A closed-circuit cycle process for recovery of carbon and valuable components from spent carbon cathode by hydrothermal acid-leaching method

Spent carbon cathode (SCC) as a hazardous solid waste produced in aluminum electrolysis industry, contains plenty valuable components but generate a seriously threat to the environment. This paper focus on a closedcircuit cycle process for direct treatment of SCC based on the hydrothermal acid-leaching method. Thermodynamic calculation, single factor experiment, orthogonal experiment and kinetic study are utilized to obtain the leaching properties of impurities, optimize the leaching conditions, study the influence of conditions on leaching, and capture the restriction factors of leaching. The results indicate that the carbon content of the treated SCC can reach 97.3% when the leaching condition attach the optimal (liquid-solid ratio of 25 mL/g, temperature of 413 K, time of 270 min and acid concentration of 4 mol/L), and liquid-solid ratio is regarded as the crucial factor influencing on that. In addition, the activation energy of impurities reaches 6.25 kJ/mol and the whole leaching process is controlled by the diffusion extent. Finally, the filtrate after the hydrothermal acid leaching is treated, and calcium fluoride, cryolite and sodium chloride are successfully separated. The proposed process eliminates the harm of SCC to the environment, and completes a closed-circuit cycle for the treatment of SCC and recovery of valuable components. It enriches the hydrometallurgical processes of SCC, and provides an attractive scheme for the treatment of SCC.

Automated summary

This paper focuses on a closed-circuit cycle process for the direct treatment of spent carbon cathode (SCC) using the hydrothermal acid-leaching method. Various experiments and analyses were conducted to study the leaching properties of impurities, optimize the leaching conditions, and investigate the factors influencing the leaching process. The results show that the proposed process can effectively treat SCC and recover valuable components.