Recovery of high specific area silica and sodium fluoride from sodium hexafluorosilicate

XU Hui(徐徽), LI Gui(李贵), CHENG Jun-feng(程俊峰), LIU Wei-ping(刘卫平)

(School of Metallurgy and Environment, Central South University, Changsha 410083, China)

Abstract:Sodium fluoride and high specific area silica were synthesized by using sodium hexafluorosilicate (Na₂SiF₆) and sodium carbonate decahydrate (Na₂CO₃·10H₂O). The influencing factors of react temperature, contact time, sodium dodecyl sulfate (SDS) and molar ratio of Na₂SiF₆ to Na₂CO₃·10H₂O were investigated. The optimum process involves the reaction of 0.075 mol Na₂SiF₆ and 150 mL, 0.225 mol Na₂CO₃·10H₂O (molar ratio of 1:3) at 85 °C for 90 min, and 2.0×10^-3 mol sodium dodecyl sulfate (SDS) as additive. The results show that the purities of SiO₂ and NaF at extraction yields of 96.5% and 98.0% are 91.0% and 98.6%, respectively. The obtained SiO₂ were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), Fourier transform infrared ray (FTIR), differential scanning calorimetry and thermogravimetric analysis (DSC-TGA), N₂ absorption/desorption (BET) and laser particle size analyzer. The result demonstrates that SiO₂ particles have a high BET surface area of 103 m²/g, and a mean grain size of 985 nm.

Key words:recovery; sodium hexafluosilicate; sodium fluoride; silica