An efficient comprehensive recycling process of overhaul slag via alkali roasting and two-stage leaching

Abstract

Overhaul slag as a hazardous solid waste generated in the aluminum electrolysis industry, contains abundant valuable substances while posing severe threats to the ecological environment. Green and scientific high-value recycling of overhaul slag can effectively prevent environmental pollution and mitigate the crisis of global resource shortage. In this paper, an alkali roasting and two-stage leaching process is proposed to purify graphite and re-prepare cryolite efficiently and environmentally friendly. Firstly, NaOH roasting converts insoluble fluorine and aluminum compounds into soluble NaF and NaAlO₂ phases, respectively. These phases are selectively extracted into the solution via water leaching. Under optimal conditions, the leaching rates of fluorine and aluminum reached 99.5 % and 98.4 %, respectively. The residue is then subjected to acid leaching to further purify the graphite purity from 86.2 % to 98.6 %. Finally, the aqueous leaching solution and acid leaching solution are mixed to recover fluorine and aluminum in the form of cryolite. The whole process is low-cost, pollution-free, and achieves harmless treatment and full-component recycling of overhaul slag, providing a green channel for the high-value utilization of hazardous wastes in the aluminum smelting process.