Iron Oxide Minerals Research Articles

Crystalline iron oxide mineral (magnetite) accelerates methane production from petroleum hydrocarbon biodegradation

Methane (CH4) emissions are a factor in climate change; in addition, CH4 production may affect reclamation of fluid fine tailings (FFT) in tailings ponds, and end-pit lakes (EPLs). In laboratory cultures, we investigated the effect of crystalline iron mineral (magnetite) on CH4 production from the biodegradation of hydrocarbons added to FFT collected from methanogenically more and less active sites in a demonstration EPL. Magnetite enhanced CH4 production from both sites, having a greater effect in more active FFT, where it increased the CH4 production rate as much as 48% (from 6.67 μmol d−1 to 9.87 μmol d−1) compared to FFT without magnetite. Correspondingly, magnetite hastened biodegradation of hydrocarbons (monoaromatics, n-alkanes and iso-alkanes), with a pronounced effect on o-xylene, ethylbenzene, m/p-xylenes, n-octane, n-nonane, and 2-methyloctane, where biodegradation rates increased by 46, 117, 11, 45, 28 and 37%, respectively, compared to FFT without magnetite. Little FeII was produced, suggesting that magnetite is not being used as an electron acceptor but rather functions as a conduit for electron transfer. Thus, magnetite may be a suitable amendment to enhance bioremediation of anaerobic environments contaminated with hydrocarbons. Importantly, our observations imply that magnetite may increase CH4 emissions from terrestrial ecosystems, thus affecting carbon budget estimations.

Biochar and Straw Amendments over a Decade Divergently Alter Soil Organic Carbon Accumulation Pathways

Exogenous organic carbon (C) inputs and their subsequent microbial and mineral transformation affect the accumulation process of soil organic C (SOC) pool. Nevertheless, knowledge gaps exist on how different long-term forms of crop straw incorporation (direct straw return or pyrolyzed to biochar) modifies SOC composition and stabilization. This study investigated, in a 13-year long-term field experiment, the functional fractions and composition of SOC and the protection of organic C by iron (Fe) oxide minerals in soils amended with straw or biochar. Under the equal C input, SOC accumulation was enhanced with both direct straw return (by 43%) and biochar incorporation (by 85%) compared to non-amended conventional fertilization, but by different pathways. Biochar had greater efficiency in increasing SOC through stable exogenous C inputs and inhibition of soil respiration. Moreover, biochar-amended soils contained 5.0-fold greater SOCs in particulate organic matter (POM) and 1.2-fold more in mineral-associated organic matter (MAOM) relative to conventionally fertilized soils. Comparatively, although the magnitude of the effect was smaller, straw-derived OC was preserved preferentially the most in the MAOM. Straw incorporation increased the soil nutrient content and stimulated the microbial activity, resulting in greater increases in microbial necromass C accumulation in POM and MAOM (by 117% and 43%, respectively) compared to biochar (by 72% and 18%). Moreover, straw incorporation promoted poorly crystalline (Feo) and organically complexed (Fep) Fe oxides accumulation, and both were significantly and positively correlated with MAOM and SOC. The results address the decadal-scale effects of biochar and straw application on the formation of the stable organic C pool in soil, and understanding the causal mechanisms can allow field practices to maximize SOC content. These results are of great implications for better predicting and accurately controlling the response of SOC pools in agroecosystems to future changes and disturbances and for maintaining regional C balance.

Comparison between Co(II) and Ni(II) cycling at goethite-water interfaces: Interplay with Fe(II)-catalyzed recrystallization

Cobalt (Co) and nickel (Ni) are critical metals for modern renewable energy technologies as well as essential micronutrients for terrestrial plant health and marine primary production. Both metals are commonly surface-adsorbed onto and/or structurally-incorporated into iron (oxyhydr)oxide minerals, such as goethite (α-FeOOH), that are ubiquitously present in soils and sediments at the Earth’s surface. In sub- and anoxic environments, aqueous ferrous iron (Fe(II)) generated from dissimilatory Fe(III) reduction can induce the recrystallization of goethite and subsequently influences the speciation and mobilization of associated metals, e.g., Co(III) being reduced to Co(II). While it is generally considered that divalent Co and Ni behave similarly at goethite-water interfaces, there lacks a direct comparison of their cycling through goethite in response to Fe(II)-catalyzed recrystallization. Here, under circumneutral anoxic conditions with and without addition of aqueous Fe(II), we performed batch reaction experiments on Co(II)-substituted goethite and Co(II) and Ni(II) sorption experiments on pure goethite. The redox state and coordination environment of Co associated with goethite were determined using high energy resolution fluorescence detected X-ray absorption spectroscopy at the Co K-edge, and the distribution of solid-bound Co and Ni in goethite following sorption was revealed by sequential dissolution. Our results show that substitution of Co(II) for Fe(III) in goethite has less negative feedback on Fe(II)-catalyzed recrystallization than Ni(II), which may be related to their differing structural distortions as evidenced by EXAFS. In the absence of Fe(II), aqueous Co(II) is more favourably adsorbed onto and incorporated deeper into goethite than Ni(II), suggesting that Co(II) is more structurally compatible with goethite. The presence of Fe(II) markedly enhances the structural incorporation of both Co(II) and Ni(II) as a result of goethite recrystallization, which in turn can be inhibited by the accumulation of metals at the mineral surface. Furthermore, structurally-incorporated Co(II) is more difficult to be released back into solution (i.e. sum of aqueous and extract fractions) than Ni(II) during Fe(II)-catalyzed goethite recrystallization. Overall, our work highlights the significant differences between Co(II) and Ni(II) in their cycling at goethite-water interfaces and intricate interplay with Fe(II)-catalyzed recrystallization. This improves our understanding of their mobilization and distribution in anoxic goethite-rich systems and can provide useful insights for their enrichment and extraction from natural and artificial laterites generated from the enhanced weathering of ultramafic mine tailings.

Hotspots of Dissolved Arsenic Generated from Buried Silt Layers along Fluctuating Rivers.

Previous studies along the banks of the tidal Meghna River of the Ganges-Brahmaputra-Meghna Delta demonstrated the active sequestration of dissolved arsenic (As) on newly formed iron oxide minerals (Fe(III)-oxides) within riverbank sands. The sand with high solid-phase As (>500 mg/kg) was located within the intertidal zone where robust mixing occurs with oxygen-rich river water. Here we present new evidence that upwelling groundwater through a buried silt layer generates the dissolved products of reductive dissolution of Fe(III)-oxides, including As, while mobilization of DOC by upwelling groundwater prevents their reconstitution in the intertidal zone by lowering the redox state. A three end-member conservative mixing model demonstrated mixing between riverbank groundwater above the silt layer, upwelling groundwater through the silt layer, and river water. An electrochemical mass balance model confirmed that Fe(III)-oxides were the primary electron acceptor driving the oxidation of DOC sourced from sediment organic carbon in the silt. Thus, the presence of an intercalating silt layer in the riverbanks of tidal rivers can represent a biogeochemical hotspot of As release while preventing its retention in the hyporheic zone.

Origin and evolution of soil materials of the Paleo-Chadian linear-dune landscape in the Far North Region of Cameroon

The mineralogy and micromorphology of associated red Arenosols and both yellow and grey Gleysols of the Paleo-Chadian linear-dune landscape of the Far North Region of Cameroon were studied in order to obtain information about depositional environments and pedogenic processes. Differences between the red soils and both others include a significant difference in clay content, which is much higher in the grey and yellow soils. The composition of the clay fraction is also different, with kaolinite and illite as main mineral phases in the red soils, whereas smectite is strongly predominant in the grey soils and a major phase in the yellow soils. Mössbauer spectroscopy analysis reveals a predominance of hematite as iron oxide mineral in the red soils, in contrast to goethite-predominance in the yellow soils. Thin section observations reveal poor sorting of the coarse fraction, differences in feldspar content, and an absence of reworked clay aggregates, as well as the presence of pore-related carbonate features in the grey soils and iron oxide nodules in the grey and yellow soils. The obtained results indicate that the red soils are derived from a different parent material than the other soils. The grey soils developed on flood-related fluvial deposits in interdune depressions, whereas the red soils formed on aeolian sands and the yellow soils show a mixed origin. In the interdune depressions, hydromorphic conditions led to iron reduction and pedogenic carbonate enrichment.

Unraveling iron oxides as abiotic catalysts of organic phosphorus recycling in soil and sediment matrices

In biogeochemical phosphorus cycling, iron oxide minerals are acknowledged as strong adsorbents of inorganic and organic phosphorus. Dephosphorylation of organic phosphorus is attributed only to biological processes, but iron oxides could also catalyze this reaction. Evidence of this abiotic catalysis has relied on monitoring products in solution, thereby ignoring iron oxides as both catalysts and adsorbents. Here we apply high-resolution mass spectrometry and X-ray absorption spectroscopy to characterize dissolved and particulate phosphorus species, respectively. In soil and sediment samples reacted with ribonucleotides, we uncover the abiotic production of particulate inorganic phosphate associated specifically with iron oxides. Reactions of various organic phosphorus compounds with the different minerals identified in the environmental samples reveal up to twenty-fold greater catalytic reactivities with iron oxides than with silicate and aluminosilicate minerals. Importantly, accounting for inorganic phosphate both in solution and mineral-bound, the dephosphorylation rates of iron oxides were within reported enzymatic rates in soils. Our findings thus imply a missing abiotic axiom for organic phosphorus mineralization in phosphorus cycling.

Influence of tartaric acid on the electron transfer between oxyanions and lepidocrocite

Iron oxide minerals control the environmental behavior of trace elements. However, the potential effects of electron transfer directions by iron oxides between organic acids and trace elements remain unclear. This study investigates the redox capacity of tartaric acid (TA) with chromate (Cr(Ⅵ)) or arsenate (As(V)) on lepidocrocite (Lep) from the perspective of electron transfer. The results demonstrated the configurations of TA (bidentate binuclear (BB)), As(V) (BB), and Cr(Ⅵ) (BB and protonated monodentate binuclear (HMB)) on Lep. Frontier molecular orbital calculations and X-ray photoelectron spectroscopy (XPS) binding energy shifts further indicated different electron transfer directions between TA and the oxyanions on Lep. The iron of Lep might act as electron acceptors when TA is adsorbed, whereas the iron and oxygen of Lep act as electron donors when As(V) is adsorbed. The iron of Lep might accept electrons from its oxygen and subsequently transfer these electrons to Cr(Ⅵ). Macroscopic validation experiments showed the reduction of Cr(VI), whereas no reduction of As(V). The XPS analysis showed a peak shift, with the possible formation of As–Fe–TA ternary complexes and electron transfer on Lep. These findings indicate that mineral interfacial electron transfer considerably influences the transport and transformation of oxyanions.

Petrological and mineralogical characteristics of “red material layer” in Patuha geothermal field, Bandung, West Java

Abstract Patuha Geothermal Field is located in Ciwidey, Bandung, West Java Province, with a total resource potential of approximately 400 Mwe (Megawatt electric). With such potential, seven power plants have been developed in Unit-1, capable of producing 60 MWe of electricity, and are currently being developed in stages for Unit-2. In the development of the Unit-2 power plant, there was a problem where collapse occurred around the drill hole area, especially since the color of the material that came out during drilling was red. We call this material the red material layer (a layer composed of red material). This problem also occurs in Unit-1. This research aims to characterize the type of red material layer to see why this problem occurs in this layer. We studied the petrological and mineralogical characteristics of the red material layer by cutting rock samples from six drill holes in Unit-1. The analytical methods used were megascopic observation, petrography, and XRD (X-ray diffraction) to determine the mineral content texture and identify the material’s origin, including clay minerals, alteration, and oxidation mineral aggregates. The petrological and mineralogical analysis found that the red-colored material is dominated by hematite, with some samples containing magnetite. We found four characteristic types of red layer material and four types of textures that appeared in iron oxide minerals: rim, vein, matrix replacements, and fragment replacements. We conclude from the visible vein texture that oxidation occurs due to oxygen penetration through gaps of a fault/fracture/joint. This oxidizes the area around the vein and then undergoes hydrothermal change. Meanwhile, those that do not have a vein texture are considered material resulting from an oxidation process on the surface, which is then deposited and undergoes hydrothermal change to contain oxide minerals such as hematite and magnetite. Apart from that, XRD observations also found high amounts of clay minerals such as chlorite, smectite, kaolinite, illite-smectite mixed layers, and chlorite-smectite mixed layers. The presence of these clay minerals is thought to cause a collapse in the area around the drill hole because its swelling and exfoliation properties are reactive to fluids, especially drilling fluids.

Improved constraints on hematite refractive index for estimating climatic effects of dust aerosols

Uncertainty in desert dust composition poses a big challenge to understanding Earth’s climate across different epochs. Of particular concern is hematite, an iron-oxide mineral dominating the solar absorption by dust particles, for which current estimates of absorption capacity vary by over two orders of magnitude. Here, we show that laboratory measurements of dust composition, absorption, and scattering provide valuable constraints on the absorption potential of hematite, substantially narrowing its range of plausible values. The success of this constraint is supported by results from an atmospheric transport model compared with station-based measurements. Additionally, we identify substantial bias in simulating hematite abundance in dust aerosols with current soil mineralogy descriptions, underscoring the necessity for improved data sources. Encouragingly, the next-generation imaging spectroscopy remote sensing data hold promise for capturing the spatial variability of hematite. These insights have implications for enhancing dust modeling, thus contributing to efforts in climate change mitigation and adaptation.

MINERALOGICAL AND PHYSICO-CHEMICAL CHARACTERISATION OF CLAY MATERIALS FROM KWILU-NGONGO (Kongo-Central, DR Congo)

Clay materials collected from two sites (Camp-Beton and Kwilu-Bricks) in the Kwilu-Ngongo region located between 5°30’0’’S and 14°40’60’’E, in the Kongo Central province (DRC), Ten samples selected and subjected to mineralogical, physico-chemical and geotechnical studies with a view to their characterization. Mineralogical analysis by X-ray diffraction made it possible to identify the following minerals: quartz, feldpasth, iron oxide and simple clay minerals including kaolinite. In addition to this kaolinite we also find illite, chlorite and vermiculite. The partical size analysis led to the differentiation of three fractions including: the fine clay fraction, the silty fraction and the sandy fraction. As for the Atterberg Limits, the plasticity Limit ranges from 17 to 30% while the average plasticity index is 13 %. Chemical analyzes made it possible to identify the major oxides elements below: SiO2, Al2O3, TiO2, Fe2O3, K2O, Na2O and MgO.

Effects of surfactants on the adsorption of norfloxacin onto ferrihydrite: comparison between anionic and cationic surfactants

ABSTRACT There is little information on how widespread surfactants affect the adsorption of norfloxacin (NOR) onto iron oxide minerals. In order to elucidate the effects of various surfactants on the adsorption characteristics of NOR onto typical iron oxides, we have explored the different influences of sodium dodecylbenzene sulfonate (SDBS), an anionic surfactant, and didodecyldimethylammonium bromide (DDAB), a cationic surfactant, on the interactions between NOR and ferrihydrite under different solution chemistry conditions. Interestingly, SDBS facilitated NOR adsorption, whereas DDAB inhibited NOR adsorption. The adsorption-enhancement effect of SDBS was ascribed to the enhanced electrostatic attraction, the interactions between the adsorbed SDBS on ferrihydrite surfaces and NOR molecules, and the bridging effect of SDBS between NOR and iron oxide. In comparison, the adsorption-inhibition effect of DDAB owning to the adsorption site competitive adsorption between NOR and DDAB for the effective sites as well as the steric hindrance between NOR-DDAB complexes and the adsorbed DDAB on ferrihydrite surfaces. Additionally, the magnitude of the effects of surfactants on NOR adsorption declined with increasing pH values from 5.0 to 9.0, which was related to the amounts of surfactant binding to ferrihydrite surfaces. Moreover, when the background electrolyte was Ca2+, the enhanced effect of SDBS on NOR adsorption was caused by the formation of NOR-Ca2+-SDBS complexes. The inhibitory effect of DDAB was due to the DDAB coating on ferrihydrite, which undermined the cation-bridging effect. Together, the findings from this work emphasize the essential roles of widely existing surfactants in controlling the environmental fate of quinolone antibiotics.

A Deep Learning Approach for Chromium Detection and Characterization from Soil Hyperspectral Data.

High levels of chromium (Cr) in soil pose a significant threat to both humans and the environment. Laboratory-based chemical analysis methods for Cr are time consuming and expensive; thus, there is an urgent need for a more efficient method for detecting Cr in soil. In this study, a deep neural network (DNN) approach was applied to the Land Use and Cover Area frame Survey (LUCAS) dataset to develop a hyperspectral soil Cr content prediction model with good generalizability and accuracy. The optimal DNN model was constructed by optimizing the spectral preprocessing methods and DNN hyperparameters, which achieved good predictive performance for Cr detection, with a correlation coefficient value of 0.79 on the testing set. Four important hyperspectral bands with strong Cr sensitivity (400-439, 1364-1422, 1862-1934, and 2158-2499 nm) were identified by permutation importance and local interpretable model-agnostic explanations. Soil iron oxide and clay mineral content were found to be important factors influencing soil Cr content. The findings of this study provide a feasible method for rapidly determining soil Cr content from hyperspectral data, which can be further refined and applied to large-scale Cr detection in the future.

Integrated Remote Sensing for Geological and Mineralogical Mapping of Pb-Zn Deposits: A Case Study of Jbel Bou Dahar Region Using Multi-Sensor Imagery

This research applies remote sensing methodologies for the first time to comprehensively explore the geological and mineralogical characteristics of the Jbel Bou Dahar region. An integrated approach with multi-sensor satellite images, including ASTER, Landsat-8, and Sentinel-2 was applied with the aim to discriminate the different lithological units in the study area. We implemented a suite of well-established image processing techniques, including Band Ratios, Principal Component Analysis, and Spectral Angle Mapper, to successfully identify, classify, and map the spatial distribution of carbonate minerals, OH-bearing minerals, and iron oxide minerals. Due to its high spectral resolution in the short-wave infrared region (SWIR), the ASTER sensor provided the most accurate results for mapping carbonate and OH-bearing minerals compared to the Sentinel-2 and Landsat-8 sensors. Conversely, Sentinel-2 offers high spectral and spatial resolution in visible and near-infrared (VNIR) corresponding to the regions where iron oxide minerals exhibit their characteristic absorption peaks. The results confirm the advantages of remote sensing technologies in the geological and mineralogical exploration of the study area and the importance of selecting the appropriate sensors for specific mapping objectives.

Iran Desert and Geology for Cultivation Potato

Geology is a branch of Earth science concerned with both the liquid and solid Earth, the rocks of which it is composed, and the processes by which they change over time. Geology can also include the study of the solid features of any terrestrial planet or natural satellite such as Mars. Iran and its neighbouring areas are considered as a complex puzzle, in which continental fragments of various origins were assembled and are now separated by discontinuous ophiolitic belts within the Alpine–Himalayan orogenic system At Kavir Iran central region on the volcanic-plutonic belt of central Iran. It is located in Rafsanjan (Kerman province). Igneous rocks in this area include volcanic rocks (andesite, Trachyandesite, basalt and dacite) and igneous rocks are calc-alkaline magma series. Sedimentary area is limestone, shale, conglomerate, sandstone. Filic and argillic alterations are most prevalent have. According to mineralogical studies, mineralization in this region includes iron oxide minerals, for example; Specularity And limonite, as well as secondary sulfide minerals such as borneite, colitis, digenite, and chalcocite, which are substitutes. Pyrite and chalcopyrite. Mineralization has occurred in the form of diffusion, veinlet, void filling and substitution. Potato is one of the most important legumes and constitutes a dominant portion of the global diet. Finally the effect of water stress. In this study, the potato savalan cultivar (StMYB) was the main factor (sandy, clayey soil, compost) and drought stress in four control levels and -0.3, -0.6, -1, and -1.5 MPa of soil water potential in three replicates form of a split plot. We show that in semnan desert the diversity in germplasm indicated that potato cultivars can be developed for production under certain degrees of drought and soil physical properties.

Hydrolysis Products of Fe(III)‐Si Systems With Different Si/(Si + Fe) Molar Ratios: Implications to Detection of Ferrihydrite on Mars

AbstractFerrihydrite, a nanocrystalline iron (oxyhydr)oxide mineral, is widely distributed in soils and sediments on Earth and is probably an important component and/or precursor of widespread nanophase iron minerals on Mars. Terrestrial ferrihydrite often co‐occurs with amorphous silica and/or contains a certain amount of Si in its structure. However, it remains ambiguous how environmental Si concentration affects the formation‐evolution and structure‐spectral features of ferrihydrite in the Fe(III)‐Si systems. To this end, hydrolysis experiments were carried out for Fe‐Si systems at an unprecedentedly wide range of initial Si/(Fe + Si) molar ratios (0–0.80), followed by characterizing the products detailly. X‐ray diffraction, Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy, Mössbauer spectroscopy, and transmission electron microscopy results showed that at Si/(Fe + Si) molar ratios ≤0.30, the main phase of the products was ferrihydrite, of which the unit cells enlarged, the crystallinity decreased, and the existing state of Fe changed with increased Si contents; at Si/(Fe + Si) molar ratios ≥0.40, ferrihydrite was no longer formed and a novel amorphous Fe‐O‐Si phase was instead obtained, with the excess Si forming amorphous silica. The visible and near‐infrared spectroscopy, the most powerful tool to detect hydrous minerals on the surface of Mars at global or regional scales, showed weakness in identifying ferrihydrite‐like materials obtained in the Fe‐Si systems. Raman spectroscopy can identify ferrihydrite and Si‐containing ferrihydrite but cannot differentiate between them. Mössbauer spectroscopy showed great potential in both identifying and differentiating between ferrihydrite and Si‐containing ferrihydrite, and thus can be used to characterize the poorly ordered iron (oxyhydr)oxides on Mars.

Integrating Tide‐Driven Wetland Soil Redox and Biogeochemical Interactions Into a Land Surface Model

AbstractRedox processes, aqueous and solid‐phase chemistry, and pH dynamics are key drivers of subsurface biogeochemical cycling and methanogenesis in terrestrial and wetland ecosystems but are typically not included in terrestrial carbon cycle models. These omissions may introduce errors when simulating systems where redox interactions and pH fluctuations are important, such as wetlands where saturation of soils can produce anoxic conditions and coastal systems where sulfate inputs from seawater can influence biogeochemistry. Integrating cycling of redox‐sensitive elements could therefore allow models to better represent key elements of carbon cycling and greenhouse gas production. We describe a model framework that couples the Energy Exascale Earth System Model (E3SM) Land Model (ELM) with PFLOTRAN biogeochemistry, allowing geochemical processes and redox interactions to be integrated with land surface model simulations. We implemented a reaction network including aerobic decomposition, fermentation, sulfate reduction, sulfide oxidation, methanogenesis, and methanotrophy as well as pH dynamics along with iron oxide and iron sulfide mineral precipitation and dissolution. We simulated biogeochemical cycling in tidal wetlands subject to either saltwater or freshwater inputs driven by tidal hydrological dynamics. In simulations with saltwater tidal inputs, sulfate reduction led to accumulation of sulfide, higher dissolved inorganic carbon concentrations, lower dissolved organic carbon concentrations, and lower methane emissions than simulations with freshwater tidal inputs. Model simulations compared well with measured porewater concentrations and surface gas emissions from coastal wetlands in the Northeastern United States. These results demonstrate how simulating geochemical reaction networks can improve land surface model simulations of subsurface biogeochemistry and carbon cycling.

Weathering trends in the Norian through geochemical and rock magnetic analyses from the Pignola–Abriola section (Lagonegro Basin, Italy)

Abstract. We investigated the geochemical and rock magnetic properties of the magnetostratigraphically calibrated Pignola–Abriola section (Italy) in order to understand the climatic perturbations that characterize the late Norian–early Rhaetian interval (Late Triassic). We performed experiments on anhysteretic and isothermal remanence (ARM and IRM) and on magnetic susceptibility (χ) to obtain the rock magnetic parameters necessary for our paleoclimatic investigation. An episode of increase in the relative quantity of hematite, suggesting the enhanced subaerial oxidation of iron minerals, was identified in the Norian from ∼ 217 Ma in the Alaunian up to ∼ 211 Ma in the early Sevatian, followed by a decline up to 207–206 Ma at the end of the Norian (late Sevatian). The results of geochemical and multivariate statistical analyses support a long-term increase and reduction in rock weathering, confirming and extending previous 87Sr / 86Sr data from the Pizzo Mondello section (Italy). Possible causes of these long-term weathering trends are the multiphase uplifting of the Cimmerian orogen, occurring at mid-northern latitudes along the southern margin of Asia in the Late Triassic, and/or the northward motion of Pangea across the equatorial humid belt. Rapid excursions in oxidized iron minerals have also been observed across the Norian–Rhaetian boundary, the origin of which still has to be determined.

Mineralogical and chemical characterization of an oolitic iron ore, and sustainable phosphorus removal

An oolitic iron ore from Gara Djebilet, Algeria was characterized by X-ray diffraction, scanning electron microscopy, and energy dispersive spectrosopy and the phosphorus distribution between various phases studied. Two ore types were identified - a haematite-dominated, oolitic type and a more massive, magnetite-dominated type. The haematite-dominated ore had a higher phosphorus content, up to 0.6% in the iron oxide minerals, than the magnetite-dominated type (0.3% P). Owing to the very fine-grained texture of the gangue minerals, reducing the phosphorus content to levels suitable for steelmaking (below 0.05% P) by conventiobal means would entail an energy-intensive process with a high carbon footprint. Preliminary leaching test work using a sulphurous geothermal water as lixiviant, assisted by solar thermal acceleration, gave very promising results, removing 0.13% of the residual P (or 21.7% removal of total P) from the high-phosphorus oolitic ore.

Activation of iron oxide minerals in an aquifer by humic acid to promote adsorption of organic molecules

In aquifers, the sequestration and transformation of organic carbon are closely associated with soil iron oxides and can facilitate the release of iron ions from iron oxide minerals. There is a strong interaction between dissolved organic matter (DOM) and iron oxide minerals in aquifers, but the extent to which iron is activated by DOM exposure to active iron minerals in natural aquifers, the microscopic distribution of minerals on the surface, and the mechanisms involved in DOM molecular transformation are currently unclear. This study investigated the nonbiological reduction transformation and coupled adsorption of iron oxide minerals in aquifers containing DOM from both macro- and micro perspectives. The results of macroscopic dynamics experiments indicate that DOM can mediate soluble iron release during the reduction of iron oxide minerals, that pH strongly affects DOM removal, and that DOM is more efficiently degraded at low rather than high pH values, suggesting that a low pH is conducive to DOM adsorption and oxidation. Spherical aberration-corrected scanning transmission electron microscopy (SACTS) indicates that the reacted mineral surfaces are covered with large amounts of carbon and that dynamic agglomeration of iron, carbon, and oxygen occurs. At the nanoscale, three forms of DOM are found in the mineral surface agglomerates (on the surfaces, inside the surface agglomerates, and in the polymer pores). The microscopic organic carbon and iron mineral reaction patterns can form through oxidation reactions and selective adsorption effects. Fourier transform ion cyclotron resonance mass spectra indicate that both synergistic and antagonistic reactions occur between DOM and the minerals, that the release of iron is accompanied by DOM decomposition and humification, that large oxygen- and carbon-containing molecules are broken down into smaller oxygen- and carbon-containing compounds and that more molecules are produced through oxidation under acidic rather than alkaline conditions. These molecules provide adsorption sites for sediment, meaning that more iron can be released. Microscopic evidence for the release of iron was acquired. These results improve the understanding of the geochemical processes affecting iron in groundwater, the nonbiological transformation mechanisms that occur at the interfaces between natural iron minerals and organic matter, groundwater pollution control, and the environmental behavior of pollutants.

Iron isotope fractionation during sulfide-promoted reductive dissolution of iron (oxyhydr)oxide minerals

Iron isotopes are a valuable tool for evaluating processes that control Fe redox cycling in modern and ancient environmental settings. However, robust evaluation of Fe isotope compositions in natural samples requires that fractionations associated with key (bio)geochemical reactions are well-defined. The reductive dissolution of Fe (oxyhydr)oxide minerals mediated by dissolved sulfide exerts a major influence on solid phase Fe mineralogy and dissolved porewater Fe profiles during early diagenesis of organic-rich sediments, but to date, no studies have investigated Fe isotope fractionations during this process. Here, we report the results of laboratory sulfidation experiments, examining apparent Fe isotope fractionations for a variety of Fe (oxyhydr)oxide minerals. The iron isotope compositions of reaction products were determined for both the reduction-dominated and dissolution-dominated steps of the reaction. The reductive step for lepidocrocite and hematite produced Fe(II) that was up to 0.25 ‰ heavier than the bulk starting mineral. By contrast, the reduction of ferrihydrite produced isotopically light Fe(II), with isotope compositions −0.1 to −0.6 ‰ lower than the initial mineral. Consistent with previous studies of the reductive dissolution of Fe (oxyhydr)oxide minerals via abiological and biological pathways, the lighter isotope was preferentially released from the mineral surface during the dissolution phase for all minerals, with dissolved Fe2+ isotope compositions up to ∼2.0 ‰ lower than the surface bound Fe(II). The magnitude of isotopic fractionation during both of these steps is directly related to rates of reaction, and is thus controlled by factors such as sulfide concentration, mineral concentration, crystal structure, surface area and pH. Our data demonstrate that dissolved Fe2+ with δ56Fe compositions approaching −1.0 ‰ is readily generated during the overall reaction, suggesting that sulfide-promoted reductive dissolution of Fe (oxyhydr)oxide minerals may contribute significantly to the generation of light Fe isotope compositions in anoxic settings.