Target immobilized phases of heavy metals in hazardous waste based lightweight aggregate

The potential leaching risk poses a concern for the large-scale recycling of hazardous waste as lightweight aggregates (LWAs). This paper investigated the combination state of heavy metals in target immobilized phases of LWA through both theoretical calculations and experimental verification. Results reveal that Pb can enter the feldspar crystal cell to form stable interstitial solid solutions, while Cu, Cr, and Ni can replace specific ions in spinel to form replacement solid solutions. The addition of target immobilized phases generally weakened the physical performance of LWAs, while reducing the leaching risk. The appropriate amount of the spinel phase favored the immobilization of Cu, Cr, and Ni, whereas albite contributed to the immobilization of Pb with low leaching values. Due to the lower melting temperature, albite could facilitate the introduction of a high-temperature liquid phase, enhancing the migration of Pb²⁺ for better immobilization in glassy phase. In contrast, anorthite exhibited a higher viscosity at 1100 °C, leading to ineffective physical encapsulation of heavy metal ions by the liquid phase. Heavy metal ions react with additional spinel phase at high temperatures to form stable solid solution phases. This study provides a novel method for regulating heavy metal leaching in hazardous waste-based LWA.