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Current technologies for removal of Cr(VI) are generally fit for acidic wastewater. In this study, a new ferrite process for removal and recycling of Cr(VI) from alkaline wastewater to produce the valuable chromium ferrite has been developed. The results show that this new ferrite method is a one-step process which can be divided into two successive reactions including Cr(VI) reduction to form coprecipitation (Cr0.25Fe0.75(OH)3) and subsequently magnetic conversion of Cr0.25Fe0.75(OH)3 induced by Fe2+ under the same alkaline condition. The total Fe/Cr mole ratio of 5:1 is at least required for the chromium ferrite transformation. Increasing temperature and pH can enhance the interaction of Fe2+ with Cr0.25Fe0.75(OH)3 and further promote the formation of chromium ferrite, while suppressing the generation of nonmagnetic by-product goethite. Almost pure chromium ferrite is formed under proposed optimum conditions (Fe/Cr = 7:1, 65 °C and pH of 9) with Cr(VI) removal ratio around 100%. The Cr(VI) remained in the filtrate can be reduced to 0.01 mg/L which is much lower than the limits concentration for surface water (≤0.05 mg/L). The chromium ferrite product whose molecular formula can be expressed as Cr0.5-xFe2.5+xO4 (where 0 ≤ x

A peerless inexpensive electrochemical engineering of spherical Pt nanoparticles (nano-Pt: ca. 100 nm in average diameter) was achieved with intersected ferric oxyhydroxide nanotubes (α-FeOOH (goethite): ca. 20 nm in average diameter). The FeOOH@Pt catalyst exhibited ca. 2.5 and 1.94-times increases in the catalytic activity and poisoning tolerance, respectively, of the formic acid electro−oxidation (FAO) – the anodic reaction in the direct formic acid fuel cells (DFAFCs). Surprisingly, with a post-activation of the FeOOH@Pt catalyst at 0.48 V vs. reversible hydrogen electrode (RHE) in 0.2 mol L−1 NaOH, a favorable Fe2+/Fe3+ transformation succeeded to eliminate the permanent CO poisoning of Pt that impaired the catalytic performance of DFAFCs. This was synchronized (relatively to nano-Pt) with a four-fold increase in the catalytic efficiency, ca. −174 mV shift in the onset potential, and eightfold enhancement in the catalyst's durability for FAO. The activated FeOOH@Pt catalyst also showed a mass activity of 296 mA mg−1Pt (at 0.8 V), which was ca. nine times higher than that (34 mA mg−1Pt) of the commercial Pt/C catalyst. The ascertained improvement in the electron transfer at the FeOOH@Pt surface foresees quick industrialization for DFAFCs.

Goethite nanoparticles attached to sand grains in column reactors increase grown in length when exposed to ferrous iron and 4-chloronitrobenzene.

There is significant environmental concern about chlorinated organic compounds (COCs) in wastewater, surface water, and groundwater due to their low biodegradability and high persistence. In this work, 1,2,4-trichlorobenzene (124-TCB) was selected as a model compound to study its abatement using wet peroxide oxidation at neutral pH with goethite as a heterogeneous catalyst, which was enhanced with visible monochromatic light-emitting diode (LED) light (470 nm). A systematic study of the main operating variables (oxidant and catalyst concentration and irradiance) was accomplished to investigate their influence in the abatement of 124-TCB in water. The reaction was carried out in a well-mixed reactor of glass irradiated by a visible LED light. The hydrogen peroxide concentration was tested from 0 to 18 mM, the goethite concentration within the range 0.1–1.0 g·L−1 and the irradiance from 0.10 to 0.24 W·cm−2 at neutral pH. It was found that this oxidation method is a very efficient technique to abate 124-TCB, reaching a pollutant conversion of 0.9 when using 0.1 g·L−1 of goethite, 18 mM of H2O2, and 0.24 of W·cm−2 . Moreover, the system performance was evaluated using the photonic efficiency (ratio of the moles of 124-TCB abated and the moles of photons arriving at the reactor window). The maximum photonic efficiencies were obtained using the lowest lamp powers and moderate to high catalyst loads. Fil: Lorenzo, David. Universidad Complutense de Madrid; España Fil: Santos, Aurora. Universidad Complutense de Madrid; España Fil: Sánchez-Yepes, Andrés. Universidad Complutense de Madrid; España Fil: Conte, Leandro Oscar. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; Argentina Fil: Domínguez, Carmen María. Universidad Complutense de Madrid; España

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.

Antimony (Sb) mobilization is widely explored with dissimilatory metal-reducing bacteria (DMRB) via microbial iron(III)-reduction. Here, our study found a previously unknown pathway whereby DMRB release adsorbed antimonite (SbIII-O) from goethite via elemental sulfur (S0) respiratory reduction under mild alkaline conditions. We incubated SbIII-O-loaded goethite with Shewanella oneidensis MR-1 in the presence of S0 at pH 8.5. The incubation results showed that MR-1 reduced S0 instead of goethite, and biogenic sulfide induced the formation of thioantimonite (SbIII-S). SbIII-S was then oxidized by S0 to mobile thioantimonate (SbV-S), resulting in over fourfold greater Sb release to water compared with the abiotic control. SbIV-S was identified as the intermediate during the oxidation process by Fourier transform ion cyclotron resonance mass spectrometry and electron spin resonance analysis. The existence of SbIV-S reveals that the oxidation of SbIII-S to SbV-S follows a two-step consecutive one-electron transfer from Sb to S atoms. SbV-S then links with SbIII-S by sharing S atoms and inhibits SbIII-S polymerization and SbIII2S3 precipitation like a “capping agent”. This study clarifies the thiolation and oxidation pathway of SbIII-O to SbV-S by S0 respiration and expands the role of DMRB in the fate of Sb.

Sorption of Mo to goethite and related iron (hydr)oxides plays an important role in controlling the mobility of Mo in soil and aquatic environments. We first performed ab-initio molecular dynamics (MD) simulations of Mo complexation at the goethite {1 0 1}-water interface. We find that molybdenum adsorbed on goethite mainly exists as the inner-sphere tetrahedral bidentate and monodentate corner-sharing complex, instead of the previous argued bidentate edge-sharing or outer-sphere complex. Different from previous literature, we didn’t find any distorted octahedral structure of Mo on goethite. The predicted Mo-Fe distances of bidentate and monodentate corner-sharing complex based on ab-initio MD is 3.53 and 3.38 A, respectively, which are consistent with the fitted Mo-Fe distances: 3.40 ± 0.15 A and 3.41 ± 0.1 A from EXAFS. We measured the adsorption of Mo (VI) on goethite (α-FeOOH) at different initial concentration and pH from 3 to 11 under N2 atmosphere and constructed a surface complexation model that is consistent with the molecular speciation based on ab-initio MD, XANES, EXAFS and reported in-situ ATR-IR analysis (Davantes and Lefevre, 2015, 2016). Application of SCM for Mo on goethite assuming iron oxides as the principal component of ferromanganese crust (containing average 276 mg/kg Mo) will have ∼0.3 μg/l Mo in seawater in equilibrium. The observed ∼10 μg/l Mo in seawater (c a. 400–800 yr) is between 0.3 (adsorption equilibrium by marine goethite) and 23 μg/l (adsorption equilibrium by marine birnessite, Kashiwabara et al., 2011), suggesting that molybdenum in seawater has reached equilibrium with ferromanganese crust, and goethite (57%) probably plays a more important role than birnessite (43%) in regulating molybdenum abundance in the ocean, which has not been fully recognized in past. Observed molybdenum isotopic fractionation between seawater and ferromanganese crust excesses the experimental molybdenum isotopic fractionation range during adsorption by birnessite and goethite (Goldberg et al., 2009). Based on reported experimental molybdenum isotopic fractionation values and our SCM prediction, the molybdenum isotopic fractionation δ98/95Mo value should vary between 1.6 and 2.3‰, which is lower than the observed range between seawater and ferromanganese crust: 2.7–3.2‰ about 1‰, suggesting the disequilibrium of molybdenum isotopic fractionation in ocean. To clarify the discrepancy, this study highlights the necessity of clarifying the molybdenum source in hydrogenic and hydrothermal ferromanganese crusts before understanding molybdenum isotopic fractionation between seawater and ferromanganese crust.

Color-induced changes in stones due to heating can be useful in determining the degree of degradation generated in their components and structure. We evaluate the effect of heating in three types of limestones, useful in building and restoration, corresponding to biomicrite (BC), biosparite (BS), and intramicrite (IM), in the range of temperature from 100°C to 600°C. Our analyses indicate that the strongest changes in reflectance occur in the samples of intramicrite, followed by biomicrite, being biosparite showing the smallest ones. Additionally, IM samples suffer the largest modifications in effective porosity due to the thermal treatment; in contrast, BS and BC samples show smaller temperature-induced alterations associated with smaller changes in reflectance. Moreover, we reveal that most of the thermally induced variations are associated, in this range of temperature, to the dehydroxylation of goethite that transforms into hematite, as well as by the burning and partial release of the organic matter present in the rock. Colorimetry analyses show that the sequence of thermally induced changes can be followed by the evolution of the three coordinates, L ∗ (lightness), a ∗ (red-green), and b ∗ (yellow-blue), of the CIE 1976 L ∗ a ∗ b ∗ space.

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.

Podzols are characterised by mobilisation of metals, particularly Al and Fe, and dissolved organic matter (DOM) in topsoil horizons, and by immobilisation in subsoil horizons. We mimicked element mobilisation during early podzolisation by irrigating the AE horizon of a Dystric Arenosol with acetic acid at different flow velocities and applying flow interruptions to study rate-limited release in experiments with soil cylinders. We used eluates in batch experiments with goethite and Al-saturated montmorillonite to investigate DOM reactivity towards minerals. Both the flow velocity and flow interruptions affected element release, pointing to chemical non-equilibrium of release and to particles, containing Fe and OM mobilised at larger flow velocity, characteristic of heavy rain or snowmelt. Based on chemical extractions, the source of mobilised Al and Fe, the vast majority of which was complexed by DOM, was no oxide phase, but rather organic. Rate limitation also affected the composition of DOM released. Carboxyl and phenolic species were the most important species adsorbed by both minerals. However, DOM composition affected the extent of DOM adsorption on goethite more distinctly than that on montmorillonite. Our findings evidence that the intensity of soil percolation affects quantitative and qualitative element release during early podzolisation and adsorptive DOM retention in subsoil horizons.

Gadolinium iron garnet was obtained from two different precursors, homogenized in isopropyl alcohol and in an aqueous environment with a fixed pH. In the first case, it was a mixture of goethite (FeO(OH)) and gadolinium oxide (Gd2O3); in the second, a mixture of GdIP (GdFeO3) and α-Fe2O3. Conditions of homogenization in the aqueous environment were selected based on the zeta (ξ) potential measurements as the function of pH. DSC measurements of the output powder mixtures allowed the identification of the effects observed during the temperature rise. In the case of the material obtained from a mixture of goethite (FeO(OH)) and gadolinium oxide, with the increasing temperature, we observe three effects, the first of which corresponds to the phase transformation of goethite into α-Fe2O3, the second corresponds to the reaction of gadolinium iron perovskite (GdIP) formation, and the third to the reaction in which a gadolinium iron garnet (GdIG) is formed. However, in the case of heat treatment of the mixture of GdIP and α-Fe2O3, we only observe the effect responsible for a solid state reaction leading to the formation of gadolinium iron garnet. Dilatometric measurements allowed to determine the changes in linear dimensions at various stages of reaction sintering. The resulting materials were sintered at temperatures of 1200, 1300, and 1400 °C. In the case of the material obtained from a mixture of perovskite and iron (III) oxide, already at the temperature of 1300 °C, a density has been obtained at around 95% of the theoretical density, and the temperature of 1400 °C allowed achieving a density of 97% of the theoretical density. Whereas, for the material obtained from a mixture of goethite (FeO(OH)) and gadolinium oxide, a density above 95% of theoretical density was achieved only at 1400 °C.

Cadmium (Cd) isotopes have great potential for understanding Cd geochemical cycling in soil and aquatic systems. Iron (oxyhydr)oxides can sequester Cd via adsorption and isomorphous substitution, but how these interactions affect Cd isotope fractionation remains unknown. Here, we show that adsorption preferentially enriches lighter Cd isotopes on iron (oxyhydr)oxide surfaces through equilibrium fractionation, with a similar fractionation magnitude (Δ114/110Cdsolid-solution) for goethite (Goe) (−0.51 ± 0.04‰), hematite (Hem) (−0.54 ± 0.10‰), and ferrihydrite (Fh) (−0.55 ± 0.03‰). Neither the initial Cd2+ concentration or ionic strength nor the pH influence the fractionation magnitude. The enrichment of the light isotope is attributed to the adsorption of highly distorted [CdO6] on solids, as indicated by Cd K-edge extended X-ray absorption fine-structure analysis. In contrast, Cd incorporation into Goe by substitution for lattice Fe at a Cd/Fe molar ratio of 0.05 preferentially sequesters heavy Cd isotopes, with a Δ114/110Cdsolid-solution of 0.22 ± 0.01‰. The fractionation probably occurs during the transformation of Fh into Goe via dissolution and reprecipitation. These results improve the understanding of the Cd isotope fractionation behavior being affected by iron (oxyhydr)oxides in Earth’s critical zone and demonstrate that interactions with minerals can obscure anthropogenic and natural Cd isotope characteristics, which should be carefully considered when applying Cd isotopes as environmental tracers.

The adsorption of cobalt ions was evaluated using sediment samples from water bodies to investigate the adsorption properties of sediment and the behavior of these natural materials in the presence of nuclear and industrial waste. The two sediments (S1 and S2) were treated to eliminate humic and fulvic acids and then they were characterized by several techniques. The minerals found in both the sediments (X-ray diffraction) were quartz and albite; plus, goethite and muscovite in S1, and kaolinite and montmorillonite in S2. Point of zero charge (PZC) of S1 and S2 was 6.00 and 5.22, respectively. The specific area of S1 (63.3 m2/g) is higher than S2 (1.5 m2/g). Adsorption kinetics data for S1 and S2 were best fitted to the pseudo second-order model. The removal efficiency of S1 for cobalt was 96% with an adsorption capacity (qe) of 0.93 mg/g, and for S2 was 45% with a qe of 0.40 mg/g. The experimental data of the adsorption isotherms were adjusted to Langmuir and Freundlich models for S1 and S2, respectively. The thermodynamic parameters (enthalpy, entropy, and Gibb's free energy) indicated that the adsorption processes were endothermic, spontaneous, and chemisorption mechanism. The results show that the adsorption capacities of the sediments depend on their composition. These water sediments have important adsorption properties for cobalt, and they can be used in the treatment of nuclear and industrial aqueous wastes.

The main ore minerals of all layers of cobalt-rich ferromanganese crusts of Guyot Govorov of the Magellanic Mountains of the Pacific Ocean are poorly crystallized, poorly structurally ordered Fe-vernadite, Mn-feroxigite. A sufficiently structurally ordered vernadite, which is mainly found in layer I–1 and in a smaller amount in layer I–2, has also been identified as goethite. As an impurity, asbolan-buzerite and buzerite-I are noted. The distribution of cations of non-ferrous, heavy, rare, and rare-earth elements in the layers of Govorov Guyot crusts indicates that they are clearly unevenly supplied to the cobalt-rich ferromanganese crusts.

Pure and Sn-doped goethite (α-FeOOH) nanoparticles with good uniformity were synthesized by a facile precipitation method. The effects of Sn doping on the particle size and shape, structural, thermal, vibrational, optical and photocatalytic properties of prepared goethite nanoparticles were investigated. The Sn4+-for-Fe3+ substitution in the crystal structure of goethite was proved by determination of a significant unit cell expansion (the effect of larger Sn4+ ions) and a substantial reduction of the hyperfine magnetic field (the effect of magnetic dilution by non-magnetic Sn4+ ions). Sn doping induced a decrease in length and an increase in thickness of goethite nanocrystallites and nanoparticles, i.e., the change in particle shape from thin goethite nanorods to shorter and thicker Sn-doped goethite nanoellipsoids and nanocuboids. Thermal dehydroxylation of goethite was shifted to significantly higher temperatures by the Sn4+-for- Fe3+ substitution. The optical band gap of goethite nanoparticles narrowed with the increased Sn4+-for- Fe3+ substitution. The visible light photocatalytic efficiency for rhodamine B (RhB) degradation by a heterogeneous photo-Fenton process was gradually enhanced by Sn doping from 38% for pure goethite nanorods to 55% for Sn-doped nanoellipsoids and 70% for Sn-doped goethite nanocuboids.

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).

Adsorption of uranium onto goethite is an important partitioning process that controls uranium mobility in subsurface environments, for which many different surface complexation models (SCMs) have been developed. While individual models can fit the data for which they are parameterized, many perform poorly when compared with experimental data covering a broader range of conditions. There is an imperative need to quantitatively evaluate the variations in the models and to develop a more robust model that can be used with more confidence across the wide range of conditions. We conducted an intercomparison and refinement of the SCMs based on a metadata analysis. By seeking the globally best fit to a composite dataset with wide ranges of pH, solid/sorbate ratios, and carbonate concentrations, we developed a series of models with different levels of complexity following a systematic roadmap. The goethite-uranyl-carbonate ternary surface complexes were required in every model. For the spectroscopically informed models, a triple-plane model was found to provide the best fit, but the performance of the double-layer model with bidentate goethite-uranyl and goethite-uranyl-carbonate complexes was also comparable. Nevertheless, the models that ignore the bidentate feature of uranyl surface complexation consistently performed poorly. The goodness of fitting for the models that ignore adsorption of carbonate and the charge distributions was not significantly compromised compared with that of their counterparts that considered those. This approach of model development for a large and varied dataset improved our understanding of U(VI)-goethite surface reactions and can lead to a path for generating a single set of reactions and equilibrium constants for including U(VI) adsorption onto goethite in reactive transport models.

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.

Red mud and coal gangue are industrial solid wastes discharged during alumina extraction and coal mining, respectively. As these are hazardous materials, their disposal leads to serious environmental issues. In this study, an innovative utilization of red mud through co-roasting with coal gangue for separation and recycling of iron and aluminum minerals is presented. Under optimum co-roasting conditions (550 °C for 50 min), an iron concentrate containing 57.25% TFe (total iron content) with the recovery of 65.22%, and an aluminum-rich product containing 27.26% Al2O3 with the recovery of 71.37% were obtained after magnetic separation. The characteristics of mixed raw material and products all indicated that the goethite and hematite phases in the mixed raw material were transformed into a magnetite phase after co-roasting, although some of the magnetite generated during co-roasting was oxidized to hematite again. This study demonstrates that co-roasting of coal gangue and red mud is a promising technology for the reduction of iron and activation of aluminum to realize resource recycling without additional materials.

The effect of pH regulation on schwertmannite bio-synthesis and its As removal ability were investigated in this study. The total Fe precipitation efficiency in a conventional schwertmannite bio-synthesis system (CK) reached 26.5%, with a mineral weight of 5.21 g/L and a mineral specific surface area of 3.18 m2/g. The total Fe precipitation efficiency increased to 88.4%-95.8%, the mineral weight increased to 17.10-18.62 g/L, and the specific surface area increased to 3.61-90.67 m2/g of five different treatments in which the system pH was continually adjusted to 2.50, 2.70, 2.90, 3.10, and 3.30 every 3 h, respectively. The very small amounts of schwertmannite were transformed to goethite when the system pH was periodically adjusted to 2.90, 3.10 and 3.30. The increased specific surface area of bio-schwertmannite was due to the contribution of mesopores, with most pores having a diameter of 2-20 nm. For actual As-containing groundwater (27.4 μg/L), the As removal rate was 52.9% for bio-schwertmannite collected from the CK system. However, the removal rate of As increased to 92.7%-97.8% for minerals which were collected after five adjusted pH treatments. The outcomes of this study provide a fresh insight into the bio-synthesis regulation of schwertmannite, and have great significance for the treatment of As-containing groundwater.

The adsorption of organic matter and phosphate on minerals is a common natural process that has an important impact on the migration and burial of carbon and phosphorus. Previous studies have focused mainly on the influence of organic matter on the adsorption of phosphate. Yet, the influence of phosphate on the adsorption of different pools of organic matter is not well understood. This study evaluates changes in different organic matter pools during their adsorption to minerals in the presence of phosphate. Firstly, the adsorption behaviors of natural organic matter (i.e., humic acid) and phosphate on goethite were evaluated separately. Secondly, humic acid and phosphate were added to goethite at different orders to elucidate the effect of phosphate on the fractionation of humic acid components adsorbed to goethite. The results showed that when phosphate and humic acid were added simultaneously, goethite was preferentially combined with phosphate. In the absence of phosphate, SUVA254 of the humic acid solution decreased and E2/E3 of the solution increased during the adsorption. Among the six EEM-PARAFAC (excitation-emission matrix fluorescence coupled with parallel factor analysis) components of the humic acid, C1, C2, and C4 (terrestrial humus-like substances) decreased significantly and exhibited strong adsorption, C3 (microbial fulvic-like substance) showed weak adsorption, whereas C5 (photodegradation products) and C6 (tyrosine-like component) did not show evident adsorption. In the presence of phosphate, phosphate inhibited, and replaced the adsorbed C1, C2, and C4, but promoted the adsorption of C5, which increased the aromaticity and the molecular weight of the humic acid solution. Our results reveal that phosphate influences the fractionation of humic acid components adsorbed onto goethite, suggesting that phosphate can alter the chemical composition of natural organic matter interacting with minerals and thus impact the burial and fractionation of natural organic matter at the mineral-water interface.

Iron reduction and sulfate reduction often occur simultaneously in anoxic systems, and where that is the case, the molar ratio between the reactions (i.e., Fe/SO42- reduced) influences their impact on water quality and carbon storage. Previous research has shown that pH and the supply of electron donors and acceptors affect that ratio, but it is unclear how their influences compare and affect one another. This study examines impacts of pH and the supply of acetate, sulfate, and goethite on the ratio of iron to sulfate reduction in semi-continuous sediment bioreactors. We examined which parameter had the greatest impact on that ratio and whether the parameter influences depended on the state of each other. Results show that pH had a greater influence than acetate supply on the ratio of iron to sulfate reduction, and that the impact of acetate supply on the ratio depended on pH. In acidic reactors (pH 6.0 media), the ratio of iron to sulfate reduction decreased from 3:1 to 2:1 as acetate supply increased (0-1 mM). In alkaline reactors (pH 7.5 media), iron and sulfate were reduced in equal proportions, regardless of acetate supply. Secondly, a comparison of experiments with and without sulfate shows that the extent of iron reduction was greater if sulfate reduction was occurring and that the effect was larger in alkaline reactors than acidic reactors. Thus, the influence of sulfate supply on iron reduction extent also depended on pH and suggests that iron reduction grows more dependent on sulfate reduction as pH increases. Our results compare well to trends in groundwater geochemistry and provide further evidence that pH is a major control on iron and sulfate reduction in systems with crystalline (oxyhydr)oxides. pH not only affects the ratio between the reactions but also the influences of other parameters on that ratio.