Study On The Mechanism Of Sodium Aluminate Crystallization Under Ultrasonic Wave

Red mud and fly ash of alumina industry in China are major high-alumina solid waste. They cover lots of area and it’ll cause serious social and environmental problems. But they are also an excellent non-traditional resource of extraction aluminum. The method of using sub-molten salt treatment to extract alumina from red mud and fly ash can realize the economic recycling of Al2O3 and get the sodium aluminate solution which has a high caustic ratio(more than 4). The solution that has high caustic ratio cannot preparation by traditional seed decomposition method which applies the sodium aluminate solution with caustic ratio about 1.5 only. But we can first reduce the caustic ratio of the solution using the method of crystallization, then the seed decomposition.To solve this problem, the new method of strengthen the crystallization of sodium aluminate solution with ultrasonic wave can increase the crystallization rate. But the mechanism is not clear. Therefore, in this paper, we first study the differences between the process of dissolution liquid crystallization and get the key affecting during the crystallization solution, then research the change regulation of the liquid such as viscosity, turbidity et al. Analyze the mechanism of the crystallization of sodium aluminate solution strengthen by ultrasonic wave. In this paper we get the following innovative achievements.(1) By comparing the different effects of crystallization progress from different fly ash which strengthen by ultrasonic wave, we find the SiO2 and Fe2O3 which in the sodium aluminate solution can seriously affect the effect of the crystallization. By changing the original conditions in the experiment such as original concentration of Al2O3, original caustic ratio et al, we find that the rate of crystallization will greatly reduce after increase the concentration of SiO2 and Fe2O3.(2) After research the effect of impurity species and impurity concentration in sodium aluminate solution to crystallization rate, caustic ratio, viscosity, turbidity, conductivity and the crystal morphology of the products and so on, we get the results that SiO2 in sodium aluminate solution is the main hinder factor.(3) We deeply research the changes of the structure in sodium aluminate solution under the action of ultrasonic, and clarify the mechanism of ultrasonic. The study shows that, SiO2 in sodium aluminate solution makes the structure more complex. With the increase of SiO2, the absorption peak of silicon oxygen bond become larger and wider, the simple structure gradually becomes the complex network structure with Si-O-Al. The absorption peak of silicon oxygen bond will be weakened and the position will be shifted under ultrasonic wave. This explains that the complex Si-O-Al bond can be broken into small pieces during ultrasonic process, the viscosity and required energy for nucleate has been reduced, this helps the precipitation of sodium aluminate crystal.