Optimization of efficient defluorination agent using response surface methodology and research on defluorination mechanism
In China,the wastewater produced by electronics,photovoltaic,inorganic fluorine chemical industry,coal mining,coal-based chemical industry generally has the problem of exceeding fluoride.As a new method of wastewater fluoride removal,there are prob-lems such as large dosage and sludge production.Preparation conditions of the defluoridation agent were designed and optimized by re-sponse surface BBD method,and the defluoridation performance was compared with that of common coagulants.Scanning electron micros-copy(SEM)and X-ray powder diffraction(XRD)were used to characterize and analyze the defluorination agents at different preparation stages.The mechanism of defluorination was explored in combination with the residual element level and the utilization rate of each element in the supernatant after treatment.The results show that the optimal preparation conditions for defluorination agents are n(M)/n(Si)(M refers to the total amount of metal)is 44.91,n(Al)/n(Mg)is 40.64,and n(Al)/n(Fe)is 34.92.Under these conditions,when the dosage of defluorination agents prepared is 1.35 g/L,the fluoride concentration can be reduced from 20 mg/L to 0.71 mg/L,which is be-low the limit of 1.0 mg/L of GB 3838-2022 Water Environmental Quality Standard Class Ⅲ standard of Surface.The fluoride removal rate reaches 96.45%,and the correlation coefficient R2 of the model established by response surface method is 0.969 0.For the fluorine-containing water samples with initial fluorine concentration of 10-200 mg/L,the fluoride removal agent is added proportioned,and the residual fluorine concentration in the supernatant is all less than 1.0 mg/L.The order of defluorination performance with com-mon coagulants is:defluorination agent＞PAC＞PAFC＞PFS.SEM and XRD analysis show that the morphology and structure of the occuri-dation agents are changed,and a variety of polyhydroxyl polymers are formed through reactive polymerization.The ion exchange occur be-tween these polyhydroxyl polymers and fluoride ions,thus the fluoride ions are removed.Based on the analysis of the residual elements in the supernatant and the concentration of metal elements in the defluorination reagent,the element utilization rates of aluminum,silicon,iron and magnesium are 99.98%,97.16%,92.22% and 18.39%,respectively.The defluorination reagent is effective and suitable for many kinds of industrial wastewater containing fluorine.
defluorination agentresponse surface methodfluorine removal propertiesdefluorination mechanismelement utilization ratio
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