Ferrous Iron Concentrations Research Articles

Enhancement effect of nanoscale zero-valent iron addition on microbial degradation of BDE-209 in contaminated mangrove sediment

Chemical and biological methods have been employed to remedy polybrominated diphenyl ether contamination, but the removal of decabromodiphenyl ether (BDE-209) by either method still has limitations. The present study aims to evaluate the combined effect of nanoscale zero-valent iron (nZVI) (from 0.1 to 10%) reduction and microbial debromination on BDE-209 removal in mangrove sediments under an anaerobic condition. During the 12-months incubation, nZVI significantly enhanced BDE-209 removal, with 17.03% to 41.99% reduction in sterilized sediments. The reduction was even higher in non-sterilized sediments with living indigenous microorganisms, achieving 15.80%, 33.50%, 55.83% and 66.95% removal of BDE-209 at 0 (control without nZVI), 0.1%, 1% and 10% nZVI, respectively. In control sterilized sediments, no debromination was found, and debromination occurred according to spiked levels of nZVI, with BDE-153 being the dominant congener. The concentrations of debrominated congeners in non-sterilized sediments also increased with nZVI levels, but were significantly higher than the respective sterilized sediment. The relative proportions of different debrominated congeners in non-sterilized sediments depended on nZVI levels, with BDE-99 being the dominant congener in low nZVI amended sediments but shifted to BDE-153 under high nZVI. Higher concentrations of ferrous iron (Fe2+) were detected in both sterilized and non-sterilized sediments spiked with more nZVI, and their concentrations significantly correlated with BDE-209 removal. Growth of total bacteria in sediments with 1% and 10% nZVI was inhibited within first two months, but their numbers resumed to that in the control at the end of 12 months. The present study demonstrates the synergy between chemical and microbiological methods, and a combination of nZVI and indigenous microorganisms could be an efficient and feasible mean to remedy BDE-209 in contaminated sediments.

The composition and redox state of bridgmanite in the lower mantle as a function of oxygen fugacity

The chemistry of bridgmanite (Brg), especially the oxidation state of iron, is important for understanding the physical and chemical properties, as well as putting constraints on the redox state, of the Earth’s lower mantle. To investigate the controls on the chemistry of Brg, the Fe3+ content of Brg was investigated experimentally as a function of composition and oxygen fugacity (fo2) at 25 GPa. The Fe3+/∑Fe ratio of Brg increases with Brg Al content and fo2 and decreases with increasing total Fe content and with temperature. The dependence of the Fe3+/∑Fe ratio on fo2 becomes less steep with increasing Al content. Thermodynamic models were calibrated to describe Brg and ferropericlase (Fp) compositions as well as the inter-site partitioning of trivalent cations in Brg in the Al–Mg–Si–O, Fe–Mg–Si–O and Fe–Al–Mg–Si–O systems. These models are based on equilibria involving Brg components where the equilibrium thermodynamic properties are the main adjustable parameters that are fit to the experimental data. The models reproduce the experimental data over wide ranges of fo2 with a relatively small number of adjustable terms. Mineral compositions for plausible mantle bulk compositions can be calculated from the models as a function of fo2 and can be extrapolated to higher pressures using data on the partial molar volumes of the Brg components. The results show that the exchange of Mg and total Fe (i.e., ferric and ferrous) between Brg and Fp is strongly fo2 dependent, which allows the results of previous studies to be reinterpreted. For a pyrolite bulk composition with an upper mantle bulk oxygen content, the fo2 at the top of the lower mantle is −0.86 log units below the iron–wüstite buffer (IW) with a Brg Fe3+/∑Fe ratio of 0.50 and a bulk rock ratio of 0.28. This requires the formation of 0.7 wt.% Fe–Ni alloy to balance the raised Brg ferric iron content. With increasing pressure, the model predicts a gradual increase in the Fe3+/∑Fe ratio in Brg in contrast to several previous studies, which levels off by 50 GPa. Oxygen vacancies in Brg decrease to practically zero by 40 GPa, potentially influencing elasticity, diffusivity and rheology in the top portion of the lower mantle. The models are also used to explore the fo2 recorded by inclusions in diamonds, which likely crystallized as Brg in the lower mantle, revealing oxygen fugacities which likely preclude the formation of some diamonds directly from carbonates, at least at the top of the lower mantle.

Recycled calcium carbonate is an efficient oxidation agent under deep upper mantle conditions

Observations of high ferric iron content in diamond garnet inclusions and mantle plume melts suggest a highly heterogeneous distribution of ferric iron in the mantle. Recycling of oxidized materials such as carbonates from Earth’s surface by subduction could explain the observed variations. Here we present high-pressure high-temperature multi-anvil experiments to determine the redox reactions between calcium-, magnesium-, or iron-carbonate and ferrous iron-bearing silicate mineral (garnet or fayalite) at conditions representative of subduction zones with intermediate thermal structures. We show that both garnet and fayalite can be oxidized to ferric iron-rich garnets accompanied by reduction of calcium carbonate to form graphite. The ferric iron content in the synthetic garnets increases with increasing pressure, and is correlated with the Ca content in the garnets. We suggest that recycled sedimentary calcium carbonate could influence the evolution of the mantle oxidation state by efficiently increasing the ferric iron content in the deep upper mantle.

The origin of gley colors in hydromorphic vertisols: the study case of the coastal plain of the Río de la Plata estuary

This work aims to contribute to the interpretation of soil colors; mainly to identify the pigments that generate the greenish colors in hydromorphic conditions (gley colors) in vertisols of the coastal plain of the Rio de la Plata estuary. These colors are of cold hues, generally greenish (olive-gray), and occur in poorly drained soils with prolonged water accumulation. For this purpose, samples of Bssg horizons of hydromorphic vertisols from the coastal plain of the Rio de la Plata estuary were analyzed using routine and chemical analyses, Mossbauer spectroscopy, determination of rocks magnetic parameters, X-ray diffraction, thermogravimetric and differential thermal analysis and petrographic-electronic microscopy. The pigments associated with the gley colors of these soils are mainly due to ferric iron content, corresponding to minerals such as ferric iron-rich smectites (nontronite/Fe-rich beidellite) and oxy-hydroxides like goethite, which colors range from green to yellow. These minerals, combined with gray or black components, e.g., manganese compounds and/or organic matter, contribute to the generation of the usual gley colors in the analyzed soils of the Pampean plain. The obtained data allows us to state that it is a mistake to assing the olive color in hydromorphic soils to the presence of ferrous iron compounds, as it is traditionally done. The oxidizing condition of iron is dominant in all the analyzed samples, integrating the composition of ferric iron-rich clay minerals and oxy-hydroxides (goethite).

Low-Temperature Chlorite Geothermometry and Related Recent Analytical Advances: A Review

Chlorite, a 2:1:1 phyllosilicate, has all the required attributes to form the basis of a geothermometer: this mineral is ubiquitous in metamorphic, diagenetic, and hydrothermal systems with a broad field of stability and a chemical composition partly dependent on temperature (T) and pressure (P) conditions. These properties led to the development of a multitude of chlorite thermometers, ranging from those based on empirical calibrations (linking T to AlIV content) to thermodynamic or semi-empirical models (linking T to chlorite + quartz + water equilibrium constant). This present study provides an overview of these geothermometers proposed in the literature for low-temperature chlorite (T < 350 °C), specifying the advantages and limitations of each method. Recent analytical developments that allow for circumventing or responding to certain criticisms regarding the low-temperature application of thermometers are also presented. The emphasis is on micrometric and nanometric analysis, highlighting chemical intracrystalline zoning—which can be considered as evidence of a succession of local equilibria justifying a thermometric approach—and mapping ferric iron content. New perspectives in terms of analysis (e.g., Mn redox in Mn-chlorite) and geothermometer (molecular solid-solution model, oxychlorite end-member) are also addressed.

Zones of PGE–Chromite Mineralization in Relation to Crystallization of the Pados-Tundra Ultramafic Complex, Serpentinite Belt, Kola Peninsula, Russia

The lopolithic Pados-Tundra layered complex, the largest member of the Serpentinite belt–Tulppio belt (SB–TB) megastructure in the Fennoscandian Shield, is characterized by (1) highly magnesian compositions of comagmatic dunite–harzburgite–orthopyroxenite, with primitive levels of high-field-strength elements; (2) maximum values of Mg# in olivine (Ol, 93.3) and chromian spinel (Chr, 57.0) in the Dunite block (DB), which exceed those in Ol (91.7) and Chr (42.5) in the sills at Chapesvara, and (3) the presence of major contact-style chromite–IPGE-enriched zones hosted by the DB. A single batch of primitive, Al-undepleted komatiitic magma crystallized normally as dunite close to the outer contact, then toward the center. A similar magma gave rise to Chapesvara and other suites of the SB–TB megastructure. Crystallization proceeded from the early Ol + Chr cumulates to the later Ol–Opx and Opx cumulates with accessory Chr in the Orthopyroxenite zone. The accumulation of Chr resulted from efficient cooling along boundaries of the Dunite block. The inferred front of crystallization advanced along a path traced by vectors of Ol and Chr compositions. Grains and aggregates of Chr were mainly deposited early after the massive crystallization of olivine. Chromium, Al, Zn and H2O, all incompatible in Ol, accumulated to produce podiform segregations or veins of chromitites. This occurred episodically along the moving front of crystallization. Crystallization occurred rapidly owing to heat loss at the contact and to a shallow level of emplacement. The Chr layers are not continuous but rather heterogeneously distributed pods or veins of Chr–Ol–clinochlore segregations. Isolated portions of melt enriched in H2O and ore constituents accumulated during crystallization of Ol. Levels of fO2 in the melt and, consequently, the content of ferric iron in Chr, increased progressively, as in other intrusions of the SB–TB megastructure. The komatiitic magma vesiculated intensely, which led to a progressive loss of H2 and buildup in fO2. In turn, this led to the appearance of anomalous Chr–Ilm parageneses. Diffuse rims of Chr grains, abundant in the DB, contain elevated levels of Fe3+ and enrichments in Ni and Mn. In contrast, Zn is preferentially partitioned into the core, leading to a decoupling of Zn from Mn, also known at Chapesvara. The sulfide species display a pronounced Ni-(Co) enrichment in assemblages of cobaltiferous pentlandite, millerite (and heazlewoodite at Khanlauta), deposited at ≤630 °C. The oxidizing conditions have promoted the formation of sulfoselenide phases of Ru in the chromitites. The attainment of high degrees of oxidation during crystallization of a primitive parental komatiitic magma accounts for the key characteristics of Pados-Tundra and related suites of the SB–TB megastructure.

泥炭沼泽湿地关键元素地球化学特征及其对碳排放的影响机制

硫、铁是泥炭沼泽湿地（泥炭地）中重要的生源要素，其参与下的生物地球化学过程对泥炭地碳循环意义重大。选取德国中部两处典型的雨养型泥炭地高海拔样点（TBP）和低海拔样点（TSP），通过原位采集泥炭剖面孔隙水和可溶性气体等，研究了硫、铁元素等地球化学变化规律，结合DOC、甲烷（CH₄）和二氧化碳（CO₂）浓度分布，探讨其对泥炭地碳排放的影响。研究结果表明：（1） TBP中总还原无机硫（TRIS）浓度随深度先增后减，且上部0-87 cm平均浓度远高于87 cm深度以下，上部硫酸盐还原作用强烈。结合上部亚铁、硫化氢（H₂S）浓度分布，得知该范围内H₂S主要是通过微生物硫酸盐还原作用（BSR）生成，同时H₂S在孔隙水扩散过程中易与亚铁结合为硫化亚铁，进而生成稳定的黄铁矿，这一反应过程在约60 cm处减缓。（2） TBP、TSP两处采样点中DOC与亚铁、硫酸盐均有较强相关性，是由于地下水位的波动影响氧化还原程度以及微生物活性。两处采样点DOC均与亚铁呈显著正相关关系，表明铁氧化物在厌氧环境中被还原溶解产生亚铁，与其结合的有机碳被释放到溶液中从而导致DOC浓度的升高。TBP中DOC与硫酸盐呈显著负相关关系，表明硫酸盐作为电子受体被还原的过程中消耗酸度使pH值升高，增强了其中微生物的活性，DOC浓度由此增加。（3） CH₄与硫酸盐、TRIS浓度在剖面上均呈现相反变化趋势，表明硫酸盐输入的增加以及硫酸盐还原活动均会抑制CH₄生成。CO₂/CH₄均大于4，表明硫酸盐作为替代电子受体会使厌氧条件下碳矿化转向多CO₂和少CH₄生成。此外，亚铁对于CH₄生成一定程度上会起到低促高抑的效果，而对于CO₂的生成的影响较弱。表明硫酸盐对于CH₄和CO₂生成的影响高于亚铁。研究着重探究硫、铁等关键元素地下部生物地球化学过程对碳排放的影响机制，研究结果可为泥炭地碳排放核算提供理论支撑。;Sulfur and iron are important biogenic elements in peatland. Their participation in biogeochemical process is of great significance to carbon cycle of peatland. This study aimed to investigate impact of key elements on carbon emission of ombrotrophic peatlands, at top broad position (TBP) and top slope position (TSP) sites. The concentrations and distributions of carbon as DOC, GHG (particularly CH₄ and CO₂) were estimated through an in-situ collection of pore water and soluble gas in peat profile. Combined with the geochemical characteristics of sulfur (S) and iron (Fe) elements, their impacts on carbon emissions from peatland were discussed. The results showed that (1) the concentrations of total reduced inorganic sulfur (TRIS) in TBP first increased and then decreased with depth. The average concentration of the upper part was much higher than that of deeper part. The sulfate reduction in the upper part was strong. Combined with the concentrations and distributions of ferrous iron and hydrogen sulfide (H₂S) in the corresponding range, it is inferred that H₂S is mainly generated by bacterial sulfate reduction (BSR) in this range. Meanwhile, during the diffusion process of H₂S in pore water, it is easy to combine with ferrous iron into FeS. And then stable FeS₂ was formed. The reaction process slowed down at about 60 cm. (2) The DOC had a strong correlation with ferrous iron and sulfate in TBP and TSP because the fluctuation of groundwater level affects the redox degree and microbial activity. DOC had a significantly positive correlation with ferrous iron in the two sampling sites, indicating that iron oxide was reduced to dissolved ferrous iron in the anaerobic environment, and the organic carbon combined with ferrous oxide was released into pore water, resulting in the increase of DOC concentration. DOC had a negative correlation with sulfate in TBP, indicating that the acidity was consumed in the reduction process of sulfate as electron acceptor, and the pH value increased, which enhanced the activity of microorganism. Thus the concentration of DOC was increased. (3) The concentrations of CH₄ and sulfate, CH₄ and TRIS in the two sampling sites showed opposite trends with depth on the profile, indicating that increasing sulfate input and sulfate reduction would inhibit the formation of CH₄. The CO₂/CH₄ ratios of the two sampling sites were greater than 4, indicating that sulfate as an alternative electron acceptor may shift carbon mineralization under anaerobic conditions to more CO₂ and less CH₄ production. In addition, high concentration of ferrous iron can inhibit the formation of CH₄, and low concentration of ferrous iron can promote the formation of CH₄. But ferrous iron had a weak effect on the formation of CO₂. The results also show that sulfate concentration plays a dominative role over ferrous iron in CH₄ and CO₂ production. In this study, the effects of underground geochemical factors such as sulfur and iron on carbon emissions were also discussed, which provided more rigorous theoretical support for the correction of carbon emissions from peatlands.

Determination of Ferrous Iron in Ferric Chloride Hexahydrate

Objective: As a pharmaceutical raw material, ferric chloride hexahydrate has been included in the British Pharmacopoeia, the European Pharmacopoeia (2008) and the United States Pharmacopoeia (2015), and there are detailed discussions on quality standards and testing methods. Ferric chloride hexahydrate has not been included in the Chinese Pharmacopoeia. This study is the part of research to establish a spectrophotometric method for the determination of ferrous iron in ferric chloride hexahydrate. In this study, the two methods were discussed in detail, and the spectrophotometric method for detecting the content of ferrous iron in ferric chloride hexahydrate was proposed. Methods: The detection method on ferrous iron in ferric chloride hexahydrate among European pharmacopoeia, United States pharmacopoeia and Chemical Reagent Ferric Chloride Hexahydrate (HG/T3474-2014) of China's Chemical Industry were compared. The last two methods were not easy to operation. On the basis of the European pharmacopoeia, a method was proposed that after Fe³⁺ were screened with H3PO4, Fe2+ was measured by spectrophotometry, and the method was verified by experiments. Results and Conclusion: The spectrophotometry method is easy to operate and has good reproducibility. The content of ferrous iron can be calculated semi-quantitatively by masking ferric iron with H3PO4 and spectrophotometric determination of ferrous ion content. Therefore, the method established in this study can more clearly detect whether the ferrous content in ferric chloride hexahydrate is up to standard.

Nitrate dynamics in groundwater under sugarcane in a wet-tropics catchment

The transport of nitrogen (N) to groundwater and surface water in the form of nitrate (NO3-), as a by-product of the application of N-rich fertilisers, has been studied extensively. Yet, in the catchments adjacent to the Great Barrier Reef (GBR) in tropical north Queensland, Australia, NO3- transport in groundwater is not regularly monitored. An assessment of groundwater chemistry in the Liverpool Creek catchment of Queensland's wet-tropics region was conducted by regular sampling and analysis of groundwater over 12 months, through wet and dry seasons. A distinct spatial variability in groundwater chemistry was observed; groundwater aquifers with very low dissolved oxygen (DO) and NO3- consistently displayed relatively higher concentrations of sulphate (SO42-), sulphur (S2-) and ferrous iron (Fe2+) and low concentrations of dissolved organic carbon (DOC) (<2 ppm). Combined with averaged measured redox potential (Eh) of <250 mV, this indicates certain regions of the catchment have conditions favourable for removal of NO3- via autotrophic denitrification (DN), while other groundwater aquifers retained NO3– concentrations just above the acceptable trigger limits defined in regional water quality guidelines. Observations indicate that the naturally heterogeneous structure of the coastal alluvium contributes to the distinct variability in groundwater chemistry over small distances, with NO3- concentrations influenced by a combination of DN, lateral shallow drainage and potential adsorption to clay surfaces within the alluvial sediments.

Ferric-ferrous iron ratios of experimental majoritic garnet and clinopyroxene as a function of oxygen fugacity

Abstract The oxidation state of iron in upper mantle minerals is widely used to constrain the Earth mantle's oxidation state. Previous studies showed high levels of ferric iron in high-pressure majoritic garnets and pyroxenes despite reducing conditions. To disentangle the effects of pressure and increasing oxygen fugacity on the Fe3+/ΣFe ratios of garnet and clinopyroxene, we performed high-pressure experiments at a pressure of 10 GPa in a 1000-ton Walker-type multi-anvil apparatus at the University of Münster. We synthesized majoritic garnets and clinopyroxenes with a total iron content close to natural mantle values at different oxygen fugacities, ranging from IW+4.7 to metal saturation at IW+0.9. We analyzed the iron oxidation state in garnets with the electron microprobe “flank method.” Furthermore, we investigated the oxidation state of iron in garnets and clinopyroxenes with transmission electron microscopy (TEM) electron energy loss spectroscopy (EELS). Although the flank method measurements are systematically lower than the EELS measurements, Fe3+/ΣFe obtained with both methods agree well within 2σ errors. The “flank method” has the advantage of being much faster and more easily to set up, whereas TEM-EELS has a much higher spatial resolution and can be applied to various non-cubic minerals such as orthopyroxenes and clinopyroxenes. We used our experimental results to compare two geobarometers that contain a term for ferric iron in garnet (Beyer and Frost 2017; Tao et al. 2018) with two geobarometers that do not account for ferric iron (Collerson et al. 2010; Wijbrans et al. 2016). We found that for garnets with low total Fe and Fe3+ (like many natural garnets), the pressures can be calculated without including the ferric iron content.

Eudialyte Group Minerals from the Lovozero Alkaline Massif, Russia: Occurrence, Chemical Composition, and Petrogenetic Significance

The Lovozero Alkaline Massif intruded through the Archean granite-gneiss and Devonian volcaniclastic rocks ca. 360 Ma ago and formed a large laccolith-type body. The lower part of the massif (the Layered complex) is composed of regularly repeating rhythms: melanocratic nepheline syenite (lujavrite, at the top), leucocratic nepheline syenite (foyaite), foidolite (urtite). The upper part of the massif (the Eudialyte complex) is indistinctly layered, and lujavrite enriched with eudialyte-group minerals (EGM) prevails there. In this article, we present the results of a study of the chemical composition and petrography of more than 400 samples of the EGM from the main types of rock of the Lovozero massif. In all types of rock, the EGM form at the late magmatic stage later than alkaline clinopyroxenes and amphiboles or simultaneously with it. When the crystallization of pyroxenes and EGM is simultaneous, the content of ferrous iron in the EGM composition increases. The Mn/Fe ratio in the EGM increases during fractional crystallization from lujavrite to foyaite and urtite. The same process leads to an increase in the modal content of EGM in the foyaite of the Layered complex and to the appearance of primary minerals of the lovozerite group in the foyaite of the Eudialyte complex.

Rhizosphere effect and its associated soil-microbe interactions drive iron fraction dynamics in tidal wetland soils

It is becoming increasingly clear that plants can affect iron (Fe) dynamics in tidal wetland soils, but whether this is rhizosphere effect-dependent remains unclear. To assess rhizosphere effects on soil Fe cycling, in-situ rhizosphere and bulk soil samples (0–60-cm) were collected from a tidal wetland across plant growth stages (regreening, shooting, and senescence). Changes in Fe fractions, the abundance of Fe-oxidizing/reducing bacteria (16S rRNA gene), root morphology traits, and soil and porewater geochemistry were examined. Overall, the rhizosphere effect decreased soil pH but increased the concentrations of dissolved organic carbon (DOC), porewater Fe2+, and bicarbonates (HCO3−). Both Fe-oxidizing and Fe-reducing bacteria were more enriched in the rhizosphere than those in the bulk soil. The rhizosphere effect increased the concentrations of amorphous and crystalline Fe(III), and also enhanced the proportion of amorphous Fe(III). The rhizosphere had higher concentrations of non-sulfidic ferrous iron [Fe(II)] but lower concentrations of ferrous sulfide (FeS) and pyrites (FeS2) than those in bulk soils, suggesting that the rhizosphere effect favors microbial Fe(III) reduction but suppresses microbial sulfate reduction. Moreover, the rhizosphere amorphous Fe(III) levels changed following the patterns of root porosity, which attained peak values at the root tips. The abundance of Fe-reducing bacteria was controlled by both DOC and amorphous Fe(III) concentrations, which were relatively higher during the regreening and shooting stages than those during the senescence stage. Taken together, our findings highlight that the rhizosphere effect transfer Fe from the bulk soil to the rhizosphere and especially redirects it from FeS associations to microbially-mediated Fe redox cycling. This rapid Fe redox cycling could be responsible for buffering soils and organisms from sulfide accumulation and stimulate C mineralization in the tidal wetland ecosystem.

Treatment of laundry wastewater by solar photo-Fenton process at pilot plant scale

Laundry sector consumes a huge amount of water which is usually discharged as wastewater instead of being reused. The application of biological treatment of laundry wastewater coupled with post-treatment utilizing advanced oxidation processes creates a possibility to recycle water to the washing process. However, the investigations on such systems are very limited. In the present work, a novel approach of post-treatment of laundry wastewater utilizing solar photo-Fenton operated at a pilot scale in a compound parabolic collector (CPC) photoreactor is proposed. Sodium dodecyl sulfate (SDS) was used as a representative of surfactants applied in the laundry system. The effect of feed matrix was investigated using distilled water as a reference matrix and synthetic wastewater simulating the composition of biologically pre-treated laundry wastewater. Different concentrations of H2O2 (50–400 mg/L) and ferrous iron (2.75–10 mg/L) were assayed. For comparison purpose, experiments at neutral pH using ethylenediamine-N,N′-disuccinic acid (EDDS) as an iron complexing agent were carried out. A high SDS removal efficiency was obtained under both neutral and acidic pH, reaching 89% and 96%, respectively, in just 8 min. However, the remaining organic load originating from EDDS needs application of further post-treatment steps. Therefore, the solar photo-Fenton operated under acidic pH was found to be a more promising approach of post-treatment of laundry wastewater aimed at its reuse.

Biosynthesis of vivianite from microbial extracellular electron transfer and environmental application

Vivianite (Fe3(PO4)2·8H2O) is a common hydrous ferrous phosphate mineral which often occurs in reductive conditions, especially anoxic non-sulfide environment containing high concentrations of ferrous iron (Fe2+) and orthophosphate (PO43−). Vivianite is an important product of dissimilatory iron reduction and a promising route for phosphorus recovery from wastewater. Its formation is closely related to the extracellular electron transfer (EET), a key mechanism for microbial respiration and a crucial explanation for the reduction of metal oxides in soil and sediments. Despite of the natural ubiquity, easy accessibility and attractive economic value, the application value of vivianite has not received much attention. This review introduces the characteristics, occurrence and biosynthesis of vivianite from microbial EET, and systematically analyzes the application value of vivianite in the environmental field, including immobilization of heavy metals (HMs), dechlorination of carbon tetrachloride (CT), sedimentary phosphorus sequestration and eutrophication alleviation. Additionally, its potential functions as a slow-release fertilizer are discussed as well. In general, vivianite is expected to make more contributions to the future scientific research, especially the solution of environmental problems. Overcoming the lack of understanding and some technical limitations will be beneficial to the further application of vivianite in environmental field.

Unraveling the confusion over the iron oxidation state in MORB glasses

The oxidation state of iron in mantle-derived melts is commonly used to determine the oxygen fugacity (fO2) of magmas and their related sources. The accurate and precise determination of the iron oxidation state ratio of Mid-Oceanic Ridge Basalt (MORB) glasses has been a matter of controversy for the last three decades. None of the wet chemical methods used in the literature to measure this ratio converge toward a consensus value. The same difficulties have been observed for the most recent data obtained by XANES spectroscopy, which allows the measurement of the iron oxidation state ratio at high spatial resolution. This study unravels the origin of the analytical biases observed between the colorimetric and direct titration wet chemistries used in the studies of Christie et al. (1986) and Bézos and Humler (2005), respectively. We demonstrate that colorimetric measurements overestimate the ferrous iron contents of sulfide-bearing samples whereas the direct titration method does not suffer from such sulfide interference. Because MORB glasses contain significant amount of sulfur in the +2 valence state, we re-assessed the average MORB FeO/FeOtotal ratio by using the bulk FeOtotal and FeO data from this study and from Bézos and Humler (2005), respectively. We calculated for 49 MORB glasses an average FeO/FeOtotal of 0.90 ± 0.02. This result agrees with colorimetric measurements corrected for sulfide interference and with the results of Bézos and Humler (2005), if corrected for the presence of plagioclase in the sample powders. The average MORB FeO/FeOtotal that we determined in this study agrees also within uncertainty with the most recent XANES spectroscopic data of Berry et al. (2018) (0.90 ± 0.02).

PROCESSING OF SLAGS OF COPPER MANUFACTURING WITH THE USE OF IDEAL MIXING EQUIPMENT

The article discusses the issues of processing slag of copper production using devices that model ideal mixing. It has been shown that the use of this type of apparatus increases the efficiency of physical and chemical processes and significantly reduces the copper content in dump slags. It has been found that the process of reduction of ferric iron oxide by the clinker in the initial period takes place in the kinetic mode. After reducing the concentration of magnetite (3-5%) in the slag, the process of reducing it passes into the diffusion region, that is, restoring the excess content of ferric iron in iron silicate melts takes a short period of time during which the process can be carried out, without significantly delaying the operation time of the main industrial equipment. The optimal slag magnetite reducing agent is determined to be zinc production waste

The neurophysiological effects of iron in early life stages of zebrafish

Trace metal/ion homeostasis, neurophysiological performance, and molecular responses to iron (Fe) exposure were investigated in the model organism zebrafish (Danio rerio). The findings demonstrated that exposure to a sublethal concentration of ferric iron (Fe3+) increased Fe contents in both the whole body and head region of developing zebrafish. Among the various trace metals and major ion examined, a dysregulation in manganese, zinc, nickel, and calcium balance was also observed in Fe-exposed larvae. Further biochemical assay and in-vivo imaging revealed that Fe exposure resulted in possible oxidative stress-induced damage, and an increased generation of reactive oxygen species in specific regions of the larvae. Using a droplet digital PCR (ddPCR) technology, it was found that the expression levels of various oxidative stress-responsive genes were temporally modulated by Fe exposure. Additionally, Fe-exposed larvae exhibited an impairment in escape response and a decrease in swimming activity. These larvae also appeared to exhibit a reduced anxiety-like behaviour. Together, our research suggested that larvae experiencing an increased Fe loading exhibited a dysregulation in metal homeostasis and a decrease in neurophysiological performance. These results suggested that neurophysiological assessments are sensitive methods to evaluate Fe toxicity in developing fish.

Analysis and Prediction of the Thiourea Gold Leaching Process Using Grey Relational Analysis and Artificial Neural Networks

The thiourea (TU) leaching of gold from refractory ores can be considered an alternative to cyanidation. However, the high reagent consumption causes an increase in cost, which seriously limits its use. In order to effectively reduce the TU consumption, it is necessary to analyze the influencing parameters of gold recovery and TU consumption and apply them to the prediction of the TU leaching process. This paper investigated six potential influencing parameters and used grey relational analysis (GRA) to analyze the relational degree between each parameter and gold recovery and TU consumption. Then, the artificial neural network (ANN) model was established to simultaneously predict the gold recovery and TU consumption in the TU gold leaching process. The results of the GRA indicated that the leaching time, initial pH, temperature, TU dosage, stirring speed, and ferric iron concentration were all well related to the gold recovery and TU consumption. Therefore, the incorporation of these parameters can significantly improve the ANN model validation. The predictive results noted that the prediction accuracy of gold recovery varied from 94.46% to 98.06%, and the TU consumption varied from 95.15% to 99.20%. Thus, the predicted values corresponded closely to the experimental results, which suggested that the ANN model can accurately reflect the relationship between the operational conditions and the gold recovery and TU consumption. This prediction method can be used as an auxiliary decision-making tool in the TU gold leaching process, and it has broad engineering application prospects in engineering.

Solar photo-Fenton treatment of the anti-cancer drug anastrozole in different aqueous matrices at near-neutral pH: Transformation products identification, pathways proposal, and in silico (Q)SAR risk assessment

Anastrozole (ANZ) is a breast cancer drug that was introduced onto the pharmaceutical market in the 1990s and is still one of the most widely consumed cytotoxic compounds. Due to the persistence of the drug, its continued presence after passing through wastewater treatment plants can lead to harm to aquatic environments. The present study investigates use of the solar photo-Fenton (SPF) process applied for ANZ degradation, considering the fate of ANZ and its transformation products (TPs). The SPF process was performed using different concentrations of ferrous iron (Fe2+) and H2O2 in solutions produced with deionized water (DW) and hospital wastewater (HWW), at pH close to neutrality. When solar irradiation in the SPF process was carried out the best ANZ removal rates were found under the following conditions: (i) for the DW matrix, [ANZ]0 = 50 μg L−1, [Fe2+] = 5 mg L−1, and [H2O2]0 = 25 mg L−1, achieving 95% primary ANZ elimination; (ii) for the HWW matrix, [ANZ]0 = 50 μg L−1, [Fe2+] = 10 mg L−1(multiple additions), and [H2O2]0 = 25 mg L−1, achieving 51% primary ANZ elimination. LC-QTOF MS analysis allowed to identify tentatively five transformation products (TPs) formed during the ANZ degradation process in DW, and two TPs when HWW was used. The main proposed degradation pathways were demethylation and hydroxylation. Different in silico models free available (quantitative) structure-activity relationship ((Q)SAR) software were used to predict the ecotoxicities and environmental fates of ANZ and the TPs. The in silico (Q)SAR predictions indicated that ANZ and the TPs were non-biodegradable compounds. In silico (Q)SAR predictions for mutagenicity and carcinogenicity end-points identified some TPs that require further study. Attention is drawn to the formation of several TPs for which statistical and rule-based positive alerts for mutagenic activities were found, requiring further confirmatory in vitro validation tests.

Effect of Sodium Chloride on Pyrite Bioleaching and Initial Attachment by Sulfobacillus thermosulfidooxidans.

Biomining applies microorganisms to extract valuable metals from usually sulfidic ores. However, acidophilic iron (Fe)-oxidizing bacteria tend to be sensitive to chloride ions which may be present in biomining operations. This study investigates the bioleaching of pyrite (FeS2), as well as the attachment to FeS2 by Sulfobacillus thermosulfidooxidans DSM 9293T in the presence of elevated sodium chloride (NaCl) concentrations. The bacteria were still able to oxidize iron in the presence of up to 0.6M NaCl (35 g/L), and the addition of NaCl in concentrations up to 0.2M (~12 g/L) did not inhibit iron oxidation and growth of S. thermosulfidooxidans in leaching cultures within the first 7 days. However, after approximately 7 days of incubation, ferrous iron (Fe2+) concentrations were gradually increased in leaching assays with NaCl, indicating that iron oxidation activity over time was reduced in those assays. Although the inhibition by 0.1M NaCl (~6 g/L) of bacterial growth and iron oxidation activity was not evident at the beginning of the experiment, over extended leaching duration NaCl was likely to have an inhibitory effect. Thus, after 36 days of the experiment, bioleaching of FeS2 with 0.1M NaCl was reduced significantly in comparison to control assays without NaCl. Pyrite dissolution decreased with the increase of NaCl. Nevertheless, pyrite bioleaching by S. thermosulfidooxidans was still possible at NaCl concentrations as high as 0.4M (~23 g/L NaCl). Besides, cell attachment in the presence of different concentrations of NaCl was investigated. Cells of S. thermosulfidooxidans attached heterogeneously on pyrite surfaces regardless of NaCl concentration. Noticeably, bacteria were able to adhere to pyrite surfaces in the presence of NaCl as high as 0.4M. Although NaCl addition inhibited iron oxidation activity and bioleaching of FeS2, the presence of 0.2M seemed to enhance bacterial attachment of S. thermosulfidooxidans on pyrite surfaces in comparison to attachment without NaCl.