Activated alumina has a wide range of uses. It is produced from gibbsite by heating dehydration or hydration after dehydration. Due to the different physical and chemical properties of raw materials and different processing processes, the chemical purity, physical properties and crystal phase composition of activated alumina products are different, so the service performance is also different, forming a series of activated alumina products.
1、 Taking natural gibbsite ore as raw material
Process flow: commercial bauxite (wet) → drying → heating treatment → classification → products of different particle sizes
The performance difference of producing activated alumina with natural gibbsite as raw material: the natural gibbsite is heated at 350 ~ 600 ℃, gibbsite is dehydrated and transformed into anhydrous Al2O3, such as γ- Al2O3 and χ- Al2O3, etc. If the ore contains boehmite, it will be transformed into boehmite above 450 ℃ γ- Al2O3 。 The residual water shall be controlled at about 5%. The specific surface area of the product is about 150m2 / g, mainly due to the high content of impurities, γ- The low content of Al2O3 affects the specific surface area of the product.
2、 The scab of aluminum oxide plant is used as raw material
Process flow: scarring → coarse crushing → storage tank → washing → drying and activation → live aluminum → secondary crushing → product
The performance difference of activated alumina produced from scab in aluminum oxide plant: the XRD spectrum of activated alumina shows that the crystalline phase is χ- Al2O3 and γ- Al2O3, a small amount of boehmite, has a relatively solid pore size distribution, and most of the pore sizes are less than 5000A.
3、 Using industrial aluminum hydroxide as raw material
Process flow: Al (OH) 3 → rapid dehydration → powder → mechanical forming + additives → hydration → drying activation → activated alumina
The performance difference of producing activated alumina with industrial aluminum hydroxide as raw material: under high temperature and vacuum or 500 ℃ hot air flow passes through the bed of Al (OH) 3, the powder is formed into spherical aggregate, and then hydrated to produce boehmite and pseudoboehmite, which are activated at about 300 ℃. The product does not contain boehmite, the specific surface area can reach 300 ~ 350m2 / g, and the crystal phase is very close to η- Al2O3 。 The dehydration temperature is also increased to about 800 ℃, but the dehydration time is very short. Colloidal products are obtained during rehydration, and the specific surface area of live aluminum can be increased to 320 ~ 380m2 / g.
4、 Using pseudoboehmite as raw material
The performance difference of producing activated alumina from pseudo bauxite is different. Although different properties of gel can be prepared by different methods, the activated alumina used for adsorption in industry requires smaller pore size, such as less than 40A, higher specific surface area and 300~400m2/g product. The specific surface area of activated alumina is 180 ~ 250m2 / g, and the crystalline phase is γ- Al2O3。
Activated alumina with different properties can be prepared from natural or artificial raw materials, such as gibbsite, industrial aluminum hydroxide, pseudo boehmite, etc. Due to different raw materials, the processing technology is also different. The common feature is the conventional heating and rapid heating phase transformation of gibbsite to obtain the required crystal structure, so as to improve the specific surface area of the product and improve the service performance of the product.