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

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.