Stabilization behavior and mechanism of heavy metals in eco-friendly glass-ceramics derived from wastes

The utilization of waste-derived products is strongly restricted by the presence of abundant heavy metals in solid wastes. Glass-ceramic could be a promising final product due to its competitive performance and outstanding stabilization efficiency of heavy metals. However, the stabilization behavior and mechanism of different heavy metals in the waste-derived glass-ceramics remains unclear. In this study, therefore, Cu and Pb were selected as two representatives to evaluate the stabilization characteristics and phase transformation of non-volatile and volatile heavy metals during the crystallization process. Oil shale ash (OSA)-derived amorphous slag was employed as the precursor to be co-crystallized with simulated Cu- and Pb-rich wastes due to its strong crystallization capacity and superior mechanical property. Different characterizations were conducted including X-ray diffraction (XRD), H2 temperature-programmed reduction (H2-TPR), differential scanning calorimetry (DSC), X-ray photoelectron spectroscopy (XPS) and high resolution transmission electron microscopy (HRTEM), in order to demonstrate the stabilization behavior and mechanism of Cu and Pb in glass-ceramics. The results showed that the obtained glass-ceramics sintered at 980 °C exhibited competitive mechanical property. Most Cu and Pb (>75%) was proven to be remained in the glass-ceramics and the leaching concentrations were much lower than the regulatory standard limits. In addition, Cu and Pb exhibited different stabilization mechanism in the glass-ceramic, where most Cu was embedded in glass-ceramics matrix as CuO crystals, while Pb was mainly distributed homogeneously in amorphous glass matrix as lead ions. The results suggested the potential and reliability of recycling Cu- and Pb-rich solid wastes into eco-friendly glass-ceramics.