Study on preparation of cryolite by chemical precipitation of fluorine from aluminum electrolytic industrial wastewater.

The industrial wastewater of aluminum electrolysis contains a large amount of fluorine and valuable metals, and the pH value is high. Direct discharge will cause water pollution. Therefore, this paper studies a process of synthesizing cryolite from aluminum electrolysis industrial wastewater by supplementing aluminum source and adjusting pH value by adding acid, which is used as electrolyte for electrolytic aluminum. Fluoride ion electrode, XRD, Fourier transform infrared spectroscopy, laser particle size analyzer, XPS and SEM-EDS were used to characterize the fluoride ion concentration, phase composition, structure characterization, particle size distribution, chemical bond and morphology-element composition. The results showed that when the synthesis temperature was 30 °C, the pH value was 7 and the ratio of aluminum to fluorine was 1:6, the fluorine recovery rate was the highest, reaching 98.7 %. The synthesized product is cryolite (molecular ratio is 2.815) with an average particle size of about 20 μm. When used as electrolyte, the liquidus temperature is 950 °C, the solubility of AlO is 6.94 %. This process solves the environmental pollution of wastewater from the aluminum electrolysis industry. It provides an efficient, economical and green way for the recycling of aluminum electrolysis industrial wastewater.