Synthesis of ultrafine silica powders based on oil shale ash by fluidized bed drying of wet-gel slurry

Ultrafine silica powders were synthesized using oil shale ash which is a solid by-product of oil shale processing. Fluidization technique was employed for the drying of wet-gel slurry at an ambient pressure. Box–Behnken statistical design was used to optimize the factors affecting the extraction efficiency of the silica such as concentration of sodium hydroxide, reaction time and reaction temperature, and to determine the optimum conditions for the extraction process. The result of statistical design shows that the extraction efficiency was in an agreement with the generated model and the experimental results. It is observed that the extraction efficiency of silica was increased by increasing the concentration of sodium hydroxide, the reaction time and the reaction temperature. Further, the ultrafine silica powders were characterized by transmission electron microscopy (TEM), X-ray fluorescence spectroscopy (XRF) and nitrogen adsorption (using BET equation). The BET surface area of the ultrafine silica powders obtained in fluidized bed is comparatively higher (652 m2/g) than that of silica powders dried in the furnace (385 m2/g). It is clear that the properties of silica powders obtained in fluidized bed are superior to that of powders dried in the furnace.