Study On Treatment Methods Of High Fluorine Wastewater

In recent years,the production and utilization of fluorine,such as aluminum smelting,petroleum,electroplating and organic fluorine high-grade lubricants,and the rapid development of the processing industry have brought about a series of problems of fluorine pollution.Fluoride is an essential trace element in human life,but excessive intake of fluoride can cause health problems.Controlling the fluoride ion content in the discharged wastewater can avoid harm to the human body.The first-level emission standard in the Integrated Wastewater Discharge Standard(GB8978-1996)stipulates that the F~-ion concentration is less than 10 mg/L.Therefore,research on fluorine-containing water treatment methods has become a hot topic at home and abroad.In this paper,the flotation liquid(fluorine content up to 19,000mg/L)of electrolytic aluminum waste cathode is treated by two-stage method:firstly,the concentration of fluorine-containing wastewater is reduced to a certain range by chemical precipitation method,and then the pre-treated water is removed.The samples were subjected to advanced treatment by modified zeolite adsorption and coagulation sedimentation,respectively,and the effects of the depth treatment were compared.At the same time,the surface morphology and chemical composition of zeolite before and after lanthanum modification were compared by scanning electron microscopy(SEM)and electron spectroscopy(EDS).In the pretreatment stage,the bleaching powder is used as a precipitant,and the optimum fluorine removal process conditions are determined by single factor test,orthogonal test and response surface test.The reason why the precipitant uses bleaching powder is as follows:First,the calcium ion provided by the bleaching powder is combined with the fluoride ion to form a precipitate to achieve the fluorine removal effect.The second is to use the hypochlorite in the bleaching powder to remove a very small amount of cyanide in the flotation liquid.In the advanced treatment stage,the flocculation and defluorination effects of PAC and PFS two kinds of polymer inorganic coagulants under different conditions were compared by single factor test.Then the optimum conditions for flocculation removal of fluorine were determined by orthogonal test and response surface test.In the process of removing fluorine by static adsorption,the natural zeolite was firstly modified,then the orthogonal test and response surface test were used to optimize the process conditions.The adsorption mechanism of lanthanum-modified zeolite was studied by adsorption thermodynamics and kinetics.The main conclusions drawn are as follows:(1)The optimal defluoridation process conditions of the chemical precipitation method are:after adjusting the pH of the wastewater to 12,7.34 g of bleaching powder is added to100 mL of the wastewater,and the mixture is shaken at an oscillating speed of 190 r/min for120 min,and then allowed to stand for 60 min.The significance factors of the influencing factors are:bleaching powder dosage>pH>station time>oscillation speed>oscillation time.The response surface model is significant,and the interaction between the three factors of bleaching powder dosage,pH and standing time is obvious.The relative error between the predicted value of the software and the actual value of the test is less than 5%,indicating that the test model is reliable.(2)After comparison,it is found that the effect of removing fluorine by PAC is better than that of PFS.The optimum fluorine removal process conditions for PAC are:PAC dosage is 300mg/L,pH is 11.Firstly,stir at 150r/min for 1min,then stir at 45r/min for 20min and let stand for 1.5h.The orthogonal test shows that the significance of the influencing factors is in order:the dosage of PAC>pH>stirring time>stirring speed>resting time.The response surface test model is significant,and the interaction between pH and stirring speed is obvious,while the interaction between pH and stirring time,stirring time and stirring speed is not strong.The relative error between the predicted value of the model and the actual value of the test is less than 5%,indicating that the test model is reliable.(3)It can be observed from the SEM image that the surface of the natural zeolite is rough and the pore structure is developed.The specific surface area of the natural zeolite is determined by BET to be 9.29 m~2/g.EDS analysis shows that lanthanum has been successfully loaded on zeolite.Optimum process conditions for static adsorption of fluorine by lanthanum modified zeolite:100 mL of fluorine-containing wastewater with a concentration of 125 mg/L at 35°C is adjusted to pH 3 with 0.1 mol/L hydrochloric acid and sodium hydroxide solution,0.6 g lanthanum modified zeolite was placed in the wastewater and placed in a constant temperature water bath shaker for 14h at an oscillation speed of 140r/min.The orthogonal test shows that the significance of the influencing factors is in order:pH>initial wastewater concentration>lanthanum modified zeolite dosage>contact temperature>contact time.The response surface test showed that the model was significant,and the interaction between pH,initial wastewater concentration,lanthanum modified zeolite dosage and contact time was significant.The relative error between the predicted value of the model and the measured value of the test is less than 5%,indicating that the test model is reliable.Thermodynamic analysis shows that the process of adsorbing fluoride ions by lanthanum modified zeolite is not a simple physical adsorption or chemisorption process,but tends to have a strong molecular interaction between the adsorbate and the adsorbent.