Study On Technics Of Ppreparing Alumina Precursor From Ammonium Aluminum Sulfate

Aluminum oxide is an important compound. Due to its various crystal shapes, it has been widely used in electrolytic aluminium, pottery and porcelai, pharmac, electronic, and machiner. Al2O3 is prepared usually through thermal decomposition of the precursor. The precursor can be prepared with acid, alkali or ammonium sulfate. Ammonium sulfate method is better because of its few pollution and high-quality products. But there are also lots of technical bottlenecks in the method of ammonium sulfate, one of which is that the precursor particles are small, resulting in a high water content in filter cake and high energy consumption in subsequent process. In allusion to the problems in the ammonium sulfate method, the preparation of Al2O3 precursor feeding on aluminium ammonium sulfate is studied and the suitable methods to prepare Al2O3 precursor, Al(OH)3, with large particles size in the preparation process from aluminium ammonium sulfate is explored.Firstly, the preparation of Al2O3 precursor, Al(OH)3 by the precipitation reactions of aluminium ammonium sulfate and alkali was studied. The effects of alkali source, adding type, pH value, temperature, dropping speed, aging time, aluminium ammonium sulfate solution concentration and seed consumption on the product properties were discussed. The optimal condition was obtained. Al(OH)3 particle size was 300~400 nm, and the content of water in filter cake was 70%.The process of Al(OH)3 preparation with precipitation was improved by adding substrate solution. Al2O3 precursors with large particle size and low water content of filter cake were prepared by adding substrate solution of ammonium sulphate and sodium sulfate, with single jet method and double jet method.The precursor prepared reactions of aluminium ammonium sulfate and alkal was handed in hydrothermal growth method. And hydrothermal conditions were investigated. The precursor with 500 nm particle size and 60~70% water content of its filter cake was prepared.On the basis of the study, Al(OH)3 under hydrothermal condition was tried to in-situ synthesized. Through the optimization of experimental conditions, optimal condition was obtained. Hydrothermal time was 9 hours. The best hydrothermal temperature was 150℃. The best hydrothermal synthesis environment was weak alkali. The best suitable addition amount of seed was 5.0 g/L. And the best ratio of ammonia and carbamide was 1:40. The best additive was K2SO4. Under the conditions, Al2O3 precursor with 450~550 nm particle size and 40~50% water content of its filter cake was prepared. The energy consumption will be reduced effectively and economic benefit will be increased.