Study On The Behavior Of Alumina Adsorb Flue Gas In Aluminum Electrolysis Cell

Alumina is not only the raw material for aluminum electrolysis,but also the adsorbent for cell exhaust gas in the dry scrubbing system.The adsorption performance of alumina directly affects the efficiency of gas treatment.With the increasingly stringent environmental requirements,alumina adsorption performance is becoming more and more important in the aluminum industry.In this study,three alumina samples including two primary alumina samples and one alumina sample which was manufactured from coal fly ash with acidic method were tested.Firstly,the water vapor adsorption experiments were carried out at different temperatures.The adsorption model and kinetic equations were employed to fit the data.The results showed that the adsorption principle of alumina for water vapor.Secondly,a set of laboratory hydrogen fluoride gas adsorption apparatus was designed and built.The adsorption experiments of two alumina samples at the temperature range of 25-180? were carried out with this apparatus.The adsorption capacities of the two alumina samples were analyzed and compared.According to the characterization results including specific surface area,particle size distribution and pore size distribution of these three alumina samples,the morphologies and parameters of the two primary alumina samples are similar and behave as a multi-particle aggregated layered structure.The alumina prepared from the coal fly ash has larger specific surface area,wider particle size distribution,higher total pore volume than the two primary alumina samples,and it also contains a certain proportion of large size particles.For the coal-fly-ash alumina,the surface of an individual particle behaves as irregular scales,this may be caused by the differences in their production processes.Adopting the static adsorption method,the adsorption experiment of water vapor on alumina was carried out.The isothermal adsorption and desorption curve of water vapor on alumina was obtained and the saturated adsorption capacity was calculated at each temperature.The saturated adsorption capacity of the coal-fly-ash alumina sample was larger than that of the primary alumina.The adsorption of water vapor on three alumina samples conform to the V curve of IUPAC classification.The adsorption mechanism is consistent with multi-molecular layer adsorption,while capillary condensation occurred during the adsorption process.Through the loop shape in the curves,the pore structure of the alumina shows a narrow-aperture type.The fitting result of BET model proves that the adsorption of water vapor on alumina is the physical adsorption of multi-layer adsorption,and the adsorption capacity is in positive correlation with the specific surface area.The fitting results of pseudo-second-order kinetic equation illustrate that the adsorption rate of water vapor on alumina is controlled by the number of active sites on the surface of alumina particles.When the partial pressure of the water vapor is increased,more active sites of bonding on the surface of alumina are involved in the adsorption process.The new bonding site adsorbs water molecules slower than the multi-molecule layer.The saturated fluoride content of the two primary alumina samples are in the range of 2.01-3.14 gHF/100gAl2O3.The saturated fluoride content increased with increasing temperature and reached up to the highest point at 95?.However,the saturated fluoride content in alumina is a bit lower at the temperature of 120-140?.While the saturated fluoride content of coal-fly-ash alumina is between 2.13-3.46 gHF/100gAl2O3.The saturated fluoride content reaches the highest value at 80? and 160?,and the lowest value at 120?.According to the saturated fluoride content of the three alumina samples,a slightly higher temperature than the room temperature is favorable for the adsorption of HF gas on alumina.The experiments carried out in this thesis proved that the adsorption capacity of the coal-fly-ash alumina has the potential to meet the requirements for the HF adsorption capacity in the aluminum electrolysis process.