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Iron hydroxides are ubiquitous in soils and aquifers and have been adopted as adsorbents for As(V) removal. However, the complexation mechanisms of As(V) have not been well understood due to the lack of information on the reactive sites and acidities of iron hydroxides. In this work, we first calculated the acidity constants (pKas) of surface groups on lepidocrocite (010), (001), and (100) surfaces by using the first-principles molecular dynamics (FPMD)-based vertical energy gap method. Then, the desorption free energies of As(V) on goethite (110) and lepidocrocite (001) surfaces were calculated by using constrained FPMD simulations. The point of zero charges and reactive sites of individual surfaces were obtained based on the calculated pKas. The structures, thermodynamics, and pH dependence for As(V) complexation were derived by integrating the pKas and desorption free energies. The pKa data sets obtained are fundamental parameters that control the charging and adsorption behavior of iron oxyhydroxides and will be very useful in investigating the adsorption processes on these minerals. The pH-dependent complexation mechanisms of As(V) derived in this study would be helpful for the development of effective adsorbent materials and the prediction of the long-term behavior of As(V) in natural environments.

The presence of iron oxides may provide a sensitive indicator of the effects of cropping practices on coffee plantations. Authors characterized the mineral phases present in soil A horizons at three different farms located in the Department of Tolima within the regions of Líbano and Villahermosa. Our analysis includes X-ray diffraction, Mössbauer spectroscopy, and remote sensing to discriminate the distribution of the different magnetic mineral phases. X-ray diffraction was used to identify the mineralogical properties of iron oxide such as hematite, goethite, and ferrihydrite (Fh), as well as tectosilicate minerals such as albite and sanidine. Mössbauer spectroscopy results for samples taken at room temperature indicate the presence of Fe2+ and Fe3+ mineral phases, which possibly correspond to ilmenite or magnetite. Finally, Sentinel-2A multi-spectral imager (MSI) data was used to map the distribution of iron oxides and study the influence of their distribution throughout the study area. A high correlation between Mössbauer spectroscopy and Sentinel-2A MSI data exists throughout the study area. The results suggest that farms close to the main Nevado del Ruíz Volcano have a more significant mineralogical variability. In contrast, more distant farms are characterized by soils with more iron oxides, the product of weathering, erosion, and human activities.

Rhodochrosite conversion to Mn (oxyhydr)oxides significantly affects the fate and transport of various substances in the environment. We examined rhodochrosite oxidation by dissolved oxygen and the oxidation product formation with an emphasis on the effects of goethite substrate. Without goethite, rhodochrosite oxidation was slow as no detectable change was observed for 28 d with microscopic and spectroscopic analyses, except a minor change in X-ray diffraction. Interestingly, by contrast, it was greatly accelerated and completed in 7 d in the presence of goethite, resulting in the heteroepitaxial growth of groutite (α-MnOOH)-like Mn oxides on the goethite (α-FeOOH) tip surfaces. The formation of this secondary Mn oxide likely induced the acidification of the microenvironment in the vicinity of rhodochrosite particles and thereby promoted their dissolution. Subsequently, their oxidative conversion to the Mn oxide was expedited by the surface catalyzed Mn(II) oxidation on the goethite tip. Our results revealed that goethite as a foreign substrate imparts a decisive control on not only the rate but also the type of the reaction product of rhodochrosite oxidation. This study presents a new insight into the geochemical roles of foreign particles on the dynamics of redox-sensitive solid phases in the environment.

As a part of Corrosion Map of Sichuan project, atmospheric corrosion behavior of carbon steel was investigated in the subtropical atmospheric environment by weight loss method at five exposure stations. Results indicated that an annual corrosion rate of carbon steel was between 0.66 and 23.6 μm/y. The morphology and composition of corrosion products formed on the exposed steels were identified by scanning electron microscopy (SEM), energy-dispersive x-ray spectroscopy (EDS) and Raman spectroscopy. Subtropical atmospheric corrosion rate of the steel increases in high-rainfall and temperature environment. Bigger and deeper pits are preferred to form in a humid atmosphere. The corrosion products exhibited an uneven distribution and consisted mainly of goethite (α-FeOOH), lepidocrocite (γ-FeOOH), magnetite (Fe3O4) and hematite (Fe2O3). The electrochemical corrosion of carbon steel in solution is an activation-controlled process, and a stable passive region was not observed for the steel. Electrochemical measurements showed that deposits on carbon steel decreased the corrosion resistance.

Interfacial chemistry of phosphorus (P) is important for understanding P sequestration and bioavailability in nature. Polyphosphate is a group of important P species in aquatic environments. The geochemical behaviors of polyphosphate at the mineral-water interface play critical roles in mediating aquatic P transformation, yet remain poorly constrained. This study investigates the hydrolysis of polyphosphate in the presence of four common iron (Fe) oxide minerals (ferrihydrite, hematite, goethite, lepidocrocite) and the subsequent precipitation of calcium phosphate minerals. Batch studies are combined with microscopic and spectroscopic characterizations to reveal P speciation and complexation state under varied solution chemistry (pH 6–9, 1 mM Ca2+, and artificial seawater). All four Fe oxides can hydrolyze polyphosphate and the hydrolysis rate and extent are both enhanced in the presence of Ca2+. In the presence of 1 mM Ca2+, the apparent hydrolysis rate fitted by first-order kinetic model follows the order of lepidocrocite > hematite > ferrihydrite > goethite. After normalization by specific surface area of Fe oxides, the hydrolysis rate is in the order of lepidocrocite ≈ goethite > hematite > ferrihydrite at pH 6, regardless of Ca2+ presence. At pH 7.5 and 9, the order of area-normalized apparent hydrolysis rate is lepidocrocite > goethite ≈ hematite > ferrihydrite. A terminal-only pathway via one-by-one cleavage of terminal phosphate groups is the dominant hydrolysis mechanism. Under alkaline conditions, amorphous calcium phosphate forms in the presence of Ca2+, which transforms to crystalline hydroxyapatite after long-term aging of 70 or 150 days. This study demonstrates the importance of natural minerals in controlling polyphosphate transformation into crystalline calcium phosphate minerals, and provides new insights for understanding P cycling and sequestration in the environment.

The magnetic properties of the loess-paleosol sequences from northern Iran provides a model for understanding pedogenic processes and their relationship to paleo-precipitation in this region. For the first time, we present diffuse reflectance spectrophotometry (DRS) analyses, color measurement analyses, and temperature-dependent susceptibility (χ-T) in argon from two late Pleistocene loess-paleosol sequences in northern Iran. Magnetic iron oxide minerals, principally magnetite, maghemite, hematite, and goethite were identified in the study sections. The results of DRS and color measurements show that a* values, the hematite to goethite ratio and the maghemite to hematite ratio, exhibit a significant positive correlation with the pedogenic process and paleosol formation and are superior to low-frequency susceptibility alone for estimating paleoprecipitation. Our data also indicates that pedogenic maghemite-magnetite formation and dissolution/reprecipitation are major contributors to the magnetic enhancement of loess-paleosol sequences and might indicate a seasonal aspect for pedogenic maghemite-magnetite formation. We propose the DRS-derived illite to chlorite ratio as a useful index for assessing the intensity of silicate mineral weathering in the northern Iranian loess-paleosol sequences. In addition, DRS can be used to discriminate between pedogenic and detrital hematite of loess-paleosol sequences. We also propose that the χ-T cooling and heating ratio model is a quantitative proxy for magnetic enhancement in soils and paleosols of loess-paleosol sequences.

Indonesia is one of the largest Ni ore producers in the world and is also expected to be an important potential source of some critical metals (e.g., Co, Sc, rare-earth elements, and platinum-group elements). However, few studies have examined Ni laterite deposits in this country. In this study, we investigate Ni enrichment and the potential accumulation of critical metals in four laterite profiles with varying degrees of serpentinization and weathering intensity in the Soroako and Pomalaa mining areas of Sulawesi, Indonesia. We integrate geochemical evaluation with a mass-balance approach and mineralogical anal ysis to better constrain the geochemical factors influencing the mobilization of Ni during lateritization. Nickel contents in the saprolite horizon of the profiles that are strongly weathered and developed over serpentinized peridotite are higher than those that are weakly weathered and developed over unserpentinized harzburgite. The bulk Ni contents of saprolite horizons are related to Ni contents of Ni-bearing Mg-phyllosilicates, which suggests that Ni remobilization is the main control on Ni enrichment in the profiles. Mass balance calculations reveal that the amounts of gained Fe and Ni in the pro files are positively correlated. This relationship indicates that the redistribution of Ni is likely controlled by the aging of Ni-bearing goethite (dissolution/ recrystallization) involving ligand-promoted dissolution by organic matter and/or reductive dissolution by microbial activity near the surface. Critical metals show enrichment in specific horizons. Enrichments in Co and rare earth elements are strongly influenced by the formation of Mn-oxyhydroxides in the oxide zone of the profiles. In contrast, Sc, Pt, and Pd show residual enrichment patterns, with grades influenced mainly by their initial contents in bedrock. The profiles show a positive correlation between Sc and Fe, as reported for other Ni laterite deposits. Among the critical metals, Sc, Pt, and Pd contents in the studied profiles are comparable with values reported from other Ni laterite deposits worldwide.

The U(VI) immobilization efficiency and mechanism of natural pyrite were investigated under both acidic and neutral oxidization conditions. The results show that, the final U(VI) removal rate was only 20% under acidic condition; however, a small amount of pyrite oxidation could enhance the immobilization of U(VI) under neutral oxidizing conditions, with the removal rate reaching 95%. A ferric hydroxide colloid, goethite and lepidocrocite were formed in the neutral oxidizing environment. It was speculated that the main U(VI) immobilization mechanisms of pyrite oxidation were adsorption. The adsorption behaviour of U(VI) to pyrite conformed to the pseudo second-order adsorption model (R2 = 0.9996).

The present paper reports an important amount of Ti-V-Ga and REE enrichments in the hitherto-unreported eighteen bodies of ferruginous and aluminous laterite capping over the Dhandraul Formation of the Vindhyan Supergroup, Eastern India. It is brown to deep reddish-brown, limonitic, massive, and having a pisolitic form which is mainly rounded to subrounded and filled up of clay, bauxite, limonite, hematite, goethite, and surface encrustation of ferruginous material. Laterites are chiefly composed of ferruginous minerals like hematite, magnetite along with secondary jaspery material and limonite, goethite, in association with silicates and clay minerals. The analyzed samples show high values of Ti, V, Ga, and LREE like La, Ce, Pr, Nd, and Eu along with some significant values of Sm, Gd, Dy, and Yb. TiO2 value is ranging from 0.72 to 18.84 % with an average of 9.77 wt. % which is twenty-two times higher than the crustal abundance. Values of vanadium vary from 48 to 1163 ppm with an average of 593 ppm, and gallium varies from 9 to 90 ppm with an average of 47 ppm, and these values are three to five times higher than the crustal abundance. The “REE is varying from 208.81 to 899.31 ppm with an average of 484.49 ppm which is three times higher than the crustal abundance. The other significant trace elements identified are in ppm: Co (5–135), Cr (76–970), Cu (5–17), Ni (7–48), Pb (6–143), and Zn (14–231 ppm). This finding has got an enormous impact on the future Ti-V-Ga and REE exploration in the Vindhyan Supergroup in the state of Bihar.

This paper looks at the pyrochlore-monazite-goethite ores of the Chuktukonsk deposit (0.98wt.% Nb2O5) and their processing with the help of acidbased (HNO3, H2SO4) and sulphatization techniques. Nitric-acid pressure leaching was found to be an efficient processing technique for this type of ore: ore size –0.074 mm; CHNO3 = 25%; CH2O2 = 5%; τ = 2 h; solid-to-liquid = 1:9; heat treatment mode: 1 h at 160 oC followed by 1 h at 230 oC. As a result, rare earth metals and manganese are leached to the solution while all of the contained niobium remains in the cake. Two different techniques were tested to recover niobium from the cake. One is based on the use of alkali (NaOH sintering), the other is an extractive leaching technique that combines acid leaching with liquid-liquid extraction of tributyl phosphate in one stage. It was established that niobium mi nerals can be efficiently decomposed when using a mixture of hydro fluoric and sulphuric acids with the concentrations of 4.08 and 8.46 mol/L, correspon dingly, as a leaching agent. At the weight ratio of 1:2:1 of the solid to aqueous to organic phase and after the slurry has been stirred intensively for 5 minutes, niobium fluorides, which form as a result of interaction between hydrofluoric acid and the cake components, can be recovered with a 50% solution of tributyl phosphate in octane. After that they transfer to an organic phase while impurities get accumulated in the solid residue. As niobium-containing cake has a high concentration of silicon, it is recommended to first remove silicon from the cake using a strong alkaline solution.

The environmental mobility of antimony (Sb) is controlled by interactions with iron (Fe) oxides, such as ferrihydrite. Under near-neutral pH conditions, Fe(II) catalyzes the transformation of ferrihydrite to more stable phases, thereby potentially altering the partitioning and speciation of associated Sb. Although largely unexplored, Sb itself may also influence ferrihydrite transformation pathways. Here, we investigated the impact of Sb on the Fe(II)-induced transformation of ferrihydrite at pH 7 across a range of Sb(V) loadings (Sb:Fe(III) molar ratios of 0, 0.003, 0.016, and 0.08). At low and medium Sb loadings, Fe(II) induced rapid transformation of ferrihydrite to goethite, with some lepidocrocite forming as an intermediate phase. In contrast, the highest Sb:Fe(III) ratio inhibited lepidocrocite formation, decreased the extent of goethite formation, and instead resulted in substantial formation of feroxyhyte, a rarely reported FeOOH polymorph. At all Sb loadings, the transformation of ferrihydrite was paralleled by a decrease in aqueous and phosphate-extractable Sb concentrations. Extended X-ray absorption fine structure spectroscopy showed that this Sb immobilization was attributable to incorporation of Sb into Fe(III) octahedral sites of the neo-formed minerals. Our results suggest that Fe oxide transformation pathways in Sb-contaminated systems may strongly differ from the well-known pathways under Sb-free conditions.

The influence of emissions of an active volcano on the composition of nanoparticles and ultrafine road dust was identified in an urban area of the Andes. Although many cities are close to active volcanoes, few studies have evaluated their influence in road dust composition. Air quality in urban areas is significantly affected by non-exhaust emissions (e.g. road dust, brake wear, tire wear), however, natural sources such as volcanoes also impact the chemical composition of the particles. In this study, elements from volcanic emissions such as Si > Al > Fe > Ca > K > Mg, and Sisingle bondAl with K were identified as complex hydrates. Similarly, As, Hg, Cd, Pb, As, H, Cd, Pb, V, and salammoniac were observed in nanoparticles and ultrafine material. Mineral composition was detected in the order of quartz > mullite > calcite > kaolinite > illite > goethite > magnetite > zircon > monazite, in addition to salammoniac, a tracer of volcanic sources. The foregoing analysis reflects the importance of carrying out more studies relating the influence of volcanic emissions in road dust in order to protect human health. The road dust load (RD10) ranged between 0.8 and 26.8 mg m-2 in the city.

Iron minerals are the most important arsenic host in As-contaminated deltaic sediments. Arsenic release from Fe minerals to groundwater exposes millions of people worldwide to a severe health threat. To understand the coupling of Fe mineralogy with As (im)mobilization dynamics, we analyzed the geochemistry and mineralogy of a 46 m long sediment core drilled into the redox transition zone where a high As Holocene aquifer is juxtaposed to a low As Pleistocene aquifer in the Red River delta, Vietnam. We specifically concentrated on mm- to cm-scale redox interfaces within the sandy aquifer. Various Fe phases, such as Fe- and Mn- bearing carbonates, pyrite, magnetite, hematite and Fe-hydroxides (goethite, lepidocrocite) with distinct As concentrations were identified by a combination of high-resolution microscopic, magnetic and spectroscopic methods. The concentration of As and its redox species in the different Fe-minerals were quantified by microprobe analysis and synchrotron X-ray absorption. We developed a conceptual model integrating Fe-mineral transformations and related As (im)mobilization across the redox interfaces. Accordingly, As is first mobilized via the methanogenic dissolution of Fe(III) (oxyhydr)oxide mineral coatings on sand grains when reducing groundwater from the Holocene aquifer intruded into the Pleistocene sands. This stage is followed by the formation of secondary Fe(II)-containing precipitates (mainly Fe- and Mn-bearing carbonates with relatively low As

Owing to the depletion of high-grade iron ore quality, many steel plants over the world are now using pellets after beneficiation of low grade ores as blast furnace feed. For the effective utilization of low-grade iron ore resources (59–62% Fe) with high loss of ignition (LOI), mineralogical characteristics play the vital role to improve the process efficiency. The present work illustrates the effect of limestone and dolomite as flux material in pelletization of an Indian goethetic-hematite iron ore with 59.75% Fe, 4.52% SiO2, 3.84% Al2O3, and 4.85% LOI. As per mineralogical analysis, this ore contains 30.11% goethite and 9.71% kaolinite, which contribute major LOI of the sample. The self-binding properties of the ore ensured the complete elimination of an external binder due to the presence of kaolinite. LOI of the ore indeed affected the quality of indurated pellets by cracking, which might be the reason for the degradation of pellet quality. Concurrently, the same LOI enhanced the pellet quality when suitable fluxes were added. Limestone, dolomite, and their combinations were used as fluxing agent. The effects of CaO and MgO for the improvement of inherent pellet properties were evaluated through the physical, mineralogical, thermal, chemical, and metallurgical properties of the fluxed pellet using different analytical techniques, i.e., Thermogravimetric Analysis (TGA), X-ray diffraction, Stereomicroscopy, Optical Microscopy, Field Emission Scanning Electron Microscopy, and Wavelength Dispersive Microscopy with Electron Microprobe. TGA results indicated the thermal decomposition of goethite, kaolinite, and fluxes at different temperatures. With the addition of dolomite and limestone in the pellet feed material, CCS (Cold Compressive Strength/kg.pellet−1), RI (Reducibility Index/%), RDI (Reduction Degradation Index/%), SI (Swelling Index/%) and porosity could be improved. Due to the loss of mass in flux materials, by increasing the MgO content, it is possible to reduce swelling index and increase the pellet porosity. Simultaneously, the strength of the pellet increases because of slag formation in the form of calcium/magnesium aluminum silicate. The physical and metallurgical properties, i.e., CCS, porosity, SI, RDI, and RI of the fluxed pellets were optimized. At particular ratio of limestone and dolomite, synergistic effect was observed with respect to pellet characteristics.

During the aging process, ferrihydrite was transformed into mineral mixtures composed of different proportions of ferrihydrite, goethite, lepidocrocite and hematite. Such a transformation may affect the fixed ability of arsenic. In this study, the stability of Fe-As composites formed with As(V) and the minerals aged for 0, 1, 4, 10 and 30 days of ferrihydrite were systematically examined, and the effects of molar of ratios Fe/As were also clarified using kinetic methods combined with multiple spectroscopic techniques. The results indicated that As(V) was rapidly adsorbed on minerals during the initial polymerization process, which delayed both the ferrihydrite conversion and the hematite formation. When the Fe/As molar ratio was 1.875 and 5.66, the As(V) adsorbed by ferrihydrite began to release after 6 hr and 12 hr, respectively. The corresponding release amounts of As(V) were 0.55 g/L and 0.07 g/L, and the adsorption rates were 92.43% and 97.50% at 60 days, respectively. However, the As(V) adsorbed by the transformation products aged for 30 days of ferrihydrite began to release after adsorbed 30 days. The corresponding release amounts of As(V) were 0.25 g/L and 0.03 g/L, and the adsorption rates were 84.23% and 92.18% after adsorbed 60 days, for the Fe/As=1.875 and 5.66, respectively. Overall, the combination of As(V) with ferrihydrite and aged products transformed from a thermodynamically metastable phase to a dynamically stable state within a certain duration. Moreover, the aging process of ferrihydrite reduced the sorption ability of arsenate by iron (hydr)oxide but enhanced the stability of the Fe-As composites.

Several recent studies have reported a strong association between Sc and goethite (α-FeOOH) in synthetic analogs and natural samples. However, the mechanism of Sc immobilization by goethite and controlling factors remain unclear. This study investigated the adsorption behavior and molecular-scale immobilization mechanisms of Sc at water/goethite interfaces through a combination of batch adsorption and desorption experiments, X-ray absorption fine structure (XAFS) analyses, and density functional theory (DFT) calculations. Results indicate that Sc is preferentially adsorbed on goethite with the formation of bidentate-binuclear inner-sphere complexes at the corner-sharing sites. Bulk Sc K-edge XAFS analyses suggest that Sc is incorporated into the goethite structure by substituting for Fe(III) within the crystal in synthetic Sc-substituted goethite, which is further confirmed in natural goethite particles in the laterite by using micro-focused XAFS (μ-XAFS). Furthermore, we demonstrate that the adsorbed Sc on the goethite surface can be structurally incorporated into the goethite lattice in the presence of aqueous Fe(II) possibly through goethite recrystallization induced by aqueous Fe(II). This process may affect the (re)partitioning of Sc between the goethite surface and the mineral bulk, which could be used to rationally explain disparate Sc speciation in laterites from different regions. Our study elucidates the molecular-scale mechanisms underlying Sc adsorption on and structural incorporation into goethite, providing critical insights into the understanding of geochemical behavior and environmental fates of Sc.

In the absence of the necessary valley topography, karst depressions are sometimes used to construct conventional impoundments in order to contain tailings. Leakage is a primary concern for such impoundments. The purpose of the current study was to determine the characteristics and barrier performance of laterite mantling karst depressions, using, as an example, the Wujiwatang (WJWT) tailings impoundment, located in the Gejiu mining area, southwestern China. The geotechnical-hydrogeological properties, geochemistry, mineral compositions, and particle shapes of the laterite were investigated by geotechnical techniques, chemical analysis, X-ray diffraction (XRD), and scanning electron microscopy (SEM). The results showed that the laterite contained poorly sorted particles that covered a wide spectrum of grain sizes (

Schwertmannite, ubiquitously found in iron and sulfate-rich acid mine drainage, is generated via biological oxidation of ferrous ions by Acidithiobacillus ferrooxidans (A. ferrooxidans). However, little information on the mechanisms of biogenic schwertmannite formation and crystal growth is available. This study deliberately investigated the relationships among mineral morphology, solution chemistry, and phase transformation of schwertmannite in A. ferrooxidans-containing ferrous sulfate solutions. The formation of schwertmannite could be divided into three stages. In the first nucleation stage, crystallites are presented as nonaggregative or aggregative forms via a successive polymerization process. In the second stage, ellipsoidal aggregates, which are identified as ferrihydrite and/or schwertmannite, are formed. In the third stage, needles appear on the surface of ellipsoidal aggregates, which is caused by the phase transformation of ferrihydrite or schwertmannite to lepidocrocite and goethite through a Fe2+ (aq) catalysis-driven pathway. After three stages, a typical characteristic "hedgehog" morphology finally appears. In addition, A. ferrooxidans could significantly speed up the mineral transformation. Solution pH affects the morphology of schwertmannite by acid leaching. The experimental results also reveal that the formation of schwertmannite depend on the content of hydroxyl complexes or the transformation of the monomers to polymers, which are greatly affected by the solution pH.

Fe(II) oxidation by O2 is an important process generating Fe (oxyhydr)oxides, which play sorptive, structural and electron-transfer roles in soils. Here we explored how native minerals and organic matter (OM) affect the rate of Fe(II) oxidation and resulting de novo Fe(III) minerals in soil slurries. A topsoil was collected from the Luquillo Experimental Forest, and a topsoil and subsoil were collected from a cultivated site at the Calhoun Experimental Forest. We oxidized 57Fe(II) in these soils either untreated or with OM and/or Fe (oxyhydr)oxides removed. We measured Fe oxidation kinetics by tracking the loss of Fe(II) and characterized the de novo Fe(III) solids using 57Fe Mossbauer spectroscopy. We find that OM retarded Fe(II) oxidation, while pre-existing Fe (oxyhydr)oxides played a significant role in catalyzing Fe(II) oxidation. The non-extractable (residual) soil minerals (i.e. phyllosilicates and quartz) after removing Fe (oxyhydr)oxides, had only a minor effect on oxidation rates. In the topsoils, OM resulted in lower-crystallinity Fe(III) minerals, including nanogoethite and highly-disordered Fe phases, relative to soils with OM-removed. Goethite of varying crystallinity was promoted by the pre-existing Fe (oxyhydr)oxides in all soils, in contrast to homogenous oxidation treatments in which lepidocrocite was formed. Fe(II) oxidation in the Calhoun subsoil, which was enriched in native crystalline Fe phases and depleted in OM, resulted in large-particle goethite with the highest crystallinity of all treatments. Crystalline hematite was also formed in the Calhoun subsoil most likely due to a templating effect of pre-existing hematite. These findings suggest that the nature of de novo formed Fe minerals in soils and sediments may depend strongly on resident existing soil OM and Fe phases. This study extends similar results from previous model mineral and organic experiments to whole, complex soils and thus constitutes a significant step forward in understanding Fe transformation in natural environments.

Understanding how natural nanoaggregates of iron (Fe) and organic matter (OM), currently identified in organic rich soil or peat, interact with metals and metalloids is environmentally significant. Coal is also organic-rich and exemplifies anoxic sedimentary environments with Fe usually as pyrite and not oxides. Here, we analyze the local structure of Fe (6880–21 700 mg kg(−1)) and As (45–5680 mg kg(−1)) in representative Guizhou coal samples using X-ray absorption near-edge structure and extended X-ray absorption fine structure (XANES and EXAFS) to illustrate how Fe(iii) and As(v) are preserved in coal formed from reduced, organic-rich precursors. Arsenic XANES indicates that >80% of As exists as As(v) with

Tanulmányunk célja a Szendrői-hegységben található Meszes település melletti Vasbánya-hegy felszíni feltárásaiból (Szendrői Fillit Formáció) gyűjtött fekete fillitek vizsgálata optikai és elektronmikroszkópiával, illetve röntgen-pordiffrakcióval a kőzetekben található grafitra és kritikus elemekre fókuszálva. Vizsgálataink alapján a grafit pikkelyes formában, 50-150 µm-es nagyságban volt észlelhető. A kritikus elemeket tekintve, a minták tartalmaztak titánt (főként TiO2-ként, ritkán ilmenitként, valamint fengitbe beépülve), nióbiumot (TiO2-ba beépülve), stronciumot (fluorapatitban és monacitban), valamint ritkaföldfémeket (xenotimban, monacitban és goethitben).

High alumina & silica content of Indian Iron ore resources require suitable beneficiation techniques to produce quality raw material for steel manufacturing. Banded Hematite Jasper (BHJ) reserves are abundantly available in India but not considered as an ore of Iron for production purposes due to its high Silica content and complex mineralogy. The ore principally consists of Hematite, traces of martite, goethite and limonite. X-Ray diffraction analysis confirmed the presence of silica & iron as major phases with alumina and goethite as minor phases. Sample collected from Barsua area containing 35.32% Fe, 49.10% silica and 2% alumina. The area lies in the famous Jamda-Koira valley of Eastern India. The intricate association of quartz and iron made liberation a tough task. The characterization study along with liberation analysis results revealed that beneficiation of BHJ can only be possible in finer size. A detailed and comprehensive characterization studies done to develop a cost-effective and beneficiation scheme.

The low-grade iron ore generally contains goethite as the major iron phase mineral and kaolinite and other minerals as gangue minerals. During the beneficiation of low-grade iron ore, a lot of fines were generated during different unit operations. These fines report to the tailing pond for the settling of the particles. The presence of kaolinite and goethite minerals reduces the settling rate. Therefore, different flocculants are used to improve the settling rate in the tailings pond. This study highlights the utilization of different flocculants in the settling of Iron Ore Tailings slurry (IOTs) in a tailings pond. Performances of different flocculants such as polyacrylamide, guar gum, and alstafloc are used to study the efficiency of the settling behaviour of IOTs. The tests were performed with fixed doses of flocculant consumption, slurry concentration, and flocculant concentration. Rheological studies were also performed on the IOTs samples to determine the viscoelastic behaviour for specific applications. From the study, it has been observed that the use of polyacrylamide as a flocculant in IOTs results in faster settling of iron ore, leaving a clear supernatant.

This research is aimed to examine the catalytic activity of Sawahlunto clay, which is enriched with Ca2+ and Cu2+ transesterification of Crude Palm Oil (CPO) to produce biodiesel. Based on the results of the analysis with X-Ray Fluorescence (XRF) and X-Ray Diffraction (XRD), Sawahlunto clay consists of about 61% Si and 24% Al with a Si/Al mole ratio of 2.7 and typical clay mineral consisting of kaolinite and illite, another mineral fund was quartz and goethite. The mineral composition changes after calcination, where kaolinite and illite disappeared. Fourier Transform Infrared (FTIR) analysis shows that calcination can remove the organic compounds Sawahlunto clay; thus, the clay was used without calcination for the next step. Clay samples can be enriched with Ca2+ ions and Cu2+ ions without damaging their mineral composition, where more Cu2+ ions are loaded than Ca2+ ions. The Sawahlunto clay enriched with Ca2+ ions showed a slightly better catalytic activity in the transesterification of crude palm oil (CPO) than its parent clay; when enriched with Cu2+ ions, the catalytic activity did not appear at all. However, the homogeneous counterpart of such catalyst, calcium nitrate, was still the most active and selective compared to all others

The products of metasomatic alteration (e.g., carbonation) of peridotites are called listvenites. Based on a description of the outcrops in the laterite deposit at Cerro Matoso located in the NW of Colombia, the mineralogical composition confirmed by petrography, and a chemical analysis performed with XRF and WDS/EDS, the previous unit called tachylite is redefined as listvenite. Two types of listvenites are described: listvenite A, with the mineralogical association of quartz + siderite + phyllosilicates + goethite +/- magnetite, and listvenite B, with the association of siderite + phyllosilicates + goethite. Cr-spinel relics accompanied by Mn-siderite and neoblastic textures, indicate their origin from peridotites, where Mn-Fe would have been deposited by hydrothermal fluids. Hydrothermal reducing environments with alkaline fluids and low temperatures should have favored the formation of listvenites that are observed along a fracture zone, oriented WNW-ESE at Pit-1 in Cerro Matoso. Due to exposure to climatic conditions since the Eocene, but definitively since the last Andean Orogeny, listvenites were affected, like all the rocks in the Cerro Matoso deposit, by intense supergene weathering and leaching processes, which could make their true origin unclear.

Schwertmannite is sensitive to changes in geochemical, thermal, and microbial conditions. Changes in aqueous pH beyond its stability, i.e. pH 2.5–4.5, triggers its transformation to jarosite or goethite in highly acidic environments (pH ≤ 2.5), depending on the availability of jarosite-directing cations (Na+, NH4+, K+, etc.), while goethite is the common stable end product at pH > 7.5. Schwertmannite with degraded morphology can stably exist for years in oxic intermediate pH environments (pH 5.5–6.5), but the presence of trace amounts of Fe(II)aq yields goethite/lepidocrocite within a few hours, especially at pH ≥ 6.5. Hematite is the sole end product at ≥ 600 °C dry heating, with goethite and ferrihydrite as intermediate phases. Siderite, maghemite, and mackinawite form in anoxic microbial conditions due to dissimilatory reduction of Fe(III) and SO42− to Fe(II) and HS−, while orpiment forms from As(V)-rich schwertmannites. Sorbed contaminants enhance schwertmannite stability by restricting Fe(II)–Fe(III) electron transfer and microbial degradation by occupying surface sites. Although Fe(III) and sorbed ion mobilization typically has negligible effects on schwertmannite transformation, complete schwertmannite-SO4 release is likely in extreme conditions, and in microbial Fe(II)aq-rich media. Dissolution–reprecipitation and solid state transformation mechanisms broadly govern schwertmannite transformation.

The interaction between mineral phases in two commercial iron ores and flux materials (CaO, MgO, SiO2, and Al2O3) was studied under 0.5 kPa O2 partial pressure while heating to different temperatures. CaO was the most effective flux for liquid phase generation during sintering. For a hematite ore with few gangue components (Ore A), the formation of an initial liquid phase commenced at ~ 1275 °C, with the liquid volume increasing dramatically as temperature increased to 1300 °C. For a goethite containing hematite ore (Ore B), the formation of an initial liquid phase through interaction between goethite and CaO was observed when heating to 1225 °C, with the majority of goethite transformed to liquid at 1250 °C. The porous morphology of sintered goethite and finely distributed quartz results in a high reactivity with CaO. The initial liquid phase penetrated into the pores within the hematite matrix, promoting assimilation and by 1300 °C, all hematite in Ore B was dissolved. The hematite/martite phase in Ore B was much easier to assimilate than that in Ore A due to the presence of goethite. MgO diffused into hematite ore grains by solid-state diffusion and formed a solid solution (Fe, Mg)O∙Fe2O3 without the formation of a liquid phase. The reaction layer formed by MgO diffusion was limited to approx. 60 μm at 1300 °C. The porous morphology in goethite facilitated MgO diffusion. However, the cavities and cracks caused by goethite dehydration significantly restricted solid phase diffusion of Mg2+. There was no observed interaction between Al2O3 and SiO2 with Ores A and B when heated to 1300 °C.

Background/Objectives: Due to soaring demand and rapid depletion of high-grade iron ores, lean grade iron ores of India like BHJ and BHQ needs to be utilized through suitable beneficiation techniques. Methods: Banded Hematite Jasper (BHJ) sample of Bonai-Keonjhar belt (BK belt), Odisha, India assayed 35.3 % Fe, 47.1% SiO2 and 0.96% Al2O3 was investigated in respect of mineralogy, liberation characteristics and chemistry to finding out its optimum beneficiation potential. In the present investigation, efforts have been made to characterize the BHJ sample with reference to its beneficiation response. The sample was subjected to various beneficiation operations like Jigging followed by hydrocyclone, two-stage tabling and magnetic Separation. Findings: Mineralogical studies indicate that quartz and hematite are the major mineral phases, whereas goethite, martitized magnetite and clay (kaolinite) are present in very minor amounts. The liberation characteristic indicates that the average band thickness of Iron bearing mineral is of 1680 microns and 80% of the iron bearing minerals are liberated at -105 microns size. The two stage tabling of jig concentrate with desliming gives better outcome as compared with direct tabling of jig concentrate. An iron ore concentrate assayed 64.5% Fe, 5.6% SiO2 and 0.80% Al2O3 with wt% recovery of 23.2% can be obtained from two stage tabling. Another concentrate from magnetic separation of table middling and hydrocyclone assayed 63.2% Fe, 7.2% SiO2 and 0.7% Al2O3 with wt% recovery of 12.4% can be obtained. Novelty/ Application: Here a conventional beneficiation flow sheet is developed with a finding that, in order to beneficiate ore like banded hematite jasper (BHJ), an integral characterization approach is very much essential. Both of the concentrates obtained through the flow sheet assayed 64% Fe, 6.2% SiO2 and 0.7% Al2O3 with a wt% recovery of 35.6% can be utilized as a feed stock for pellet making in iron ore industries. Keywords: Banded Hematite Jasper (BHJ); mineral beneficiation; wet high intensity magnetic separator (WHIMS); jigging; Bonai-Keonjhar belt

The kinetics of atmospheric sulfuric acid leaching from a Brazilian nickel laterite ore was assessed using distinct reducing agents and ore mineralogy. This transitional ore contains 1.63% Ni distributed as 1.27% in coarse size (− 500 + 150 μm), mainly as silicates (lizardite and chlorite — 28.6%), and 2.06% in the fines fraction (− 75 μm), mainly as iron oxy-hydroxides (goethite and hematite — 49%). The effects of temperature, acid concentration, reducing reagent type, and concentration were evaluated. The − 75 μm fraction limited the leaching efficiency and the use of reducing media with thiosulfate improved leaching and Ni-Fe selectivity. However, at constant Eh of 626–743 mV and a pH range between 0.2 and 1.1, no substantial rise in metals extraction, except for Co and Mn, has been observed. In order to determine the process control at 95 °C, two regions in the extraction curves were used in combination with the shrinking core model. Control by porous diffusion was observed and the kinetic constant was found to be in the order kFe

Considering the recent focus of the Nigeria Government to grow and develop the nation’s economy through the solid minerals sector reform, this study has been devoted to the kinetics of a Nigerian goethite ore by hydrochloric acid leaching for improved iron and steel industries applications. This study was performed in three different phases. In the first phase, acidic leaching of iron from a goethite ore was examined and the influence of the operating variables including: HCl concentration, leaching temperature, stirring speed and particle sizes was examined experimentally. The optimum condition was found to be HCl concentration of 1.81M, temperature of 80°C, 200 rpm stirring speed and particle size 0.09 μm for iron in the range of investigated parameters. Under those conditions, the highest iron recovery was obtained to be 95.67 %. In the second phase, the dissolution kinetics of iron was evaluated by the shrinking core models. The finding reveals that diffusion through the fluid was the leaching kinetics rate controlling step of the iron. The activation energy (Ea) was found to be 14.54 kJmol-1 for iron. Equation representing the leaching kinetic of iron was achieved to be 1−2/3α - (1 − x)2/3 = 0.7272 × e−38.29/8.314×T × t. The final stage of the experiment was carried out by characterizing the leached residues by X-ray diffractometer (XRD) and scanning electron microscopy (SEM), the result showed majorly the presence of rutile (TiO2), anglesite (PbSO4), and traces of iron-silicate face like pyrite (FeS), quartz (SiO2). Keywords: kinetics modelling, leaching, low-grade, recovery, shrinking core

This study applies a combination of geochemical, mineralogical, and WorldView-2 (WV-2) data for gold prospecting in the Siyah Jangal area, southeastern Iran. Geochemical and mineralogical studies, image processing, and field studies were used to identify areas of high-potential gold mineralization. Elemental concentrations in samples collected from exploration trenches in a well-known gold mineralization area were applied to identify Au pathfinders using bivariate and multivariate statistics. Visible-near infrared-shortwave infrared spectroscopy was applied to identify mineral phases. Correlation analysis, principal component analysis, and cluster analysis of measured element concentrations showed that Au has strong associations with As, Pb, Fe, and Cu, among which, Fe is the only element that forms major minerals in the area. The spectroscopy analyses showed that iron oxide-hydroxide bearing minerals including jarosite, hematite, and goethite are the major Fe-bearing phases in the surficial environment. Therefore, mineral fraction images of these minerals were produced by performing matched filtering method on WV-2 data, and the fractions of more than 0.25 of goethite, 0.15 of hematite, and 0.10 of jarosite were combined and converted as map layers to generate a false color composite (RGB) image for targeting potential areas of gold mineralization. The accuracy of iron oxide-hydroxides mapping was proven by field observations and XRD analyses of surficial samples. Moreover, concentrations of Au in samples collected from exploration boreholes in previously mapped areas showed good correlations between enhanced areas by remote sensing studies and gold occurrences.

The water-soluble components originated in coniferous litters desorb into solution the native organic substances from the solid phase of the eluvial horizons of podzols and podzolic soil. In podzols, the water-soluble organic matter (WSOM) extracted from litter and then passing through the E horizons are sorbed by the BFH horizons if their concentration in solution exceeds 35 mg C/L. The sorption ranges from tens to hundreds of milligrams of carbon per kilogram of the BFH horizon. The WSOM can be sorbed by the BT horizons of podzolic soil when the concentration of organic substances in the liquid phase is higher than in podzols. The model experiments with minerals show that kaolinite and illite interact with the soluble substances percolating from the litter and selectively extract more hydrophilic and less aromatic components with relatively low molecular weights. On the contrary, goethite interacts with the WSOM prevalently sorbing hydrophobic components, substances of phenolic nature, components enriched in aromatic carbon, and substances with molecular weights less than 7 kDa. The spectral characteristics of WSOM change after the sorption interaction with minerals: the fluorescence associated with the humus substances with the longest conjugation chain decreases or disappears, while new fluorophores containing fragments of phenolic and/or protein structures emerge. The presence of kaolinite and illite in the eluvial horizons and their interaction with WSOM most likely contribute to the transformation of WSOM composition and appearance of the properties maximally favorable for their sorption on iron hydroxides in the lower horizons.

A two-step closed circuit, operated at 90–95oC, was found suitable for practical iron removal from real sulfuric acid leach liquors, resulting in low losses of nickel and cobalt to the solid phase....

In the current study, 62 groundwater samples were collected (31 each in premonsoon and postmonsoon seasons) and analyzed for various physicochemical parameters and trace metals in the Trans-Varuna region, Uttar Pradesh. From the cationic fields of piper chart, it is viewed that 78% and 81% samples in premonsoon and postmonsoon, respectively, fall in no dominance type, while all the samples in postmonsoon and 97% samples in premonsoon fall in bicarbonate type in anionic facies. The Ca/Mg ratio with an average of 1.44 and 1.15 in pre-monsoon and post-monsoon correspondingly points out that carbonate dissolution is the leading cause of Ca in the Trans-Varuna region. A plot between [(Na + K) − Cl] and [(Ca + Mg) − (HCO3 − SO4)] suggests that ion exchange also add ions in the groundwater. According to the Gibbs plot, the hydrogeochemistry of samples signifies that most of the samples are from rock dominance. Saturation indices point out that the groundwater of the Trans-Varuna region is saturated with chalcedony, goethite, hematite, and quartz and undersaturated with reference to anhydrite, aragonite, gypsum, halite, and fluorite. 36% sample in premonsoon and 52% samples in postmonsoon shows high NO3 concentration which is above the WHO standard for drinking purpose. In terms of Fe, 74% of samples are beyond the permissible limit of WHO. Various indices to estimate the aptness of groundwater for agricultural function indicate that most of the samples in both the seasons are safe of farming uses. Chronic daily intake values show that infants and children of the investigative region are very vulnerable to nitrate contamination. Target health quotient of heavy metals was established in the sequence of Pb > Zn > Mn > Fe > Ni > Cu.

Many lateritic soils contain goethite and hematite, which have a low thermal expansion coefficient and also enhance the formation of soil aggregates. The influence of these minerals on the thermo-mechanical soil behaviour, however, has not been well understood. In this study, cyclic thermal strain of a small number of specimens of saturated lateritic clay was investigated over a temperature range of 5 to 70 °C, using a thermal oedometer equipped with an invar ring. Both compacted and reconstituted specimens, which were expected to have different degrees of aggregation, were tested. The soil was characterised in terms of its mineralogy and microstructure determined respectively using x-ray diffraction (XRD) and scanning electron microscopy (SEM). It was found that a semi-empirical equation over-estimated the thermal expansion coefficient of normally consolidated (NC) lateritic clay by about 3 times. The discrepancy is mainly because the goethite and hematite in the lateritic clay enhance the formation of aggregates and stiffen the specimen. Even the reconstituted specimen contains many aggregates, as clearly revealed by the result SEM tests. Goethite and hematite have much lower thermal expansion coefficient (TEC) than many clay minerals. On the other hand, it was found that both NC compacted and reconstituted specimens showed an accumulation of irreversible contraction under cyclic heating and cooling, but at a decreasing rate, where for a given number of thermal cycles, the measured thermal strain of NC reconstituted specimens was about 30% lower than that of the NC compacted specimens. This is mainly because the density of NC reconstituted specimen is much higher than the NC compacted specimen, even though they had experienced the same effective stress.

Microbial iron reduction is a ubiquitous biogeochemical process driven by diverse microorganisms in a variety of environments. However, it is often difficult to separate the biological from the geochemical controls on bioreduction of Fe(III) oxides. Here, we investigated the primary driving factor(s) that mediate secondary iron mineral formation over a broad range of environmental conditions using a single dissimilatory iron reducer, Orenia metallireducens strain Z6. A total of 17 distinct geochemical conditions were tested with differing pH (6.5-8.5), temperature (22-50 °C), salinity (2-20% NaCl), anions (phosphate and sulfate), electron shuttle (anthraquinone-2,6-disulfonate), and Fe(III) oxide mineralogy (ferrihydrite, lepidocrocite, goethite, hematite, and magnetite). The observed rates and extent of iron reduction differed significantly with kint between 0.186 and 1.702 mmol L-1 day-1 and Fe(II) production ranging from 6.3% to 83.7% of the initial Fe(III). Using X-ray absorption and scattering techniques (EXAFS and XRD), we identified and assessed the relationship between secondary minerals and the specific environmental conditions. It was inferred that the observed bifurcation of the mineralization pathways may be mediated by differing extents of Fe(II) sorption on the remaining Fe(III) minerals. These results expand our understanding of the controls on biomineralization during microbial iron reduction and aid the development of practical applications.

The mineralogical characteristics of three kinds of gibbsitic high-iron bauxite and the effects of various digestion conditions on the enrichment and separation of iron minerals were investigated. The results show that adding an appropriate organic reductant such as glycerol can promote the digestion of concomitant diaspore, boehmite and alumogoethite as well as the conversion of goethite to hematite in the reductive Bayer digestion. Processing Bauxite A with A/S of 25.41 can directly produce qualified iron concentrates (TFe>56%) by the reductive Bayer digestion, and thus realize the zero red mud discharge. For Bauxite B and Bauxite C with A/S of 7.82 and 3.35, the iron recoveries of 65.13% and 79.13% can be achieved with the corresponding TFe of 52.05% and 50.16% in the iron concentrates by gravity separation, respectively, resulting in the red mud discharge reduction of ~50% or above.

Biogenic nanoscale vanadium magnetite is produced by converting V(V)-bearing ferrihydrites through reductive transformation using the metal-reducing bacterium Geobacter sulfurreducens. With increasing vanadium in the ferrihydrite, the amount of V-doped magnetite produced decreased due to V-toxicity which interrupted the reduction pathway ferrihydrite–magnetite, resulting in siderite or goethite formation. Fe L2,3 and V L2,3 X-ray absorption spectra and data from X-ray magnetic circular dichroism analysis revealed the magnetite to contain the V in the Fe(III) Oh site, predominately as V(III) but always with a component of V(VI), present a consistent V(IV)/V(III) ratio in the range 0.28 to 0.33. The bacteriogenic production of V-doped magnetite nanoparticles from V-doped ferrihydrite is confirmed and the work reveals that microbial reduction of contaminant V(V) to V(III)/V(IV) in the environment will occur below the Fe-redox boundary where it will be immobilised in biomagnetite nanoparticles.

The corrosion behaviour of mill-scaled X65 pipeline steel with and without a primer layer was studied in a simulated near-neutral pH soil solution. Results revealed a three-stage corrosion process of the mill-scaled pipeline steel surface. The first stage included an initial preferential dissolution of goethite (α-FeOOH) and lepidocrocite (γ-FeOOH) in mill scale. The second stage was marked by enhanced localized corrosion and pit-formation because of either galvanic corrosion or acidic dissolution in areas enclosed by mill scale. The final stage was general corrosion after the mill scale flaked off the steel surface. When the primer layer was applied, localized corrosion was significantly enhanced on the steel surface and persisted for an extended period as compared to the mill-scaled condition. The precipitation of siderite (FeCO3) was observed at flawed locations of mill scale, although the bulk chemistry is not favorable for its formation on the steel surface free of mill scale. The local precipitation of siderite formed a capped mill scale enclosure where localized corrosion can be further enhanced.

Three typical litho-types such as ‘saprolite,’ ‘bauxite’ and ‘laterite/lateritic ore’ from different levels of khondalite-hosted bauxite profile of Baphlimali plateau, Rayagada district, Odisha, Eastern India, have been studied. Mineralogical variations between different size fractions are interpreted for their optimum utilization. Mineralogy of individual bulk and its respective classified fractions are established from their XRD, DTA and TGA patterns. The saprolite, present in the lower most level of the profile, is rich in aluminum silicate (kaolinite), does not find use in alumina refinery and is usually considered as waste. However, if it is size-classified, the − 2.0 + 0.50 mm fraction, measuring over 21% by volume of the bulk, is found to contain substantial amount of gibbsite that can be separated and utilized for alumina recovery. The bauxite, present at the intermediate level of the profile, is rich in aluminum hydroxide (gibbsite). However, sometimes it contains hematite as major impurities (Fe ~ 10%). Though such ore is of metallurgical grade, around 26 vol% of the ore can be used for refractory purpose by simple separation of

Aqueous Fe(II) can induce recrystallization of ferrihydrite and goethite [α-FeOOH] to their more crystalline or molecularly homogeneous counterparts. Despite common association with these and other...

Potential acid sulfate soils (PASS) are drained for agriculture, resulting in the formation of active acid sulfate soils (AASS), which gradually evolve into post-active acid sulfate soils (PAASS). Various redox concentrations (precipitates, costings, and mottles) occur in these soils as a result of pedogenic processes including biological activity and effects of land management. Although several studies have determined the mineralogy and geochemistry of ASS, the mineralogy and geochemistry of redox concentrations occurring in a sequence of ASS through PASS to PAASS have not been investigated. This study examined the mineralogy and geochemistry of redox concentrations and matrices within 5 PASS, 8 AASS, and 5 PAASS in Thailand. The labile minerals were predominantly controlled by oxidation status and management inputs. The unoxidized layers of PASS, AASS, and PAASS contained pyrite and mackinawite. The oxidation of Fe sulfides caused acidification and accumulation of yellow redox concentrations of jarosite and Fe (hydr)oxides at shallow depths. As the soils became well developed, they were recognized as PAASS, and the jarosite and goethite transformed to hematite. As ASS were drained, Co, Mn, Ni, and Zn moved downward and were associated with Fe sulfides and Mn oxides in the unoxided layer. Concentrations of As, Cu, Cr, Fe, and V did not change with depth because these elements became associated with jarosite and Fe (hydr)oxides in yellow and red redox concentrations, as well as the root zone, in the partly oxidized layer of AASS and PAASS. Arsenic was associated with pyrite under reducing conditions.

Iron ore deposits hosted by Precambrian banded iron formation (BIF) are the most important source of mineable iron. In Cameroon, they are located in the southern part of the country. This study reports the petrological and geochemical data of iron ores collected from a weathering profile in the Mamelles BIF deposit, SW Cameroon. The profile is composed of three levels which are from the bottom to the top: the saprock, the ferruginous horizon, and the loose horizon. Eight representative iron ore samples (rock fragments and loose clayey material) were collected along the profile and were subjected to petrographic and geochemical analyses. Their mineralogy consists of martite, goethite, quartz, and lesser amounts of hematite, magnetite, kaolinite, and halloysite. The presence of minerals such as kaolinite and goethite in the Mamelles iron ores suggests their supergene origin. Geochemically, the saprock is characterized by high iron content (70.25 wt% Fe2O3t), and low silica (26.38 wt% SiO2) and alumina (1.14 wt% Al2O3). The rock fragments collected from the ferruginous horizon display higher Fe2O3t (72–76.40 wt%), Al2O3 (2.80–5.43 wt%), and lower SiO2 (16.70–18.35 wt%) contents, suggesting the leaching of silica during the enrichment process. The loose clayey samples collected from both the ferruginous horizon and the upper loose horizon show lower iron and higher silica contents. When normalized to the underlying BIF saprock, both rock fragments and loose clayey ores display LREE enrichment, suggesting that they formed through supergene processes. Economically, most of the Mamelles iron ores are classified as medium-grade ores and a few display acceptable contents in contaminants. Overall, this petrological and geochemical study of the Mamelles iron ores revealed encouraging results. Given its strategic location near the deep seaport, the deposit should be investigated in more detail for its mining potential.

Diffuse reflectance spectroscopy (DRS) parameters, such as the redness index and hematite/goethite ratios are popular in the study of loess-paleosol sequences. The suggested parameters, however, have their limitations: only some parts of the whole reflectance spectrum are being used, and the spectra of some important components may be excluded from the analysis. A mathematical statistical method, hierarchical cluster analysis, was applied to the loess-paleosol succession at Mala nad Hronom (Slovak Republic) in order to characterize the entire reflectance spectrum and to classify sediment groups. The sedimentary units were classified into seven different cluster groups such as sediments, weak and well-developed paleosols. The distribution of the spectral features in the reflectance spectra was located by using the key-wavelength, provided by the Wilk's lambda analysis. The key-minerals, which play an important role in the classification, were determined by characteristic extrema in the second derivative of reflectance spectra of the seven reference minerals (hematite, goethite, muscovite, illite, montmorillonite, kaolinite and calcite). Mineral groups influence certain wavelengths within the measured range, therefore curve sections modified by individual minerals only in a few cases. The mentioned mineral groups refer to characteristics of the formation environment and to climate change during the Pleistocene.

Neutrophilic, microaerobic Fe(II)-oxidizing bacteria (FeOB) from marine and freshwater environments are known to generate twisted ribbon-like organo-mineral stalks. These structures, which are extracellularly precipitated, are susceptible to chemical influences in the environment once synthesized. In this paper, we characterize the minerals associated with freshwater FeOB stalks in order to evaluate key organo-mineral mechanisms involved in biomineral formation. Micro-Raman spectroscopy and Field Emission Scanning Electron Microscopy revealed that FeOB isolated from drinking water wells in Sweden produced stalks with ferrihydrite, lepidocrocite and goethite as main mineral components. Based on our observations made by micro- Raman Spectroscopy, field emission scanning electron microscopy and scanning transmission electron microscopy combined with electron energy-loss spectroscopy, we propose a model that describes the crystal-growth mechanism, the Fe-oxidation state, and the mineralogical state of the stalks, as well as the biogenic contribution to these features. Our study suggests that the main crystal-growth mechanism in stalks includes nanoparticle aggregation and dissolution/re-precipitation reactions, which are dominant near the organic exopolymeric material produced by the microorganism and in the peripheral region of the stalk, respectively.

The Haleo-Danielle Plateau bauxite deposit forms the largest part of the 15 km long Minim-Martap Bauxite ore district in the Adamawa Region of Cameroon. The plateau is covered with thin Upper Pleistocene to Holocene alluvial layer. It covers by laterites and bauxites formed on Tertiary-Quaternary basalts. Gibbsite and boehmite are the aluminum oxide found in the bauxite, while goethite is the main oxyhydroxide iron mineral. Bauxite rock samples from the plateau were collected and investigated with the XRF technique for their chemical composition and parent rocks. Chemical investigation reveals average concentration of the major ore components as: Al2O3 (43.73%), Fe2O3 (24.53%), SiO2 (2.12%), and TiO2 (3.54%). Abundant trace and rare elements include Zr (667.25 ppm), V (446.4 ppm), Ce (107.93 ppm), Sr (98.46 ppm), Nb (92.1 ppm), La (58.05 ppm), Ga (55.3 ppm), Ba (53.53 ppm), Nd (37.96 ppm), and ΣREE (245.8%). Calculations of the degree of chemical weathering (Ruxton Ratio) and geochemical coefficient (CIA) indicate that plateau rocks were subjected to intensive weathering, which led to the formation of industrial bauxite deposits. According to the results of processing the chemical composition of bauxites using three independent classification systems, plateau deposits can be classified as ferruginous bauxites. Parent rocks investigation indicates that bauxite was formed due to the decomposition of magnesium-ferrous andesite-basalts under conditions with a near neutral redox potential.

The complex of modern physical methods for studying authigenic carbonate crusts in the Miocene bryozoan bioherms of the Kazantip Cape (Kerch Peninsula) has made it possible to reveal fossil biofilms and glycocalyx for the first time. These finds indicate that methanotrophic carbonate-precipitated bacteria during their activity strengthened brittle bryozoan skeletons. The presence of cavities in bioherms incrusted with goethite crusts, the presence of bitumen, pyrite, strontianite, barite, kutnagorite in the composition of carbonate crusts, and traces of the vital activity of methanotrophic bacteria are associated with the significant influence of near-bottom local gas–fluid seeps. This situation was determined by the occurrence of a discharge zone of rising gas–fluid flows in the Kazantip Cape area as a result of activation of mud volcanism, typical of the Neogene–Holocene interval of the Kerch–Taman Region.

The dynamic interactions among iron (Fe) oxides, organic matter (OM) and heavy metals/metalloids play crucial roles in controlling the geochemical cycling of carbon (C) and heavy metals/metalloids in natural environments. Although the inhibitory effects of arsenate (As(V)) or OM on the ferrihydrite transformation process have been studied previously, there is still a lack of mechanistic and quantitative understanding on the kinetics of As(V) and C sequestration during the Fe(II)-induced ferrihydrite transformation. In this study, we employed a suite of techniques to elucidate the underlying mechanisms accounting for the temporal changes of As(V) and C distributions and speciation on Fe oxides during the Fe(II)-induced ferrihydrite transformation process. Characterizations with X-ray diffraction (XRD), X-ray absorption spectroscopy (XAS), and the spherical aberration corrected scanning transmission electron microscopy (Cs-STEM) at different times indicated that the presence of As and/or FA resulted in the formation of more lepidocrocite than goethite. Besides surface adsorption, a portion of As(V) may be incorporated into the lattice structures of newly formed crystalline Fe oxides, and the amount of As(V) sequestration within Fe oxides were correlated with the formation of crystalline Fe oxides. In comparison, FA molecules were either adsorbed on the surfaces of goethite or diffused into the defects or nano pore spaces of lepidocrocite. Our results shed the light on different nanoscale mechanisms accounting for the sequestration of C and As(V) on Fe oxides. The defects or nano pore spaces formed in the structures of lepidocrocite may provide an effective way to sequester C through physical isolation, while the crystal structures of Fe oxides may sequester As(V) through isomorphic substitution. The knowledge on the dynamic coupling between Fe oxide transformation and C/As(V) sequestration provided the basis for accurately predicting the geochemical cycling of trace elements and OM.