Iron Oxyhydroxides Research Articles

Seawater‐Fluid Composition Records From Molybdenum Isotopes of Sequentially Extracted Phases of Seep Carbonate Rocks

AbstractAuthigenic molybdenum (Moauth) in marine sediments holds great potential to archive the Mo isotopic composition of seawater and biogeochemical processes. However, the factors that control authigenic Mo isotope (δ98Moauth) distribution patterns remain poorly constrained. Here, we report Mo abundances and δ98Mo compositions for bulk‐rock (bulk) and sequentially extracted fractions—including total authigenic (auth; i.e., non‐lithogenic fraction), carbonate (carb), iron and manganese oxyhydroxides, pyrite (py), and organic fractions (OM)—of authigenic carbonates recovered from various hydrocarbon seep sites in the Gulf of Mexico and the South China Sea. Extracted pyrite fractions exhibit Mo contents varying from 0.1 to 23.4 μg/g and generally dominate the Mo budget of seep carbonate rocks. Our data indicate large ranges of δ98Mobulk and δ98Moauth values relative to NIST 3134 (0.25‰), varying from 1.02 to 1.98‰ (n = 4) and from 0.15 to 3.07‰ (n = 34), respectively. The difference in δ98Mo values between carbonate and pyrite fractions of seep carbonate rocks formed under sulfidic conditions increases with higher Moauth contents, suggesting a control of dissolved hydrogen sulfide concentrations on Mo isotope fractionation during carbonate precipitation. Compared with δ98Moauth and δ98Mopy, δ98Mocarb of seep carbonate rocks formed under sulfidic conditions shows a relatively narrow range with an average of 1.98 ± 0.31‰ (1 SD; n = 10), providing constraints on the δ98Mo composition of seawater in the course of Earth history. Overall, our findings show that the δ98Mo composition of sequentially extracted phases of carbonate‐rich sedimentary rocks can provide insights into seawater‐sediment interactions and biogeochemical pathways of Mo during early diagenesis.

Temporal Changes in Cd Sorption and Plant Bioavailability in Compost-Amended Soils

The application of Cd-contaminated phosphate fertiliser has enriched concentrations of this non-essential element in many agricultural soils. Consequently, concentrations of the metal in some agricultural products exceed the Maximum Limit in foods. Composts can reduce the transfer of Cd from soil to plants; however, it is unclear how long this beneficial effect endures. We aimed to determine temporal changes of phytoavailable Cd in two market garden soils (an Allophanic Orthic Granular Soil and a Recent Silt Loam). Soils were amended with either municipal green waste compost or sawdust and animal waste compost at a rate of 2.5% w/w under three incubation regimes: at 19 °C, at 30 °C, and at 30 °C with additional N added as urea at 0.6 g urea/kg soil added over 1 year. Each replicate was sampled after 1, 5, 9, 13, 21, 31, and 49 weeks, and phytoavailable Cd was estimated through 0.05 M Ca(NO3)2 extraction. Seed potato (Solanum tuberosum), ‘Nadine’ variety, was grown in the Pukekohe Allophanic Orthic Granular Soil, freshly amended with municipal compost and the same soil aged for one year. The concentration of Cd in all samples was analysed using an ICP-OES (Inductively Coupled Plasma-Optical Emission Spectrometer). The C concentration in the soil—compost mixtures decreased over the year, with the greatest decreases occurring in the soils incubated at 30 °C with added N. Unexpectedly, the concentration of Ca(NO3)2-extractable Cd in the compost-amended soils did not increase over time and in some cases even decreased. This was confirmed through a pot experiment, which showed the Cd concentration in potato was reduced by 50% in both the freshly amended soil and the amended soil aged for one year. Cadmium immobilisation in soils might be due to both the sorption of Cd by organic matter and the occlusion of sorbed Cd by oxy-hydroxides of iron and aluminium. Over 49 weeks, soluble Cd does not increase as organic matter oxidises. The application of municipal compost to soil will reduce both plant Cd solubility and plant Cd uptake for at least one year in the soils tested.

Efficient Hydrazine Electro‐Oxidation Achieved by Tailored Electron Injection into Fe (III) Sites Activating Dehydrogenation

AbstractTailoring the d‐orbital electron of Fe (III) in oxyhydroxide is highly expected to realize an efficient hydrazine oxidation reaction (HzOR) for assisting seawater electrolysis. Although interface engineering can effectively change electron states on Fe sites by charge injection or extraction, most interfaces have a directional electric field for inaccessible regulation. Herein, the combination of iron oxyhydroxide and biphasic nickel phosphide is established to obtain a dual built‐in electric field (BEF) with opposite direction, which aims to manipulate the d‐orbital electron configuration of Fe (III) sites, thereby optimizing the binding strength and activating of N2H4 intermediates. Both computational and experimental analyses reveal that the moderate Fe─*N2H4 binding strength originating from tailored electron injection plays the key role in accelerating dehydrogenation. Impressively, such a promising promotion endows the catalyst with a remarkable HzOR activity, realizing working potentials of −8 and 44 mV for 10 and 100 mA cm−2 in alkaline seawater, respectively, and achieving outstanding long‐term stability for over 100 h. H2 production from a hybrid seawater electrolyzer (HSE) requires a dramatically low power consumption of 16.4 Wh L−1 H2 with ≈100% Faraday efficiency. It is believed that the work sheds new inspiration on d‐orbital regulation for obtaining advanced HzOR electrocatalysts.

FeS2 Nanoparticles in S-Doped Carbon: Ageing Effects on Performance as a Supercapacitor Electrode

Although transition metal sulfides have prodigious potential for use as electrode materials because of their low electronegativities, their large volume changes inhibit broad application. Moreover, there is only limited knowledge of the ageing processes of these materials at the nanoscale. Herein, nano-C/FeS2 materials were prepared via one-pot syntheses from green biodegradable carbon precursors, followed by activation and sulfidation. The increased activation/sulfidation time led to an increase in the size of the nanoparticles (7 to 17 nm) and their aggregation, as well as in an increase in the specific surface area. The materials were then used as electrodes in 2-electrode symmetric supercapacitors with 2 M KOH. The activation process resulted in improved capacitance (60 F g−1 at 0.1 A g−1) and rate capability (36%) depending on the composite porosity, conductivity, and size of the FeS2 particles. The ageing of the FeS2 nanoparticles was investigated under air, and a progressive transformation of the nano-FeS2 into hydrated iron hydroxy sulfate with a significant morphological modification was observed, resulting in drastic decreases in the capacitance (70%) and retention. In contrast, the ageing of nano-FeS2 during cycling led to the formation of a supplementary iron oxyhydroxide phase, which contributed to the enhanced capacitance (57%) and long-term cycling (132% up to 10,000 cycles) of the device.

Formation of Iron Phosphide Nanobundles from an Iron Oxyhydroxide Precursor.

Iron phosphide (FeP) nanoparticles have excellent properties such as fast charge transfer kinetics, high electrical conductivity, and high stability, making them a promising catalyst for hydrogen evolution reaction (HER). A challenge to the wide use of iron phosphide nanomaterials for this application is the available synthesis protocols that limit control over the resulting crystalline phase of the product. In this study, we report a method for synthesizing FeP through a solution-based process. Here, we use iron oxyhydroxide (β-FeOOH) as a cost-effective, environmentally friendly, and air-stable source of iron, along with tri-n-octylphosphine (TOP) as the phosphorus source and solvent. FeP is formed in a nanobundle morphology in the solution phase reaction at a temperature of 320 °C. The materials were characterized by pXRD and transmission electron microscopy (TEM). The optimization parameters evaluated to produce the phosphorus-rich FeP phase included the reaction rate, time, amount of TOP, and reaction temperature. Mixtures of Fe2P and FeP phases were obtained at shorter reaction times and slow heating rates (4.5 °C /min), while longer reaction times and faster heating rates (18.8 °C/min) favored the formation of phosphorus-rich FeP. Overall, the reaction lever that consistently yielded FeP as the predominant crystalline phase was a fast heat rate.

Amorphous iron oxyhydroxides nano precursors used for Reactive Yellow 84 removal from aqueous solutions

In this research, we investigated the potential use of amorphous iron oxyhydroxides, ferrihydrite (FHY), for the removal of persistent pollutants from aqueous solutions. Ethylenediaminetetraacetic acid (EDTA) and ethylenediamine-N, N′-disuccinic acid (EDDS) were used as complexing agents during synthesis aiming to enhance the FHY properties. Synthesized materials were characterized by X-ray diffraction, SEM and TEM Microscopy, N2 sorption/desorption, and FT-IR Spectroscopy for their mineralogy, crystallinity, morphology and size, surface properties, and the organic content in their structure. The addition of chelating agents led to differences in nanoparticles morphology, amorphic degree, and surface properties. Reactive Yellow 84 dye was chosen as a representative refractory pollutant and laboratory-scale adsorption studies were conducted at varying dye concentrations. Ca. 100 % RY 84 dye removal efficiency was achieved within one hour at dye concentrations of 5–10 mg/L for an adsorbent dosage of 1 mg/L FHY. Adsorption kinetics and isothermal studies were considered, the uptake capacity was calculated for each nanomaterial and empiric mechanistic information was derived. The results showed that ferrihydrite exhibits the best performance, with a maximum uptake capacity of 40.73 mg Reactive Yellow 84 dye per gram adsorbent followed by FHY_EDTA and FHY_EDDS (up to 35.86 mg/g). Coupling the adsorption with photodegradation processes led to a significant increase in removal efficiencies of persistent RY 84 from polluted aqueous solution, in good timing, suggesting a feasible alternative at sites where dye concentration in effluents is elevated.

Yttrium speciation variability in bauxite residues of various origins, ages and storage conditions

Bauxite residues (BRs) are highly alkaline wastes generated during alumina production from bauxite ore. Billions of tons have been accumulating worldwide for more than 100 years, they are stored in various forms, and pose environmental and societal issues. At the same time, BRs are promising secondary sources for the production of critical metals including rare earth elements (REEs). However, knowledge on REE speciation is lacking, and is consequently an obstacle to the development of large-scale extraction process. This study analyses the influence of origin of the bauxite ore (lateritic or karstic), the storage conditions and storage time on the properties of ten BR samples, with a particular focus on the speciation of yttrium, which is used as a proxy to identify the behaviour of heavy REE. A multi-scale approach linked yttrium speciation and the origin of the bauxite ore whereas no major variation was observed as a function of storage conditions or ageing of the BRs. Yttrium is mainly found in the form of xenotime phosphate particles in BRs of lateritic origin, while in karstic BRs, the majority of yttrium is probably adsorbed or incorporated into other minerals including iron oxyhydroxide and hydroxyapatite minerals.

Geology, fluid inclusions and C−O−S−Pb isotopic compositions of the Chahmileh Pb-Zn deposit, Central Iran: Implications for ore genesis

AbstractThe Chahmileh Pb–Zn deposit, located northwest of the Central Iran Zone, is a sediment-hosted Pb–Zn deposit in the ‘Yazd-Anarak Metallogenic Belt’. It is hosted in Middle Triassic carbonate rocks and is mainly controlled by NW-trending faults. The main ore minerals are galena and sphalerite with minor chalcopyrite, pyrite, and quartz, dolomite, along with minor calcite and baryte as gangue minerals. Cerussite, hemimorphite, wulfenite, mimetite, smithsonite, malachite and iron oxy-hydroxides are the main non-sulphide ore minerals. The main styles of mineralization are vein-veinlet, breccia, disseminated and replacement in association with silicification and dolomitization. Microthermometry of fluid inclusions in dolomite and quartz indicates that the ore precipitated from a warm to hot basin-derived saline fluid. Dolomite samples have δ13CVPDB and δ18OVSMOW values of −0.99 to +1.99‰ and +20.74 to +25.48‰, respectively, and are plotted in the marine carbonate rocks field. These isotopic values suggest that CO2 in the hydrothermal fluids mainly originated from marine carbonate rock. The δ34S values range from +6.3 to +8.2‰ for galena, +5.9 to +6.2‰ for sphalerite, +1.4 to +3.4‰ for chalcopyrite and +15.0 to +17.4‰ for bayite are compatible with a predominant thermochemical sulphate reduction process, and with sulphur sourced from Triassic seawater. Galena samples have a homogeneous Pb isotopic composition that is indicative of a continental crustal reservoir as the main source of lead and probably for the other ore metals. Based on geology, mineralogy, texture and fluid characteristics, the Chahmileh deposit is classified as a carbonate-hosted Mississippi Valley-type deposit.

Identification of in situ Generated Iron‐Vacancy Induced Oxygen Evolution Reaction Kinetics on Cobalt Iron Oxyhydroxide†

Comprehensive SummaryDeveloping highly efficient and low‐cost electrocatalysts towards oxygen evolution reaction (OER) is essential for practical application in water electrolyzers and rechargeable metal‐air batteries. Although Fe‐based oxyhydroxides are regarded as state‐of‐the‐art non‐noble OER electrocatalysts, the origin of performance enhancement derived from Fe doping remains a hot topic of considerable discussion. Herein, we demonstrate that in situ generated Fe vacancies in the pristine CoFeOOH catalyst through a pre‐conversion process during alkaline OER result from dynamic Fe dissolution, identifying the origin of Fe‐vacancy‐induced enhanced OER kinetics. Density functional theory (DFT) calculations and experimental results including X‐ray absorption fine‐structure spectroscopy, in situ UV‐Vis spectroscopy, and in situ Raman spectroscopy reveal that the Fe vacancies could significantly promote the d‐band center and valence states of adjacent Co sites, alter the active site from Fe atom to Co atom, accelerate the formation of high‐valent active Co4+ species, and reduce the energy barrier of the potential‐determining step, thereby contribute to the significantly enhanced OER performance.

Synergistic effect between the iron (III) oxyhydroxide and Gd-Fe2O3 photoanode interface resulted in an ultra-low onset potential for photoelectrochemical water oxidation

The onset potential is an important descriptor of the photoelectrochemical water oxidation performance of photoanodes. Herein, we prepared Gd-doped hematite (Gd-Fe2O3)/iron (III) oxyhydroxide (FeOOH) core-shell photoanodes by in-situ isovalent doping and secondary hydrothermal treatment. This Gd-Fe2O3/FeOOH photoanode shows a record alkaline water oxidation onset potential (0.59 V vs. reversible hydrogen electrode) in hematite-based photoanodes and a 2.4-fold increase in photocurrent density over pristine hematite. Detailed studies demonstrate that the origin of the ultra-low onset potential is mainly attributed to the synergistic effect of isovalent Gd-doping and FeOOH cocatalyst. Specifically, Gd doping enhances donor density and reduces charge transport resistance, and FeOOH cocatalyst significantly improves water oxidation kinetics. In addition, the strong interfacial coupling of FeOOH and Gd-Fe2O3 promotes electron flow, which also improves the charge separation remarkably. This work gives hope for the achievement of stable and bias-free hematite-based photoanodes.

Labile Fe(III) phase mediates the electron transfer from Fe(II,III) (oxyhydr)oxides to carbon tetrachloride

Labile Fe(III) phase (includes Fe(III)aq, Fe(III)ads, or Fe(III)s species) is an important intermediate during the interaction between Fe(II) and Fe(III) (oxyhydr)oxides, but how does labile Fe(III) influence the electron transfer from Fe(II) to oxidant environmental pollutant during this Fe(II)-Fe(III) interaction is unclear. In this work, the dynamic change of Fe(II,III) (oxyhydr)oxides at the same time scale is simulated by synthesizing Fe(III)-Fe(II)-I (Fe(III)+NaOH+Fe(II)+NaOH) with different Fe(II)/Fe(III) ratios. CCl4 is used as a convenient probe to test the reduction kinetics of mixed valence Fe(II,III)(oxyhydr)oxides with different Fe(II):Fe(III) ratios. The Mössbauer spectra results reveal the Fe(III)labile in the solid phase is in octahedral coordination. The electron-donating capability of Fe(II) was improved with increasing Fe(III) content, but suppressed when [Fe(III)] ≥ 30 mM. The reductive dechlorination of CT by Fe(III)-Fe(II)-I decreased gradually with the increase of Fe(III) content, because more amount Fe(III)labile in solid phase is accumulated. This shows that the electron transfer from Fe(II) to Fe(III)labile rather than to CT is enhanced with increasing Fe(III) content. FTIR data shows that the hydroxylation of Fe(II) with Fe(OH)3 occurs preferentially in the non-hydrogen bonded hydroxyl group, causing the decrease of its reductive reactivity. The presence of [Fe(III)-O-Fe(II)]+ in Fe(III)-Fe(II)-I can stabilize the dichlorocarbene anion (:CCl2−), favouring the conversion of CT to CH4 (13.1%). The aging experiment shows that Fe(III)labile surface may maintain the reductive reactivity of Fe(II) during aging when [Fe(III)] = 5-20 mM. This study deepens our understanding of the mass transfer pathway of iron oxyhydroxides induced by Fe(II) and its impact on the reductive dechlorination of CT.

Ferrihydrite Nanoparticles Alleviate Rheumatoid Arthritis by Nanocatalytic Antioxidation and Oxygenation.

Oxidative stress and hypoxia are two key biochemical factors in the development of rheumatoid arthritis (RA). As both reactive oxygen species (ROS) and oxygen gas (O2) are oxygen-related chemicals, we suggest that a redox reaction converting ROS into O2 can mitigate oxidative stress and hypoxia concurrently, synergistically modulating the inflammatory microenvironment. In this work, ferrihydrite, a typical iron oxyhydroxide, is prepared in nanodimensions in which tetrahedrally coordinated Fe can form a composite catalytic center by coupling with an adjacent hydroxyl group, cooperatively facilitating H2O2 decomposition and O2 generation, presenting a high catalase-like activity. In the RA region, the nanomaterial catalyzes the conversion of excess H2O2 into O2, achieving both antioxidation and oxygenation favoring the alleviation of inflammation. Both cellular and in vivo experiments demonstrate the desirable efficacy of ferrihydrite nanoparticles for RA treatment. This work provides a methodology for the catalytic therapy of inflammatory diseases featuring both oxidative stress and hypoxia.

Design of iron oxyhydroxide nanosheets coated on Co species embedded in nanoporous carbon for oxygen evolution reaction

There is still a tremendous challenge in designing environmentally friendly oxygen evolution reaction (OER) catalysts that are inexpensive and high-performing for practical applications. Herein, the self-sacrificing template zeolitic imidazolate framework-67 (ZIF-67) was pyrolyzed under N2 atmosphere to generate Co species embedded in nanoporous carbon (Co-NC). Then, iron oxyhydroxide (FeOOH) was wrapped onto the Co-NC surface via electrodeposition to shape the Co-NC@FeOOH composites. Benefiting from the core–shell structure, high conductivity, and distributed active sites, Co-NC@FeOOH presents distinguished OER performance with a low overpotential (336 mV) at 10 mA cm−2 and small Tafel slope (49.46 mV dec-1). This work furnishes a rosy passage for receiving cost-effective electrocatalysts with high efficiency for OER.

Cooperative Fe-Sites in Nickel and Cobalt Oxyhydroxides

With incorporated iron, nickel and cobalt oxyhydroxides display the highest known oxygen evolution activities of any catalyst in alkaline media. To leverage this high activity in low temperature electrolysis systems, a comprehensive understanding of where Fe-based active sites form, their local chemical structure, and how this structure evolves under electrochemical conditioning is critical. Here we show that incorporation of Fe into NiOxHy and CoOxHy films during constant potential chronoamperometry yields NiFeOxHy and CoFeOxHy catalysts with extremely high TOFs of up to ~40 s-1 and 0.7 s-1, respectively, at 350 mV overpotential. Further, we discover that the TOF of these materials is linearly related to the amount of Fe incorporated with this method. We propose a mechanism involving cooperative catalysis involving multiple Fe sites to explain this linear dependence. Density functional theory calculations are used to show this cooperativity may arise from increased ability to delocalize oxidative charge in active sites comprised of neighboring FeOxHy monomers. We then show that cycling these films lowers the per-Fe TOF substantially, to a level similar to that of co-deposited NiFe and CoFe films. This loss of activity during cycling and similarity to co-deposited films in which Fe occupies intraplanar lattice sites is consistent with migration of high activity Fe clusters initially adsorbed at surface edges and defects during chronoamperometry to less active sites within the oxyhydroxide lattice via cycling-driven dynamic substrate behavior. Further evidence for this Fe relocation into bulk lattice sites is provided using the redox features of adsorbed Ni2+ and Co2+ as probes for monitoring the extent to which ions are incorporated into the bulk of NiOxHy and CoOxHy.

Critical raw materials associated with the lateritic bauxite and red mud in West Kalimantan, Indonesia

The Western Indonesia Bauxite Province in Kalimantan is a lateritic bauxite region with a complex history and poorly known sustainable metal contents within the bauxite residue. Bauxite residue produced using the Bayer process contains, notably, scandium. We present new geochemical, mineralogical and geological data from the lateritic bauxite and red mud from the active mine and deposit, which allow us to investigate the behaviour of critical elements during weathering. The geochemical analysis and translated isocon results have shown that the content of scandium in red mud is higher than the average concentration of crustal rocks and is concentrated in the ferrite layer and bauxite residue. A positive correlation between the existence of iron oxyhydroxide mineral in the residual iron-rich layer and red muds with the rare earth elements (REEs) and scandium concentrations may be interpreted as a scavenging effect of mobile REEs. The weathering and leaching processes in bauxite allows the adsorption of the trivalent scandium cation (Sc 3+ ) on goethite and are followed by ionic substitution with other trivalent cations in crystals of hematite. The study illustrates the importance of understanding processes during weathering and laterization for geochemical processes and REE exploration in tropical areas. Supplementary material: Material A, (A) Mineralogical profile of the bauxite, ferrite, and tonalite in Tayan and Mempawah, (B) Ternary diagram of bauxite and their parent rocks, (C) Trace element ratios in bauxite; Material B, Spearman's correlation rank of bauxite and associated rocks from Tayan mine ( n = 35); Material C, (A) XRD patterns of representative samples from the Tayan mine and Mempawah deposit, West Kalimantan, (B) Typical normal (left) and continuum (right) removed reflectance spectral curves of samples are available at https://doi.org/10.6084/m9.figshare.c.6689139 Thematic collection: This article is part of the Geochemical processes related to mined, milled, or natural metal deposits collection available at: https://www.lyellcollection.org/topic/collections/geochemical-processes-related-to-mined-milled-or-natural-metal-deposits

Ni-modified FeOOH integrated electrode by self-source corrosion of nickel foam for high-efficiency electrochemical water oxidation

The construction and application of efficient iron oxyhydroxide (FeOOH) is still a challenge in the field of energy conversion. Here, a facile preparation method is developed by directly utilizing commercialized nickel foams (NF) as the nickel source and the supporting framework, as well as the ingenious use of etching effect originating from acidic medium in the process of iron salt hydrolysis. As a result, a Ni-modulated FeOOH integrated electrode (Ni-FeOOH/NF) is obtained. Unexpectedly, the implementation of our scheme effectively activates the catalytic intrinsic activity of FeOOH, successfully transforming the inert NF into an integrated electrode with high oxygen evolution reaction (OER) performance. Specifically, the Ni-FeOOH/NF exhibits the overpotential of 277 mV (@100 mA cm−2) and superior stability for OER. Additionally, the as-prepared Ni-FeOOH/NF electrode could also operate steadily for OER in alkaline adjusted saline water. Our research provides a new idea for the preparation of satisfactory Fe-based metal materials as OER electrocatalysts.

Asbestos and Iron.

Theories of disease pathogenesis following asbestos exposure have focused on the participation of iron. After exposure, an open network of negatively charged functional groups on the fiber surface complexes host metals with a preference for iron. Competition for iron between the host and the asbestos results in a functional metal deficiency. The homeostasis of iron in the host is modified by the cell response, including increased import to correct the loss of the metal to the fiber surface. The biological effects of asbestos develop in response to and are associated with the disruption of iron homeostasis. Cell iron deficiency in the host following fiber exposure activates kinases and transcription factors, which are associated with the release of mediators coordinating both inflammatory and fibrotic responses. Relative to serpentine chrysotile, the clearance of amphiboles is incomplete, resulting in translocation to the mesothelial surface of the pleura. Since the biological effect of asbestos is dependent on retention of the fiber, the sequestration of iron by the surface, and functional iron deficiency in the cell, the greater clearance (i.e., decreased persistence) of chrysotile results in its diminished impact. An inability to clear asbestos from the lower respiratory tract initiates a host process of iron biomineralization (i.e., asbestos body formation). Host cells attempt to mobilize the metal sequestered by the fiber surface by producing superoxide at the phagosome membrane. The subsequent ferrous cation is oxidized and undergoes hydrolysis, creating poorly crystalline iron oxyhydroxide (i.e., ferrihydrite) included in the coat of the asbestos body.

Historical contamination with a current problem: Can mining tailings enhance coastal arsenic pollution?

The coast of Espírito Santo state (Southeast Brazil) is recognized for its environmental arsenic (As) enrichment and, over the years, mining operations have potentialized it. We aimed to evaluate the effect of Rio Doce discharge on As inputs and the role of iron ore tailings from the Fundão dam disaster in enhancing As contamination in the marine sediment. Two scenarios were evaluated: Predisaster and Postdisaster; dry and wet conditions were considered in each period. High As concentrations were found in the Predisaster (28.44 ± 13.53 µg g-1 ), but a significant increase in As was remarkable during the Postdisaster in the wet season, one year after the disaster (maximum of 58.39 µg g-1 ; geoaccumulation index (Igeo ) Class 3, moderately severe pollution). On that occasion, iron (Fe) oxy-hydroxides from tailings were remobilized from the Rio Doce channel and deposited on the continental shelf bottom. Therefore, chemical interactions among Fe, As, and carbonates were enhanced, resulting in As and Fe coprecipitation and the trapping by carbonate adsorption. Rio Doce discharge seems to be the main factor in As inputs to the inner continental shelf when flooding do not occur previously in samplings, which allows further dispersion of contaminants, although this hypothesis should be tested further. Integr Environ Assess Manag 2024;20:159-168. © 2023 SETAC.

Antimony(V) removal from water within ferrihydrite transformation: Influence of humic acid

Antimony (Sb), a widely distributed heavy metal pollutant, poses a formidable threat to human health and the delicate ecological environment. Anthropogenic activities such as mining, industrial processes and the widespread use of Sb-containing products aggravate the toxicity and potential risks of Sb to the environment. The mobility and fate of Sb(V) in the water environment is affected by ferrihydrite (Fhy) transformation and humic acid (HA). However, the key role of HA on Sb(V) removal in the transformation of iron minerals remains unclear. In this study, the transformation of Fhy into goethite was significantly inhibited as a result of HA structural coating, while active functional groups of HA enhanced the combination with iron minerals and Sb(V) under acidic conditions. Residual Sb(V) concentration in water was less than 5 µg/L, which meets the United States Environmental Protection Agency (USEPA) recommended Sb concentration of 6 µg/L. Under alkaline conditions, the dissociation of HA provided more negative charges for the surface of transformed hematite and magnetite. Due to the stronger electrostatic repulsion and steric effects of HA, further removal of Sb(V) was limited. This work provided multiple secondary mineralization pathways of Fhy under the impact of HA and mechanistic insights into the removal process of Sb(V), which could contribute meaningful information regarding the interaction between Sb(V) and iron oxyhydroxides.

Data-centric approach for predicting critical metals distribution: Heavy rare earth elements in cretaceous Mediterranean-type karst bauxite deposits, southern Italy

In the last few years, many efforts have been devoted to the factors controlling the distribution of CMs in karst bauxites, residual deposits hosted in carbonate rocks. Most of these efforts regard Mediterranean-type karst bauxite deposits of Cretaceous age occurring in southern Italy. Further, there is an increasing interest in assessing the usefulness of machine learning applications devoted to geochemically based datasets. With this in mind, we explored a data-centric machine learning arrangement aiming to find the proper input, limited to Al2O3, Fe2O3, TiO2, and SiO2, the most abundant major oxides occurring in these ores, for predicting the HREE distribution in southern Italy karst bauxite deposits.Among the machine learning techniques used, Artificial Neural Network (ANN), Support Vector Machine (SVR), Random Forest (RF) and Extreme Gradient Boosting (XGBoost) are those that effectively predict HREE concentrations. A predictive model based on just Al2O3, Fe2O3, and SiO2, is one conducing at the worst performance impact suggesting that TiO2 is a relevant input variable in order to predict HREE concentrations in considered karst bauxite deposits. The XGBoost model was found to deliver the highest accuracy in predicting HREE for the validation data records (R2 ~ 0.830, RMSE~7.299, MAE ~ 5.091).Moreover, Fe2O3 is the highest correlated input variable with the output variable and is a significant predictor in our model suggesting iron oxyhydroxides play a relevant role in distributing HREE, likely through a scavenging mechanism at the expense of soil solutions.A further step of our research will involve comprehensive cross-validation studies across multiple areas where Mediterranean-type karst bauxite deposits occur, thus providing a thorough assessment of the model's performance. By addressing these tasks and exploring avenues for improvement, the data-centric approach can advance its potential as a cheap and fast technique to perform a preliminary economic evaluation of potentially HREE abundance, as well as other CMs, in karst bauxite ores benefiting applications reliant on these critical resources.