Preparation of CaO–SiO2–Al2O3 inorganic fibers from melting-separated red mud

Abstract To investigate the feasibility of preparing CaO–SiO2–Al2O3 inorganic fibers with melting-separated red mud, the properties of the melting-separated red mud were analyzed by X-ray fluorescence, X-ray diffraction, and differential thermal-thermogravimetric analyses. The composition of the melting-separated red mud satisfied the requirements for the composition of inorganic fibers. During the melting of the melting-separated red mud, tetrahedral skeleton fracture reactions occurred at 1,234°C, anionic group reverse binding occurred at 1,250°C, and there was no other obvious reaction peak during the whole melting process, which lasted for 51 min. The minimum suitable fiber forming temperature of the melting-separated red mud melt was 1,433°C, which was 83°C greater than its crystallization temperature, 1,350°C. Within this temperature range, the activation energy of particle movement in the melt was 1008.65 kJ·mol−1, and the melt exhibited good fluidity. Considering the temperature distribution corresponding to the melting properties of the melting-separated red mud, CaO–SiO2–Al2O3 inorganic fibers could be prepared when the melting-separated red mud was subjected to component reconstruction by increasing the silicon content, reducing the aluminum content, and adding a moderate amount of calcium. Quartz sand and light burnt dolomite were used as modifying agents and inorganic fibers were prepared under laboratory conditions. The fibers prepared from the modified melting-separated red mud by adding different amounts of melting-separated red mud had smooth surfaces and were arranged in a crossed manner at the macroscopic level. Their color was grayish-white, and small quantities of slag balls were doped inside the fibers. With an increase in the amount of melting-separated red mud from 50 to 100%, the average fiber diameter increased from 5.5 to 8.0 μm, and their slag ball content increased from 2.9 to 6.0%. Overall, under laboratory conditions, when the amount of melting-separated red mud added was 50%, dolomite was 22.5% and quartz sand was 27.5%, the performance of the fiber was the best.