title: Microscopic level investigation of Ni(II) sorption on Na-rectorite by EXAFS technique combined with statistical F-tests.
abstract: Extended X-ray absorption fine structure (EXAFS) spectroscopy combined with statistical F-tests is used to investigate the local atomic structures of Ni(II) adsorbed on Na-rectorite. The EXAFS analysis results of Ni(II) sorption samples indicate that the first coordination shell consists of ~6 O at the Ni-O interatomic distance (R) of ~2.04 Å. The presence of Ni backscattering at R(Ni-Ni) = 3.06 Å in the second coordination shell suggests the formation of Ni(II) precipitate. The results of F-tests show that the Ni(II) precipitate is Ni-Al layered double hydroxide (LDH). Our results demonstrate that Ni(II) ions are retained via different mechanisms depending on solution conditions. At low pH, Ni retention is controlled mainly by the outer-sphere surface complexation. With increasing pH, outer-sphere and inner-sphere surface complexation dominate Ni uptake. Furthermore, Ni surface loading increases with temperature increasing at pH 6.5 due to the formation of inner-sphere surface complexes and Ni-Al LDH. The formation of Ni-Al LDH becomes the dominate mechanism at the elevated pH and temperature. In the presence of humic substances, the sorption of Ni(II) on Na-rectorite is dominated by the formation of ternary surface complexes. These results are important to understand the physicochemical behavior of Ni(II) in the natural environment.
authors.affiliation: School of Chemistry and Environment, North China Electric Power University, Beijing 102206, China.
authors.forename: Xuemei
authors.initials: X
authors.lastname: Ren
authors.forename: Shitong
authors.initials: S
authors.lastname: Yang
authors.forename: Fengchun
authors.initials: F
authors.lastname: Hu
authors.forename: Bo
authors.initials: B
authors.lastname: He
authors.forename: Jinzhang
authors.initials: J
authors.lastname: Xu
authors.forename: Xiaoli
authors.initials: X
authors.lastname: Tan
authors.forename: Xiangke
authors.initials: X
authors.lastname: Wang
mesh_terms: D000327:Adsorption; D000536:Aluminum Hydroxide / Q000737:chemistry*; D000538:Aluminum Silicates / Q000737:chemistry*; D001578:Benzopyrans / Q000737:chemistry*; D003627:Data Interpretation, Statistical; D006812:Humic Substances; D006863:Hydrogen-Ion Concentration; D008903:Minerals / Q000737:chemistry*; D009532:Nickel / Q000737:chemistry*; D013696:Temperature; D056928:X-Ray Absorption Spectroscopy
chemical_list: D000538:Aluminum Silicates; D001578:Benzopyrans; D006812:Humic Substances; D008903:Minerals; C546376:rectorite; D000536:Aluminum Hydroxide; D009532:Nickel; C005023:fulvic acid