A novel process to fully utilize red mud based on low-calcium sintering

Red mud is a hazardous waste generated during the alumina production industry, and the harmless utilization of red mud is one of the main development directions of cleaner production. In the present work, a novel low-calcium sinter process mainly including low-calcium sintering, atmospheric-pressure leaching followed by hydrothermal transition was proposed to recover alkali and alumina from red mud. Different from the traditional lime-soda sinter process, the low-calcium sinter process can significantly reduce the lime addition and residue amount, and realize full utilization of red mud. The effects of sintering temperature, time, CaCO3 and Na2CO3 dosages on the mineral formation mechanism and alumina-alkali recovery property of low-iron red mud were investigated by XRF, XRD and SEM-EDS methods. The main phases in the sintered samples are NaAlO2, Na0.68Fe0.68Si0.32O2, Na2CaSiO4 and CaTiO3. Increasing the sintering temperature, time and the additions of Na2O and CaO can promote the transition of Na1.95Al1.95Si0.05O4 and Na1.75Al1.75Si0.25O4 to NaAlO2. The recovery efficiencies of alumina and alkali under the optimum sintering conditions can reach over 93% and 96% respectively, and the Na2O content in the dealkalized product is less than 0.5% after the hydrothermal transition. The final dealkalized product is mainly composed of tobermorite, which can be widely used in building materials.

Automated summary

A novel low-calcium sinter process was proposed for alkali and alumina recovery from red mud, achieving full utilization of the waste material. Under optimal sintering conditions, the recovery efficiencies for alumina and alkali reached over 93% and 96% respectively, with the final product suitable for widespread use in building materials.