Recovery and in-situ utilization of calcined petroleum coke from flotation spent carbon anodes

Abstract

Spent carbon anodes (SCAs) are hazardous solid wastes continuously generated during the production of electrolytic aluminum. They are rich in toxic substances (soluble fluoride) and high-quality carbon resources (low-sulfur calcined petroleum coke). Froth flotation is typically preferred for the large-scale treatment of SCA. However, the resource utilization of recycled products is limited because of the low carbon content and residual leaching toxicity (138.70 mg L⁻¹). Here, we aimed to achieve clean recovery and in-situ utilization of calcined petroleum coke (CPC) from flotation SCA (F-SCA). Fluorination roasting coupled with hydrometallurgical purification was used for CPC extraction and purification The critical process parameters of the above links were optimized. Thermodynamics and a variety of characterization tools were used to explore the reaction mechanisms of noncarbon components. Results showed that the treatment of F-SCA was accompanied by a considerable increase in carbon content (82.67 wt% → 99.02 wt%) and efficient detoxification of leaching toxicity (138.70 mg L⁻¹ → 17.50 mg L⁻¹). Subsequently, the recovered CPC, owing to its low catalytic impurity content, powder resistivity, and CO₂ reactivity, was innovatively used to replace the residual carbon anodes in the recirculating preparation of aluminum electrolytic carbon anodes. At low dosages, the doped anodes were superior to the original anodes for all types of performances. Wastewater and exhaust gas were successfully used to regenerate the reaction agents, and crystallization was achieved through ammonia neutralization, pH control, and low-temperature evaporation. The proposed technical path facilitated clean and low-cost transformation of SCA from hazardous waste to high-value mineral resources.