Fluorine Migration And Transformation During The Reduction Of Copper Slag By Spent Cathode In Aluminum Electrolysi

In this paper,in view of the demand for carbonaceous reductants in the traditional pyrolysis depleted copper slag,combined with the characteristics of a large amount of carbonaceous materials in the hazardous waste generated in the aluminum electrolysis production process,this paper studies the use of waste cathode materials to replace traditional carbonaceous reductant metals.Recover copper and iron from converter copper slag,and at the same time study the migration path and phase transformation of fluorine in waste cathode materials during the reduction process,so as to promote the transformation of soluble fluoride to insoluble fluoride.The main work and research results are as follows:The effects of reduction temperature,reduction time and waste cathode material addition on the copper recovery and fluorine fixation rate were investigated using single-factor experiments.The results showed that at 1460℃,the temperature was maintained for 90 minutes,and 10wt.%SCC,the maximum recovery of copper was 95.53%after metallization reduction.After metallization reduction,57.92%of the fluorine migrated into the slag phase,41.75%into the gas phase and 0.33%into the alloy phase.The presence of fluorine in the spent cathode material was mainly in the form of NaF and Na₃AlF₆.After the metallization reduction,the presence of fluorine was transformed,and the main forms of fluorine in the slag phase were Na₃AlF₆,NaF and CaF₂,and the main forms of fluorine in the gas phase were NaF,AlF₃,SiF₄ and Na₃AlF₆.In the reduction process,the fluorine in the spent cathode material react with CaO and Si O₂ to produce CaF₂,which is insoluble in water,facilitating the migration of fluorine into the slag phase and reducing the hazard of soluble fluoride.The response surface method was used to study the interactive effects of reduction temperature,reduction time,and CaO addition on the fluorine fixation rate and copper recovery rate,and the relationship between the dependent variable and the response value was obtained.Under single factor conditions,the amount of CaO added is the main factor affecting the fluorine fixation rate,while the reduction temperature is the main factor affecting the copper recovery rate.Under multi-factor conditions,the interaction between reduction temperature and CaO addition is the main factor affecting the fluorine fixation rate,while reduction temperature and reduction time are the main factors affecting copper recovery.The effect of different calcium-based fluorine-fixing agents on the fluorine-fixing rate in the metallization reduction process was studied to further reduce the hazards of waste cathode materials.The experimental results show that the fluorine fixation rate of three common calcium-based fluorine fixatives at high temperature is Ca（OH）₂>CaCO₃>CaO.The mixed fluorine fixation effect of NaCl and CaO is significantly better than the other two alkali metal additives（K₂CO₃,Na₂CO₃）.The fluorine-fixing effect of the alkaline earth metal increases with the increase of the atomic number,and the hydroxide of the same alkaline earth metal has a better fluorine-fixing effect than the carbonate.