Preparation Of Nano Aluminum Nitride Powder By Recycling Of Secondary Aluminum Dross Resources

Secondary aluminum dross is a hazardous waste generated during the production of aluminum,which poses serious environmental risks and incurs high costs for safe disposal,while exhibiting low rates of resource utilization.Currently,there is no economically and efficiently feasible recovery and treatment process available.In this study,water washing pretreatment was performed on secondary aluminum dross to selectively remove soluble salts（chlorides and fluorides）and aluminum nitride.Then,the ammonium sulfate roasting-water leaching method and the sodium hydroxide roasting-water leaching method were employed to recover aluminum from the washed residue,and an efficient method for extracting aluminum from secondary aluminum dross was determined after comparison.Additionally,the alumina extracted from secondary aluminum dross was used as a raw material to prepare aluminum nitride precursor by the hydrothermal synthesis method and aluminum nitride powder by the carbothermal reduction method.The main results of this study are as follows:（1）The ammonium sulfate roasting-water leaching method involves low-temperature roasting of aluminum and its compounds in secondary aluminum ash with ammonium sulfate,followed by water leaching to extract aluminum.Under optimal reaction conditions（with a roasting temperature of 425℃,an m（（NH₄）₂SO₄）/m（washed residue）of 6:1,a roasting time of90 min,a leaching temperature of 60℃,a leaching time of 90 min,and a L/S（mL/g）of 8）,the leaching efficiencies of Al,Ca,Mg,Si,and Fe were 82.01%,36.46%,69.78%,1.76%,and48.06%,respectively.Cooling crystallization was used to prepare ammonium aluminum sulfate crystals from the ammonium sulfate roasting-water leaching solution with stirring to accelerate the crystallization efficiency.The purity of Al₂O₃ in the product after calcination of ammonium aluminum sulfate crystals was 98.36%,and the impurity metal content was less than 0.7%.（2）The sodium hydroxide roasting-water leaching method involves high-temperature reaction of aluminum and its compounds in secondary aluminum ash with sodium hydroxide to produce water-soluble sodium aluminate,followed by water leaching to extract aluminum.Under optimal conditions（with a roasting temperature of 700℃,an m（Na OH）/m（washed residue）of 1.2:1 of 1.2:1,a roasting time of 60 min,a leaching temperature of 60℃,a leaching time of 60 min,and a L/S of 15）,the leaching efficiencies of Al,Ca,Mg,Si,and Fe were93.63%,0.25%,0.03%,25.77%,and 0.16%,respectively.Desilication of the sodium hydroxide roasting-water leaching solution was performed using calcium oxide,with a maximum desilication efficiency of 98.82%and 26.81%aluminum precipitation efficiency.The pH of the desilicated solution was adjusted to 7-8 to prepare aluminum hydroxide with a precipitation rate of 99.96%.The purity of Al₂O₃ in the product after calcination of aluminum hydroxide was99.41%,and the impurity metal content was less than 0.06%.（3）Al₂O₃ extracted from secondary aluminum dross using the sodium hydroxide roasting-water leaching method was used as a raw material to prepare aluminum nitride precursor by the hydrothermal synthesis method using glucose as a carbon source.The effects of process parameters such as the mass ratio of glucose to alumina（C/A,g/g）and the amount of surfactant（CTAB,m（CTAB）/m（Al₂O₃）,wt%）were investigated.The aluminum nitride precursor was then carbothermally reduced under a reaction temperature of 1973 K and a pressure of 9.5×10⁴Pa to produce aluminum nitride powder.Results showed that high-purity aluminum nitride powder was obtained under conditions where the mass ratio of glucose to alumina was 3:1 and the CTAB amount was 2.4%.The content of impurity elements C,O,Ca,Fe,and Si in the aluminum nitride powder was 0.0422%,0.3040%,0.0163%,0.0095%,and 0.0055%,respectively.The particle size distribution of aluminum nitride was D10=0.364μm,D50=0.923μm,and D90=3.047μm.