Reuse of mill scale waste from the steel industry as raw material in the production of red ceramics

Mill scale is waste from the processing of steel mills that is little explored in construction materials, unlike blast furnace slag, for example. It originates from the lamination process and is rich in iron oxide. The main objective and novelty of this research is to evaluate the influence of the application of mill scale waste in the production of red ceramics. For this purpose, the waste was characterized through X-ray diffraction (XRD) and X-ray fluorescence (XRF), proving that the material is rich in magnetite (Fe3O4), hematite (Fe2O3) and wustite (FeO). Test specimens containing 0, 5, 10 and 20% of the studied waste were subsequently produced and calcined at temperatures of 750, 850 and 950 degrees C. The specimens were produced by vacuum extrusion, measuring 120 mm x 30 mm x 18 mm, in a local laboratory extruder. The properties of plasticity, linear shrinkage, water absorption and flexural strength were evaluated. It was observed that mill scale waste is non-plastic, helping to reduce the high plasticity of the clays used to produce ceramic materials, reducing linear shrinkage, promoting a reduction in ceramic porosity, because it increases the material's density. This reduces the water absorption of the material, essential for the commercial application of red ceramic products. However, as it is a non-plastic material, it does not form a liquid phase, which is the main mechanism for increasing the strength of ceramics. Furthermore, the magnetite, hematite and wustite present in the waste do not transform into other phases after calcination. This causes a reduction in strength with the use of mill scale waste. For example, the 0% composition presents a strength of approximately 3.8 MPa at the calcination in 750 degrees C, while the 20% composition presents a reduction of strength for 2.1 MPa. Even with the reduction, the values are higher than 2 MPa, which is the minimum limit for ceramic bricks. Therefore, it is concluded that the application of mill scale waste is viable in the proposed application, if it is used for the production of ceramic bricks, where the required strength was compatible.