Precipitation Of Al And Si From Depth Carbonation Process Of Sodium Aluminate Solution

Carbonation of sodium aluminate solution is one of the important operations of the lime-soda-sinter process in the production of alumina. And it has been the key process for producing sandy alumina which can satisfactorily meet the requirements of modern aluminium molten salt electrolysis in the alumina production by the sinter process. Furthmore, carbonation is a more complicated process which combines interactions of three phase of CO2-containing gas, liquid and solid. So it's very important to investigate the forming of dawsonite and the concentration changes of SiO2 during the carbonation process of sodium aluminate solution.This paper studies the effects of temperature, initial concentration of Al2O3 and CO2 on carbonization process, the forming of dawsonite and the precipitation mechanism of SiO2. Main contents and conclusions are as follows:(1) Carbonization process is affected obviously by temperature. When the temperature is above 70℃, gibbsite is precipitated quickly from sudium aluminate solution.(2) The particle size of gibbsite is affected directly by the concertration of Al2O3. But in depth carbonation process, the carbonation products from sodium aluminate solution transforms to dawsonite. And the concertration of Al2O3 has little influence on the morphology and the particle size of dawsonite.(3) During the carbonization process, CO2 reacts with caustic soda in solution at the initial reaction stage. Gibbsite is almost completely precipitated from the sodium aluminate solution when the pH of solution reaches 10.5. And the precipitation product was transformed into dawsonite by increasing the ventilation rate of CO2 in late period.(4) The research shows that the supersaturation of liquor increases at first, and then declines. The induction period of gibbsite precipitation will be shortened with high concentration of carbon dioxide, and there is not consistent changes in the induction period with the increasement of temperature.