Secondary aluminum dross self-heating enhances hazardous waste vitrification

Abstract

This study demonstrates the potential of secondary aluminum dross (SAD) to enhance the vitrifying hazardous waste incineration fly ash (FA) and bottom slag (BS). Based on the CaO-SiO₂-Al₂O₃ ternary phase diagram, a liquid phase can be achieved at relatively low temperatures by carefully adjusting the Al₂O₃ content, particularly when the CaO to SiO₂ ratio is around 0.66. Theoretical melting temperature calculations indicate that substituting Al₂O₃ reagent with SAD enables the vitrification of FA and BS at temperatures below 1300 °C. TG-DSC results confirm this theoretical prediction, showing that the mixed system of FA, BS, and SAD lowers the liquid-phase formation temperatures compared to FA, BS, and SAD individually. Vitrification experiments, employing a composition of 55 wt%–60.5 wt% FA, 34 wt%–39 wt% BS, and 0.5 wt%–11 wt% SAD, achieved successful vitrification at 1350 °C for 2 h. This resulted in a high-quality vitrified product with a vitreous content exceeding 87.38%, an acid dissolution loss ratio below 2.32%, and heavy metals leaching toxicity below 0.15 mg/L. The exothermic nature of aluminum in SAD during the melting process contributes to enhance vitrification, making SAD a promising alternative to Al₂O₃ reagent.