| Fluoride pollution in drinking water has been recognized as one of themajor serious problems worldwide to affect human health, due to natural andhuman activities. Therefore, it is very necessary to seek efficient and economicdefluoridation in wastewater treatment.Modified attapulgite adsorbents exhibit high adsorption capacity forfluoride in aqueous solution. In the study, the lanthanum modifiedattapulgite（La-ATP）, cerium loaded attapulgite（Ce-ATP） and zirconium modifiedattapulgite（Zr-ATP） were prepared, and these adsorption and desorptionbehaviors for fluoride in aqueous solution were investigated. Through theanalysis of experimental data and adsorbent characterization, the adsorptionmechanism of fluoride was explored. In the study, some conclusions are asfollow:Adsorption of fluoride on La-ATP（1） The chemical composition of La2O3was3.30%in La-ATP materials byXRF analysis.（2） La-ATP showed high adsorption capacity for fluoride. The maximumadsorption amount of fluoride were15.93mg/g,21.05mg/g and25.31mg/g at15,25and35oC, respectively. Adsorption isotherms obeyed Langmuir model andadsorption kinetics followed pseudo-second-order equation at different initialconcentration, and with increasing concentrations, the adsorption rate wasreduced.（3） Fluoride adsorption on La-ATP was highly dependent on solution pH.As the pH increases, the decreasing trend of adsorption capacity is relativelyslow at pH＜6.0. And adsorption capacity decreases rapidly at pH>6.0. Thepresence of cations can inhibit the adsorption and the effect of different anionswas in the order of CO32> SO42> Cl-> NO3-.（4） Fluoride adsorbed on La-ATP could be effectively desorbed in NaOH solution. After four adsorption-regeneration cycles, adsorption amount offluoride was14.38mg/g, and adsorbent still possessed high adsorption amountfor fluoride in aqueous solution.Adsorption of fluoride on Ce-ATP（1） Cerium mainly in the form of an oxidation state scattered on the surfaceof attapulgite.（2） Under the experimental conditions, adsorption isotherm of fluoride ontoCe-ATP could be fitted Langmuir equation, and correlation coefficient R2＞0.99.The sorption of fluoride was an endothermic reaction. At different initialconcentrations, adsorption kinetics of fluoride were in line withpseudo-second-order equation.（3）With the increasing pH, the adsorption amount of fluoride was reduced.At the experiment, the different anion intensity effect the adsorption amount offluoride and followed the order of CO32> SO42> Cl-> NO3-.（4） Fluoride saturated Ce-ATP could be desorbed and recycled by0.1mol/LNaOH solution. The adsorption capacity of fluoride was12.34mg/g after fourdesorption and regeneration.Adsorption of fluoride on Zr-ATP（1）The amount of ZrO2in Zr-ATP（5mmol/g）ã€Zr-ATP（10mmol/g）andZr-ATP（15mmol/g） was5.55%,5.97%and6.14%. And zirconium surfacemodification did not change the crystallinity of the ATP.（2）The adsorption amount of fluoride onto Zr-ATP increased, withincreasing temperature, and the adsorption amount of fluoride were27.97,33.27and39.49mg/g at25,35and45oC. The adsorption isotherm of fluoride ontoZr-ATP could be modeled by Freundlich equation, and the pseudo-second-orderkinetics could fit the adsorption data very well.（3） Adsorption amount of fluoride is highly dependent on solution pH andthe maximum fluoride adsorption was found to be pH5.0. The presence ofcompetitive ions in solution decreased the fluoride adsorption amount andfollowed the order of HCO-3> SO42> NO3-> Cl-.（4） Fluoride adsorbed can be effectively desorbed by NaOH solution andregenerated adsorbents still showed high adsorption capacity for aqueousfluoride. The results In this study, the results indicated that La-ATP and Ce-ATP andof Zr-ATP could effectively remove the fluoride in solution, with the theadvantages of large adsorption amount, fast adsorption and ease regeneration. |
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