Goethite

About: Goethite is a research topic. Over the lifetime, 4043 publications have been published within this topic receiving 166853 citations.

Arsenate and Chromate Retention Mechanisms on Goethite. 2. Kinetic Evaluation Using a Pressure-Jump Relaxation Technique

Abstract: The kinetics of arsenate and chromate adsorption/desorption on goethite (α-FeOOH) were investigated using a pressure-jump (p-jump) relaxation technique. Information provided by this technique was used to elucidate the fate of arsenate and chromate in natural environments. Chemical relaxations resulting from rapidly induced pressure changes were monitored via conductivity detection. The adsorption/desorption of these oxyanions on goethite involved a double relaxation event. The proposed mechanism for the adsorption of arsenate and chromate on goethite is a two-step process resulting in the formation of an inner-sphere bidentate surface complex. The first step, associated with the fast τ values, involved an initial ligand exchange reaction of aqueous oxyanion species H2AsO4- or HCrO4- with OH ligands at the goethite surface forming an inner-sphere monodentate surface complex. The subsequent step, associated with the slow τ values, involved a second ligand exchange reaction, resulting in the formation of an ...

Mechanisms of arsenic uptake from aqueous solution by interaction with goethite, lepidocrocite, mackinawite, and pyrite: An X-ray absorption spectroscopy study

Abstract: The mechanisms whereby As(III) and As(V) in aqueous solution (pH 5.5−6.5) interact with the surfaces of goethite, lepidocrocite, mackinawite, and pyrite have been investigated using As K-edge EXAFS and XANES spectroscopy. Arsenic species retain original oxidation states and occupy similar environments on the oxyhydroxide substrates, with first-shell coordination to four oxygens at 1.78 A for As(III) and 1.69 A for As(V). In agreement with other workers, we find that inner sphere complexes form, apparently involving bidentate (bridging) arsenate or arsenite. Interaction of As(III) and As(V) with the sulfide surfaces shows primary coordination to four oxygens (As−O: 1.69−1.76 A) with further sulfur (∼3.1 A) and iron (3.4−3.5 A) shells suggesting outer sphere complexation. Arsenic species were also coprecipitated with mackinawite (pH 4.0), and these samples were further studied following oxidation. At high As(III) or As(V) concentrations, arsenate or arsenite species form, probably as sorption complexes, al...

Reduction of Substituted Nitrobenzenes by Fe(II) in Aqueous Mineral Suspensions.

Abstract: The kinetics of the reduction of 10 monosubstituted nitrobenzenes (NBs) by Fe(II) has been investigated under various experimental conditions in aqueous suspensions of minerals commonly present in soils and sediments. Aqueous solutions of Fe(II) were unreactive. In suspensions of Fe(III)-containing minerals (magnetite, goethite, and lepidocrocite), Fe(II) readily reduced the NBs to the corresponding anilines in a strongly pH-dependent reaction. Our results suggest that on other mineral surfaces (γ-aluminum oxide, amorphous silica, titanium dioxide, and kaolinite) iron (hydr)oxide coatings are indispensable to promote the reduction of NBs by adsorbed Fe(ll). Apparent pseudo-first-order rate constants, k obs , were used to describe the initial kinetics of the NB reduction, covering several half-lives of the compounds. The distinct effect of substituents on k obs and the observed pronounced competition between different NBs indicate that precursor complex formation as well as the (re)generation of reactive surface sites are rate-determining steps in the overall reduction of the NBs. The results of this study demonstrate that Fe(ll) adsorbed on iron (hydr)oxide surfaces or surface coatings may play an important role in the reductive transformation of organic pollutants in subsurface environments. Our findings may also contribute to a better understanding of the various redox processes involved in groundwater remediation techniques based on Fe(0) as the bulk reductant.