| In the process of aluminum electrolysis,lots of gas containing CO2,PFCs and HF will be produced.With the increasingly strict requirements of environmental protection,the flue gas treatment is more and more important now.Based on the current flue gas treatment of aluminum electrolysis industry,this paper carried out the breakthrough adsorption experiment of HF on alumina,and studied the adsorption mechanism of HF adsorption on the surface of alumina at the same time.The adsorption behavior and adsorption mechanism of Bayer process alumina and Fly-ash alumina were compared also.In this study,micro morphology,particle size and pore size distribution and ignition loss of two kinds of alumina were measured.A fixed bed adsorption device designed and built by the laboratory was used to carry out the breakthrough experiment of two kinds of alumina at 25℃ and 70℃ respectively.Then,X-ray diffraction analysis and X-ray photoelectron spectroscopy were used to characterize the fluorinated samples after experiment,and to explore the chemical adsorption mechanism of HF on two kinds s of alumina.It can be found from the comparison results of two kinds of alumina that the main differences between them,which concentrate on micro morphology,particle size distribution,pore size distribution and ignition loss.The single particle of Bayer process alumina and Fly-ash acid leaching alumina are usually composed of several smaller alumina particle with obvious orientation slit inside.On the surface of Fly-ash acid leaching alumina,a thin layer cover.However,the internal gap is larger.Compared with Bayer process alumina,the average particle size of Fly-ash acid leaching alumina is obviously larger which is 155μm and its distribution range is wider.The specific surface area of B.E.T of the two kinds of alumina is similar.Bayer process alumina is 97-79m2/g,and Fly-ash acid leaching alumina is 101.31m2/g.The pore size distribution of B.J.H shows that the Fly-ash’s pore size distribution of alumina is wider than Bayer’s.The most suitable pore size of Fly-ash acid leaching alumina is 7.94nm,and the Bayer’s is 5.46nm.The ignition loss of Fly-ash leaching alumina is greater than that by Bayer process,which indicates that alumina prepared by Fly-ash leaching has high hydroxyl group content.In the adsorption mechanism aspect,the influence of MOI on the breakthrough adsorption capacity and adsorption mechanism of two kinds of samples were studied.When MOI content increased from 0%to 3.83%,the breakthrough adsorption capacity of Bayer process alumina increased from 34.85mgHF/gAl2O3 to 47.99mgHF/gAl2O3.And the breakthrough adsorption capacity of Fly-ash acid leaching alumina was not increased significantly.When the MOI content was 0%and 3.91%,the breakthrough capacity of it was 35.71mgHF/gAl2O3 and 37.34mgHF/gAl2O3,respectively.When the adsorption temperature increased to 70℃,the breakthrough adsorption capacity of both alumina decreased,and the breakthrough adsorption capacity of Fly-ash acid leaching alumina decreased by 36.69%.The X-ray photoelectron spectroscopy(XPS)was used to characterize the two kinds of alumina and the original samples.It was found that the existence of Al-F and F-O/F-OH bonds existed in both kinds of alumina.The bond contents of Al-F and FO/F-OH decreased with the increase of MOI.The modified auger parameters of fluorine were calculated,and the results showed that the fluorine bonding in the samples with 0%MOI content was closer to that of AlF3.It shows that more and more HF molecules adsorbed to alumina through the water molecules but not attached to alumina directly with the MOI content increase. |
