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This paper discusses colorants found in Tumulus MM, the tomb of King Midas or his father, at Gordion, the capital of the Phrygian kingdom. Chromophores, colorants, and auxiliaries are preserved largely independent of the textiles they once colored. The Tumulus MM textiles are now fragmentary due to the degradation processes that occurred inside the tomb chamber. For DHA 26 (Vienna, Austria, 2007), we discussed a group of golden-yellow fragments from Tumulus MM that appeared to be tabby cloth but were skeletal lattices of goethite, αFeOOH (yellow ochre), as identified by FTIR, with SEM/EDS, XRD with molybdenum Kα radiation, NIR, and Raman spectroscopy. The “dyeing” has been replicated using a patented method; originally it may have involved a controlled redox reaction, based on our preliminary experiments. Amidst the goethite lattices, some skeletal fragments were green, with near-black lines within the yarn spiral, identified as indigo by FTIR at the time. Other masses with colorations of red, orange/brown, and purple with deep red veins did not yield identifiable inorganic coloration profiles with SEM/EDS. A purple fragment (2003-Tx-6 Front) was assayed by ICP-MS for mordants and for bromine, but neither could be found. Recently, direct analysis in real time mass spectrometry (DART-MS) enabled us to successfully detect organic colorants. For one fragment, indoxyl, isatin, indigo, and leuco-indigo were identified. One striated red-to-brown mass (2003-Tx-3) contained alizarin, purpurin, xanthopurpurin, lucidin, and other madder substituents; it also contained indigo/isatin but neither indoxyl nor leuco-indigo. Other beige-brown masses like 2003-Tx-5 sometimes contained alizarin, xanthopurpurin, rubiadin, and lucidin but rarely purpurin or indigo-related compounds. The purple (2003-Tx-6) shared the madder analogues with browner hues. The versatility appears related to that found in Anatolian pile carpets and flat weaves. Our new analyses confirm that the Phrygian textile colorists were indeed superb, versatile dyers.

The iron and steel industries currently face the depletion of high-grade ore and high CO2 emissions. Some initiatives that effectively utilize alternative carbon sources and abundant low-grade ores become the preferable solutions. This novel study aims to utilize municipal solid waste (MSW) as a reducing agent in ironmaking using low-grade (goethite) ores. As an initial fundamental approach, the comparison of decomposition behaviors between the model and actual MSW was investigated in thermogravimetric analysis. Both model and actual MSWs mainly decompose at 300-500 degrees C. As for reduction tests, pellets containing MSWs and ores with different pretreatments were prepared. The pellets were reduced in an Ar atmosphere at different temperatures. The effect of different ores: high-grade and low-grade ones, on the decomposition of MSW and the iron reduction, were investigated. As a result, interestingly, the low-grade, goethite ore-containing pellet exhibits a more significant reduction degree than the high-grade ones. The reduction is completed in 5 minutes at 700 degrees C and above, indicating a significant reduction by the decomposed carbon. The reduction degree extends at elevated temperature, which reaches more than 94% at 900 degrees C.

Hematite, the mineral that gives color to bright red iron ochres, occurs naturally, but there is much evidence that early humans sometimes artificially produced hematite by heating a related mineral, goethite, in wood fires. This represents an important cognitive and technological advance in early human prehistory. Thus, there is a need to distinguish natural hematite from hematite generated by heating goethite in a wood fire. Measuring the line widths of powder X-ray diffraction (XRD) in hematite has been explored, and synthetic goethite heated in a modern furnace has been used as a model system for studying this process. We now show that to be an inappropriate model. Although chemically identical, natural goethite is physically different from and much more variable than goethite produced in a laboratory. Furthermore, by replicating the process using Stone Age technology, we show that heating goethite in a wood fire complicates the interpretation of XRD line widths of the resulting hematite. We conclude that strategies other than powder XRD are necessary to draw conclusions about the ancient processing of iron ochres.

Interactions between aqueous ferrous iron (Fe(II)) and secondary Fe oxyhydroxides catalyze mineral recrystallization and/or transformation processes in anoxic soils and sediments, where oxyanions, such as silicate, are abundant. However, the effect and the fate of silicate during Fe mineral recrystallization and transformation are not entirely understood and especially remain unclear for lepidocrocite. In this study, we reacted (Si-)ferrihydrite (Si/Fe = 0, 0.05, and 0.18) and (Si-)lepidocrocite (Si/Fe = 0 and 0.08) with isotopically labeled 57Fe(II) (Fe(II)/Fe(III) = 0.02 and 0.2) at pH 7 for up to 4 weeks. We followed Fe mineral transformations with X-ray diffraction and tracked Fe atom exchange by measuring aqueous and solid phase Fe isotope fractions. Our results show that the extent of ferrihydrite transformation in the presence of Fe(II) was strongly influenced by the solid phase Si/Fe ratio, while increasing the Fe(II)/Fe(III) ratio (from 0.02 to 0.2) had only a minor effect. The presence of silicate increased the thickness of newly formed lepidocrocite crystallites, and elemental distribution maps of Fe(II)-reacted Si-ferrihydrites revealed that much more Si was associated with the remaining ferrihydrite than with the newly formed lepidocrocite. Pure lepidocrocite underwent recrystallization in the low Fe(II) treatment and transformed to magnetite at the high Fe(II)/Fe(III) ratio. Adsorbed silicate inactivated the lepidocrocite surfaces, which strongly reduced Fe atom exchange and inhibited mineral transformation. Collectively, the results of this study demonstrate that Fe(II)-catalyzed Si-ferrihydrite transformation leads to the redistribution of silicate in the solid phase and the formation of thicker lepidocrocite platelets, while lepidocrocite transformation can be completely inhibited by adsorbed silicate. Therefore, silicate is an important factor to include when considering Fe mineral dynamics in soils under reducing conditions., Environmental Science & Technology, 56 (9), ISSN:0013-936X, ISSN:1520-5851

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

Asbestos bodies (AB) form in the lungs as a result of a biomineralization process initiated by the alveolar macrophages in the attempt to remove asbestos. During this process, organic and inorganic material deposit on the foreign fibers forming a Fe-rich coating. The AB start to form in months, thus quickly becoming the actual interface between asbestos and the lung tissue. Therefore, revealing their composition, and, in particular, the chemical form of Fe, which is the major component of the AB, is essential to assess their possible role in the pathogenesis of asbestos-related diseases. In this work we report the result of the first x-ray diffraction measurements performed on single AB embedded in the lung tissue samples of former asbestos plant workers. The combination with x-ray absorption spectroscopy data allowed to unambiguously reveal that Fe is present in the AB in the form of two Fe-oxy(hydroxides): ferrihydrite and goethite. The presence of goethite, which can be explained in terms of the transformation of ferrihydrite (a metastable phase) due to the acidic conditions induced by the alveolar macrophages in their attempt to phagocytose the fibers, has toxicological implications that are discussed in the paper.

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.

In this paper, we report a first-principles Molecular Dynamics (FPMD) study of interfacial structures and acidity constants of goethite. The pKa values of the groups on (010), (110), and (021) surfaces (space group Pbnm) are derived with the FPMD based vertical energy gap technique. The results indicate that major reactive groups include ≡Fe2OH2 and ≡FeOH2 on (010), ≡FeOH2, ≡Fe3OLH, and ≡Fe3OUH on (110), and ≡FeOhH2 and ≡Fe2OH on (021). The interfacial structures were characterized in detail with a focus on the hydrogen bonding environment. With the calculated pKa values, the point of zero charges (PZCs) of the three surfaces are derived and the overall PZC range of goethite is found to be consistent with the experiment. We further discuss the potential applications of these results in future studies toward understanding the environmental processes of goethite.

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.

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.

The combination of biochar (BC) and iron minerals improves their pollutant adsorption capacity. However, little is known about the reactivity of BC-iron mineral composites regarding their interaction and change in the pore structure. In this study, the mechanism of cadmium (Cd) adsorption by BC-iron oxide composites, such as BC combined with ferrihydrite (FH) or goethite (GT), was explored. The synergistic effect of the BC-FH composite significantly improved its Cd adsorption capacity. The adsorption efficiencies of BC-FH and BC-GT increased by 15.0% and 10.8%, respectively, compared with that of uncombined BC, FH, and GT. The strong Cd adsorption by BC-FH was attributed to stable interactions and stereoscopic pore filling between BC and FH. The scanning electron microscopy results showed that FH particles entered the BC pores, whereas GT particles were loaded onto the BC surface. FTIR spectroscopy showed that GT covered a larger area of the BC surface than FH. After loading FH and GT, BC porosities decreased by 9.3% and 4.1%, respectively. Quantum chemical calculations and independent gradient mode analysis showed that van der Waals interactions, H-bonds, and covalent-like interactions maintained stability between iron minerals and BC. Additionally, humic acid increased the agglomeration of iron oxides and formed larger particles, causing additional aggregates to load onto the BC surface instead of entering the BC pores. Our results provide theoretical support to reveal the interfacial behavior of BC-iron mineral composites in soil and provide a reference for field applications of these materials for pollution control and environmental remediation.

The issue of the formation of iron hydroxides in deep horizons of the vertical weathering crust of the Saksagan iron-ore strip of the Kryvyi Rih basin (the Yuvileina Mine) has been studied. А stable presence of iron hydroxides in the ore strata has been revealed at considerable depths (1300-1400 m) using the method of traditional microscopy and phase analysis of iron. They are represented by goethite. Ontogenic observations have identified four main varieties of goethite. Each variety is characterized by their own forms, conditions and method of formation such as: pseudomorphic, dispersed (earthy), colloform, cementing ones. It was found that martite aggregates were the only source of iron for all four varieties. It has been proven that the depth factor, by itself, does not determine the formation of goethite. The formation of the necessary physical and chemical parameters in the system of mineralogenesis is of decisive importance. Iron hydroxides were suggested to be considered as hypergene-metasomatic formations in the abyssal weathering crust.

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.

Water can be stored in nominally anhydrous minerals as substitutional hydroxyl, generating vast but commonly unrecognized H2O reservoirs in ostensibly dry regimes. Researchers have long known that hematite (α-Fe2O3) can accommodate small concentrations of hydroxyl through the substitution of Fe3+ by 3H+. Our study of natural hematite has demonstrated the occurrence of “hydrohematite” phases that are 10–20 mol% deficient in Fe and accordingly contain 3.6–7.8 mol% structural water. Intergrown with natural hydrohematite samples were superhydrous goethite-like phases exhibiting an Fe deficiency of 10–20 mol% relative to end-member goethite (α-FeOOH). We synthesized hydrohematite in alkaline solutions (pH 9–12) at low temperatures (T < 200 °C) using fresh ferrihydrite as the transient precursor, and we observed a nonclassical crystallization pathway involving vacancy inoculation by Fe as nanocrystals evolved. The high level of incorporation of H2O in iron (hydr)oxides dramatically alters their behaviors as catalysts and pigments, and the presence of hydrohematite in rocks may rule out high-T diagenesis. We propose that hydrohematite is common in low-T occurrences of Fe oxide on Earth, and by extension it may inventory large quantities of water in apparently arid planetary environments, such as the surface of Mars.

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.

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.

Simulation Data and Analysis Programs

Adsorption and transport of levofloxacin (LEV) and ofloxacin (OFL) enantiomers in a matrix containing goethite and natural organic matter (NOM) were investigated using batch and column experiments. In batch studies, competition and enantioselectivity were observed in the adsorption of LEV and OFL. Enantioselectivity upon adsorption was investigated by comparing changes in the enantiomer fraction (EF) (the ratio of LEV to the sum of LEV and OFL remaining in the solution) after and before adsorption. At pH < 7, there was hardly any selectivity in adsorption of OFL and LEV to goethite. At pH > 7, OFL showed a stronger adsorption than LEV to goethite, and this preference remained when NOM samples of Leonardite humic acid (LHA) and Elliott Soil fulvic acid (ESFA) were added. However, when Suwannee River NOM (SRNOM) was added, the preference was reversed, and LEV was adsorbed more strongly. In single systems, the presence of different types of NOM increased adsorption of LEV and OFL, especially LEV. In column studies, preloaded NOM decreased the transport of LEV and OFL through goethite-coated sand. The EF values in the effluent increased with retention time and reached the largest values (0.59–0.72) at around 1.5 pore volume (PV), and then decreased again, reaching a stable value at 5.0–30.0 PV. Both batch and column experiments showed that, fractionation of LEV and OFL occurred during adsorption and transport in the presence of NOM-goethite complexes, which would eventually affect their environmental fate

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.

Iron ores always contain several forms of alumina, which may have different effect on sintering performance. In this paper, sinter pot tests were systematically conducted with various alumina types and contents by means of alumina additives substituting for the corresponding types of alumina, and the relevant action mechanism on sintering performance was clarified by the mineralogy of product sinter. The results show that kaolinite is beneficial to the granulation process rather than other three alumina types. In addition, it contributes to relatively better sintering performance while aluminous goethite ranks the only next, followed by gibbsite and free alumina. Mechanism analysis indicates that kaolinite and aluminous goethite are preferable to achieve relatively lower sinter porosity and higher amount of silico-ferrite of calcium and alumina (SFCA) compared with gibbsite and free alumina. Besides, the former two alumina types are apt to promote the formation of higher strength SFCA such as dendritic and acicular SFCA. Furthermore, much tighter interlocking texture in product sinter is formed as alumina occurs in kaolinite or aluminous goethite. Kaolinite and aluminous goethite are the preferably desirable alumina types for sintering rather than free alumina and gibbsite.

In this study, transport behaviors of graphene oxide (GO) in saturated uncoated (i.e., clean sand) and goethite-coated sand porous media were examined as a function of the phosphate. We found that phosphate enhanced the transport of GO over a wide range of solution chemistry (i.e., pH 5.0–9.0 and the presence of 10 mmol/L Na+ or 0.5 mmol/L Ca2+). The results were mainly ascribed to the increase of electrostatic repulsion between nanoparticles and porous media. Meanwhile, deposition site competition induced by the retained phosphate was another important mechanism leading to promote GO transport. Interestingly, when the phosphate concentration increased from 0.1 to 1.0 mmol/L, the transport-enhancement effect of phosphate in goethite-coated sand was to a much larger extent than that in clean sand. The observations were primarily related to the difference in the total mass of retained phosphate between the iron oxide-coated sand and clean sand columns, which resulted in different degrees of the electrostatic repulsion and competitive effect of phosphate. When the background solution contained 0.5 mmol/L Ca2+, phosphate could be bind to sand/ goethite-coated sand surface by cation bridging; and consequently, promoted competition between phosphate and nanoparticles for deposition sites, which was an important mechanism for the enhanced effect of phosphate. Moreover, the DLVO theory was applicable to describe GO transport behaviors in porous media in the absence or presence of phosphate. Taken together, these findings highlight the important status and role of phosphate on the transport and fate of colloidal graphene oxide in the subsurface environment.

Natural and synthetic iron oxide pigments are by far the most important colored pigments. Their high importance is based on the variety of stable colors ranging from yellow via orange, red and brown to black. Iron oxide yellow (α-FeOOH), iron oxide red (α-Fe2O3) and iron oxide black (Fe3O4) are the most important representatives of the iron oxide pigments. Synthetic iron oxide pigments are produced industrially on a large scale by solid-state processes, precipitation processes and by the Laux process. Main advantages of synthetic iron oxide pigments compared with natural types are their pure hue, the consistent, reproducible quality and their tinting strength. Iron oxide pigments are mainly used in construction materials, paints, coatings, and plastics, but also in cosmetics, pharmaceuticals and special applications such as ceramics, magnetic coatings and toners.

Environmental pollution by petroleum hydrocarbon is one of the significant concerns of the contemporary world. This paper deals with the relevant environmental issues concerning the oil pollution o...

Treatment of aqueous leachate from acid mine tailings with pristine biochar (BC) resulted in the removal of more than 90% of the dissolved arsenic with an attendant rapid and sustained pH buffering from 3 to 4. Pine forest waste BC was transformed to a highly effective adsorbent for arsenic remediation of acid mine drainage (AMD) because the dissolved iron induced “activation” of BC through accumulation of highly reactive ferric hydroxide surface sites. Physicochemical properties of the BC surface, and molecular mechanisms of Fe, S, and As phase transfer, were investigated using a multi-method, micro-scale approach (SEM, XRD, FTIR, XANES, EXAFS, and STXM). Co-located carbon and iron analysis with STXM indicated preferential iron neo-precipitates at carboxylic BC surface sites. Iron and arsenic X-ray spectroscopy showed an initial precipitation of ferrihydrite on BC, with concurrent adsorption/coprecipitation of arsenate. The molecular mechanism of arsenic removal involved bidentate, binuclear inner-sphere complexation of arsenate at the surfaces of pioneering ferric precipitates. Nucleation and crystal growth of ferrihydrite and goethite were observed after 1 h of reaction. The high sulfate activity in AMD promoted schwertmannite precipitation beginning at 6 h of reaction. At reaction times beyond 6 h, goethite and schwertmannite accumulated at the expense of ferrihydrite. Results indicate that the highly functionalized surface of BC acts as a scaffolding for the precipitation and activation of positively charged ferric hydroxy(sulf)oxide surface sites from iron-rich AMD, which then complex oxyanion arsenate, effectively removing it from porewaters. Graphical abstract Supplementary Information The online version contains supplementary material available at 10.1007/s11356-021-13869-8.

We report infrared reflectance and ultraviolet fluorescence spectra of the surfaces and cleaved side of Beacon Sandstone from Antarctica that harbours a cryptoendolithic microbial community - a photosynthesis-based consortium of algae, lichen and bacteria present a few millimetres below the surface. Chlorophyll absorptions were present in the reflectance spectra of the exposed interior but not on the top or bottom surfaces and their band depths changed < 4% between measurements taken 19 years apart, indicating the stability of the microorganisms when the sample is kept dry. The presence of subsurface organic layers was detected in reflectance at 3.41 μm on the sample's surface. Fluorescence spectra of the cleaved side showed the blue fluorescence peaks expected from chlorophyll but no 0.65–0.80 μm peaks seen in fluorescence measurements of green vegetation. A weak fluorescence signal was detectable at the surface of the sample, presumably due to some light leaking into the subsurface through pores or cracks in the goethite coating the sample's surface. Theoretically, this weak fluorescence signal could possibly be observed in rock surfaces broken by erosion or meteor impacts on Mars. Sandstone outcrops have been reported on Mars and detection of organic layers in sandstones there would be of interest.

Ising core-shell model was proposed to reconstruct superparamagnetism hysteresis in nano-goethite (α-FeOOH). Core and shell set as antiferromagnetic and paramagnetic state respectively. Core and shell radius varies until the theoretical hysteresis fit with experiment hysteresis. At low temperature, the hysteresis reconstructed nicely with 55% antiferromagnetic core contribution and 45% paramagnetic shell contribution. At high temperature, the core-shell model show unrealistic result compared to the pure paramagnetic state.

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.

A reactor model has been built to simulate the goethite process for iron removal. A three-factor designed set of boundary conditions was applied to determine the effect of stirring speed, gas inlet flow rate, and Fe2+ concentration. The two-phase flow velocity field, gas volume fraction distribution, mass transfer rate, and Fe2+ concentration were obtained as simulation results. The results showed that stirring has a significant effect on the distribution of the fluid field. The reaction rate and mass transfer were greatly influenced by the gas inlet flow rate. Based on the results, the following suggestions can be made for the goethite process for iron removal in this system: the number of stirrers should be increased, and the type and size of stirring paddle should be changed to enhance the fluidity of the solution; the rate of gas inlet flow should be increased to enhance the mass transfer and accelerate the iron removal reaction.

Copper oxide and hematite (CuO/α-Fe2O3) composite catalysts were prepared by using goethite as precursor adopted impregnation way and applied to the dielectric barrier discharge (DBD) catalytic dec...