SODIUM SILICATE MANUFACTURING FROM MODIFIED SILICA GEL AS BY-PRODUCT OF ALUMINUM FLUORIDE

The article considers the waste-free production of sodium silicate from modified silica gel. The proposed method corresponds the principles of green chemistry. Synthesis is carried out from industrial raw materials at atmospheric pressure without the formation of unrecyclable by-products. Silica gel is an amorphous silica with impurities of aluminum fluoride and fluorosilicic acid, which is obtained as a by-product of aluminum fluoride production from Cherepovets "Phosagro". The goal of this study is to investigate the possibilities of using modified silica gel, for manufacture of sodium silicate with minimum waste production. Studies show, that sodium hydroxide can be used for chemical modification of the surface of silica gel at 20 °C. Optimal alkali concentration and time of silica modification was determined. Alkaline solution with concentration 25% or more could be used multiple times in a process of silica modification. The following variables in this work had been analyzed: time of reaction (varying of 0 to 90 min), molar ratio SiO2/NaOH (1, 2, 3), mass ratio H2O/SiO2 (1; 2.5; 5) and reaction temperature (60, 80, 95, and 105 °C). It is observed that the SiO2/NaOH ratio reaching 2.8 at 95 °C, in 12-15 min of reaction. In the process of dissolving the modified microsilica, it was possible to achieve a transition to soluble sodium silicate about 92% of silicon dioxide.