Abstract:

Taking the particle size and water content as indicators,the feasibility for synthesis of big-size cryolite from fluo-rine-containing wastewater by the crystallization process was studied.The experimental results showed that under the condition that the wastewater fluorine concentration was lower than 4.5 g/L,the wastewater flow rate was 1.3 L/h,the crystallization re-action pH was 4.1 to 6.6 and the reaction temperature was 45 ℃,prolonging the seed residence time was favor for increasing particle size and reducing water content of cryolite,and the fluorine recovery rate was stable at about 80%.The wastewater with a fluorine concentration of 4.0 g/L was treated by a precipitation and solid-liquid separation integrated reactor continuously,under the condition of wastewater flow rate of 20 L/h,crystallization pH of 4.0 to 7.0,reaction temperature of 45 ℃,reasonable control of seed residence time,and depending on the effect of the seed crystals remaining at the bottom of the reactor,it was possible to synthesize cryolite products with low water content（<30%） and particle sizes satisfying the requirements.

Key words: fluorine-containing wastewater, cryolite, crystallization process, seed residence time