In-depth purification of spent pot-lining by oxidation-expansion acid leaching – A comparative study

Spent pot lining (SPL) is a hazardous solid waste generated after overhauling the aluminum electrolytic cell. SPL contains carbon resources with high graphitization and toxic impurities, such as NaF, Na3AlF6, and CaF2. These toxic substances are difficult to remove from graphite completely. This study introduces an innovative method of oxidation-expansion acid leaching (OEAL) to eliminate impurities inside the graphitized carbon. For such a purpose, typical purification methods (conventional leaching, flotation-acid leaching) were investigated and compared to OEAL. The experimental outcomes indicated that the process efficiency for removing SPL impurities by various methods had the following sequence from high to low: OEAL > flotation-acid leaching > conventional leaching. The maximum SPL impurities removal rate by conventional leaching and flotation-acid leaching was 89.65 %, while it was 99.36 % with the OEAL method. For understanding fundamental aspects of the SPL impurity removal, their rejection mechanisms in the examined methods were systematically studied by different instrumentals and chemical analysis techniques. As a result of the reaction between H+ and residuals during OEAL process, the distance between graphitized carbon layers expands. This expansion resulted in a qualitative improvement in the SPL impurity removal by OEAL, making SPL one of the graphite or graphene oxide resources.