Pseudo-Boehmite Preparation From Aluminum Dross Resource Treatment And Derived Aluminum-Based Aerogel

Aluminum dross is a solid waste generated in the aluminum production process that contains high-value components,but it is also classified as hazardous waste due to its reactive aluminum nitride and leaching toxic fluoride components.It was found that the harmless and resourceful utilization of aluminum dross has great practical significance.The pseudo-boehmite can be used as a binder,catalyst carrier and raw material in the petroleum,construction and environmental protection industries because of its properties,such as strong adhesive and thixotropic gelation under acidic conditions.However,the preparation and application of pseudo-boehmite are limited by the low purity of the traditional inorganic aluminum process and the high cost of the alcoholic aluminum production process.In this paper,the amount,nature and disposal of aluminum dross produced by the Guangxi aluminum industry were found out through a survey;aluminum dross was treated with sodium carbonate,calcium chloride,and roasting for harmless treatment,and then aluminum resources were recovered through alkali leaching.Based on experimental results,the optimal conditions for extracting aluminum resources and recovering Na Al O₂ solution are determined.The response surface methodology design was used to investigate the single factor influence and the interaction between factors in the hydrothermal reaction for preparing pseudo-boehmite,and the effect of washing on the peptizing property of pseudo-boehmite was investigated,we obtained pseudo-boehmite with high purity and peptizing property.Finally,aluminum-based aerogel was prepared with the pseudo-boehmite as a raw material,and the aerogel was investigated by heat treatment.The conclusions of this paper are as follows:（1）The aluminum industry of Guangxi was concentrated in Baise,Nanning,Laibin,Liuzhou,and Hezhou.Aluminum dross was generated in the process of melting and refining by adding refining agents with an annual output of 15-30 thousand tons.The composition of aluminum dross contains valuable components such as Al₂O₃,Mg Al₂O₄,and metal aluminum elements,but it was a reactive and leaching toxic waste due to the presence of Al N,Al F₃,Na F,Na₃ Al F₆ and toxic metals,etc.（2）The mass percentage of sodium carbonate and the mass concentration of sodium hydroxide solution influence the extraction rate of aluminum during the roasting process and the alkali solution leaching process,which were investigated.The aluminum dross was roasted by adding Na2CO₃ and Ca Cl₂ mixed with aluminum dross at a mass percentage of 40% sodium carbonate and 10% calcium chloride,respectively,and the roasted aluminum dross was leached by adding the mass concentration of 3% Na OH solution with a liquid-solid mass ratio of 5:1.The method can effectively remove the Al N component,and the Na F and Al F₃ components were converted into Ca F₂ to achieve the harmlessness of the hazardous waste components,and the highest extraction rate of aluminum is 36.59%（3）In single-factor experiments,the optimal levels of heating temperatures,the mass concentration of Na HCO₃ solution,and reaction time on the hydrothermal reaction of Na Al O₂ solution for the preparation of pseudo-boehmite were investigated.The response surface experimental design was used to determine the optimal conditions of hydrothermal reaction were heating temperature of 98 ℃,the mass concentration of 11% Na HCO₃ solution,and reaction time of 2 h.The primary and secondary order of factors were the mass concentration of Na HCO₃ solution > heating temperature > reaction time.The pseudo-boehmite prepared by the hydrothermal reaction was washed twice,which could remove impurities from the pseudo-boehmite,promote crystallization and enhance the structural hydroxyl polarity.The peptizing index of the dried product reached 95.22%.（4）Aluminum-based aerogels were prepared from derivatization of resource treatment pseudo-boehmite.The thermal conductivity of aluminum-based aerogel was only 0.046 W/（m·k）at room temperature,which is very low for a thermal conductivity material.After heat treatment at 1150 ℃,the specific surface area of the aerogel was still 106.6 m²/g,and the aerogel still had a porous structure.Compared with the results of the aerogels prepared by commercial pseudo-boehmite,the aerogel properties and thermal stability of this paper showed good performance.