Research On The Dissolution And Settlement Process Of Al/Si Solution

In the whole process of alumina production, the desilication is throughout all long. The level of alumina quality was decided by silicon content, which was decided to applicate in the industrial production at last. Therefore, It is one of important projects that research on the separation of silicon aluminium in alumina production. It will be very significant to research the behavior of silicon/aluminum ions in the solution.This topic studied the pH value change on the influence of the solution states in the sodium silicate solution, aluminum chloride solution and the system of silicon aluminium solution. The thesis analysed aluminum ion content, silicon content and silicon polymer morphology by EDTA complexometry, silicon molybdenum blue spectrophotometry and the Si-Mo complexation-timed spectrophotometric methods. And also studied the fall-out of structure characterization by the infrared spectroscopy and X-ray spectrum iffraction.The results of the study showed as follows:Sodium silicate solution mainly existed silicate positive ions in acid conditions, whose content increased with pH value increased. When pH>5.38, the silicate positive ions were easy to condense and generate gel or precipitation; In alkaline conditions, the solution mainly had silicate anion. When pH<10.80, silicate anion was easy to condense and generate gel or precipitation. The pH range of Acid sol was wider than alkaline sol. When pH<9.30, there were mainly aluminum ion in aluminium chloride solution, whose content was less with the increase of pH value; When PH>9.30, there was mainly partial aluminum root ion, whose content increased with the pH value; Aluminum ion was more in acid solution; the range of PH value from9to11, the precipitation solid had majority of alumina, others mainly had aluminum hydroxide; when the sedimentation rate was relatively slow, the generation of solid was crystallization type; when the sedimentation rate was faster, generated solid was amorphous. The change of silicon aluminium could be divided into three parts as follows, precipitation of silicon and aluminum, adsorption of Silicon in the surface of aluminum hydroxide and Silicon aluminium acid sodium wuding type. When the pH value range from11.70to7.49in aluminum silicon solution, the lower pH would make AIO2-into Al (OH)2+and AI(OH)3, and make H2SiO42-into H3SiO4-and H4SiO4, which existed in solid phase, When pH<3.48, silicon aluminium constantly transferred from fallout to solution with the pH lower. When the pH value dropped to1.42, the silica was stability, which can realize the separation of silicon and aluminium.In the summary, through the study on the influence of pH value on the ion nature in the solution, it is the purpose to look for a best process scheme on physics separation of silicon and aluminum with different forms from the solution. It will open up a new way to eliminate the influence of silica production process, the optimization of the technical and economic indexes in alumina industry of China.