Study On The Preparation Of High Purity Aluminium Oxide Using Aluminum Ammonium Sulfate

High-purity aluminum oxide(Al2O3)has many excellent characteristics and its application fields are extensive.In this project,a new process route for producing high-purity Al2O3 was explored using industrial-grade ammonium aluminum sulfate as a raw material.The impurities such as Fe,Si,and Ca in the raw materials were removed by the recrystallization method and the flocculation-filtration method;the intermediate aluminum hydroxide was obtained by mixing the raw materials with the purified ammonia;and then hydrothermal,centrifugal washing,dry grinding,calcining,and the like were performed.At the end of the process,4N-grade a-Al2O3 was obtained.Finally,the purity,phase,morphology,specific surface area and pore size of the product were characterized.In the raw material purification stage,determined the crystallization conditions:heating temperature 90?,cooling temperature 20?,under stirring,crystallization three times;In addition to the conditions of silicon and calcium:pH was about 1.25,adding 3-4 drops of flocculation PAM,hot filter three times.The iron content was 2.54x10-4%,the silicon content was 1.36×10-4%,and the calcium content was 8.08×10-4%in the resulting crystalline aluminum ammonium sulfate.In the synthesis stage,the best experimental conditions were obtained:the endpoint pH was 9.0,the initial concentration of ammonium aluminum sulfate was 0.50 mol/L,the reaction temperature was 55?,the dropping rate was 4 mL/min,and the precipitation was reversed;the best conditions in the hydrothermal process:hydrothermal medium 1.0 mol/L refined ammonia,hydrothermal temperature 205×.The SO42-content was 0.0015%and the Fe content was 0.0002%in the resulting alumina.The intermediate is pseudo-boehmite,which was well crystallization and high purity.The particle size is about 10 ?m.Moreover,choosing ammonia in the medium can effectively increase the particle size of the intermediate,which reducing the surface adsorption of SO42-,and favoring the removal of SO42-in the alumina.Compared with the traditional method of directly roasting ammonium aluminum sulfate,a large amount of SO42-impurities were washed out before the calcination,which effectively avoided the disadvantages that insufficient calcination leaded to large SO42-content in the alumina.In the calcination phase,as the calcination temperature increases,the product crystallization becomes better and better,the particle size becomes larger,the specific surface area and the pore size become smaller and smaller,and finally the product ?-Al2O3 is obtained at 1200?.Its purity is about 99.9904%,particle size is about 8 ?m,specific surface area is about 10.67 m2/g,pore size is about 16.24 nm.It belongs to mesoporous materials.Its crystallization and dispersion are good.