A sustainable strategy for efficient arsenic reduction, detoxification, and environmental assessment during the...

Multi-metallic tailings with tremendous reserves have been recognized as one of the most scalable and strategic resources, while posing significant hazards to the eco-environment owing to arsenic (As) exceeding 5 million tons. A novel strategy for As efficient reduction, detoxification, and environmental assessment of multi-metallic tailings was proposed based on significant differences in carbonaceous reducers. The results indicated that complex As phases generally existed as arsenate/As-Fe oxides, and that temperature and Fe minerals exerted a significant influence on As hazardous waste redistribution and toxicity. At 673-973 K, (Fe,As)₂O₃ was reduced to Fe_xAs_3-xO₄, while Ca-Fe arsenate was transformed to highly toxic (As₂O₃) physically adsorbed and doped into stable (Fe,As)₂O₃ and Fe_xAs_3-xO₄. As the temperature increased to 973-1273 K, 45 % of Fe_xAs_3-xO₄ was converted to As₄ (g) and enriched in the dust. However, part of Fe_xAs_3-xO₄ was reduced to Fe-As compounds and subsequently Fe-As solution, leading to As leaching contents exceeding 10 mg/L, which restricted As waste reduction and harmless treatment. At higher temperatures, As₄ (g) was released from the Fe-As solution, while Fe₂SiO₄ and Ca(Fe,Mg)SiO₄ were transformed to Fe. Under 2 wt% B + 6 wt% P, 1348 K and 90 min, 99.19 % of As hazardous wastes were redistributed to the dust and further processed to 99.5 % As₂O₃ (chemical product), with a dust-to-pellet mass ratio of only 0.08. Meanwhile, Fe resources were converted into a high-value Fe powder material (Fe: 98.12 wt%, As: 0.020 wt%). As efficient reduction and harmless treatment were realized for the first time during the high-value processing of multi-metallic tailings, minimizing global As-related eco-environmental pollution. This approach could be significant for the reuse of typical hazardous wastes, such as red mud and Zn-leached residue.