Preparation of ultrafine silica from potash feldspar using sodium carbonate roasting technology

A novel process was developed for the preparation of ultrafine silica from potash feldspar. In the first step, potash feldspar was roasted with Na2CO3 and was followed by leaching using NaOH solution to increase the levels of potassium, sodium, and aluminum in the solid residue. The leaching solution was then carbonated to yield ultrafine silica. The optimized reaction conditions in the roasting process were as follows:an Na2CO3-to-potash feldspar molar ratio of 1.1, a reaction temperature of 875°C, and a reaction time of 1.5 h. Under these conditions, the extraction rate of SiO2 was 98.13%. The optimized carbonation conditions included a final solution pH value of 9.0, a tem-perature of 40°C, a CO2 flow rate of 6 mL/min, a stirring intensity of 600 r/min, and an ethanol-to-water volume ratio of 1:9. The precipita-tion rate and granularity of the SiO2 particles were 99.63%and 200 nm, respectively. We confirmed the quality of the obtained ultrafine sil-ica by comparing the recorded indexes with those specified in Chinese National Standard GB 25576―2010.