Preparation Of Cryolite From Industrial Grade Sodium Fluorosilicate

A novel method of preparing cryolite has been studied from industrial grade sodium fluorosilicate-a-by-product of a phosphate fertilizer factory, which avoids the problems of ammonia wastewater caused by ammonium method. First, carbon white and sodium fluoride filtrate were prepared during decomposition process of sodium fluosilicate. Effects of ingredient ratio of sodium hydroxide and sodium fluosilicate, filling rate of sodium hydroxide, reaction temperature and decomposition pH value, etc. on the recycling and quality of the carbon white were investigated. According to the single factor experiment and the orthogonal experiment, the suitable reaction conditions are established: pH8.5, filling rate of sodium hydroxide is9.0ml/min, n(NaOH)/n(Na2SiF6) is4.10:1and decomposition temperature is above75℃. Under these conditions, the carbon white prepared could meet the national quality standard of ChinaThen cryolite was synthesized by sodium fluoride filtrate, hydrofluoric acid and Aluminum hydroxide. Effects of Na/Al (molar ratio of Na to Al in the raw materials), reaction temperature, pH and reaction time, etc. were investigated on the fluoride and aluminum contents, the ignition loss and granularity of cryolite products. The results show that the suitable reaction conditions are as follows:pH3.0to5.0, Na/Al2.7to3.0, temperature is above70℃and reaction time120min. Under these conditions, the cryolite products produced could meet the national first-grade quality standard of China. In addition, the phase composition and crystalline morphology of cryolite products are determined by X-Ray diffraction meter (XRD), energy dispersive x-ray analysis (EDAX) and scanning electron microscope (SEM). The results show that its X-Ray diffraction diagram is similar to the diagram of natural cryolite, energy dispersive x-ray analysis diagram demonstrates main mineral phase composition is cryolite, and the examination of scanning electron microscope diagram shows cryolite particulates distribute uniformly and shape of them are like the garnet phase.