Study On Treatment Of Aluminum Electrolysis Spent Carbon Cathodes By Molten Salt Roasting

As an inevitable solid waste of aluminum electrolysis industry,spent carbon cathodes not only contain harmful components such as fluoride and cyanide,but also contain a large number of valuable components such as high-quality carbon resources and electrolytes,which have the dual attributes of environment and resources.Exploring the safe disposal of harmful components of spent carbon cathodes and the comprehensive recycling of valuable components is of great significance for promoting the recycling of resources in aluminum electrolysis industry and realizing green and high-quality development.In this paper,the spent carbon cathodes discharged from an electrolytic aluminum plant in Henan Province is taken as the research object.The spent carbon cathodes is preliminarily treated by the combined treatment process of molten salt roasting and water immersion,and then the graphite carbon recovered under the optimal process parameters is deeply purified by the mechanical activation assisted acid leaching treatment process.The two-stage fluorine-containing waste liquid is harmless treated by p H adjustment and evaporative crystallization,and the non-carbon valuable elements are extracted.On this basis,aluminum electrolytic carbon anode was prepared by using spent carbon cathodes,recycled graphite carbon and high-purity graphite carbon,and the comprehensive utilization way of recycled carbon powder was explored.The main research results obtained are as follows:(1)The effects of molten salt roasting water leaching process parameters such as raw material particle size,reagent dosage,roasting temperature,roasting time,heating rate,leaching temperature,leaching time,liquid-solid ratio and stirring rate on the carbon content of recovered graphite carbon were studied.At the same time,the action mechanism of molten salt roasting water leaching combined treatment process was analyzed by advanced in-situ characterization techniques such as TG-MS and high temperature XRD.The results show that the molten salt roasting process can regulate the phase of the refractory aluminosilicate in the spent carbon cathodes,convert it into soluble substances and remove it by water immersion treatment.Under the optimum process parameters,the carbon content of recovered graphite carbon can reach 94.92%,and the fluorine ion leaching concentration can be reduced from 3790.63mg/l to 37.18mg/l.(2)The effects of mechanical activation conditions such as rotating speed,activation time and ball material ratio on the carbon content of high-purity graphite carbon were studied.At the same time,the particle characteristics of recovered graphite carbon under different mechanical activation conditions were characterized by laser particle size distribution instrument,automatic specific surface area analyzer and scanning electron microscope,and the strengthening mechanism of mechanical activation for acid leaching treatment was explored.The results show that appropriate mechanical activation is conducive to the reduction of particle size and increase of specific surface area of recovered graphite carbon,so as to improve the chemical reaction activity and promote the deep purification of recovered graphite carbon.Under the optimum process parameters,the carbon content of high-purity graphite carbon can reach 99.52%,and the fluorine ion leaching concentration can be reduced from 37.18mg/L to 7.6mg/l.(3)The p H value of the leaching solution was adjusted by molten salt roasting flue gas,and the effect of the p H value of the leaching solution on the removal rate of metal impurities was studied.Then,the acid leaching solution was added to the impurity removal filtrate to adjust the p H value of the solution,and the effect of the change of p H value of the solution on the crystallinity of the product was studied.Under the optimum process parameters,the crystallinity of the recovered product is high.(4)The effects of carbon materials on the performance of carbon anode(bulk density,compressive strength,resistivity,ash content,air reactivity and carbon dioxide reactivity)were studied.The results show that the performance of carbon anode prepared by mixing spent carbon cathodes and recycled graphite carbon is poor,while the overall performance of carbon anode prepared by mixing high-purity graphite carbon is close to that prepared by all petroleum coke.