Research On Multiphase Reaction Of Physical Chemistry Under Anode Base In Aluminum Smelting Process

During the aluminum smelting process,the bubbles produced anode have great influence on the electrolysis process,mainly on bubble generation and movement.The effects of bubble movement can be summarized into two aspects.On the one hand,the bubble release drives the electrolyte circulation movement,accelerates the dissolution of alumina,and promotes mass and heat transfer.This reduces the concentration gradient of alumina and temperature gradient in the reduction cell,and then improves the current efficiency.On the other hand,when the big bubbles release at anode edge,they push the surrounding electrolyte forward,resulting in the interface of bath-metal pad fluctuation,and then reducing the current efficiency.In most serious situations,the bubble release can cause anode effects.In addition,the movement of electrolyte will accelerate the damage of side ledge and carbon block,and reduce the service life of the cell.When the content of alumina in electrolyte decreases to a certain level,the anode effect will be induced for the carbon electrode in the cryolite-alumina system.Once the anode effect occurs,the wettability between the electrolyte and carbon anode reduces dramatically,and the gas in the anode cathode distance(ACD)is difficult to release.The real current density under anode base becomes larger than the critical current density,which leads to the anode effect.At the same time,the increase in the real current density causes a rise in the anode potential.When the potential exceeds that of the discharge reaction of fluoride ions,non-conductive fluorocarbon compounds can thus be produced.The existences of these compounds make the interface properties of anode-electrolyte worse.This paper summarized the previous research results,and a large-scale and multi-view transparent aluminum electrolytic cell high temperature has been built.Based on the design of quartz crucible with three chambers,the basic research on multiphase reaction of the physical chemistry on anode base has been carried out.The main contents and results of this paper are listed below:(1)For two kinds of anodes,the graphite and industrial anodes,the bubble behavior of carbon dioxide,bubble period,bubble coverage and cell voltage fluctuation under different current densities have been studied in a large transparent cell.(2)The image pro plus 6.0 has been used to calculate the coverage area of the largest bubble.It found that during the formation of large bubbles in the early stage,the coverage rate is linear with time,and the maximum gas coverage rate is between 48%and 65%.(3)Based on the statistics of bubble position and the analysis of anode surface structure,it found that the bubble position is related to the microstructure of anode surface.From the results of SEM/EDS,the high layer structure is more easily to attach oxygen atoms which combine with carbon atoms to form of carbon dioxide.Hence,the locations of anode base with the layer structure are easier to reach the critical condition of bubble nucleation.(4)The anode effect was observed from the bottom,when the industrial carbon anode was used.During the anode effect,no bubbles or persistent bubble layer covering the anode bottom were observed.It also found that the growth of bubble free area and the distribution of ’fireball’electric spark on the anode bottom.The results reveal three reasons for anode effect,the increase in current density under anode base,the decrease in surrounding alumina concentration and the formation of passive film caused by non-conductive fluorocarbon compounds.