Environmentally friendly and efficient green recovery of fluoride from waste aluminum electrolytic sediment using Al2O3

Green and efficient recovery of solid waste from aluminum electrolysis is of great significance. In this study, the sediment generated by aluminum electrolysis at the bottom of the waste tank was used as an alternative F resource. A new process of low-temperature acidification roasting with Al2O3 as the catalyst was performed to effectively recover F. The results of the single-factor experiment showed that a long reaction time and high acid-material ratio were conducive to improving the extraction rate of F. Under the conditions of 275 °C and 5 doses of sulfuric acid, the optimum F extraction rate was realized by roasting for 4 h with 1 dose of Al2O3 as the catalyst. The results of the XRD, SEM and chemical analyses showed that NaAl(SO4)2 was the main component produced in the calcination reaction using Al2O3 as the catalyst, rather than NaHSO4 (produced in the calcination process without a catalyst). This ensured complete combination of H and F, which greatly improved the extraction rate of F (from 80.76 to 99.76%). The proposed mechanism can provide not only an optimization scheme for the roasting of waste sediment at the furnace bottom, but also a more effective recovery treatment for the acidification roasting of other solid wastes with low Al2O3 content.