Process Mechanism Of Aluminum Extraction From Secondary Aluminum Dross By Roasting With Ammonium Sulfate And The Law Of Fluorine Migration

With the rapid development of our country’s aluminum industry,the discharge of primary and secondary aluminum dross during the electrolytic aluminum and aluminum recycling processes continues to increase.Secondary aluminum dross contains fluoride and nitride and is regarded as a hazardous waste.Due to the complex composition of secondary aluminum dross,the aluminum resources contained in it have not been effectively recycled,which not only leads to waste of aluminum resources,but also causes serious harm to the ecological environment.This paper takes the secondary aluminum dross from an electrolytic aluminum plant in Henan as the research object,the aluminum resources in the secondary aluminum dross were recovered by ammonium sulfate roasting-water leaching method,and studies the mechanism of the roasting-leaching aluminum extraction process and the law of fluorine migration.On the premise of ensuring a high aluminum leaching rate,the fluoride is decomposed as much as possible during the roasting process,the fluorine content in the leaching slag is reduced,and the secondary aluminum dross and harmless treatment are realized,providing a theory for the resource utilization of the secondary aluminum dross basis.The main research content and progress of this paper can be summarized as follows:(1)The basic properties of secondary aluminum dross were analyzed,and the test methods of fluorine content in secondary aluminum dross and leaching solution were determined.The results show that the particle size of secondary aluminum dross is less than 500μm,d90 is 130.29μm,and its main phase composition is Al2O3,AlN,Al,NaCl,Si,CaF2,NaAl11O17 and Na3AlF6;the fluorine content in secondary aluminum dross is 1.29%,and the main phase composition is Al2O3,AIN,Al,NaCl,SiO2,CaF2,NaAl11O17 and Na3AlF6.In the form of Na3AlF6 and CaF2,its leaching toxicity exceeds the national standard.(2)The mechanism of the aluminum extraction process of the secondary aluminum dross ammonium sulfate roasting is studied,and the results show that the thermal decomposition process of the secondary aluminum dross and ammonium sulfate mixture can be divided into 6 stages,at 30-215℃,mainly physical water volatile;at 215～300z,(NH4)2SO4 decomposes into NH4HSO4 and produces NH3;at 300～337℃,NH4HSO4 decomposes into SO2,NH3,H2O;at 337～437 ℃,Al2O3 reacts with(NH4)2SO4 to produce NH4Al(SO4)2 and produce NH3,H2O,other aluminum-containing phases(Al,AlN and NaAl11O17)and fluorides(Na3AlF6,CaF2)gradually react with ammonium sulfate to form the corresponding sulfate;at 437-556℃,NH4Al(SO4)2 decomposition produces Al2(SO4)3 to produce SO2,NH3,H2O;556～900℃,Al2(SO4)3 decomposes to produce Al2O3 and SO2.(3)The migration of fluorine in the secondary aluminum dross ammonium sulfate roasting-water leaching aluminum process was studied.The results show that extending the roasting time,increasing the roasting temperature,and increasing the ammonium sulfate ratio can promote the fluorine in the secondary aluminum dross to enter the roasting tail gas;extending the leaching time,increasing the leaching temperature,and increasing the liquid-to-solid ratio are beneficial to reduce the fluorine in the leaching residue Content and proportion.Optimal conditions:roasting temperature 450℃,roasting time 2h,material ratio 6:1,leaching temperature 85℃,leaching time 80 min,liquid-solid ratio 6:1,43.85%of fluorine in secondary aluminum dross is in gaseous form Into the tail gas,23.92%of the fluorine enters the leaching solution,and 32.23%of the fluorine remains in the leaching residue in the form of AlF3 and AlF3·3H2O.