The microstructure and properties of ceramic tiles from solid wastes of Bayer red muds

As solid wastes in the alumina production of Bayer method, four kinds of Bayer red muds were successfully added to prepare ceramic tile samples for better waste utilization. The effects of four kinds of red muds on the properties of tile samples were discussed by XRD, SEM and EPMA analyses. Simultaneously, as by-products during the process of alumina production, Fe2O3 impurities were also investigated due to their high level ranging from 24 wt% to 36 wt% in the red muds. According to the radioactive inspection results, the four red muds were radioactive solid wastes which could be used for interior surface of class II civil buildings and exterior surface of buildings (GB6566-2010 China). The main phases of four red muds are boehmite, calcite, quartz and gibbsite. Preferable physical properties were obtained to be 0.12~9.92% in water absorption (belong to stoneware) and 30.57~60.96 MPa in bending strength, when the addition of red muds was 40 wt% (the addition of red muds was designed to be 40 wt% by the Method of Satisfied Chemical Compositions according to our previous experiments) and the firing temperatures were 940~1100 °C, 1080~1140 °C, 1080~1140 °C, 960~1120 °C, respectively. The main mechanism can be explained by the well-crystallized phases below 1100 °C with red muds as raw materials and non-excessive liquid phases at low firing temperatures that prompt the densification of samples. Although the liquid phases could lower the oxygen partial pressure around Fe2O3 and make unfavorable reduction of Fe2O3 into Fe3O4 and gas, they ultimately improved rather than decreased the performance of samples. Excellent properties of the samples make the four red muds appropriate to be used as raw materials for ceramic tiles, in accordance with Chinese National Standard (GB/T4100-2015), European Normalization (EN14411:2012), and American National Standard (ANSIA137.1-08).