Process Research Of Recycled Preparation Of Porous Al₂O₃ From Aluminium Salt Slag

Porous Al₂O₃has good pore structure and large specific surface area.It is an excellent medium and high temperature thermal insulation material and an excellent carrier for energy storage materials.Existing Al₂O₃production mainly takes bauxite as raw material,consumes a lot of natural resources,and causes environmental damage at the same time.Aluminum salt slag is a solid waste produced by aluminum smelting process,which still contains 5-20%aluminum resources,which can be reused as a resource.The preparation of porous Al₂O₃materials by using industrial aluminum-containing solid waste can not only greatly reduce the cost of Al₂O₃materials,but also reduce the waste of resources.It has great significance to realize the green sustainable development of industry.Porous Al₂O₃was prepared by removing impurities,forming colloids,foaming and calcining of aluminum salt slag.Effects of foaming agent on formation and pore size distribution of Al₂O₃porous structure were studied.Further discuss the effect of preparation parameters on the thermal insulation performance of porous Al₂O₃.The main elements are three parts:（1）Industrial aluminum salt slag was used as raw material to design a chemical reaction process to remove impurities from industrial aluminum salt slag.The effects of acid species,concentration and acid ratio on acid leaching reaction during acid leaching were studied.Finally,high purity Al（OH）₃colloids were prepared.The test results show that the acid leaching process is mainly divided into three stages by selecting the dilute sulfuric acid with a concentration of 20%and the acid leaching reaction with a ratio of15:1.（2）The Al（OH）₃obtained by removing impurities from aluminum salt slag was used as raw material to study the effect of calcination temperature and time on the Al₂O₃phase transition,and the mechanism of phase transition during calcination was discussed.The results show that in the range of 300-800℃,theγ-Al₂O₃gradually crystallized.In the range of 800-900℃,the products appeared in the product range of 900-1100℃,γ-Al₂O₃gradually disappeared,theθ-Al₂O₃first increased and then decreased,while the products appeared and gradually decreased increased.After 1200℃,all the phases in the product becameαphase,and after 1300℃the purityα-Al₂O₃reached 99.1%.Heating time only changes the degree of Al₂O₃crystallization.With the gradual increase of calcination temperature,in the range of 300-800℃,the micro-morphology gradually changed from smooth leveling to circular stacking.In the range of 800-900℃,strip crystallization gradually formed.In the range of 900-1100℃,strip crystallization first increased and then decreased,and flake stacking crystallization appeared.Its content gradually increased with the increase of temperature.After 1200℃,Al₂O₃micro-morphology completely changed to sheet stacking.Al₂O₃microscopic morphology was completely transformed into lamellar stacking after 1200℃.During the whole morphology change process,between the two temperature nodes that produce the initial phase change,the Al₂O₃morphology gradually changes from the surface to the interior.（3）The Al（OH）₃obtained by removing impurities from aluminum salt slag was used as raw material Na HCO₃as auxiliary foaming agent to study the effect of calcination temperature and foaming agent content on the morphology,specific surface area,pore size distribution of porous Al₂O₃and to discuss the pore forming mechanism during calcination.The results show that in the range 600-800℃,the specific surface area of the product and the number of pores increase gradually with the increase of temperature,and the number of micropores with average pore size of 10-20 nm at 800℃is the most.In the range of 800-1200℃,with the temperature continues to increase,the specific surface area of the product and the number of pores show a decreasing trend.With the increase of Na HCO₃content,surface area and pore number of the product increased gradually,and the number of medium-sized pores with average pore size of 200-500 nm at 1.0 wt%Na HCO₃was the most.The Na HCO₃content only affects the number,distribution and shape of the medium pores;After the temperature is higher than 300℃leading to the full decomposition of the Na HCO₃,the continuous change of temperature only affects the number,distribution and shape of the micropores.Testing the porosity of the samples,combined with the negative correlation between porosity and thermal conductivity,and then obtained the effect of calcination temperature,foaming agent content on the thermal conductivity of porous Al₂O₃.