Mechanism and optimization of sintered ultra-lightweight aggregates with sand washing slurry and red mud

Sand washing slurry, red mud, and waste sawdust are major solid wastes produced by the construction, mining, and wood processing industries, respectively. Their accumulation poses significant environmental hazards and results in substantial wastage of resources. This study utilized a novel rapid roasting method to prepare ultra-lightweight ceramsite aggregates (ULC) using sand washing slurry, red mud, and sawdust as raw materials. A new process for preparing ultra-lightweight clay aggregates (ULCA) utilizing waste sand washing sludge is proposed, achieving a utilization rate of the wash sand sludge exceeding 60%. Ultra-lightweight clay aggregates with a loose bulk density of 264.3 kg/m(3) were produced. The influence of material formulation on the performance of ultra-lightweight clay aggregates was studied. The phase changes and expansion mechanism of the clay aggregates were revealed from microscopic and chemical perspectives. The synergistic effect of red mud and sawdust significantly enhanced the foaming effect of the ceramsite (i.e., porosity), reducing its loose bulk density while slowing the rate of strength reduction. Additionally, increasing the content of red mud and sawdust promoted ceramsite expansion. When the mass ratio of sand washing slurry, red mud, and sawdust was 29: 12: 1, with Fe2O3 content at 13% and sawdust content at 3%, preheating at 500 degrees C for 5 minutes followed by roasting at 1150 degrees C for 5 minutes produced ultra-lightweight ceramsite with a compressive strength of 1.7 MPa. This study provides a promising method for producing ULC from industrial solid wastes.