title: Macroscopic and microscopic investigation of Ni(II) sequestration on diatomite by batch, XPS, and EXAFS techniques.
abstract: Sequestration of Ni(II) on diatomite as a function of time, pH, and temperature was investigated by batch, XPS, and EXAFS techniques. The ionic strength-dependent sorption at pH < 7.0 was consistent with outer-sphere surface complexation, while the ionic strength-independent sorption at pH = 7.0-8.6 was indicative of inner-sphere surface complexation. EXAFS results indicated that the adsorbed Ni(II) consisted of ∼6 O at R(Ni-O) ≈ 2.05 Å. EXAFS analysis from the second shell suggested that three phenomena occurred at the diatomite/water interface: (1) outer-sphere and/or inner-sphere complexation; (2) dissolution of Si which is the rate limiting step during Ni uptake; and (3) extensive growth of surface (co)precipitates. Under acidic conditions, outer-sphere complexation is the main mechanism controlling Ni uptake, which is in good agreement with the macroscopic results. At contact time of 1 h or 1 day or pH = 7.0-8.0, surface coprecipitates occur concurrently with inner-sphere complexes on diatomite surface, whereas at contact time of 1 month or pH = 10.0, surface (co)precipitates dominate Ni uptake. Furthermore, surface loading increases with temperature increasing, and surface coprecipitates become the dominant mechanism at elevated temperature. The results are important to understand Ni interaction with minerals at the solid-water interface, which is helpful to evaluate the mobility of Ni(II) in the natural environment.
authors.affiliation: Key Laboratory of Novel Thin Film Solar Cells, Institute of Plasma Physics, Chinese Academy of Sciences, P.O. Box 1126, Hefei, 230031, PR China.
authors.forename: Guodong
authors.initials: G
authors.lastname: Sheng
authors.forename: Shitong
authors.initials: S
authors.lastname: Yang
authors.forename: Jiang
authors.initials: J
authors.lastname: Sheng
authors.forename: Jun
authors.initials: J
authors.lastname: Hu
authors.forename: Xiaoli
authors.initials: X
authors.lastname: Tan
authors.forename: Xiangke
authors.initials: X
authors.lastname: Wang
mesh_terms: D000327:Adsorption; D007692:Diatomaceous Earth / Q000737:chemistry*; D004785:Environmental Pollutants / Q000737:chemistry*; D007700:Kinetics; D009532:Nickel / Q000737:chemistry*; D056951:Photoelectron Spectroscopy; D056928:X-Ray Absorption Spectroscopy
chemical_list: D004785:Environmental Pollutants; D007692:Diatomaceous Earth; C033787:diatomite; D009532:Nickel