Research On The Harmless And Resource Recycling Technology Of Secondary Aluminum Dross

Aluminum dross is an industrial by-product in aluminum processing production,mainly from electrolytic aluminum production,cast aluminum production and wasteg76 aluminum regeneration process.As it contains aluminum nitride,aluminum carbide,soluble fluorine and chlorine salts and other hazardous substances,Aluminum dross was listed in the National Hazardous Waste Inventory by Ministry of Environmental Protection and National Development and Reform Commission in 2008.This study proposes a harmless and resourceful recycling process of secondary aluminum dross.The main experiments and research results involve the following three aspects:（1）Thermodynamic studies show that the hydrolysis of Al N is a self-reaction;kinetic studies show that the hydrolysis rate is mainly dominated by diffusion control and chemical reaction control,with a reaction activation energy of 37.05 KJ.mol^-1.The experiments of condition optimization show that the most significant factors affecting the hydrolysis are the washing temperature and the washing time.The hydrolysis rate of Al N is 82.72%at a temperature of 90°C,a washing time of 15 h,and a liquid-solid ratio of 8:1 and a stirring speed of 300 rpm.（2）The fluoride content of the fluoridated washing solution is 2.0 g/L.When Ca Cl₂ is used as the fluorine fixing agent,the fluorine content of the washing solution is<10 mg/L at a molar ratio of F to Ca Cl₂ of 1:2.0,a reaction time of 0.75 h and a stirring speed of 150 rpm,and the resulting sludge is mainly Ca F₂ and Ca CO₃.（3）The washed sludge is subjected to calcined alkali roasting using Na OH and Ca O.The thermodynamics shows that aluminum dissolving and fluorine curing are theoretically feasible,while Ca O and Na OH dosage are the main factors affecting fluorine curing.The condition optimization experiments show that the curing rate of fluorine and the leaching rate of aluminum interplay with each other under certain conditions.To maximize the harmlessness and resourcefulness of Aluminum dross,the leaching rate of aluminum is 52.97%and the curing rate of fluorine is 99.79%at a molar ratio of Al and Na OH of 1:0.6,a molar ratio of F and Ca O of 1:2.5,a reaction temperature of 1000°C,and a roasting time of 2 h.The residue can be reused as raw material for quick-setting cement;the water leach solution is evaporated and crystallized to obtain Na Al O₂ product in accordance with the national industrial standard（HG/T 4518-2013）.