Fluoride Removal Process For Fluoride Wastewater From Aluminum Industry

High concentration fluoride,sodium and aluminum wastewater produced by the disposal process of fluorine-containing materials from aluminum industry.The paper conducted research on fluorine removal from this fluorine wastewater according to its characteristics,from the perspective of fluorine resource recycling and protection of ecological environment.The main conclusions are as follows:（1）A two-stage process consisting of precipitation followed by adsorption was adopted to investigate the deep fluorine removal from high fluorine-containing wastewater.The optimum operation parameters for precipitation were as follows:the reaction termination p H is 8,the reaction time is 40min,the stirring strength is 400 r/min,the concentration and dosage of polyaluminum chloride（PAC）are both 5%,and the sedimentation time is 25 min.And the most suitable adsorption conditions:the volume ratio of adsorbent to solution is 2:10,the concentration of residual fluoride ion in the wastewater could be decreased to 9.5 mg/L.（2）The cryolite method was used to research the the fluorine removal process of fluorine-containing wastewater,and the optimum operation parameters for fluorine removal process conditions were obtained.When reaction termination p H is 9,alkali concentration is 160 g/L,alkali droplet acceleration is 1 m L/min,reaction temperature is 50℃,the remaining fluoride ion concentration in the solution decrease to 59.32 mg/L,but the precipitation product has high impurity content and imperfect filtration performance,moisture content is 41.35%,filtration coefficient is25.22×10^-4 cm/s,the size of average volume particle is 75.94μm.（3）The p H-F ion equilibrium diagram was drawn to reveal the mechanism of fluoride removal by cryolite method from the perspective of thermodynamics,and to explain the precipitation morphology of F element under different p H conditions.When the reaction termination p H<5,the precipitation of F is mainly Al₂（OH）_2.76F_3.24·H₂O.F element mainly co-precipitation of by Na₃Al F₆ and Al₂（OH）_2.76F_3.24·H₂O,which the p H is in the range of 5 to 8.When the reaction termination p H>8,F is mainly precipitated by Na₃Al F₆.（4）The induced crystallization based on the defluorination of cryolite was investigated.The results showed that the addition of commercial cryolite as seed could induce the growth of solute on the seed surface,and improve the product filtration performance:the seed addition amount is40%,the aging time is 2 h,the fluorine concentration in the solution is reduced to 48.20 mg/L,and the moisture content and filtration coefficient are obtain as 29.59%,30.24×10^-4cm/s,respectively.The average volume particle size is 105.89μm,The precipitation product with low moisture content and impurity content,with good filtration performance that created a good condition for the later precipitation product to be returned to the aluminum electrolysis cell.