Co-treatment of spent carbon cathodes and oily sludge residues for toxic substance immobilization and resource utilization

Abstract

Spent cathode carbon (SCC) and oily sludge residue (OSR) are serious threats to the ecological environment as carbonaceous hazardous wastes due to a variety of substantial leaching toxicity (F, CN, and heavy metals). Currently, no appropriate technologies have been proposed for the harmless disposal of SCC and OSR owing to the prohibitively high treatment costs and ambiguous application pathways. The aim of this study is to achieve synergistic detoxification and all component utilization of SCC and OSR based on their resource interaction properties. First, high-temperature oxidation co-treatment was designed based on the physicochemical properties and thermodynamic characteristics of SCC and OSR. Second, the coprocessing parameters were optimized sequentially. Third, multiple detection techniques and simulation methods were used to explore the synergistic detoxification mechanism. Finally, the cotreated waste residue and flue gas are used to prepare cementitious materials and synthesize high-value fluorides, respectively. Results show that various toxic substances were efficiently dissociated and immobilized through the co-treatment. The dissociation rates of soluble fluoride and cyanide in SCC were 99.45 % and 99.34 %, respectively. The leaching concentrations of heavy metal elements (Zn, Ni, Pb) in OSR were all below the safety thresholds. Simultaneously, the flue gas was successfully converted into cryolite with similar phase composition and elemental content to commercial products. The compressive strength of the cementitious material incorporating 7 wt% roasted residue is higher than that of the initial sample (4.05 → 4.55 MPa). These results ensure the technical feasibility of SCC and OSR co-treatment from the aspects of environmental risk elimination and all components utilization. The proposed co-treatment strategy provides a new technical path for the synergistic detoxification and cross-industry utilization of multi-source carbonaceous wastes.