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

As an approach for reusing greater amounts of red mud, which has high CaO and Na2O content, batches of novel SiO2-Al2O3-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 Na2O 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 degrees C, widest sintering range from 1110 to 1140 degrees 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.