Self-reduction with escaped sulfur and immobilization of toxic chromium in Co-vitrification for synergistic recovery of chromium sludge and blast furnace slag

Vitrification technology has been widely used to treat hazardous solid waste to form molten glasses. But the heavy metals with active valence in the glass matrix are unstable and easy to dissolve, easily leading to potential environmental risks. Based on the laboratory simulated preheating feed mode, this study first explored the feasibility of using high-temperature melting metallurgical blast furnace slag to synergistic melt chromium sludge to form the stabilized glass matrix. The results found that the stabilization of chromium in the molten glass was highly enhanced by the self-reduction effect of escaping sulfur when chromium sludge and blast furnace slag were co-melted by preheating feed. The leaching concentration of chromium decreased to 0.03 mg/L, which met the limit requirements of resource utilization for molten glasses. TG-MS and XPS supported that SO2 generated from chromium sludge uninterruptedly made more chromium kept in low valence during the co-melting process. As a result, 22.13% of Cr(III) species existed in molten glass produced from preheating feed larger than 6.3% of the heating feed. The polarizing microscope also showed that the increase of the Cr(III) species promoted the formation of micro-crystals, thereby improving the stability of chromium in molten glass. Therefore, this study highlights the new perspective on realizing high value-added utilization of chromium sludge with low energy consumption and higher stability.