Preparation and Physical Properties of Red Mud Based Artificial Lightweight Aggregates

Highly alkaline and highly toxic red mud and other bulk industrial solid wastes become severely accumulated, posing huge risks such as soil degradation and environmental pollution. It is urgent to develop a long-term and stable resource disposal method. In the present research, artificial lightweight aggregates were fabricated utilizing industrial solid residues including red mud, phosphate tailing powder, and fly ash as raw materials. The physical characteristics, microstructure, heavy metal leaching attributes, and freeze-thaw resistance under different mixed water and curing conditions were studied. The results showed that, under the optimal curing condition (steam curing temperature of 80 °C and curing time of 10 h), lightweight aggregates exhibited the best comprehensive performance, with favorable trends in bulk density, apparent density, softening coefficient, and 1 h water absorption. In addition, the impact of extending the curing time on the further enhancement of the cylinder crush strength is limited. The microscopic morphology study showed that the hydration products in lightweight aggregates are primarily N-A-S-H and C-(A)-S-H, forming a strong colloidal structure and evenly dispersed on the particle surface, thereby improving its strength. Moreover, the heavy metal leachates (Cr, Pb, As, Cu, and Ni) from the lightweight aggregates met the environmental discharge criteria for non-hazardous substances.