| Fluorine is a common pollution index in municipal drinking water and industrial wastewater,and the pollution concentration varies greatly.The fluorine concentration in municipal drinking water is generally lower than 10mg/L,while the fluorine concentration in industrial wastewater can generally reach 10～1000mg/L.Different technical methods need to be adopted for fluorine treatment of different concentrations.At present,the traditional fluorine removal process in the market can not adapt to the changes of high and low concentrations of fluorine,especially for low fluorine treatment efficiency,and the treated water quality can not meet the standard.The chemical crystallization circulating granulation fluidized bed is based on the principle of induced crystallization technology.It can not only deal with high concentration fluorine,but also has a good removal effect on low concentration fluorine.Moreover,it has no by-products and is green.In this study,based on the chemical crystallization circulating granulation fluidized bed technology,different concentrations of fluorine-containing water were studied.The methods of inducing calcium fluoride crystallization and inducing calcium fluorophosphate crystallization were used to remove fluorine.This paper focuses on:(1)the influencing factors(induction period,Ca/F,p H,crystal seed type),kinetic conditions(rising flow rate,internal circulation,static bed thickness)and the way to reduce the effluent turbidity of calcium fluoride crystallization induced by chemical crystallization circulating granulation fluidized bed.(2)The effect and influencing factors of chemical crystallization circulating granulation fluidized bed induced calcium fluorophosphate crystallization to remove low fluorine in water were studied in a pilot scale test.The main conclusions are as follows:(1)A small-scale crystallization granulation fluidized bed is used to treat high fluorine containing wastewater with influent fluorine concentration of 100～150mg/L.by controlling Ca/F=0.6,the fluorine ion removal rate of effluent can reach 80%;1.0≤Ca/F≤1.5,the fluoride ion removal rate of effluent can reach 87%;Continue to increase Ca/F,and the improvement of fluoride removal effect is limited.The influent Ca/F has the greatest influence on the fluoride ion removal rate in the calcium fluoride crystallization process,and the calcium fluoride crystallization reaction is relatively less affected by the rising flow rate,the thickness of static bed and the type of crystal seed.(2)The chemical crystallization circulating granulation fluidized bed induces calcium fluoride crystallization for fluoride removal,which requires a certain start-up time to achieve stable effluent quality.Increasing the inlet Ca/F will shorten the start-up time of the equipment.When Ca/F=1,the start-up time is 9h.The treatment effect of chemical crystallization circulating granulation fluidized bed on 30～600mg/L high fluorine containing wastewater is studied.The results show that when PAC and PAM are added to the effluent,when the influent Ca/F≥0.6,the effluent fluorine ion concentration can be reduced to less than 10.77mg/L.When Ca/F≥1,the effluent fluorine ion concentration can be reduced to less than 8mg/L,the effluent turbidity and calcium ion concentration can also be effectively reduced.The crystal product on the surface of crystal seed is calcium fluoride,and the surface morphology before and after crystallization is quite different.The decrease of p H is conducive to the crystallization reaction of calcium fluoride.When Ca/F ≥ 1 and p H ≤ 6.24,the fluoride ion concentration in the effluent can be stabilized below 10mg/L.the existence of internal circulation in the chemical crystallization circulating granulation fluidized bed promotes the internal circulation of crystalline particles and improves the load rise and crystallization efficiency.Chemical crystallization circulating granulation fluidized bed can treat large flow and high concentration fluorine-containing water,but it needs to be connected with solid-liquid separation equipment to reduce effluent turbidity.(3)The pilot scale chemical crystallization circulating granulation fluidized bed is used to induce the crystallization of calcium fluorophosphate.Dolomite is the best choice for removing the fluoride crystal seed,and sodium dihydrogen phosphate is used as the phosphorus source to operate in the way of influent p Hosphorus source tt the fluorine-containing water with influent fluorine concentration of less than 10mg/L,adjust F:P:Ca to 1:10:40,reduce the effluent fluorine ion concentration to less than1mg/L,and the required dosing ratio increases with the decrease of influent fluorine ion concentration.When calcium fluorophosphate crystal is used to treat fluorinated water below 3.2mg/L,Na OH can be added to ensure that the calcium and phosphorus in the effluent can be reduced to 1mmol/L and 1.9mg/L respectively when the p H of the effluent is 8.8.The increase of temperature is helpful to improve the fluoride removal capacity of calcium fluorophosphate crystallization,but the rising flow rate has a great impact on the crystallization of calcium fluorophosphate,and sufficient residence time should be ensured in the crystallization fluidized bed.The crystallization of calcium fluorophosphate induced by chemical crystallization circulating granulation fluidized bed is suitable for the treatment of low concentration fluorine-containing water. |
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