Study On Detoxifying And Clean Extraction Of Alumina From Secondary Aluminum Dross By Pyrogenic Process

Aluminum dross is a solid waste produced in the process of electrolytic aluminum,aluminum processing and recycled aluminum production.It was added in the new National Hazardous Waste List by the Ministry of Environmental Protection and the National Development and Reform Commission in 2021.Due to the lack of large-scale treatment technology,about 95%of the aluminum dross is directly deposited or buried each year.Such disposal will not only lead to the leakage of toxic components such as fluoride and nitride in the aluminum dross,aggravating environmental and health problems,but also cause the loss of the valuable component of alumina.Therefore,harmless treatment and resource utilization of aluminum dross is becoming urgent.The physical properties of secondary aluminum dross(SAD)raw materials,roasting detoxification process and mechanism,and clean extraction process of alumina are studied in this thesis.The aim is to realize the co-disposal of harmless treatment and resource utilization for SAD.The main experimental contents and research results are as follows:(1)Physical property analysis of secondary aluminum dross.The results of XRD,XRF,Laser particle sizer and SEM-EDS characterization of SAD show that the valuable component Al exists in the form of?-Al₂O₃,and the toxic components are mainly Al N and fluoride in Na₃AlF₆.(2)Study on pyrogenic harmless technology and mechanism.The effects of roasting temperature and roasting time on innocuous effect were investigated by single factor experiments.The results showed that the optimum combustion conditions for the innocuous process of SAD were as follows:roasting temperature of 1000?,roasting time of 1.5 h.By analyzing the changes of phase and microscopic morphology of SAD before and after innocuous treatment,and combining with thermodynamic calculation,the mechanism of detoxication was explored.Al N was detoxified by oxidation reaction,while fluoride chemically reacted with Si O₂ to generate Si F₄ gas.(3)Study on the process of clean extraction of alumina by alkali sintering.The sintering,leaching and purification processes were optimized by single factor variable method.The optimum conditions were obtained as follows:alkali/cement ratio of 1.1,sintering temperature of 1000? and sintering time of 1.5 h;leaching temperature of80?,leaching time of 90 min,liquid-solid ratio of 4:1;the dosage of Ca O was 10 g/L,the purification temperature was 80?,and the purification time was 100 min.Under these conditions,the leaching toxicity of F in the leaching residue obtained was 39.09mg/L(less than the concentration limit of 100 mg/L specified in the standard),which realized the purpose of harmless treatment.Besides,carbonation decomposition and calcination were carried out to obtain?-Al₂O₃ powder(the average particle size(D₅₀)is 45.79?m),realizing resource utilization.To sum up,the synergistic technology of Resources and Harmlessness is adopted to process SAD in this article,which has the advantages of environmental friendliness and high resource utilization,establishing a theoretical foundation for the subsequent promotion of large-scale industrialization.