The Study On Preparation Of High-purity Aluminum Oxide From Industrial Sodium Aluminate Solution And Industrial Application

It is a promising technical route to prepare high-purity alumina with industrial sodium aluminate solution as raw material due to low cost and low environmental pollution.The concentration of alumina in industrial sodium aluminate solution is high,the silicon content index is low,and there are many kinds of coloring substances,which affect the seeding process and the purity of products.In this work,industrial sodium aluminate solution is used as a raw material,based on desiliconization thermodynamics,the solution is decolorized,the species decomposition process is studied,and the industrialization process is optimized and improved to produce a high-purity aluminum hydroxide intermediate,then the pure alumina was obtained by roasting.This work provides technical guidance for the preparation of high-purity alumina by industrial sodium aluminate solution.The desilication and decolorization mechanism of industrial sodium aluminate solution was studied.Studies have shown that hydrated calcium aluminate is formed after adding CaO into sodium aluminate solution,and then hydrated garnet with silicate ions is precipitated from the solution to achieve desilication.The formation conditions and reaction thermodynamics of hydrated garnet were studied.The desiliconization ability of calcium-containing compounds was in the order:CaO>3CaOAl₂O₃·6H₂O>Ca（OH）₂.The coloring substances are mainly organic substances and iron-containing substances.Filtration can remove large-molecule organic substances,and adding CaO can remove small-molecule organic substances and iron-containing substances.The purification process of adding CaO to desiliconization and decolorization simultaneously was determined.The research on preparation of aluminum hydroxide intermediate by sodium aluminate solution was carried out.Using the synthetic sodium aluminate solution,the influence of the decomposition concentration and decomposition temperature on the impurity content in the seeding process was inspected.On this basis,sodium bicarbonate was used as the initiator to prepare seed crystals,and the purified industrial sodium aluminate solution was used as the raw material to prepare aluminum hydroxide.The influence rules of temperature system,seed crystal dosage and additives on impurity content were studied.The results shown that:Adding additives A or B can inhibit the precipitation of sodium carbonate and sodium sulfate,increasing the decomposition rate of the solution,and reducing the alkali content of the product.When the seeding time is 24³6 h,the decomposition rate can reach55.29%,the average particle size of aluminum hydroxide is less than 5μm,and the purity reaches more than 99.90%.Optimized and adjusted the key processes in the industrialization process,modified the float control system to improve the whiteness of aluminum hydroxide;Optimized the seed preparation process to form an active seed preparation process,reducing the content of entrained impurities;Using two Multi-stage decomposition process to control the precipitation of impurities in the separation process,supplemented by de-ironing and sieving multi-level impurity removal technology,reducing the particle size and impurity content of the decomposition products;According to product characteristics and filtration equipment operating parameters,the industrialization filtration process has been optimized and adjusted,using the slurry vertical pressure filtration process,with series filtration washing technology,online washing water control technology,enhanced stirring technology,multi-point multi-density detection control technology,which greatly reduces the alkali and conductivity of the product.The high purity alumina was obtained after roasting,which has a whiteness of more than 96%,a SEM particle size ranging from 1 to 3μm,and a long column shape.The impurity content meets the requirements of 3N high purity alumina,and the goal of industrial production of high purity alumina is achieved.There are 47 figures,35 tables and 75 references in this paper.