Kinetic and Microscopic Studies of Reductive Transformations of Organic Contaminants on Goethite

Abstract

Reactions mediated by iron mineral surfaces play an important role in the fate of organic contaminants in both natural and engineered systems. As such reactions proceed, the size, morphology, and even the phase of iron oxide minerals can change, leading to altered reactivity. The reductive degradation of 4-chloronitrobenzene and trichloronitromethane by Fe(II) associated with goethite (alpha-FeOOH) was examined by performing sequential-spike batch experiments. The particle size and size distribution of the pre- and postreaction particles were quantified using transmission electron microscopy (TEM). Results demonstrate that the degradation reactions result in goethite growth in the c-direction. Furthermore, pseudo-first-order reaction rate constants for the degradation of 4-chloronitrobenzene and trichloronitromethane and for the loss of aqueous Fe(II) decrease dramatically with each subsequent injection of organic compound and Fe(II). This result indicates that the newly formed material, which TEM and X-ray diffraction results confirm is goethite, is progressively less reactive than the original goethite. These results represent an important step toward elucidating the link between mineral surface changes and the evolving kinetics of contaminant degradation at the mineral-water interface.

Mineralogical and morphological constraints on the reduction of Fe(III) minerals by Geobacter sulfurreducens

“…Presumably, the formation of acicular laths with relatively large (1 1 0) faces affords goethite crystallites relative thermodynamic stability. This is consistent with observations made by Chun et al (2006) who report that the growth of goethite laths in response to the incorporation of Fe(III) generated by the reduction of organic compounds occurs only parallel to the c-axis. The authors note that the lattice fringes associated with added material are continuous with those of the existing goethite lath, and that growth occurs at the expense of the reactive (0 2 1) facets which become poorly defined as Fe(III) reduction and growth proceeds (cf.…”

“…For example, Cwiertny et al (2008) note that: ''normalising the Fe(II) sorption densities and rate constants for nitrobenzene reduction to the BET surface area leads to the conclusion that goethite nanoparticles are less reactive that larger particles", and also conclude that particle aggregation is responsible for the observed size dependence so that BET values should not be used to quantify the amount of surface area accessible for sorption and reaction in wet nanoparticle suspensions. Furthermore, previous studies of the reductive transformation of 4-chloronitrobenzene and trichloronitromethane by Fe(II) spiked goethite suspensions indicate that the reduction of the organic contaminants occurs preferentially on the (0 2 1) face (Chun et al, 2006). This study also indicates that extended exposure to the organic contaminants as a result of the addition of successive spikes results in increases in the average length of goethite crystallites due to the incorporation of Fe(III), accompanied by roughening of the (0 2 1) facets.…”

“…Thus, for G4, the (0 2 1) facets represent a greater fraction of the total exposed surface in comparison to crystallites within G5. The latter are bounded by relatively large (1 1 0) faces, that have been shown to exhibit lower reactivity than the (0 2 1) faces (Chun et al, 2006). Also, images of G4 indicate that the (0 2 1) facets are serrated further increasing the surface area and therefore the bioavailability of Fe(III).…”

Optimizing Cr(VI) and Tc(VII) Remediation through Nanoscale Biomineral Engineering

“…Particles remained well crystalline with a size of 10-20 nm, although they appeared to become more rounded in shape with a more unifoem particle size distribution.. We interpret these changes as the result of particle ripening in response to exposure to aqueous chromate. Similar changes in iron oxide nanoparticle morphology due to interfacial redox reactions have been documented (46). [47][48][49], together with our own XPS analyses of a range of pure Cr salts, indicates that for Cr(VI), the 2p 3/2 peak is located between 579 eV-579.8 eV BE, and that spin-orbit splitting observed for Cr(VI) is 8.7 eV-9.4 eV (1, 47,48).…”

Effect of sodium dithionite on the surface composition of iron‐containing aquifer sediment

“…[4] Fe(II) chemical reducing agents are commonly selected for the active metal component because iron is an inexpensive electron donor that is abundant in soils and is environmentally compatible in its fully oxidized (spent) form. Iron-containing minerals have been used in the form of oxides, [5 -7] hydroxides, [8,9] iron sulfides [10,11] and green rusts, [12 -14] and are suitable for remediating water, soil and sediment contaminated with explosives, heavy metals, nitrates and chlorinated organic compounds, among other pollutants. [4] For these iron-rich soils and aquifer sediments, pretreatment is often necessary to activate the remediant surface prior to use.…”