Anisotropic goethite nanoparticles play a critical role in the environmental behavior of nutrient and contaminant due to their abundance, high surface area, and strong binding affinity; however, their transformation into smaller, more mobile nanocolloids under natural setting remains underexplored. Here, we show that natural wet-dry cycles at alkaline pH in the presence of As(V) or P(V) induce extensive goethite nanorod (GtNR) fragmentation into nanospheres (GtNS) and the formation of ferrihydrite single-digit nanospheres (FhSDNS), driven by drying-induced surface reactions, oxyanion-mediated dissolution, reprecipitation, passivation, capillary stress, and defect sites. Under identical conditions, nanospheres of hematite, maghemite, and magnetite exhibit minimal transformation, underscoring the unique susceptibility of GtNR. Passivation by As(V) or P(V) enhances nanocolloid mobility, potentially facilitating long-distance transport of sorbed nutrients and pollutants. This mechanism helps explain persistently low phosphorus availability-even under intensive fertilization-as well as the heightened mobility of As(V) and P(V), posing increased risks to water systems. Furthermore, current analytical methods for phosphorus detection could not address single-digit nanocolloids, complicating efforts to track their mobilization. Collectively, these findings highlight how common agricultural practices, including repeated irrigation and surface fertilization, may inadvertently foster goethite-based nanocolloid formation. Recognizing these mechanisms is crucial for mitigating adverse environmental impacts and improving nutrient-use efficiency.

Spinel-structured hausmannite (Mn(II)Mn(III)2O4) is a vital intermediate in Mn mineralogy and a key player in redox chemistry in the environment. Its transformation into other Mn oxides is a critical factor in controlling its environmental occurrence and reactivity. Yet structural impurities and solution pH, as well as the fate of impurities during transformation, which influence hausmannite transformation processes and products, remain largely unknown. In the present work, we address this knowledge gap by investigating pristine and metal-substituted hausmannite, specifically nickel (Ni) or cobalt (Co), equilibrated at two time periods (8 h and 30 days) and three different pH levels (4, 5, and 7). Solution chemistry data revealed that both the equilibration period and pH had a significant impact on hausmannite dissolution rates and the concomitant repartitioning of Ni or Co. Hausmannite with Ni or Co substitution exhibited lower dissolution rates than pristine mineral under acidic conditions. Mineralogy and crystal chemistry data indicated that hausmannite was the major host phase after 30-day equilibration, followed by minor transformed products, including birnessite and manganite. Although minor, birnessite became more abundant than manganite at low pHs. Analytical high-resolution transmission electron microscopy (HRTEM) analyses revealed a poorly crystalline, nano-scaled MnO2 formed from hausmannite and the majority of metal impurities remaining in the host hausmannite. Yet Co was associated with both hausmannite and the newly formed birnessite, whereas Ni was only found with hausmannite, indicating the strong sequestration of Co by Mn(II/III) and Mn(IV) mineral phases. This study highlights the significant impacts of metal impurities and pH on the stability of hausmannite and its transformation into birnessite, as well as the control of Mn-oxide minerals on the solubility and sequestration of transition metals in the environment.

The solubility and transport of Cr(VI) is primarily controlled by adsorption-desorption reactions at the surfaces of soil minerals such as iron oxides. Environmental properties such as pH, ionic strength, and ion competition are expected to affect the mobility and fate of Cr(VI). Sea level rise (SLR), and consequent seawater intrusion, is creating a new biogeochemical soil environment at coastal margins, potentially impacting Cr(VI) retention at contaminated sites. We employed in-situ ATR-FTIR spectroscopy and DFT calculations to investigate at the molecular level the adsorption of Cr(VI) on the hematite surface and its desorption by sulfate, as a function of pH and ionic strength. We further used a batch experiment to assess Cr(VI) desorption at varying artificial seawater (ASW) concentrations. IR results demonstrate the complexity of Cr(VI) adsorption, showing a combination of monodentate inner-sphere complexation at high pH and dichromate outer-sphere (∼75%) at low pH. The Cr(VI)-complexes exhibited desorption induced by increasing pH values (58% of desorption) and sulfate competition (∼40% desorption). ASW desorbed ∼20% more Cr(VI), even at just 1% concentration. Our findings provide insight into Cr(VI)-adsorption complexation that controls the retention and remobilization of Cr(VI) on Fe-oxide minerals. The results point to an elevated risk of Cr(VI) mobilization in contaminated soils affected by SLR.

Agriculture in highly weathered tropical soils often requires considerable application of lime and fertilizers to ensure satisfactory plant nutrient levels. The consequences of these continue long-term applications is not well understood may induce changes in soil chemical properties, the abundance, and speciation of potentially toxic trace element and as well as of micronutrients in agriculture soils. In this study, we evaluated the adsorption (at pH 5) and speciation of Zn in tropical soils (both agricultural and native vegetation) as a function of fertilization and contact time using chemical fractionation analyses and X-ray absorption spectroscopy. The soils overall had high Zn adsorption capacities (similar to 700 mg kg (-1)), but the agricultural soil was approximately 30 % higher than of the soil under native vegetation, and the proportion of Zn in the mobile fraction was 35 % in native vegetation and 21 % in agricultural soils. Zn speciation via linear combination analysis showed a strong relationship with soil mineralogical composition and reveled that Zn associated with organic matter decreased while Zn associated with P increased after the conversion of soils from native vegetation to highly fertilized soil. Aluminosilicate soil minerals were identified as major sinks of soil Zn, accounting for 34 % of total Zn retention regardless of soil origin and land use. Association of Zn with phosphate (i.e., hopeite) was observed in the agricultural soil

While soil salinization is a major threat to the food security and sustainability of humanity, information on salinization in developing countries is limited. In this study, Landsat data were used to predict the salinization process from 1986 to 2021 in the Kur-Araz lowland of Azerbaijan, and water movement and salinity transport models were developed to calculate the effects of climate change and water management. The model results showed that increases in rainfall and drainage have led to dramatic improvements in soil salinity and agricultural productivity and that these changes were caused by the synergistic effect of climate change and water management. The future predictions indicate that rainfall will decrease due to the decrease in evaporation in the neighboring Caspian Sea, leading to further re-salinization. Soil re-salinization would be a severe threat to the sustainability of the agricultural industry and food security of Azerbaijan and neighboring countries. More scientific attention and efforts should be devoted to developing countries in preparation for the impact of climate change.

Green rusts (GR) are important drivers for trace metal and nutrient cycling in suboxic environments. We investigated whether green rusts would incorporate aluminum (Al) or other elements from naturally-formed clay minerals containing easily-weatherable clay minerals (e.g. mica, interlayered clays). We isolated the clay min-erals from a Matapeake silt loam soil by removal of silt and sand, organic matter, and reducible oxides to study mechanisms of interaction between Fe(II) and soil-sourced clay minerals. We conducted batch Fe(II) sorption experiments at multiple near-neutral pHs (6.5-7.5) and reaction times (2 h-365 days). Mineral transformations were characterized by selective extractions, X-ray diffraction (XRD), and Fe X-ray absorption spectroscopy (XAS) analyzed by shell-fitting and linear combination fitting (LCF) with natural and synthetic standards.Clay mineral fraction contained a mixture of quartz, kaolinite, interlayered vermiculite, mica, and chlorite with significant structural Fe (2.6% wt). Uptake of Fe(II) increased with pH and kinetics were rapid until 5 days, followed by slow continuous Fe(II) uptake. Citrate-bicarbonate desorption kinetics from Fe(II) sorbed clay released more Al and silicon (Si) compared with unreacted soil clay fraction whereas magnesium (Mg) and potassium (K) were unaffected. Citrate-bicarbonate extracted Fe contained more Fe(II) than an ideal GR with an Fe(II)/Fe(III) molar ratio of 5.50. Analysis of the Fe EXAFS by both LCF and shell fitting was best modeled as a combination of Fe(III)-clay reduction to Fe(II) and precipitation of GR and Fe(II)-Al LDH. After 7 days of Fe(II) sorption, LCF identified 55.2% total Fe in clay, 33.4% GR(Cl) and 11.4% Fe(II)-Al LDH. These results provide novel evidence of Fe(II)-Al LDHs precipitating on naturally-formed soil clay minerals as a minor phase to GR. The geochemical implications are that GRs formed in soils and sediments should be considered to have Al and Si as well as Mg substitutions affecting their structure and reactivity.

Sea level rise (SLR) is estimated to impact 25% of the world's population along coastal areas leading to an increase in saltwater intrusion. Consequently, changes in the soil biogeochemistry of currently non-saline and/or well-drained soils due to saltwater intrusion are of major concern. Saltwater intrusion is expected to affect farmland across large broiler producer regions, where large amounts of manure containing organic arsenicals were applied over the past decades. To determine how SLR may impact the speciation and mobility of adsorbed inorganic and organic As, we used in situ real-time attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) to determine the adsorption and desorption mechanisms of As(V) and 4-aminophenylarsonic (p-ASA, a poultry feed additive) on ferrihydrite (Fh) in the presence of sulfate at varying pH. The adsorption of As(V) and p-ASA increased at lower pH, with As(V) showing IR features consistent with the formation of inner-sphere of As-Fh surface complexes, while p-ASA also formed others structures as H-bonded As-surface complexes, likely mediated by outer-sphere complexes, based on our FTIR and batch experiments data. No observable As(V) or p-ASA desorption from the Fh surface was promoted by sulfate, however sulfate adsorption on the Fh surface was remarkably larger for p-ASA than for As(V). Complimentary, we carried out batch studies of As(V) and p-ASA desorption by Fh, using artificial seawater (ASW) at varying concentrations. The 1% ASW desorbed ∼10% of initially sorbed p-ASA, while at 100% ASW desorbed ∼40%. However, <1% of As(V) was desorbed by 1% ASW solution and only ∼7.9% were desorbed at 100% ASW. The spectroscopic data support the more extensive desorption of p-ASA compared to As(V) observed in batch experiments, suggesting that organoarsenicals may be easily desorbed and, after conversion to inorganic forms, pose a risk to water supplies.

The sorption of aqueous Mn(II) (1 mM) and Co(II) (50 and 200 mu M) onto hexagonal birnessite (0.1 g L-1) was studied under anoxic conditions at pH 6.5 and 7.5 in binary and ternary experiments using batch kinetic ex-periments and XRD, ATR-FTIR, and Co K-edge EXAFS analyses. In the binary systems, sorption of Co(II) was accompanied by partial oxidation to Co(III) yielding a mixture of corner-sharing Co(II) and edge-sharing Co(III) complexes at both pH values, while Mn(II)-birnessite interaction resulted in coordination of Mn(II/III) at layer vacancy sites at pH 6.5, and led to reductive transformation of birnessite into feitknechtite at pH 7.5. In the ternary systems, strong mutual interferences between Co(II) and Mn(II) co-sorbates reduced the rate and extent of sorption relative to the binary experiments. The introduction of Mn(II)aq into the high-Co systems (200 mu M) halted the slow sorption of Co(II) that was attributed to the incorporation of Co(III) into layer vacancies, while Co (II)aq prevented Mn(II)-driven transformation of birnessite into feitknechtite at pH 7.5. In the low-Co system (50 mu M), reductive transformation of birnessite by Mn(II)aq at pH 7.5 produced Co(II)-substituted feitknechtite, a conversion that was accompanied by reduction of sorbed Co(III) to Co(II) which was partially released to so-lution. The strong effects of co-sorption are attributed to the similarity in sorption mechanisms of Co(II) and Mn (II), which both sorb as a mixture of di-and trivalent species. The results of this work demonstrate that aqueous Mn(II) may significantly affect the reactivity of phyllomanganate sorbents towards dissolved Co(II), and there-fore impact the speciation and solubility of this trace metal in anoxic and suboxic geochemical environments.

Abstract Studies suggest that feitknechtite (β-MnOOH) is a prevalent, and perhaps necessary, intermediate phase during the synthesis of birnessite-like phases, the abiotic oxidation of Mn2+, and the transformation of biogenic hexagonal phyllomanganates to more complex Mn oxides in laboratory and natural systems. Researchers have generally described feitknechtite as consisting of pyrochroite-like (or cadmium iodide-like) Mn-O octahedral layers, but a detailed crystal structure has not been reported. We used TEM/SAED and powder XRD and Rietveld refinements to derive the unit cell and, for the first time, report a complete structure description for feitknechtite (β-MnOOH). Rietveld refinements were also completed for three natural feitknechtite/hausmannite samples, and time-resolved synchrotron XRD experiments were used to follow the thermal transformation of feitknechtite to hausmannite. Additionally, we identified and report the structure for a second, and perhaps novel, MnOOH polymorph (proposed designation ε-MnOOH), mixed with the synthetic feitknechtite, that is similar to β-MnOOH but with a different layer stacking.

Batch kinetic experiments are combined with X-ray absorption spectroscopy (XAS) to compare the sorption of Mn(II), Co(II), Ni(II), Zn(II), and Cd(II) with sulfated green rust (GR) in anoxic pre-equilibrated suspensions at pH 8 over a timespan of 1 h to 1 week. The XAS data suggest that all five divalent metals coordinate at Fe(II) sites of the GR sorbent, whereas the batch results show that GR exhibits bimodal sorption behavior, with fast but limited uptake of Mn(II) and Cd(II) and much more extensive sorption of Co(II), Ni(II), and Zn(II) that continues throughout the entire experimental timeframe. We attribute these observations to differences in the affinity and extent of divalent metal substitution in Fe(II) sites of the GR lattice as controlled by ionic size. Divalent metals smaller than Fe(II) [i.e., Co(II), Ni(II), and Zn(II)] are readily accommodated and undergo coprecipitation during GR dissolution-reprecipitation. In contrast, divalent metals larger than Fe(II) [i.e., Mn(II) and Cd(II)] have a low affinity for substitution and remain coordinated at the surface following limited exchange with Fe(II)(s) at GR particle edges. These results imply that GR may strongly affect the solubility of Co(II), Ni(II), and Zn(II) in reducing geochemical systems but will have little impact on the retention of Cd(II) and Mn(II).

We have investigated the structure and activity of electrocatalysts for the oxygen evolution reaction (OER) that had low loadings of Ir incorporated into the 2D layered MnO2, (birnessite, nominally delta-MnO2) and the 3D MnO2 (pyrolusite, beta-MnO2). The Ir-incorporated beta-MnO2 (Ir/beta-MnO2) electrocatalysts were prepared for the first time via a thermally induced phase transition of delta-MnO2 containing 16-22 wt% Ir. This phase transition of delta-MnO2 to beta-MnO2 was facilitated by the presence of Ir in the structure, as both Ir in IrO2 and Mn in beta-MnO2 could adopt a thermodynamically favored rutile structure. Extended X-ray absorption fine structure (EXAFS) of Ir/beta-MnO2 showed that the catalyst consisted of Ir substituted into the crystalline beta-MnO2 lattice. 22 wt% Ir/beta-MnO2 (60 mu g(Ir)cm(geo)(-2) exhibited an OER overpotential ( eta ) of 337 mV, lower than the eta for commercial IrO2. This eta was constant for 6 h, at 10 mA cm(geo)(-2) in 0.5 M H2SO4. EXAFS, high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and X-ray absorption near edge structure (XANES) showed that 22 wt% Ir/beta-MnO2 had a strained structure containing similar to 41 % Mn3+, an OER active species, along with a modified Ir bond covalency consisting of both Ir-O-Ir and Ir-O-Mn.

The mineralogy and oxidation state of aerosol iron (Fe) play important roles in controlling aerosol Fe solubility and consequent bioavailability in seawater. In this study, the spatial variability of Fe mineralogy and oxidation states in aerosols collected during the US GEOTRACES Western Arctic cruise (GN01) were determined using synchrotron-based X-ray absorption near edge structure (XANES) spectroscopy. Both Fe(II) minerals (biotite, ilmenite) and Fe(III) minerals (ferrihydrite, hematite, Fe(III) phosphate) were found in these samples. However, aerosol Fe mineralogy and solubility observed during this cruise varied spatially and can be grouped into three clusters based on the air masses that affected aerosols collected in different regions: (1) biotite-enriched particles (87 % biotite, 13 % hematite) with the air masses passing over Alaska, showing relatively low Fe solubility (4.0 ± 1.7 %); (2) ferrihydrite-enriched particles (82 % ferrihydrite, 18 % ilmenite) collected in the remote Arctic air, showing relatively high Fe solubility (9.6 ± 3.3 %); (3) the fresh dust derived from North America and Siberia, primarily dominated by hematite (41 % hematite, 25 % Fe(III) phosphate, 20 % biotite, 13 % ferrihydrite), showing relatively low Fe solubility (5.1 ± 3.5). A significant positive correlation was found between Fe oxidation state and Fe fractional solubility, suggesting that long-range transport could modify iron (hydr) oxide such as ferrihydrite through atmospheric processing, influencing aerosol Fe solubility and consequently Fe bioavailability in the remote Arctic Ocean.

Stormwater runoff is a significant source of heavy metals, including cadmium (Cd), chromium (Cr), and nickel (Ni), which pose ecological and human health problems. Various filter media have been evaluated for heavy metal removal from stormwater via adsorption, most involving chemical-or energy-intensive processes. Aluminum-based drinking water treatment residuals (WTR), a non-hazardous byproduct of drinking water treatment, are an inexpensive sorbent for heavy metals. However, the low permeability of WTR is a problem and requires mixing with sand and carbon materials to improve flow; but such amendments also reduce its sorption capacity. To overcome this problem, a granulated WTR sorbent was generated using a green technique involving organic materials and a low-energy process. Batch studies showed that WTR granules remove Cd, Cr, and Ni simultaneously. Metal removal was adequately described by pseudo-second -order kinetic models and Langmuir and Freundlich isotherm models. The overall removal performance was Cr > Cd > Ni. The presence of divalent cations in solution negatively affected metal removal; anions had a strong effect on Cd removal. A triple-layer surface complexation model adequately described metal removal. Results demonstrated the strong potential of the WTR granules to emerge as green filter media for the removal of heavy metals from stormwater runoff.(c) 2022 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

In this study, we investigated Ni2+, Zn2+, and Co2+ mineralogical incorporation and its effect on green rust transformation to magnetite. Mineral transformation experiments were conducted by heating green rust suspensions at 85 °C in the presence of Ni2+, Zn2+, or Co2+ under strict anoxic conditions. Transmission electron microscopy and powder X-ray diffraction showed the conversion of hexagonal green rust platelets to fine grained cubic magnetite crystals. The addition of Ni2+, Zn2+, and Co2+ resulted in faster rates of mineral transformation. The conversion of green rust to magnetite was concurrent to significant increases in metal uptake, demonstrating a strong affinity for metal sorption/co-precipitation by magnetite. Dissolution ratio curves showed that Ni2+, Zn2+, and Co2+ cations were incorporated into the mineral structure during magnetite crystal growth. The results indicate that the transformation of green rust to magnetite is accelerated by metal impurities, and that magnetite is a highly effective scavenger of trace metals during mineral transformation. The implications for using diagenetic magnetite from green rust precursors as paleo-proxies of Precambrian ocean chemistry are discussed.

The iron (Fe) speciation and oxidation state have been considered critical factors affecting Fe solubility in the atmosphere and bioavailability in the surface ocean. In this study, elemental composition and Fe speciation in aerosol samples collected at the Palmer Station in the West Antarctic Peninsula were determined using synchrotron-based X-ray fluorescence (XRF) and X-ray Absorption Near-Edge Structure (XANES) spectroscopy. The elemental composition of coarse-mode (>1 μm) Fe-containing particles suggests that the region's crustal emission is the primary source of aerosol Fe. The Fe minerals in these aerosol particles were predominantly hematite and biotite, but minor fractions of pyrite and ilmenite were observed as well. The Fe oxidation state showed an evident seasonal variation. The Fe(II) content accounted for 71% of the total Fe in the austral summer, while this fraction dropped to 60% in the austral winter. Multivariate linear models involving meteorological parameters suggested that the wind speed, relative humidity, and solar irradiance were the factors that significantly controlled the percentage of Fe(II) in the austral summer. On the contrary, no relationship was found between these factors and the Fe(II) percentage in the austral winter, suggesting that atmospheric photoreduction and regional dust emission were limited. Moreover, the snow depth was significantly (p < 0.05) correlated with the aerosol Fe concentration, confirming the limiting effect of snow/ice cover on the regional dust emission. Given that the Antarctic Peninsula has experienced rapid warming during recent decades, the ice-free areas in the Antarctic Peninsula may act as potential dust sources.

Sorption processes at the mineral–water interface are fundamental to the chemical functioning of soils, and impact the biogeochemical cycling of both trace and major elements in soil and sediment environments [...]

Hausmannite and manganite, the most abundant Mn(II/III) oxides in the environment, commonly contain cobalt (Co) as a structural impurity, yet the effects of Co substitution on the structure, stability, and reactivity of Mn(II/III) oxides have not been experimentally assessed. Using pristine and Co-substituted minerals with varying Co loadings (1 and 2 wt%), the present study observed changes in the structural properties, as well as stability and reactivity of these minerals toward acidic and reductive dissolution with arsenite (As(III)). Cobalt substitution in hausmannite produced significant changes in the lattice parameters and surface areas of the mineral, while manganite presented little to no Co substitution effects. In both minerals, Mn and Co release was accelerated in reductive dissolution, although more than 85% of the Co remained in the mineral structure. Only hausmannite showed increased oxidation of As(III) to As(V) with increased Co substitution, where the stoichiometric [Mn(II)]aq to [As(V)]aq ratio was at/close to 2. X-ray absorption spectroscopy analysis indicated the co-presence of Co(II) and Co(III) at tetrahedral and octahedral sites, respectively, with structural Co(II) dominating in hausmannite. The sole occupancy of Co(II) at octahedral sites in manganite appeared to induce changes in the average Mn oxidation state. Multiple surface complexes of arsenate were observed on the mineral surfaces, with the bidentate binuclear mode being the major species. Thus, Co substitution altered the stability and reactivity of the Mn(II/III) oxides under dissolution conditions, although the extent varied by the Co coordination chemistry, valence, and quantity in the mineral structures.