Basic Research On The Preparation Of Pseudo-boehmite By Using High-alumina Coal Fly Ash

China is the world’s largest country of discharging fly ash. The alumina content in the fly ash is commonly17～35%and some even come up to40～60%. Fly ash is a very important unconventional aluminum resource. With the increasingly strict environmental protection policy and the shortage crisis of high grade bauxite resources, it is of great strategic significance to find the utilization technologies of fly ash. Meanwhile, exploiting the recycling method of fly ash produce high value-added multi-alumina product is also very important to alleviate the pressure of the environment and to improve the competitiveness of the alumina industry of China in the international market.In this paper,preparation of pseudo-boehmite by using Inner Mongolia Datang fly ash sintering clinker as raw material studied. Experiments were carried out to explore the optimum process conditions of dissolution experiment, desiliconization experiment, carbonation decomposition experiment and seed precipitation experiment. Moreover.XRD spectrum, SEM and the analysis of the specific surface area and pore structure method was adopted to analyze the properties of the product. The physical properties of carbonation product and seed precipitation product were compared as well. The results are as follows:(1) Through the study of dissolution and desilication experiment, the results show that:the best dissolution condition is80℃,60min, and liquid solid ratio is4:1. The best condition of first stage desilication condition is120min,170℃and sodium silicon slag is100g/L. The best condition of sec-stage desilication is120min,90℃, and CaO content is15g/L. Under the above condition, the silicon index of the solution can reach up to838, which conforms to the requirement of the industry.(2)Using arbonation decomposition method to prepare pseudo-boehmite is presented. Results show that:under the solution concentration of30-50g/L, lower than50℃when aging time is4h, lower than60℃when aging time is8h, terminal pH is10.5, and CO2volume fraction is larger than35%, the gelatinizing effect of product is better. Under the condition of aging temperature90℃and aging time4-8h, the aging effect is better. In addition, the wash and dry condition of the product is studied,The results show the phase of product is pseudo-boehmite when hot distiller water is used to wash the product to neutral, and dry temperature is lower than100℃.(3) Through the analysis of carbonation product’s specific surface area and pore structure, results show that:under the condition of aging time4h, the solution concentration of40g/L, and temperature30℃, mesoporous pseudo-boehmite can be prepared. Its specific surface area is356.4m2/g, while pore volume is0.6920cm3/g. When aging time is8h, the solution concentration is30g/L, and temperature is50℃, microporous pseudo-boehmite can be prepared. Its specific surface area is445.0m2/g, while pore volume is0.2932cm3/g.(4) Through the study of seed precipitation experiment, results show that:the pore volume of the seed precipitation product can reach up to0.8291cm3/g, which is almost the same with seed’s. However, it’s specific surface area,is393.00m2/g, which is larger than the seed’s.(5) This paper also presents the study of removing sodium by washing, results show that:The conventional washing method can make the product of Na2O content lower0.3%, which can meet the requirements of general catalyst. Further reducing sodium content in pseudo-boehmite product method needs further study.