Hazards Of Secondary Aluminum Dross And Its Transformation Mechanism In Treatment

Aluminum dross is a kind of solid waste produced in electrolytic aluminum and aluminum processing.At present,the main disposal method of aluminum dross is landfill and accumulation in situ.This simple method of disposal is likely to cause certain hazards to the atmosphere,water and soil in the environment due to the complex composition of aluminum dross and the easy reaction of active substances.Therefore,country lists aluminum dross in the"National Hazardous Waste List"since 2008,and prohibits stacking without disposal.In view of this,this article clarifies the hazardous characteristics of the secondary aluminum dross in different workshops of the Lanzhou branch of Aluminum Corporation of China,and studied the best process conditions of traditional wet and fire methods,and realized the harmlessness and reduction of the final product.It also clarified the gas components released during the treatment process,evaluated the risk of the treatment process,and explored the reaction kinetics of the treatment process.The main research is as follows:1.The particle size,phase and morphology characteristics of secondary aluminum dross from different workshops of Lanzhou Branch of Aluminum Corporation of China were analyzed,and the hazardous characteristics of secondary aluminum dross were judged according to national standards.The experimental results show:secondary aluminum dross contains alumina,magnesia-aluminum spinel,and aluminum nitride phases.And depending on the source of the aluminum dross,there may also be phases such as aluminum,aluminum carbide,sodium chloride,sodium fluoride,and calcium fluoride.Secondary aluminum dross is not corrosive,and has certain leaching toxicity and reactivity.These hazardous characteristics are different due to the different sources and components of aluminum dross.2.The secondary aluminum dross is treated by the classic wet method,and the optimal process conditions were studied,and the gas composition and content released during the process were clarified,and the reaction kinetics of the wet treatment process were explored,and the risk of the process was evaluated.The results show that the aluminum dross particle size is less than 2000?m,the initial pH is 13,and the washing temperature is 80? for 4 hours,the final residue has no leaching toxicity and reactivity,and the aluminum dross is harmless.During the treatment,the weight of aluminum dross increased by 17.66%,and the amount of gas released was 147.68mL·g^-1.The main gas components are hydrogen(above 99%),methane and ammonia.The p H of the extract is 12.33,and the fluoride concentration is 166.28mg·L^-1.Therefore,the wet treatment process has high reactivity and high toxicity.At the same time,the reaction of the aluminum dross active material in the wet process conforms to the Avrami-Erofeyev model of nucleation reaction,and the process is controlled by diffusion.The dissolution of fluoride in aluminum dross is not a chemical reaction,but a diffusion control,which conforms to the internal diffusion control model.3.The secondary aluminum dross was treated by adding calcium salt fire method,the optimal process conditions were studied,the tail gas composition and content were clarified,the reaction process of the fire treatment process was explored,and the risk of the process was evaluated.The results show that the baking temperature is 1300? and 3% calcium chloride is added for 3 hours,the final aluminum dross roasting slag is reduced by 13.96%,and the fluoride concentration in the aluminum dross roasting slag is only 3.02mg·L^-1,and gas release volume is 2.01mL·g^-1.At this time,the roasting slag does not have leaching toxicity and reactivity,and the aluminum dross is reduced and harmless.The main components of exhaust gas are N₂,CO₂ and H₂.Among them,the N₂ content is the highest.The reaction process of the active material in the process can be regarded as an unreacted nucleus model,and the reaction is controlled alternately by the diffusion mechanism and the reaction mechanism.The fire treatment of secondary aluminum dross not only removes the risk of residues,but also produces no toxic and harmful substances during the process,thus achieving the harmlessness of the entire process.