Leaching Kinetics of Aluminum from Alkali-Fused Spent Cathode Carbon Using Hydrochloric Acid and Sodium Fluoride

Abstract

Abundant carbon resides in spent cathode carbon (SCC) of aluminum electrolysis and its high-purity carbon powder is conducive to high-value recycling. The alkali-fused SCC was separated and effectively purified using an HCl/NaF solution. Effects of particle size, leaching temperature, time, initial acid concentration, and sodium fluoride dosage, on the purity of carbon powder and aluminum removal rate, were investigated. Using aluminum as the research object, kinetics of aluminum acid leaching were examined by single-factor experiments. Results showed that under an initial 4 M HCl concentration, particle size D(50) = 67.49 μm, liquid-solid ratio of 15:1, 333 K, 120 min, 0.3 M NaF, carbon powder with ash level below 1% were obtained in subsequent purification of SCC. The leaching process was described by Avram equation, the model characteristic parameter was 0.75147 and the apparent activation energy was 22.056 kJ/mol, which indicated a mixed control mechanism between chemical reactivity and diffusion. The kinetic reaction equation of leaching aluminum from alkali-fused SCC in a mixed HCl/NaF system was established.