Harmless Treatment And Recycling Of Waste Cathode Carbon From Aluminum Electrolysi

As a typical hazardous solid waste generated in the electrolytic aluminum industry,spent cathode carbon（SCC）is widely concerned by practitioners.Since the SCC contains a large amount of toxic components,which poses a great threat to the environment,the harmless treatment and recycling of SCC has become a hot spot for research.In this paper,SCC was treated by microwave hydrothermal method to achieve deep purification and detoxification of SCC,and it was prepared into reduced graphene oxide materials for application in supercapacitor electrode materials to achieve recycling of SCC.The specific research contents are as follows:（1）Microwave hydrothermal alkaline leaching treatment was used to remove soluble fluoride components from SCC.The main process parameters（temperature,time and alkali concentration）of the microwave hydrothermal alkaline leaching process were optimized using Box-Behnken Design in response surface methodology.The optimization results showed that the soluble fluoride removal rate could reach98.05%under the optimal reaction conditions,i.e.,the temperature was 80℃,the alkali concentration was 1.16 mol/L,and the reaction time was 8.4 min.The results of multiple validation experiments showed that the average soluble fluoride removal rate reached 97.54%,and the validation experimental data were basically consistent with the model predictions.In addition,compared with the traditional hydrothermal treatment（91.74%）,the microwave hydrothermal alkaline leaching treatment not only shortened the reaction time by 99.4%,but also improved the removal rate of soluble fluoride by 5.8%.Therefore,microwave hydrothermal alkaline leaching treatment can achieve rapid and harmless treatment of SCC,minimizing environmental pollution.（2）Through microwave hydrothermal alkaline leaching treatment,the soluble fluoride in the SCC was effectively removed,but there were still more insoluble calcium fluoride residues,which would have an obvious impact on the reuse process of SCC.Therefore,microwave hydrothermal acid leaching was used for the treatment of insoluble calcium fluoride components in SCC,and dilute sulfuric acid was used as leaching agent to achieve rapid and efficient removal of insoluble calcium fluoride.The effects of different process parameters on the leaching and separation of insoluble calcium fluoride during microwave hydrothermal acid leaching were investigated.The results of the leaching kinetics study of insoluble calcium fluoride showed that the apparent activation energy of the leaching process of calcium fluoride was 17.55k J/mol and the leaching process was mainly controlled by the diffusion process.The SCC treated by microwave hydrothermal sulfuric acid leaching has complete fluoride removal and good reuse value.（3）Reduced graphene oxide（rGO-SCC）was prepared by treating the SCC after complete detoxification by a modified Hummer method.Two-dimensional Ni,Co-OH/rGO-SCC composites were synthesized by a one-pot microwave hydrothermal method.Subsequently,an asymmetric supercapacitor device was assembled with Ni,Co-OH/rGO-SCC composite as the positive electrode and activated carbon as the negative electrode.Subsequently,an asymmetric supercapacitor device was assembled with Ni,Co-OH/rGO-SCC composite as the positive electrode and activated carbon as the negative electrode.The electrochemical characterization results show that the asymmetric supercapacitor can reversibly cycle between 0 and 1.6 V in 6M KOH solution and can reach an energy density of 35.93 Wh kg^-1at a power density of 375 W kg^-1.After 1000 charge/discharge cycles,this asymmetric supercapacitor maintains 100%Coulomb efficiency.Compared with supercapacitors in the literature,this supercapacitor has certain advantages and achieves recycling reuse of SCC.