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1. Anisotropic oxidative growth of goethite-coated sand particles in column reactors during 4-chloronitrobenzene reduction by Fe( ii )/goethite

   https://doi.org/10.1039/D1EN00788B  

   Soroush, Adel; Penn, R. Lee; Arnold, William A. (January 2022, Environmental Science: Nano)

   Reduction of nitroaromatic compounds (NACs), an important class of groundwater pollutants, by Fe( ii ) associated with iron oxides, a highly reactive reductant in anoxic aquifers, has been studied widely, but there are significant differences between the well-controlled, batch reactor conditions of the laboratory and the complicated conditions encountered in the field. Continuous flow column reactors containing goethite-coated sand and aqueous carbonate buffer were continuously exposed to 0.05 mM 4-chloronitrobenzene (4-ClNB) and 0.5 mM Fe( ii ) to emulate more realistic scenarios and to allow study of the oxidative growth of goethite particles using both saturated and unsaturated flow conditions. The experiments were designed to test how attachment to a surface affected particle growth and how particle growth affected the extent of reaction over time. After reaction, particles from different sections of each column were collected, and the goethite was detached from the sand grains for characterization using transmission electron microscopy. The amount of oxidative growth varied as a function of distance from the column inlet, with the most growth observed at the inlet end (bottom) of the column. Similar to previous work using batch reactors, newly oxidized Fe( iii ) was mostly added to the goethite particle tips, resulting in up to an 81% increase in length under saturated flow and a 50% increase in length under unsaturated flow after 220 pore volumes. With saturated flow, reactant concentrations and the extent of the reaction are important factors determining the extent of mineral growth. For unsaturated column conditions, however, flow path substantially impacts mineral growth in the column. Reactors sacrificed after 220 pore volumes under saturated flow conditions resulted in an overall 70% increase in goethite mass while the unsaturated flow column resulted in a 40% increase in goethite mass, more variable mineral growth as a function of distance from the inlet, and overall, 50% less 4-ClNB conversion. The results demonstrate that quantitative characterization of oxidative mineral growth of goethite nanoparticles attached to an underlying mineral is practical and elucidates the major variables impacting the reactivity of mineral nanoparticles in contaminated groundwater systems. 

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2. Suppressing alkali-silica reaction through incorporation of calcined kaolinite–montmorillonite clay blends

   Wei, Jianqiang (September 2019, 15th International Congress on the Chemistry of Cement)

   Cement substitution with calcined kaolinite–montmorillonite clay blends as an effective way to suppress alkali-silica reaction in cement composites containing reactive aggregates is investigated. Expansion, cracking behavior, mechanical properties and microstructure of the cement composites were investigated. Hydration of the ternary cement blends was also characterized. The results indicate that cement modification with a combination of calcined kaolinite–montmorillonite clays can effectively mitigate alkali-silica reaction-induced deteriorations. By incorporating 30% clays, the volume expansion of the cement composites was decreased from deleterious to innocuous level. Amount of cracks was decreased with increasing clay incorporations. In the presence of combined calcined clays, the strength gain of the cement composites is more significant the strength loss caused by alkali-silica reaction indicating the effective mitigation of this virulent reaction in concrete. 

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3. Discovery and potential ramifications of reduced iron-bearing nanoparticles—magnetite, wüstite, and zero-valent iron—in wildland–urban interface fire ashes

   https://doi.org/10.1039/d2en00439a  

   Baalousha, Mohammed; Desmau, Morgane; Singerling, Sheryl A.; Webster, Jackson P.; Matiasek, Sandrine J.; Stern, Michelle A.; Alpers, Charles N. (November 2022, Environmental Science: Nano)

   The increase in fires at the wildland–urban interface has raised concerns about the potential environmental impact of ash remaining after burning. Here, we examined the concentrations and speciation of iron-bearing nanoparticles in wildland–urban interface ash. Total iron concentrations in ash varied between 4 and 66 mg g −1 . Synchrotron X-ray absorption near-edge structure (XANES) spectroscopy of bulk ash samples was used to quantify the relative abundance of major Fe phases, which were corroborated by transmission electron microscopy measurements. Maghemite (γ-(Fe 3+ ) 2 O 3 ) and magnetite (γ-Fe 2+ (Fe 3+ ) 2 O 4 ) were detected in most ashes and accounted for 0–90 and 0–81% of the spectral weight, respectively. Ferrihydrite (amorphous Fe( iii )–hydroxide, (Fe 3+ ) 5 HO 8 ·4H 2 O), goethite (α-Fe 3+ OOH), and hematite (α-Fe 3+ 2 O 3 ) were identified less frequently in ashes than maghemite and magnetite and accounted for 0–65, 0–54, and 0–50% of spectral weight, respectively. Other iron phases identified in ashes include wüstite (Fe 2+ O), zerovalent iron, FeS, FeCl 2 , FeCl 3 , FeSO 4 , Fe 2 (SO 4 ) 3 , and Fe(NO 3 ) 3 . Our findings demonstrate the impact of fires at the wildland–urban interface on iron speciation; that is, fires can convert iron oxides ( e.g. , maghemite, hematite, and goethite) to reduced iron phases such as magnetite, wüstite, and zerovalent iron. Magnetite concentrations ( e.g. , up to 25 mg g −1 ) decreased from black to gray to white ashes. Based on transmission electron microscopy (TEM) analyses, most of the magnetite nanoparticles were less than 500 nm in size, although larger particles were identified. Magnetite nanoparticles have been linked to neurodegenerative diseases as well as climate change. This study provides important information for understanding the potential environmental impacts of fires at the wildland–urban interface, which are currently poorly understood. 

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4. The role of defects in Fe(II)-goethite electron transfer

   Notini, L.; Latta, D.E.; Neumann, A.A.; Pearce, C.I.; Sassi, M.; N’Diaye, A.T.; Rosso, K.M.; Scherer, M.M. (February 2018, Environmental science & technology)

   Despite substantial experimental evidence for Fe(II)–Fe(III) oxide electron transfer, computational chemistry calculations suggest that oxidation of sorbed Fe(II) by goethite is kinetically inhibited on structurally perfect surfaces. We used a combination of 57Fe Mössbauer spectroscopy, synchrotron X-ray absorption and magnetic circular dichroism (XAS/XMCD) spectroscopies to investigate whether Fe(II)–goethite electron transfer is influenced by defects. Specifically, Fe L-edge and O K-edge XAS indicates that the outermost few Angstroms of goethite synthesized by low temperature Fe(III) hydrolysis is iron deficient relative to oxygen, suggesting the presence of defects from Fe vacancies. This nonstoichiometric goethite undergoes facile Fe(II)–Fe(III) oxide electron transfer, depositing additional goethite consistent with experimental precedent. Hydrothermal treatment of this goethite, however, appears to remove defects, decrease the amount of Fe(II) oxidation, and change the composition of the oxidation product. When hydrothermally treated goethite was ground, surface defect characteristics as well as the extent of electron transfer were largely restored. Our findings suggest that surface defects play a commanding role in Fe(II)–goethite redox interaction, as predicted by computational chemistry. Moreover, it suggests that, in the environment, the extent of this interaction will vary depending on diagenetic history, local redox conditions, as well as being subject to regeneration via seasonal fluctuations. 

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5. Mineralogical Associations of Sedimentary Arsenic within a Contaminated Aquifer Determined through Thermal Treatment and Spectroscopy

   https://doi.org/10.3390/min13070889  

   Varner, Thomas S.; Kulkarni, Harshad V.; Bhuiyan, Mesbah Uddin; Cardenas, M. Bayani; Knappett, Peter S.; Datta, Saugata (July 2023, Minerals)

   Sedimentary arsenic (As) in the shallow aquifers of Bangladesh is enriched in finer-grained deposits that are rich in organic matter (OM), clays, and iron (Fe)-oxides. In Bangladesh, sediment color is a useful indicator of pore water As concentrations. The pore waters of orange sediments are usually associated with lower As concentrations (<50 µg/L) owing to abundant Fe-oxides which sorb As. Using this color signal as a guide, spectroscopic measurements alongside thermal treatment were extensively utilized for analyzing the properties of both Fe-oxides and clay minerals. This study uses Fourier transform infrared (FTIR) and diffuse reflectance (DR) measurements along with thermal treatment to evaluate the solid-phase associations of As from sediment collected along the Meghna River in Bangladesh. The samples analyzed in this study were chosen to represent the various lithologies present at the study site and included riverbank sands (1 m depth), silt (6 m depth), aquifer sand (23 m depth), and a clay aquitard (37 m depth). The concentrations of sedimentary As and Fe were measured by X-ray fluorescence, and the spectroscopic measurements were taken on the samples prior to the thermal treatment. For the thermal treatment, sediment samples were placed in a preheated furnace at 600 °C for 3 h. The thermal treatment caused a deepening of reddish-brown hues in all samples, and the greatest change in color was observed in the finer-grained samples. The FTIR spectral analysis revealed that the clay minerals were composed primarily of illite, smectite, and kaolinite. The DR results indicate that the majority of Fe in sands was present as goethite; however, in the clay and silt samples, Fe was incorporated into the structure of clay minerals as Fe(II). The amount of structural Fe(II) was strongly positively correlated with the sedimentary As concentrations, which were highest in the finer-grained samples. After thermal treatment, the concentrations of As in the finer-grained samples decreased by an average of 40%, whereas the change in the As concentrations of the sand samples was negligible. These findings indicate that significant proportions of solid-phase As may be retained by OM and Fe(II)-bearing clay minerals. 

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