Effect Of Fluorine And Its Solidification Mechanism In The Process Of Copper Slag Reduction By Waste Cathode Of Aluminum Electrolysi

The spent cathode carbon of aluminum electrolysis is classified as hazardous solid waste in China because of containing harmful substances such as fluoride and cyanide,which is harmful to the environment.Therefore,it is necessary to recycle and harmlessly treat the spent cathode carbon.High temperature treatment is an important way of spent cathode carbon resource treatment.It has a good effect on the removal of harmful substances,but it is easy to cause a large amount of fixed carbon combustion waste and the purity of the product is not high.In view of the problems existing in the high temperature treatment process of spent cathode carbon,combined with the disadvantage that the electric furnace often used in the copper slag cleaning industry needs to consume a large amount of non-renewable fossil fuel consumption,this paper uses the spent cathode carbon produced in the process of aluminum electrolysis to reduce the copper slag.Based on the study of the combustion and reduction characteristics of the spent cathode carbon,the role of fluorine in the reduction of copper slag by spent cathode carbon is clarified.Ca O is used as an additive to realize the solidification of harmful element fluorine and reveal its solidification mechanism.It could reduce the leaching toxicity of harmful element fluorine while realizing the full utilization of fixed carbon in spent cathode carbon and the efficient recovery of copper from slag,which provides theoretical support for finding the resource and harmless treatment method of spent cathode carbon.The results of combustion and reduction characteristics show that the combustion characteristic index(0.013×10^-7)of spent cathode carbon is lower than that of semi-coke(0.114×10^-7),anthracite(0.078×10^-7)and fine coal(0.079×10^-7).The spent cathode carbon has the best reducibility to Fe₂O₃,which could replace the fine coal in the high temperature reduction process of copper slag.In the reducing experiment of copper slag by spent cathode carbon instead of fine coal,Na₃Al F₆ improves the fluidity of slag by decomposition and chemical reaction to form Na F,and promotes the aggregation of fine copper particles from 60μm to 200μm.Ca F₂ and Na F reduce the degree of polymerization and improve the viscosity of copper slag by destroying the bridge oxygen bond in the silicate structure of copper slag.When Ca F₂ and Na F were added to 7%,the activation energy of slag viscosity decreased from7.2k J·mol to 6.57k J·mol and 6.47k J·mol,respectively.The copper particles in the slag increased from 60μm to 150μm and 500μm,respectively.The spent cathode carbon improves the fluidity of slag and promotes the recovery of copper by reducing Fe₃O₄ and under the combined action of fluorine.However,some fluorine volatilizes under high temperature conditions,which would cause environmental pollution.For reduce the harm of fluorine,Ca O was used as an additive to fix fluorine while increasing recovery of copper.Ca O was added from 0%to 2.4%,the fluorine fixation rate and copper recovery rate increased from 61.43%and 90.94%to 81.32%and94.05%,respectively.Fluorine was mainly fixed in the slag in the form of Ca F₂.Ca O was added to 16%,the fluorine fixation rate increased to 93.02%,and fluorine was fixed in the form of Ca F₂ and Ca₄Si₂O₇F₂.The leaching toxicity of fluorine in the tailings is lower than the national standard（100mg/L）.The results show that Ca O could be used to control the slag type,improve the recovery rate of copper,and fix the fluorine element to reduce the leaching toxicity of fluorine.