Precipitation of silica by CO2 bubbles/microbubbles and kinetics research

In China, the production of silica is mainly achieved through its precipitation process. Carbonization of precipitated silica makes full use of carbon-containing flue gases, such as lime kiln gas, thereby reducing the cost of silica production and making it an effective way of CO2 resource utilization. It is an important research field of cleaner production. The research in this study focuses on the production of precipitated silica through carbonation. This study evaluated the impact of Na2O·3.45SiO2 concentration and carbonization temperature during the process. The pH and temperature of the suspension were observed in order to evaluate the proposed process and contrast it with the traditional bubble generator process. The optimization of carbonization mass transfer by microbubbles was preliminarily studied by experiments and computational analysis methods. The results demonstrated that when the Na2O·3.45SiO2 concentration was at 0.2 mol/L and the temperature was 60 °C, the microbubbles could improve the efficiency of CO2 utilization by 1.9 times. The research on the specific surface area (BET) of the prepared silica powder revealed that BET decreased with the increase of Na2O·3.45SiO2 concentration when bubbling was present. Under bubbling/microbubble conditions, when the temperature was 60 °C, with the Na2O·3.45SiO2 concentration increased from 0.1 M to 0.5 M, the BET decreased by 29.2% and 16.8%, respectively. However, when the concentration of Na2O·3.45SiO2 increased to 0.5 M, the introduction of microbubbles made the BET higher than the bubble by 13.3%. Under bubbling/microbubble conditions, when the temperature increased from 25 °C to 60 °C, BET decreased with the increase of temperature, with the BET decreased by 13.5% and 12.8%, respectively. Furthermore, the kinetics of carbonation at room temperature and 0.2 mol/L Na2O·3.45SiO2 with bubbling were calculated. The results showed that carbonation was pseudo second-order reaction process. The process realized the solid waste utilization of CO2, and had important guiding significance for the preparation of high-performance silica.