Theory And Technology Of High Purity Ultrafine Alumina Preparation From Spent Al₂O₃-based Catalyst

Spent Al₂O₃-based catalyst is a kind of catalyst,using Al₂O₃as the carrier and vanadium,molybdenum,nickel and cobalt as active constitutent,but which can not be regenerated.Comprehensive utilization of spent catalyst shows great economic and environmental significance, not only for avoiding unacceptable drains of valuable metals,but also for alleviating environmental pollution.Aimed at a spent Al₂O₃-based catalyst,on the basis of thermodynamic analyses,the extraction and separation of aluminum and other metals in spent catalyst and the preparation of high purity ultrafineα-Al₂O₃ from purified sodium aluminate solution were studied.A comprehensive utilization technology for preparing high purity ultrafine alumina from spent Al₂O₃-based catalyst was proposed,and good results were achieved by pilot experiments.Main conclusions are obtained as follows:1.The separation of Al and Ni,Co in spent Al₂O₃-based catalystAccording to the thermodynamic calculation and analysis result, alumina,vanadium and molybdenum can react with sodium carbonate when the temperature is above 962.2K,and the sodium salts generated can be converted into respective ionic forms.Having no reaction with sodium carbonate at higher temperature,nickel and cobalt occur in solid forms of oxide or hydroxide in alkali medium.This provides theoretical basis for separation of aluminum,vanadium,molybdenum and nickel, cobalt from spent Al₂O₃-based catalyst.After roasting the mixture of Na₂CO₃ and spent catalyst with mol ratio of 1.1 at 1000℃for 30 min,the roast was leached at 80℃for 30 min with liquid to solid ratio 4 and stirring speed 400 rpm.Under this condition,the extractions of Al,V and Mo all could reach above 96%, while Ni and Co were totally enriched in leaching residue.2.The separation of Al and V,Mo in alkali mediumThe thermodynamic analyses for reaction systems of VO₄^3-,MoO₄^2- and Al(OH)₄^- with calcium and barium indicate that,in the alkali medium containing Al,V and Mo,calcium will be inclined to react with VO₄^3- firstly,thus V is separated from Al and Mo;barium will react with MoO₄^2- successively,and Mo is separated from Al.Based on this result,a new technique to separate Al and V,Mo in alkali medium by step precipitation is proposed.By adding CaO and BaAl₂O₄ successively in sodium aluminate solution,Al is considerably sperated from V and Mo. Under optimum condition,the precipitation rate of V and Mo reaches 97%and 99%,respectively,moreover,the sodium aluminate solution is highly purified.3.The preparation of high purity ultrafine alumina from purified sodium aluminate solutionThe neutralization process of sodium bicarbonate with sodium aluminate solution can prepare micron spherical Al(OH)₃ particle with multiple crystals;the carbonation decomposition of sodium aluminate solution can prepare well-distributed nano spherical Al(OH)₃ particle with single crystal.In the carbonation decomposition process,temperature is the dominating factor influencing the particle size of Al(OH)₃ powder,the effect of final pH on particle size is secondary,while CO₂ flow velocity and PEG-1000 dosage have no remarkable effect.By roasting alumina particle or aluminum hydroxide particle with reagent and water-washing roasted product,most Na₂O can be removed. The Na₂O removal effect of Al(OH)₃ particle roasting with NH₄F is the best,under proper condition,fineα-Al₂O₃ particle with purity near 99.99%and average diameter of 155nm can be obtained.4.Recovery of V and Ni,Co from residue V-bearing residue is treated by sodium bicarbonate leaching, purification of leach liquor and vanadium precipitation with ammonium salt,92.5%vanadium in V-bearing residue can be recycled in the form of V₂O₅ with purity of 98.25%.Sulfuric acid leaching Ni-Co residue indicates that,under suitable condition,97.8%nickel and 98.6%cobalt can be leached.Nickel sulfate and cobalt oxalate may be obtained with the further treatment of leach liquor.5.Research on the comprehensive utilization technology for preparing high purity ultrafine alumina from spent Al₂O₃-based catalyst Based on theoretical analyses and experimental research,a comprehensive utilization technology for preparing high purity ultrafine alumina from spent Al₂O₃-based catalyst was proposed and pilot experiment in terms of lkg spent catalyst was carried out.The results show that,by this technology,spent Al₂O₃-based catalyst can be comprehensively utilized,and four kinds of products including Al₂O₃, BaMoO₄,V₂O₅ and Ni-Co sulfate solution can be obtained.The integrated recovery of Al,V,Mo,Ni and Co is 83.73%,86.64%,91.8%, 95.47%and 96.53%,respectively.The preparedα-Al₂O₃ particle with purity of 99.99%and average diameter of 134nm has a higher added value.