Fluoride Removal And Mechanism Of Y-Type Molecular Sieve Loaded With Lanthanum Hydroxide

As one kind of widespread-element in nature,fluorine is the component of the human body(90%existing in bones and teeth either).Traces fluorine intake can significantly prevent dental caries,however,chronic excessive intake can lead to fluorosis,and some studies indicated that the prolonged ingesting of F may cause severe damage to the central nervous system.Rare-earth modified materials with high specific surface area and high mass transfer efficiency provide active sites of complex or ligand exchange with fluoride simultaneously,of which lanthanum is widely used in the preparation of modified adsorbents due to its peculiarity of high affinity and low cost.La-modified Y-type molecular sieve(LHMS)synthesized by coprecipitation was applied to the defluorination of solution with low-concentration fluoride imitated wastewater,and the performance of which is evaluated by the experimental results of kinetics,isotherms and effect of pH and co-existing anions.SEM,FESEM-EDS,XRD,FT-IR and XPS analyses were used in the characterization of material and elucidation of the adsorption mechanism.The fluoride adsorption kinetics by LHMS was better fitted with the pseudo-second-order model,in the first 60min,the adsorption capacity reached 83.1%.The maximum adsorption capacity at conditions of pH=7 and 25? was 7.58 ± 0.11 mg/g,at all three temperatures investigated,the adsorption equilibrium data showed that the Freundlich model was more suitable than One-site Langmuir and Two-site Langmuir models.A better performance of LHMS showed stable efficiency in a wide range of pH at 6 to 11 at the condition of acid.High-concentration SiO32-and HCO3-in aqueous solution,to a certain extent,affected the adsorption process.The mechanism of fluoride adsorption on LHMS was mainly accounted by ligand exchange,which was proved through the new peak appeared in FT-IR spectrum of LHMS-F compared with LHMS and the F 1s spectra in XPS.In order to solve the problem of the separation of defluorinated adsorbents and the loss of effective components,SA@LHMS adsorbents were prepared with sodium alginate(SA)and lanthanum hydroxide modified Y zeolite(LHMS)as raw materials.The optimum preparation conditions of adsorbent were determined by orthogonal experiment,SA concentration was 2%,CaCl2 concentration was 2%,crosslinking time was 24h,and LHMS embedding amount was 80g/L.The adsorption performance of SA@LHMS was evaluated by batch adsorption experiment,including dosage,adsorption rate,effect of pH value,adsorption isotherm,and effect of co-existing ions.The results showed that the removal efficiency of F-was the highest when the SA@LHMS dosage was 10g/L.The adsorption rate curve of the particles conforms to the second-order reaction rate equation.Adsorption isotherm accords with the Freundlich model and BET adsorption model,and conform to the type ? isotherm,multilayer physical adsorption.The initial pH(3?12)had no significant effect on the adsorption effect.High concentration of co-existing anions(50mg/L)inhibited the adsorption process.The regeneration effect of 1mol/L and 2mol/L NaOH solution on SA@LHMS was better,and SA@LHMS still retained a high adsorption capacity after three regeneration.The surface and cross section morphology of SA@LHMS as well as the surface morphology before and after adsorption were significantly different.EDS component analysis and FT-IR spectrum analysis before and after adsorption showed that ligand exchange occurred between F-and-OH on the surface and inside of particles during adsorption.