Study On Synergistic Treatment Of Spent Potlining And Red Mud For Iron Recovery And Fluoride Behaviors

In order to solve the disposal problems caused by spent potlining（RM）and red mud（RM）in the aluminum industry,this work proposes reduction roasting for synergetic treatment of SPL and RM.Utilization of the rich carbonaceous materials in SPL as a reducing agent to reduce the iron components in RM achieve valuable resources recovery.Utilization of the rich calcium-containing minerals in the RM as a curing agent to stabilize the soluble fluoride in SPL achieve harmlessness and detoxification of pollutants.Established a technical route of waste control by waste for harmlessness and recycling and an effective system of resources circulation.（1）For recovery of the iron component in the RM,this study adopts the method of reduction roasting-magnetic separation to enrich the iron-containing minerals in the RM.The factors as roasting temperature,retention time and SPL mass ratio are systematically investigated.Under optimal conditions of roasting temperature of 800℃,retention time of 1h and SPL mass ratio of 10%,the iron recovery rate reach 66.86%.XRD patterns indicates that the iron phase in the magnetic residues is mainly magnetite,followed by hematite.（2）For detoxification of harmful pollutants,this work proposes reduction roasting of SPL and RM to transform soluble fluorides into stable fluorite,mainly investigating roasting temperature and SPL mass ratio for detoxification of fluorides.Under optimal conditions of roasting temperature of 800℃,SPL mass ratio of 10%,and retention time of 1h,fluorine leaching concentration is 14.32 mg·L^-1,and fluorine leaching rate is 2.84%.Fluorine toxicity leaching test indicates fixed fluorides stabilized in solid phase under conditions of leaching temperature of 25～85℃,or p H of 3～10.（3）For determination of migration and transformation of fluorides in thermal treatment processes,this work investigates the contents of fluorine in bottom residues,fly ash and exhaust gas.Experiments shows that the content of fluorine in exhaust gas increased with the increased roasting temperature and prolonged retention time,and the content of fluorine in fly ash is invariant.Based on the distribution of fluorine and the content of leached fluorine,the optimal stabilized conditions for SPL mass ratio of 20%are roasting temperature of 800℃and retention time of 30 min to reach stabilization rate of 93.24%.The results of TG-MS demonstrate that the main form of gaseous fluorides is hydrogen fluoride（HF）,and cyanide decompose in thermal process.The research of synergetic reduction roasting of SPL and RM achieve harmlessness of hazardous materials and recycling of valuable resources providing significant scientific value and practical significance for the sustainable aluminum industry.