Ultralight hydrophobic foam ceramics derived from secondary aluminum dross.

Secondary aluminum dross (SAD) is a hazardous solid waste that poses significant environmental risks. To promote its high-value utilization, an ultralight hydrophobic foam ceramics was fabricated using SAD as the primary raw material through particle-stabilized foaming followed by polydimethylsiloxane (PDMS) modification. The thermal insulation performance of the material for exterior wall applications was systematically evaluated. Under the optimized sintering conditions of a sintering time of 24 min, a sintering temperature of 1498 °C, and a heating rate of 10 °C/min, the SAD-derived foam ceramics exhibited a porosity of 94.25%, a compressive strength of 0.64 MPa, and a bulk density of 0.23 g/cm3, meeting the requirements for Type L products specified in GB/T 33500-2017. Under the optimized PDMS modification conditions of a PDMS coating amount of 0.46 wt%, a coating temperature of 30 °C, a curing temperature of 92 °C, and a curing time of 100 min, the volumetric water absorption was reduced from 22.75% to 1.90% while maintaining excellent lightweight characteristics. The modified foam ceramics exhibited a low thermal conductivity of 9.878 × 10-2 W/(m·K) and excellent thermal insulation performance in building model tests. Heavy metal leaching concentrations remained well below the regulatory limits. After 15 freeze-thaw cycles, the foam ceramics exhibited only 4.17% mass loss and 21.17% compressive strength loss, while the residual compressive strength remained compliant with GB/T 33500-2017. These results demonstrate that SAD-derived foam ceramics are promising exterior wall insulation materials for energy-efficient buildings.