Fluorine migration, solidification, and secondary release mechanisms during high-value utilization of spent carbon...

Spent carbon cathode(SCC) is generated at 1.56-1.95 million tons per year and is classified as a typical hazardous waste owing to severe F pollution. Although co-treatment with bulk solid waste provides a promising route for SCC disposal and resource recovery, uncontrolled F partitioning into gas and dust phases still leaves most SCC for open stockpiling or landfilling. In this study, F migration and toxicity were systematically examined for the first time during the co-processing of SCC with polymetallic iron tailings. F was mainly present as Na₃AlF₆ in SCC and decomposed into NaF(g) and AlF₃(s) at 673-1173 K. CaO derived from CaMg(CO₃)₂ captured NaF(g) efficiently and generated Na₂O(g), lowering the F toxicity. NaF(g) was also regenerated by the reaction of AlF₃(s) with Na₂O(g). When the temperature exceeded 1273 K, the F-containing pollutant release was intensified. CaF₂ was incorporated with Si, Na, Ca, and Fe components into slag liquid phase, facilitating Fe reduction, whereas SiF₄(g) evolved from the slag liquid phase and induced secondary pollution. ZnF₂ also formed in the slag liquid phase and transferred into dust, causing a marked decline in dust quality. The F redistribution and F-bearing slag liquid-phase toxicity were controlled by cooling rate. The slow cooling accelerated generation of the high content amorphous (F)_{slag liquid phase}, increasing F-related risks. Under optimized conditions, 95.16% of F was immobilized, and the dust quality was improved. Magnetic separation produced high-value metallic Fe powder from Fe resources. This strategy supports high-value utilization of SCC and typical solid waste through integrated waste-to-waste treatment.