Preparation Of High Purity Al₂O₃ By Alcoholization-Hydrolysis Of Industrial Aluminum

When preparing high purity alumina by alkoxide hydrolysis,the reaction speed between aluminium and organic alcohols is fast and the purity of the product is high.Isopropanol used in the reaction process can also be reused after treatment.It is not only environmentally friendly but also cost-saving.The whole reaction process does not produce harmful gases and is environmentally friendly.However,the use of high-purity aluminium as raw material for alcoholic hydrolysis,for industrialization,the use of high-purity aluminium means that the cost of raw materials has increased exponentially.Therefore,the preparation of high purity alumina by industrial aluminium as reaction material is of great significance to reduce production costs,expand the width of the aluminium industry and enhance the added value of aluminium.The experimental results show that the purity of aluminium isopropoxide is99.9737%,and the content of silicon is very high,accounting for 0.0175%.The purity of aluminium isopropoxide is increased to 99.9862%by adding desiliconizer lanthanum oxide.The structure of synthesized aluminium isopropoxide was characterized by infrared analysis,which proved that the product was the structure of aluminium isopropoxide needed.The study on the preparation of alumina precursor by hydrolysis of aluminium isopropoxide shows that the crystalline form of the hydrolysate is the same under different hydrolysis conditions,all of which are pseudoboehmite.The optimum hydrolysis conditions are as follows:the temperature is 55 C,the ratio of hydrolysate to aluminium isopropoxide is 4:1,the concentration of hydrolysate reaches 80%,the hydrolysis time is 4 h,the average particle size of hydrolysate is 4.75 micron,and the particle size distribution is uniform.The structure of the hydrolysate was characterized by infrared analysis,which proved that the hydrolysate was the pseudo-boehmite structure needed.The results of alumina calcination experiment show that the crystal structure changes when calcined at 500-1200℃,and the pure phase is a-Al₂O₃ at 1200℃The total content of impurities in alumina powder is0.0139%when the calcination temperature is 1200℃for 1 h.The purity of alumina after ultrasonic pickling is 99.9916%,which meets the purity requirement of high purity alumina.Thermal decomposition kinetics of pseudo-boehmite during calcination shows that the calcination process of hydrolysate can be divided into two stages.The first stage is surface dehydration,following the D₃ model reaction mechanism,and the second stage is internal structure water removal process controlled by three-dimensional diffusion reaction D₄ model.The average activation energy corresponding to the first endothermic peak and the second endothermic peak of hydrolysate during calcination is 44.67 kJ/mol and 97.03 kJ/mol respectively.