Abstract
Spent carbon anode (SCA) is a dangerous solid waste that is continuously discharged from the aluminum electrolysis industry and has a large number of valuable resources and a high risk of environmental pollution. Its safe disposal and resource utilization have become a resource and environmental problem that must be solved urgently. Current methods for SCA disposal include flotation, vacuum metallurgy, physical activation, roasting, bubbling fluidized bed combustion, alkali fusion, alkali leaching, and chemical leaching combined with high temperature graphitization. In this paper, the material composition, resource properties, and environmental risks of SCA are discussed. Working principle, treatment process, advantages and disadvantages of the above methods are also briefly described and compared. Results showed that flotation is the safest disposal and comprehensive utilization technology that is suitable for characteristics of SCA raw materials and has the most large-scale application potential. In addition, characteristics of SCA recovery products are correlated to the recycling of aluminum reduction cells. This technology can alleviate the shortage of high-quality petroleum coke resources in China’s carbon material industry and the high cost of raw materials in aluminum electrolysis industry.
Highlights
Hall–Heroult method is currently used to produce aluminum
The recovered carbon materials with high purity and graphitization degree directly returned to the aluminum electrolysis cell for recycling
Some problems such as large consumption of chemical reagents and high production cost must be addressed
Summary
Hall–Heroult method is currently used to produce aluminum. High-purity primary aluminum is produced by electrolysis with aluminum electrolysis cell as the carrier, cryolite (Na3AlF6) as the reaction solvent, and alumina (Al2O3) as the raw material. Under the optimal parameters of vacuum degree of 5 Pa, reaction temperature of 950°C, raw material size of 0.50 mm, and reaction time of 4 h, the separation rate of electrolytes reached 83%, and the carbon content of SCA was improved from 36 to 74%. The effects of alkali fusion temperature, reaction time, and alkali–material mass ratio on the carbon content of recovered carbon materials were investigated through single factor experiments. Carbon materials with a carbon content of 99.10% were recovered under the optimized parameters of alkali fusion temperature of 600°C, reaction time of 6.50 h, mass ratio of alkali to material of 5.5:1, and acid leaching. The high treatment temperature is accompanied by high energy consumption and equipment loss
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