title: [Adsorption Properties of Fluorine onto Fulvic Acid-Bentonite Complex].
abstract: Fulvic Acid-Bentonite (FA-BENT) complex was prepared using coprecipitation method, and basic properties of the complex and sorption properties of fluorine at different environmental conditions were studied. XRD results showed that the d₀₀₁ spacing of FA- BENT complex had no obvious change compared with the raw bentonite, although the diffraction peak intensity of smectite in FA-BENT complex reduced, and indicated that FA mainly existed as a coating on the external surface of bentonite. Some functional groups (such as C==O, −OH, etc. ) of FA were observed in FA-BENT FTIR spectra, thus suggesting ligand exchange-surface complexation between FA and bentonite. Higher initial pH values of the reaction system were in favor of the adsorption of fluorine onto FA-BENT, while the equilibrium capacity decreased with the increase of pH at initial pH ≥ 4.50. The adsorption of fluorine onto FA-BENT was also affected by ionic strength, and the main reason might be the "polarity" effect. The adsorption of fluorine onto FA-BENT followed pseudo-second-order kinetic model and was controlled by chemical process ( R² = 0.999 2). Compared with the Freundlich model, Langmuir model was apparently of a higher goodness of fit (R² > 0.994 9) for absorption of fluorine onto FA-BENT. Thermodynamic parameters indicated that the adsorption process of fluorine was an spontaneously endothermic reaction, and was an entropy-driven process (ΔH 32.57 kJ · mol⁻¹, ΔS 112.31 J · (mol · K)⁻¹, ΔG −0.65- −1.76 kJ · mol⁻¹).
authors.forename: Dun
authors.initials: D
authors.lastname: Fang
authors.forename: Hua-jing
authors.initials: HJ
authors.lastname: Tian
authors.forename: Xin
authors.initials: X
authors.lastname: Ye
authors.forename: Ci-li
authors.initials: CL
authors.lastname: He
authors.forename: You-meng
authors.initials: YM
authors.lastname: Dan
authors.forename: Shi-yong
authors.initials: SY
authors.lastname: Wei
mesh_terms: D000327:Adsorption; D001546:Bentonite / Q000737:chemistry*; D001578:Benzopyrans / Q000737:chemistry*; D005461:Fluorine / Q000737:chemistry*; D007700:Kinetics; D009994:Osmolar Concentration; D013816:Thermodynamics
chemical_list: D001578:Benzopyrans; D001546:Bentonite; D005461:Fluorine; C005023:fulvic acid