Study On Fluoride Removal From Groundwater Using CTAB Modified Composite Material Of Lanthanum And Iron

Fluoride is a common pollutant in groundwater,many areas in China need to develop and use groundwater for production and daily drinking,long-term drinking of the high-fluorine water is harmful to human health and will cause diseases such as fluorosis and skeletal fluorosis.The World Health Organization（WHO）stipulates that the maximum fluoride concentration in drinking water is 1.5 mg/L.China’s"Standard for Groundwater Quality"（GB/T14848-2017）Class III and above standards and"Standards for Drinking Water Quality"（GB5749-2006）stipulate that the fluoride concentration limit is 1.0 mg/L.The adsorption method is currently widely used in the advanced treatment stage of the water treatment field,and is suitable for treating low-concentration polluted water bodies.In this study,a lanthanum-iron composite material modified with cetyltrimethylammonium bromide（CTAB）（hereinafter referred to as CTAB-CLI）was used to treat fluorine-containing groundwater,and explored the performance and mechanism of fluoride removal by batch experiments.The main research results were as follows:（1）Obtained by the single factor influence experiments of the preparation conditions and the analysis of the response surface model,the order of the influence of the preparation factors on the performance of fluoride removal was:the concentration ratio of lanthanum and iron,p H,the dose of CTAB.Considering the performance of fluoride removal and the economic benefits,the suitable preparation conditions for the CTAB-CLI material were:the concentration ratio of lanthanum and iron was 0.4/1,the dose of CTAB was 5.5 m L,and the p H of the preparation solution was 6.0.The material prepared under this condition successfully reduced the fluorine concentration of 10mg/L of fluorine-containing water to below 1.0 mg/L,and the removal rate reached90.58%.（2）The CTAB-CLI material was analyzed through a series of characterization methods.The SEM and BET tests found that the surface of CTAB-CLI could clearly observe the needle-like substances and porous morphology,the specific surface area of the material was as high as 234.228 m²/g.CTAB had a good modification effect on the surface of the material;The XRD test proved the existence of Fe₂O₃,Fe OOH,La₂O₃and La（OH）₃ crystals in the CTAB-CLI material,the addition of lanthanum enhanced the affinity of the adsorbent for fluoride;The Zeta potential test found that the surface of the material was positively charged in a wide p H range,which was conducive to the adsorption of fluorine;The FTIR spectroscopy proved that there were a large number of-OH functional groups on the surface,which could be ion-exchanged with fluoride;The XPS spectrum showed that after the adsorption,the binding energy of fluorine appeared,the content of-OH decreased,and the binding energy of lanthanum and iron changed;The EDS test found that the material detected the presence of fluorine after the adsorption.These conclusions indicated that the material successfully adsorbed fluoride.（3）The optimal dosage of CTAB-CLI was 1 g/L for 10 mg/L of the fluorinated water;In a wide initial p H range,the material had a good adsorption effect on fluoride;The common anions NO₃^-and HCO₃^-in groundwater had small effects on the performance of fluoride removal in the range of 0–100 mg/L,and PO₄^3-and SO₄^2-had significant effects on the performance of fluoride removal at high concentrations;The CTAB-CLI material could be reused many times after desorption and regeneration,and it had good treatment effects on the actual fluorine-containing groundwater.（4）The fluoride adsorption reaction in this study conformed to the Langmuir isotherm adsorption model and the pseudo second order kinetic model,the type of adsorption was mainly monolayer chemical adsorption,and the maximum adsorption amount predicted by Langmuir model reached 86.13 mg/g at 45°C.（5）In this study,the mechanism of fluoride adsorption by the CTAB-CLI material was mainly the ion exchange between fluoride and hydroxyl or chloride,the complexation of metal（lanthanum,iron）and fluorine,and the electrostatic attraction of fluoride on the surface of the adsorbent.