Sulfate Ion Binding on Goethite and Hematite

Inorganic Ligand Effects on Pb(II) Sorption to Goethite (α-FeOOH)

“…Early infrared investigations of sulfate bonding to goethite, conducted on air-and/or vacuum-dried samples, were interpreted as evidence for bridging bidentate sorption to adjacent surface hydroxyls that are singly bound to structural Fe (i.e., A-type 3 ) (25,(29)(30)(31). Similar complexes have also been proposed for other tetrahedral oxoanions including phosphate, arsenate, and selenate (31)(32)(33).…”

“…Although the strong ionic strength dependence of sulfate sorption on goethite suggests weak outer-sphere binding (26), inner-sphere complexes show a similar dependence if their charge is assumed to extend into the β-plane (e.g., (23)). The inner-sphere model for sulfate sorption is further supported by thermal gravimetric analysis (25), whereas outer-sphere binding is suggested by the fact that sulfate sorption is observed only for pH < pH pzc and by electrophoretic mobility measurements, which indicate that sulfate binding energy is dominated by electrostatics (27). The ambiguity of these macroscopic results highlights the need for direct structural analyses to determine the mode(s) of sulfate binding.…”

“…Macroscopic studies have interpreted sulfate sorption to Fe-(hydr)oxides variously as outer-sphere complexation (21,22), inner-sphere complexation (23), and a combination of both (24,25). Although the strong ionic strength dependence of sulfate sorption on goethite suggests weak outer-sphere binding (26), inner-sphere complexes show a similar dependence if their charge is assumed to extend into the β-plane (e.g., (23)).…”

Adsorption of Sulfate and Copper(II) on Goethite in Relation to the Changes of Zeta Potentials

“…Previous macroscopic studies explained SO 2− 4 adsorption to Fe-(hydr)oxides variously as outer-sphere complexation (19,20), inner-sphere complexation (17), and a combination of both (21,22). The strong ionic strength dependence of SO 4 binding continues even in the recent spectroscopic studies; e.g., the diffuse reflectance spectra (24) and in situ attenuated total reflection-FTIR data (25,26).…”

Increase in Cation Adsorption Induced by Surface Complexation of Sulfate on Andisols and Prediction by “Four-Plane Model”

“…4 and 5. The adsorption form of sulfate ion (Turner and Kramer 1991) and phosphate ion (Nanzyo 1989) was considered to be mostly the same. In the Four-plane model an anion can replace either a water molecule or a hydroxyl ion.…”