, which has high CaO and Na 2 O content, batches of novel SiO 2 -Al 2 O 3 -CaO-MgO (10 wt%) ceramics that were mixed with 20 wt%, 35 wt% and 50 wt% red mud were prepared. Na + -leaching and physical properties of these ceramics were tested. Crystal evolution and sintering process were investigated using thermal gravity analysis-differential thermal analysis, X-ray diffraction, and scanning electron microscopy. Results showed that, although Na 2 O content in the ceramics increased from 2.15 wt% to 4.21 wt%, Na + -leaching rates of fired ceramics were almost constant and were about 6 times lower than that of green samples. Main crystal components were diopside ferroan, augite, and anorthite, each of which solidified Na + . Moreover, their solidifying abilities increased with increasing temperature. Of these components, anorthite had the greatest ability to solidify Na + . Ceramics with highest content of red mud (50 wt%) had lowest optimum sintering temperature of 1130 °C, widest sintering range from 1110 to 1140 °C and excellent properties, including a bending strength of 115.88 MPa, water absorption of 0.07%, Na + -leaching rate of 0.33%, and K + -leaching rate of 0.10%. This work provides important basis for long-term work on the reuse of red mud in the ceramics industry.