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This study explored the feasibility of depositing protective coatings with an Sb scavenger function on mine waste rocks derived from the exploitation of stibnite deposits. Encapsulation treatments were performed using ferrous sulfate as the coating precursor. Different Fe/Sb leachable molar ratios (0.1, 1, and 10) were evaluated using hydrothermal and thermal processes at various temperatures (30, 50, 100, and 150 °C). The environmental characterization of the coated mine waste was established using standard leaching tests. The most effective coatings were analyzed for their mineralogy, chemical composition, and Sb attenuation using X-ray powder diffraction, scanning electron microscopy, and digestion/extraction processes. Additionally, stability tests were conducted to assess the effectiveness of encapsulation under changing environmental conditions. The Fe/Sb leachable molar ratio was found to be a critical factor in reverting the toxic and hazardous characteristics of mine wastes, with an optimal value of 10. The coatings were primarily composed of Fe oxyhydroxy sulfates/Fe oxyhydroxides and calcium sulfate minerals with a bulk Sb content of approximately 1 %. The adsorbed Sb content in the coatings was a small fraction of the total Sb content (< 0.5 %), indicating a strong retention. Moreover, such coatings were stable under different pH (3-8) and redox (100 to -100 mV) conditions., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier B.V. All rights reserved.)

This study systematically examines the roles of positive goethite on the retention and release of negative plastic nanoparticles (PSNPs) with different surface functional groups (Blank, -COOH, and -NH 2). It provides the first evidence for the dual roles of goethite coatings on colloid transport; e.g., increased transport caused by surface morphology modification or decreased transport due to increased surface roughness and charge heterogeneity. Although previous work has shown that goethite-coated sand increases the retention of negative colloids, this work demonstrates that collector surface roughness can also reduce the retention of PSNPs due to increased interaction energy profiles. Nonmonotonic retention of all the different functionalized PSNPs was observed in goethite-coated rough sand, and the magnitude of variations was contingent on the PSNP functionalization, the solution ionic strength (IS), and the goethite coating. The release of PSNPs with IS decrease (phase I) and pH increase (phase II) varied significantly due to differences in energy barriers to detachment, e.g., release in phase I was inhibited in both goethite-coated sands, whereas release in phase II was enhanced in coated smooth sand but completely inhibited in rough sand. The findings of this study provide innovative insight into transport mechanisms for colloidal and colloid-associated contaminants. [Display omitted] • Dual roles of goethite coating on nanoplastic (PSNP) transport are first evidenced. • Collector surface roughness dominates over charge heterogeneity in PSNP transport. • Nonmonotonic retention in goethite-coated rough sand varies with surface roughness. • Interactions of PSNP functional groups with goethite enhance PSNP-COOH/NH 2 retention. • PSNP release varies with its functionalization due to different energy barriers to detachment. [ABSTRACT FROM AUTHOR]

The research on the impact of water-soluble polymers (WSPs) on the migration and fate of plastic particles is extremely limited. This article explored the effects of polyacrylic acid (PAA, a common WSP) and physicochemical factors on the transport of polystyrene nanoparticles (PSNPs-NH 2 /COOH) with different functional groups in QS (quartz sand) and FOS (goethite-modified quartz sand, simulates mineral colloids). Research has shown that PAA can selectively adsorb onto the surface of PSNPs-NH 2 , forming ecological corona heterogeneous aggregates. This process increased the spatial hindrance and elastic repulsion, resulting in the recovery of PSNPs-NH 2 always exceeding that of PSNPs-COOH. Overall, PAA can hinder the migration of PSNPs in QS but can promote their migration in FOS. When multivalent cations coexist with PAA, the transport of PSNPs in the media is primarily affected by cation bridging and CH-cation-π interaction. The presence of oxyanions and PAA prevents PSNPs from following the Hofmeister rule and promotes their migration (PO 4 3-: 82.34 ± 0.16% to 94.63 ± 2.82%>SO 4 2-: 81.38 ± 2.73% to 91.15 ± 0.93%>NO 3 -: 55.85 ± 0.70%−87.16 ± 3.80%). The findings of this study contribute significantly to a better understanding of the migration of WSPs and group-modified NPs in complex saturated porous media. [Display omitted] • Polyacrylic acid (PAA) enhances the repulsion to facilitate the migration of PSNPs-NH 2. • The migration ability of PSNPs-NH 2 is always stronger than that of PSNPs-COOH. • The Eco crown formed by PAA on the PSNPs surface dominated the migration of PSNPs. • Al3+ bridges PAA and PSNPs to form microaggregate, suppressing PSNPs transport. • PAA broke the Hofmeister rule, the migration of PSNPs follow PO 4 3- > SO 4 2- > NO 3 -. [ABSTRACT FROM AUTHOR]

The widespread use of Cd-based quantum dots (Cd-QDs) has led to their inevitable release into the environment, and the prevalent iron oxides and natural organic matter (NOM) are the key factors affecting the environmental behavior and fate of Cd-QDs. However, the impact of NOM adsorbed on iron oxides on the behavior of Cd-QDs with iron oxides and the mechanism of its interaction are not clear. In this study, two kinds of water-soluble QDs (CdSe QDs and core-shell CdSe/ZnS QDs) were selected to study the aggregation and adsorption behavior on goethite (Goe) and goethite-humic acid/fulvic acid composites (Goe-HA/FA). Aggregation kinetics and adsorption experiments between QDs and Goe(-HA/FA), characterization, and extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory calculations indicated that electrostatic interaction was the dominant force for QDs adsorption on Goe(-HA/FA). HA/FA changed the surface charge of Goe and increased the electrostatic repulsion and steric hindrance between the particles, which in turn inhibited the adsorption of QDs on Goe. Besides, unsubstituted aromatic carbons, carboxy carbons, and carbonyl carbons played an important role in the adsorption process, and chemisorption occurred between QDs and Goe(-HA/FA). Our findings are important for better assessing the transport, fate, and potential environmental impacts and risks of Cd-QDs in iron-rich environments. [Display omitted] The continuous production and use of cadmium-based quantum dots (Cd-QDs) leads to their unavoidable release into the environment, where natural organic matter (NOM) and iron oxides could affect their fate. In this study, we demonstrated that electrostatic interaction dominated the adsorption of Cd-QDs on goethite, while NOM adsorbed on the surface of goethite inhibited the adsorption of Cd-QDs by changing its surface charge and increasing the electrostatic repulsion and steric hindrance. Our findings provide a theoretical basis for understanding the interactions of Cd-QDs with iron oxides and iron oxide-organic matter adsorption composites. • There were adsorption behaviors between QDs and Goe(-HA/FA). • Electrostatic interaction dominated the adsorption of QDs on Goe(-HA/FA). • Adsorption of HA/FA transformed the Goe surface from positively to negatively charged. • HA/FA inhibited the adsorption of QDs on Goe by electrostatic repulsion and steric hindrance. [ABSTRACT FROM AUTHOR]

The environmental fate of arsenic (As) relies substantially on its speciation, which occurs frequently coupled to the redox transformation of manganese. While trivalent manganese (Mn(III)), which is known for its high reactivity, is believed to play a role in As mobilization by iron (oxyhydr)oxides in dynamic aquifers, the exact roles and underlying mechanisms are still poorly understood. Using increasingly complex batch experiments that mimick As-affected aquifer conditions in combination with time-resolved characterization, we demonstrate that Mn(III)-NOM complexes play a crucial role in the manganese-mediated immobilization of As(III) by ferrihydrite and goethite. Under anaerobic condition, Mn(III)-fulvic acid (FA) rapidly oxidized 31.8% of aqueous As(III) and bound both As(III) and As(V). Furthermore, Mn(III)-FA exerted significantly different effects on the adsorption of As by ferrihydrite and goethite. Mn(III)-FA increased the adsorption of As by 6–16% due to the higher affinity of oxidation-produced As(V) for ferrihydrite under circumneutral conditions. In contrast, As adsorption by crystalline goethite was eventually inhibited due to the competitive effect of Mn(III)-FA. To summarize, our results reveal that Mn(III)-NOM complexes play dual roles in As retention by iron oxides, depending on the their crystallization. This highlights the importance of Mn(III) for the fate of As particularly in redox fluctuating groundwater environments. [Display omitted] • T(4-CP)P spectrophotometric method was firstly applied to quantify manganese species with iron under aquifer conditions. • Mn(Ⅲ)-NOM could oxidize aqueous As(Ⅲ) efficiently. • Mn(Ⅲ)-NOM exerted significantly distinct impacts on As immobilization by ferrihydrite and goethite. [ABSTRACT FROM AUTHOR]

The coexistence of microplastics (MPs) and arsenic (As) in terrestrial ecosystems presents challenges to controlling soil pollution and performing environmental risk assessments. In this study, the interactions among As, polystyrene MPs, and goethite in porous media were investigated and the individual and combined toxicities of MPs and As on wheat germination were evaluated. An additional experiment was conducted to assess the mitigating effect of goethite on the toxicity of the two contaminants. The results showed that the presence of MPs reduced As accumulation in wheat and decreased the acute lethal toxicity of As pollutants (the half-lethal concentration of As during wheat germination increased by 68.21%). However, MPs exhibited inhibitory effects on wheat germination and served as carriers to promote the migration of As within the plant body. The addition of goethite mitigated both individual and combined toxicities and further increased the half-lethal concentration for the combined pollution of As and MPs by 39.48%. This was primarily attributed to the adsorption and immobilization of arsenate and MPs on the medium and root surfaces. In our study, goethite reduced soluble As by 48.29% under the combined pollution scenarios and formed iron plaques on wheat roots, effectively obstructing pollutant entry. Thus, iron minerals serve as pioneering barriers to combined toxicity. Our findings contribute to the understanding of the combined toxicity of MPs and As in crops and offer potential strategies for managing combined pollution. [Display omitted] • The combined toxicity mechanisms of As and MPs on wheat seed were revealed. • MPs migration in wheat were visualized, quantified, and correlated with As. • Iron plaque acted as a barrier to prevent As and MPs from entering wheat. • Iron minerals could effectively against the combined toxicity of As and MPs. [ABSTRACT FROM AUTHOR]

Clay minerals and iron (hydr)oxides are important geosorbents in controlling the migration of heavy metal cations in the environment. Despite the widespread occurrence of clay minerals/iron (hydr)oxides composites, their complex mutual effects on the fate of heavy metal cations are not well recognized. In this work, we investigated the effect of clay minerals on the redistribution of Cd(II) during the phase transformation of ferrihydrite containing coprecipitated Cd(II) (Cd-Fh). Three systems were considered: i.e., Cd-Fh, Cd-Fh/kaolinite composite, and Cd-Fh/montmorillonite composite. Our results showed that the transformation of Fh into goethite and hematite caused the release of Cd(II), while the presence of kaolinite and montmorillonite inhibited the phase transformation of Fh and the release of Cd(II), with montmorillonite being more effective in these process. Multiple factors contributed to the reduced release of Cd(II), including the retarded transformation of Fh, the buffering of solution pH, and the re-adsorption of the released Cd(II). Our findings show that clay minerals have multiple effects in reducing the release of heavy metal cations from Fh during its transformation process, which sheds new light on understanding the critical roles of nanominerals in modulating the migration and bioavailability of heavy metal cations in the environment. [Display omitted] • The release of Cd(II) during the aging of Cd-Fh coprecipitates was inhibited by Kln and Mnt. • Multiple factors contribute to clay minerals' inhibition effect on Fh transformation and Cd(II) release. • Clay minerals regualte Fh transformation products (fusiform morphology with less crystallinity and obvious defects). • The Cd(II) partition between iron (hydr)oxides and clay minerals before and after transformation was calculated. • Mnt inhibited Fh transformation and Cd(II) release more effectively than Kln. [ABSTRACT FROM AUTHOR]

Highlights • The oxidation process of V(IV) was greatly promoted by goethite. • Surface hydroxyl groups on goethite are key medium for the oxidation of V(IV). • The formation of hydroxo complexes changes the interface pH of goethite-water. • The hydroxo complexes mediate the electron transfer reactions between VO2+ and O 2. Abstract The most toxic and mobile form of vanadium (V) is V(V). Thus, the oxidation of V is a subject of considerable importance since the process may increase environmental risks of V. V(IV) is known to be stable when pH < 4.5. However, in this study, stable V(IV) was oxidized almost completely in goethite suspension within 60 min at pH 2.0 and pH 4.0, correspondingly, only 25%–30% and 15%–20% of V(IV) were oxidized in equimolar Fe3+ solution and the blank solution, respectively. The promoted oxidation of V(IV) by FeOOH is attributed to the formation of the complex, VO(OFe<)+ or VO(OFe<) 2. On the one hand, the formation of the complex caused higher pH in the interface of solid FeOOH and corresponding lower conditional potential of V(V)/V(IV) than those in bulk solutions, which facilitates the oxidation of V(IV). On the other hand, the surface group OFe < may serve as a medium that facilitating the electron transfer from V(IV) ions to dissolved oxygen molecules, also favoring the oxidation of V(IV). This study not only deepens our understanding of the transfer, transformation, and risk of V in environments, but also provides a reference to speculate the fate of similar elements in environments. [ABSTRACT FROM AUTHOR]

Highlights • S. epidermidis enhanced the adsorption rates of U(VI) on Al-goethite at pH < 9.0. • The adsorbed U(VI) can be reduced to U(IV) by S. epidermidis. • High removal of U(VI) was attributed to structural Fe(III) and functional groups. Abstract Effect of Staphylococcus epidermidis (S. epidermidis) on U(VI) sequestration by Al-goethite were conducted under different geologic conditions. The batch experiments showed that S. epidermidis significantly enhanced the adsorption rates of U(VI) at pH < 9.0 due to the additional metal binding sites. The maximum adsorption capacities of U(VI) on Al-goethite and Al-goethite + S. epidermidis at pH 4.0 and 310 K were calculated from Langmuir equation to be 13.16 and 47.86 mg/g, respectively. The decreased adsorption of U(VI) on Al-goethite+ S. epidermidis at high carbonate and pH conditions were primarily driven by the electrostatic repulsion between negatively charged U(VI)-carbonate complexes and the negatively charged adsorbents. According to XPS analysis, the adsorbed U(VI) can be reduced to U(IV) by S. epidermidis, whereas inhibited reduction of U(VI) on Al-goethite + S. epidermidis at high pH could be attributed to the complexation of structural Fe(III) with the oxygen-containing functional groups of S. epidermidis. FT-IR analysis further demonstrated that the bonding of structural Fe(III) with functional groups (e.g., carboxyl and phosphate groups) of S. epidermidis. These results herein are important to understand the fate and transport of U(VI) on the mineral-bacteria ternary systems in the near-surface environment. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Goethite and Fe2+-modified goethite as ozonation catalysts for water treatment. • Fe2+-modified goethite with low defects reveals high catalytic activity. • The hydroxyl groups on goethite and Fe2+-modified goethite was active site. • Introducing Fe2+ increased the density of surface hydroxyl groups. Abstract In this study, Fe2+-modified goethite with low defects (α-Fe(Fe2+)OOH) was synthesized and characterized. Results revealed that α-Fe(Fe2+)OOH is a nano magnetic material with goethite (α-FeOOH) -type structures and has fewer Lewis acid of Fe3+ on its surface. Moreover, α-Fe(Fe2+)OOH was effective in catalytic ozonation of 4-chloronitrobenzene (4-CNB), which is a probe contaminant that cannot be efficiently removed through sole ozonation. The removal of 4-CNB increased with ozone concentration and α-Fe(Fe2+)OOH dosage, but decreased with the presence of carbonate, sulfate and phosphate. The catalytic activity of α-Fe(Fe2+)OOH also showed a dependence on solution pH. The presence of humic acid accelerated 4-CNB removal at low concentration but inhibited the removal at high concentration. In comparison with α-FeOOH, α-Fe(Fe2+)OOH significantly enhanced hydroxyl radicals generation and reduced Fe ions release in this process. The hydroxyl groups of Fe3+ on α-FeOOH and α-Fe(Fe2+)OOH surface was active site for ozone decomposition into hydroxyl radicals. Introducing Fe2+ significantly increased the density of surface hydroxyl groups relative to α-FeOOH. This enhancement significantly promoted hydroxyl radicals generation and 4-CNB degradation in the solution. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • The sequestration of As(III), Cr(VI) and competitive As(III)-Cr(VI) on/in nanostructured minerals was reinvestigated. • The minerals have high potential to remove As and Cr from water. • As and Cr sorption isotherms were modelled with a Langmuir and Hill models. • As(III) was partially oxidized (up to 22%) in the competitive system with Cr(VI). • As(III) sorbed on ferrihydrite and goethite adopted edge and corner sharing geometries. Abstract Sorption isotherms remain a major tool to describe and predict the mobility of pollutants in natural and anthropogenic environments, but they are typically determined by independent batch experiments. In the present study, the sequestration of As(III), Cr(VI) and competitive As(III)-Cr(VI) on/in 6L-ferrihydrite, siderite and goethite nanostructured minerals was reinvestigated using stirred flow-through reactor experiments. Herein, sorption isotherms were particularly determined from breakthrough curves for inert and reactive tracers monitored simultaneously in a single percolation experiment. In complement, X-ray absorption spectroscopy (XAS) was used to identify As sorption sites on 6L-ferrihydrite and goethite. As expected, the minerals have high potential to remove As and Cr from water (siderite = ferrihydrite (about 60 mg/g) > goethite (20 mg/g)). As and Cr sorption isotherms were modelled with a Langmuir model, and with a sigmoidal Hill model in the case of the competitive sorption. XAS measurements have revealed that As(III) was partially oxidized (up to 22%) in the competitive system with chromate oxyanion Cr(VI). As(III) sorbed on ferrihydrite and goethite adopted edge-sharing and corner sharing complex geometries. Nowadays, a new class of adsorbing phases is being developed for wastewater treatment, including engineered nanostructured materials and nanocomposites. The use of flow through reactor experiments as a high throughput method, combined with XAS, should be considered as efficient screening methods to test their sorbing properties on various contaminants. [ABSTRACT FROM AUTHOR]

Highlights • Bosea was confirmed as a novel genus for Sb(III) oxidization. • The preference of Bosea sp. AS-1 to oxidize As(III) or Sb(III) depended on the carbon source. • AS-1 preferred to oxidize As(III) with yeast extract and oxidize Sb(III) with sodium lactate. • The combined system of AS-1 and goethite could remove 99% of As (III) in the presence of Sb. Abstract Arsenic (As) and antinomy (Sb) usually coexist in natural environments where both of them pollute soils and water. Microorganisms that oxidize arsenite [As(III)] and tolerate Sb have great potential in As and Sb bioremediation, In this study, a Gram-negative bacterial strain, Bosea sp. AS-1, was isolated from a mine slag sample collected in Xikuangshan Sb mine in China. AS-1 could tolerate 120 mM of As(III) and 50 mM of antimonite [Sb(III)]. It could also oxidize 2 mM of As(III) or Sb(III) completely under heterotrophic and aerobic conditions. Interestingly, strain AS-1 preferred to oxidize As(III) with yeast extract as the carbon source, whereas Sb(III) oxidation was favored with lactate in the medium. Genomic analysis of AS-1 confirmed the presence of several gene islands for As resistance and oxidation. Notably, a system of AS-1 and goethite was found to be able to remove 99% of the As with the initial concentration of 500 μg/L As(III) and 500 μg/L Sb(III), which suggests the potential of this approach for As removal in environments especially with the presence of high Sb. [ABSTRACT FROM AUTHOR]

Iron oxide may interact with other pollutants in the aquatic environments and further influence their toxicity, transport and fate. The current study was conducted to investigate the biodegradation of 2,4-dinitrophenol (2,4-DNP) in the presence of iron oxide of goethite under anoxic condition using nitrate as the electron acceptor. Experiment results showed that the degradation rate of 2,4-DNP was improved by goethite. High performance liquid chromatography-mass spectra analysis results showed that goethite promoted degradation and transformation of 2,4-diaminophenol and 2-amino-4-nitrophenol (2-nitro-4-aminophenol). Microbial community analysis results showed that the abundance of Actinobacteria , which have the potential ability to degrade PAHs, was increased when goethite was available. This might partially explain the higher degradation of 2,4-DNP. Furthermore, another bacterium of Desulfotomaculum reducens which could reduce soluble Fe(III) and nitrate was also increased. Results further confirmed that nanomaterials in the aquatic environment will influence the microbial community and further change the transformation process of toxic pollutants. [ABSTRACT FROM AUTHOR]

Extracellular polymeric substances (EPS) play a crucial role in controlling the mobility and bioavailability of heavy metal(loid)s in water, soils, and sediments. The formation of EPS-mineral complex changes the reactivity of the end-member materials. However, little is known about the adsorption and redox mechanisms of arsenate (As(V)) in EPS and EPS-mineral complexes. Here we examined the reaction sites, valence state, thermodynamic parameters and distribution of As in the complexes using potentiometric titration, isothermal titration calorimetry (ITC), FTIR, XPS, and SEM-EDS. The results showed that ∼54% of As(V) was reduced to As(III) by EPS, potentially driven by an enthalpy change (ΔH) of − 24.95 kJ/mol. The EPS coating on minerals clearly affected the reactivity to As(V). The strong masking of functional sites between EPS and goethite inhibited both the adsorption and reduction of As. In contrast, the weak binding of EPS onto montmorillonite retained more reactive sites for the reaction with As. Meanwhile, montmorillonite facilitated the immobilization of As to EPS through the formation of As-organic bounds. Our findings deepen the understanding of EPS-mineral interfacial reactions in controlling the redox and mobility of As, and the knowledge is important for predicting the behavior of As in natural environments. [Display omitted] • Both the functional sites and morphology changed after EPS coating on minerals. • Reactions of As in EPS-mineral complexes were both enthalpy and entropy changes driven. • Strong site masking between EPS and goethite inhibited the reaction. • Weak binding of EPS onto montmorillonite promoted As-organic bounds. [ABSTRACT FROM AUTHOR]

Due to its mobility and toxicity, chromate [Cr(VI)] partitioning in soils, especially in the vadose zone, is an important environmental concern. The aim of this study was to develop a mechanism-based multi-surface complexation model using published parameters to predict the soil/water partitioning of Cr(VI) in 12 soils (previously depleted of organic matter) from China. The retention of Cr(VI) in soils was attributed to two reactive oxide surfaces: goethite and hydrous ferric oxide (HFO); however, modeling results showed that the best prediction was obtained with goethite alone, whereas the addition of HFO resulted in an overestimation of adsorption in some soils. Cr(VI) adsorption onto goethite could be described using our previously proposed CD-MUSIC model. In the absence of a specific value for the soil-reactive surface area of goethite, a general value of 45.8 m 2 /g was used. The available phosphate in soils was identified as a strong competitor for Cr(VI) adsorption; thus, for soils with a low Fe/P ratio (<1) the effect of phosphate on Cr(VI) retention should not be neglected. The simple method presented herein can be applied to soils with a wide range of properties, pH values, and Cr(VI) loading concentrations. [ABSTRACT FROM AUTHOR]

Although reductive dissolution of Fe(III) oxides has been well accepted for As mobilization in alluvial aquifers, the key factors controlling this process are poorly understood. Arsenic(V)-adsorbing ferrihydrite, goethite and hematite were used to examine in-situ mobilization and transformation of adsorbed As(V) and Fe(III) oxides. In the Hetao basin, seven wells with wide ranges of groundwater As were selected to host As(V)-Fe(III) oxides sand. During 80 d experiments, As was firstly desorbed and then released via reductive dissolution of iron oxide from ferrihydrite, while only desorption was observed from goethite/hematite sand. Desorbed As was predominantly controlled by groundwater HCO 3 − and DOC, while reductive dissolution-related As release was mainly regulated by ORP values, DOC and Fe(II) concentrations. Mineral transformation from ferrihydrite to lepidocrocite and goethite/or mackinawite would also contribute to As release. Arsenic species was transformed from As(V) to As(III) on ferrihydrite, but remained unchanged on goethite and hematite. Arsenic partition between As-Fe(III) oxide sand and real groundwater ranged between 0.012 and 0.102 L/g. K d-sand between As-goethite sand/As-hematite sand and groundwater fell within the ranges observed between sediments and groundwater. This study suggests that As desorption, reductive dissolution and mineral transformation of ferrihydrite would be the major processes controlling As mobility. [ABSTRACT FROM AUTHOR]

Coupled reactions among chromium (Cr), organic matter (OM), and iron (Fe) minerals play significant roles in Cr and carbon (C) cycling in Cr-contaminated soils. Although the inhibitory effects of Cr or polysaccharides acid (PGA) on ferrihydrite transformation have been widely studied, mechanistic insights into detoxification of Cr(VI) and immobilization of Cr and C during the microbially mediated reductive transformation of ferrihydrite remain unclear. In this study, underlying sequestration mechanisms of Cr and C during dissimilatory Fe reduction at various Cr/Fe ratios were investigated. Solid-phase analysis showed that reductive transformation rates of ferrihydrite were impeded by high Cr/Fe ratio and more magnetite was found at low Cr loadings. Microscopic analysis showed that formed Cr(III) was immobilized by magnetite and goethite through isomorphous substitution, whereas PGA was adsorbed on the crystalline Fe mineral surface. Spectroscopic results uncovered that binding of Fe minerals and PGA was achieved by surface complexation of structural Fe with carboxyl functional groups, and that the adhesion order of PGA functional groups and Fe minerals was influenced by the Cr/Fe ratios. These findings have significant implications for remediating Cr contaminants, realizing C fixation, and developing a quantitative model for Cr and C cycling by coupling reductive transformation in Cr-contaminated environments. [Display omitted] • Only reductive dissolution occurred before complete reduction of Cr(VI) by Fe(II) and S. oneidensis MR-1. • Reductive transformation of ferrihydrite into goethite and magnetite was hindered by Cr loadings. • High Cr/Fe molar ratios are not conducive to Cr(III) incorporation into the crystal structures of Fe minerals. • PGA was mainly adsorbed on goethite and magnetite surface via carboxyl functional group. [ABSTRACT FROM AUTHOR]

Nanoplastics (NPs) are emerging contaminants in the environment, where the transport and fate of NPs would be greatly affected by interactions between NPs and minerals. In the present study, the interactions of two types of polystyrene nanoplastics (PSNPs), i.e., bare-PSNPs and carboxylated PSNPs–COOH, with iron (hydr)oxides (hematite, goethite, magnetite, and ferrihydrite), aluminum (hydr)oxides (boehmite and gibbsite), and clay minerals (kaolinite, montmorillonite, and illite) were investigated. The positively charged iron/aluminum (hydr)oxide minerals could form heteroaggregates with negatively charged PSNPs. Electrostatic and hydrophobic interaction dominate for the heteroaggregation of bare-PSNPs with iron/aluminum (hydr)oxide minerals, while ligand exchange and electrostatic interaction are involved in the heteroaggregation of PSNPs–COOH with iron/aluminum (hydr)oxides minerals. However, heteroaggregation between PSNPs and negatively charged clay minerals was negligible. Humic acid markedly suppressed such heteroaggregation between PSNPs and minerals due to enhanced electrostatic repulsion, steric hindrance, and competition of surface attachment sites. The heteroaggregation rates of both bare-PSNPs and PSNPs–COOH with hematite decreased with increasing solution pH. Increased ionic strength enhanced the heteroaggregation of PSNPs–COOH but inhibited that of bare-PSNPs. The results of the present study suggested that the heteroaggregation of PSNPs in environments could be strongly affected by minerals, solution pH, humic acid, and ionic strength. [Display omitted] • Surface charges and groups affect the heteroaggregation of polystyrene nanoplastics (PSNPs). • Iron (hydr)oxides and aluminum (hydr)oxides facilitate the heteroaggregation of PSNPs. • Negligible interaction and heteroaggregation occur between PSNPs and clay minerals. • Humic acid suppresses the heteroaggregation between PSNPs and iron/aluminum (hydr)oxides. • Increasing pH decreases the heteroaggregation of PSNPs with hematite. [ABSTRACT FROM AUTHOR]

This study investigated multiple (di-, tri- and tetra-)incorporation of selected minor and trace elements (Al3+, Cr3+, V3–5+, Zn2+, Mo6+ and As5+) into hematite. The purpose was to improve understanding of how hematite may control trace element mobility in the environment, and how physical and chemical properties of hematite are impacted by multi-element incorporation at x /Fe molar ratios of up to 10%. Simultaneous structural incorporation of Al±Cr±V±Zn into hematite was achieved, with both synergistic and antagonistic effects occurring between certain element combinations. Cr+Al had synergistic effects on their co-incorporation, while V negatively affected Al incorporation, and both V and Zn negatively affected Cr incorporation. In contrast, Mo was minimally associated with hematite, and As prevented hematite formation completely. X-ray diffraction indicated contraction and expansion of the hematite unit-cell upon substitution was related to the ionic radius of the substituting element in single-element samples, while V predominantly controlled the direction of deviation in multi-element samples. X-ray absorption near-edge structure spectroscopy indicated V was present as a mixture of V3+-V5+, with a higher average V oxidation state associated with multi-element samples. Results provide new insights into trace element geochemistry within hematite, and highlight the importance of multi-element studies to better understand natural and anthropogenic systems. [Display omitted] • Trace element combinations influenced hematite versus goethite formation from precursor ferrihydrite. • Chromium and V had synergistic effects on co-incorporation of Al, while Zn acted to lower Al incorporation in hematite. • Vanadium and Zn acted antagonistically to lower co-incorporation of Cr in hematite. • Vanadium's oxidation state was influenced by co-incorporation of other trace elements. • Vanadium exhibited a major control on unit-cell deviations in multi-element samples. [ABSTRACT FROM AUTHOR]

The oxidation and immobilization of arsenic (As) by manganese oxides have been shown to reduce As toxicity and bioavailability under abiotic conditions. In this study, we investigate the impact of manganese oxide (δ-MnO 2) on the fate of different Fe-minerals-adsorbed As in the presence of As(V)-reducing bacteria Bacillus sp. JQ. Results showed that in the absence of δ-MnO 2 , As release in goethite was much higher than in ferrihydrite and hematite during microbial reduction. Adding 3.1 mM Mn reduced As release by 0.3%, 46.3%, and 6.7% in the ferrihydrite, goethite, and hematite groups, respectively. However, aqueous As was dominated by As(III) in the end, because the oxidation effect of δ-MnO 2 was limited and short-lived. Additionally, the fraction of solid-phase As(V) increased by 9.8% in ferrihydrite, 39.4% in goethite, and 7.4% in hematite in the high-Mn treatments, indicating that δ-MnO 2 had the most significant oxidation and immobilization effect on goethite-adsorbed As. This was achieved because goethite particles were evenly distributed on δ-MnO 2 surface, which supported As(III) oxidation by δ-MnO 2 ; while ferrihydrite strongly aggregated, which hindered the oxidation of As(III). Our study shows that As-oxidation and immobilization by manganese oxides cannot easily be assessed without considering the mineral composition and microbial conditions of soils. [Display omitted] • The As(III) oxidation by δ-MnO 2 is limited under biotic-reducing conditions. • The oxidation and immobilization of δ-MnO 2 on As in Gt is higher than Fh and Hm. • Fe-minerals aggregation extent and their interactions with δ-MnO 2 controls As fate. • The remediation effect of δ-MnO 2 on As may be more predominant in soils rich in Gt. [ABSTRACT FROM AUTHOR]

The oxygenation of Fe(II)-bearing minerals for hydroxyl radicals (HO•) formation and contaminant attenuation receive increasing attention, while the mechanisms for specific Fe(II) species in manipulating HO• formation and contaminant attenuation are unclear. Herein, a total of four Fe(III)-bearing minerals were applied in the reduction-oxygenation processes to produce HO•. Results showed that the total HO• generated from the Fe-(oxyhydr)oxides were significantly higher than those from the Fe-silicates, with the order of goethite and hematite (~1500 μmol kg-1) > Fe-montmorillonite (~550 μmol kg-1) > chlorite (~120 μmol kg-1). The HO• formation was largely hinged on the reactive Fe(II) species, i.e., the surface-adsorbed/low-crystalline Fe(II) in the Fe-bearing minerals. For the co-incubation of minerals and phenanthrene, the concentrations of phenanthrene decreased from the initial 3.0 mg L-1 to 0.7 mg L-1 and 1.9 mg L-1 for Fe-montmorillonite and goethite, respectively, suggesting the HO• mediated by the Fe-montmorillonite was more conducive for phenanthrene attenuation. The goethite tended to promote the formation of free HO•, while the Fe-montmorillonite with interlayer structure can provide attachment sites for the surface-adsorbed/low-crystalline Fe(II), resulting in high potential for surface-bound HO• formation and phenanthrene attenuation. This study highlights the importance of Fe-bearing minerals in manipulating HO• formation, providing new insight into the removal of contaminants in ecosystems. [Display omitted] • HO• mediated by Fe minerals and its effects on phenanthrene removal were studied. • HO• formation potential exhibited high heterogeneities from 120 to 1500 μmol kg-1. • The surface-adsorbed/low crystalline-Fe was the key Fe species for HO• formation. • Surface-bound HO• mediated by Fe-montmorillonite was more conducive for phenanthrene removal. [ABSTRACT FROM AUTHOR]

Natural organic matter (NOM) and iron oxides have been proved to be crucial factors controlling the behaviors of nanoparticles in heterogenous environment. Here, we conducted experimental and modeling study on the transport of titanium dioxide nanoparticles (TiO 2 NPs) in iron oxide-coated quartz in the presence of NOM under acidic conditions. Results showed the antagonistic effects of iron oxides and NOM on TiO 2 NPs mobility. The inhibition of iron oxides coated on quartz was crystal form-dependent other than quantity-dependent. Amorphous ferric oxyhydroxide with higher specific surface area brought more positive charge and favorable deposition sites onto quartz, and induced more retention of nanoparticles than two crystalline iron oxides, goethite and hematite. Dissolved organic matter (DOM) facilitated TiO 2 NPs transport in iron oxide-coated quartz. In comparation with the limited enhancing effects of DOM, the NOM coatings on media surface partially or largely offset the inhibition of goethite on nanoparticles mobility through direct occupation of attachment sites and sites screening due to the steric repulsion of the macromolecules. Owing to the higher steric hindrance, humic acid, both in dissolved and media surface-bound states, exerted stronger facilitating effects on TiO 2 NPs mobility relative to fulvic acid. [Display omitted] • The inhibition of iron oxides on TiO 2 NPs mobility depended on the crystal form. • DOM had limited enhancing effects on TiO 2 NPs mobility in iron oxide-coated quartz. • Media-bound NOM alleviated/offset the inhibition of iron oxides on TiO 2 NPs mobility. • HA with stronger steric hindrance exerted higher enhancing effects than FA. [ABSTRACT FROM AUTHOR]

Acid mine drainage sludge (AMDS) is a solid waste generated following the neutralization of acid mine drainage (AMD). This material entrapped in calcium alginate was investigated for the sorption of As(III) and As(V). Three different adsorbent materials were prepared: AMDS alginate beads (AABs), goethite alginate beads (GABs), and pure alginate beads. The effects of pH and the adsorption kinetics were investigated, and the adsorption isotherms were also evaluated. The optimum pH range using the AABs was determined to be within 2–10 for As(III) and 2–9 for As(V). Adsorption equilibrium data were evaluated using the Langmuir isotherm model, and the maximum adsorption capacity q max was 18.25 and 4.97 mg g −1 for As(III) on AAB and GAB, respectively, and 21.79 and 10.92 mg g −1 for As(V) on AAB and GAB, respectively. The adsorption of As(III) and As(V) was observed to follow pseudo-second order kinetics. The As K-edge X-ray absorption near-edge structure (XANES) revealed that the adsorbed As(III) on the AABs was oxidized to As(V) via manganese oxide in the AMDS. [ABSTRACT FROM AUTHOR]

In this study, reductive dissolution of As(V)-ferrihydrite and the mobilization of As(V) in the presence of S(-II) were investigated under anoxic conditions. Mobilization of As(V) strongly depended on the S(-II):Fe ratio and the amount of As(V) loading on ferrihydrite. High S(-II):Fe ratio caused a more complete dissolution of ferrihydrite and a large fraction of As(V) could be released into solution. The percentages of the released As(V) were 2.5% and 7.5% at S(-II):Fe ratios of 0.240 and 24.0, respectively, at pH 6.1, while the released As(V) were 5.5%, 16.3% at pH 8.0 under similar conditions. As(V) loading showed a negative effect on the release of arsenate, with smaller fraction of arsenate released into solution when more As (V) adsorbed on ferrihydrite. After 43 h, 14.1%, 5.5%, 1.6% and 0.7% of As(V) were released as for 10, 20, 50 and 100 mg L −1 of As(V) loading, respectively, at pH 8.0. During the dissolution, secondary minerals such as goethite, magnetite and FeS were detected and played different roles in the mobilization of As(V). The released As(V) was mainly repartitioned on the residual ferrihydrite, the newly-formed goethite and magnetite but not FeS. [ABSTRACT FROM AUTHOR]

The interactions between dissolved organic matter (DOM) molecules and minerals play significant roles in affecting the fate of carbon and contaminants in soil environment. However, the mechanisms controlling the variations of DOM molecules distribution during the transformation of Fe (oxyhydr)oxides, and the effects of these variations on contaminant behaviors are still largely unknown. In this study, the dynamic variations of DOM properties and distributions, and the kinetics of uranium adsorption on and desorption from Fe (oxyhydr)oxides during the transformation were investigated, employing a combination of Orbitrap mass spectrometry (MS), high-resolution transmission electron microscopy (HR-TEM), and kinetic experiments. Orbitrap MS results indicated that aliphatic molecules and phenolic and polyphenolic molecules with lower O/C values were preferentially released to solution. HR-TEM results indicated that the coprecipitated DOM molecules by ferrihydrite were mainly released to solution rather than sorbed on the newly formed lepidocrocite or goethite during the transformation. Furthermore, the stirred-flow experiment results suggested that soil DOM significantly reduced the adsorption of uranium on, and accelerated the release of uranium from Fe (oxyhydr)oxides, which was ascribed to the changed distribution of DOM molecules and the structure and composition of Fe (oxyhydr)oxides. Our results contribute to predicting contaminant behaviors in soils. [Display omitted] • Soil DOM strongly inhibited the transformation of Fe (oxyhydr)oxides. • Phenolic and condensed aromatic molecules were preferentially coprecipitated by Fh. • Aliphatic molecules were selectively released during the transformation. • Soil DOM decreased uranium adsorption and accelerated the release of uranium. [ABSTRACT FROM AUTHOR]

Arsenic (As) redox-induced mobilisation and speciation in polluted gold mine sites in tropical climates largely remains unknown. Here, we investigated the impact of changes in soil redox potential (E H) (−54 mV to +429 mV) on mobilisation of As and its dominant species in an abandoned spoil (total As = 4283 mg/kg) using an automated biogeochemical microcosm set-up. Arsenic mobilisation increased (85–137 mg/L) at moderately reducing conditions (−54 mV to + 200 mV)), while its reduced (6–35 mg/L) under oxic conditions (+200 to +400 mV). This indicates the high risk of As potential loss under reducing conditions. The mobilisation of As was governed by the redox chemistry of Fe. XANES and EXAFS analyses showed that sorbed-As(V)-goethite, sorbed-As(III)-ferrihydrite, scorodite and arsenopyrite were the predominant As species in the mine spoil. As(V) dominated at oxic conditions and As(III) predominated at moderately reducing conditions, which may be attributed to either inability of arsenate bacteria to reduce As or incomplete reduction. Lower Fe/As molar ratios during moderately reducing conditions show that the mine spoil may migrate As to watercourses during flooding, which may increase the hazardous effects of this toxic element. Therefore, encouraging aerobic conditions may mitigate As release and potential loss from the mine field. [Display omitted] • As mobilisation in mine spoil was higher at low E H (<200 mV) than high E H (>200 mV). • As mobilisation was mainly governed by Fe chemistry. • As (V) in sediments persisted during moderately reducing conditions. • Lower Fe/As molar ratios at low E H show potential As migration to water. • As mitigation measures at the minefield should limit reducing conditions. [ABSTRACT FROM AUTHOR]

Natural iron oxides nanomaterials have important roles in biogeochemical processes. In this study, the effects of pH, natural organic matter, and cations on aggregation and sedimentation of natural goethite and artificial Fe 3 O 4 nanoparticles in water were investigated to learn more about the environmental behaviors of engineered and natural nanomaterials and how they differ. In addition, a novel extended DLVO theory that considered steric, gravitational, and magnetic attraction forces concurrently was specifically developed to provide mechanisms explanations. Specifically, Fe 3 O 4 NPs were more likely than bulk goethite to aggregate (because of magnetic attraction interactions) at low HA concentrations and disperse at high HA concentrations. Besides, goethite was less prone to settle with the same concentration of NaCl than Fe 3 O 4 NPs, but the opposite trend was found for the same concentration of CaCl 2 because of the difference in maximum net energy (barrier) and strong Ca2+ bridging effectiveness of goethite in CaCl 2 solution. Statistical models were established to evaluate colloidal stability of the particles. XPS and molecular dynamics simulation results suggested that ions were adsorbed onto particles via ionic polarization and that the binding free energies at high coverage followed the order Ca2+ > Na+ > Cl- and presence of cation bridging between particles. [Display omitted] • Aggregation and sedimentation of engineered and natural nanomaterials were different. • XDLVO theory provided better explanations for the colloidal behaviors of particles. • Good statistical models were established to predict colloidal stability parameters. • MD simulation verified that ions were adsorbed onto particles via ionic polarization. • Presence of cation bridging between particles and cations was confirmed. [ABSTRACT FROM AUTHOR]

Lavrio is a Greek town with several abandoned Ag/Pb mines. In this study, 19 potentially toxic elements (PTEs) were measured in soil, weeds, and olives. Levels of seven of the studied PTEs in soil were highly elevated: Zn (56.2–58,726 mg kg-1), Pb (36.2–31,332), As (7.3–10,886), Cu (8.3–1273), Sb (0.99–297.8), Cd (0.17–287.7), and Ag (0.09–38.7). Synchrotron-based X-ray absorption near edge structure analysis of the soils revealed that As was predominantly associated with scorodite, Pb with humic substances, Zn with illite, Zn(OH) 2 and humic substances, and Fe with goethite-like minerals. The transfer of the PTEs to weeds was relatively low, with the transfer coefficient being less than 1.0 for all PTEs. Cadmium in table olives surpassed 0.05 mg kg-1 fresh weight (the limit in EU), while Pb surpassed its limit in approximately half of the samples. Health risk assessment confirmed soil contamination in the study area where As and Pb hazard quotients were well above 1.0 and the average hazard index equaled 11.40. Additionally, the cancer risk values exceeding the 1 × 10-4 threshold. The results obtained in the study indicate that Lavrio urgently requires an adequate ecofriendly remediation plan, including revegetation with tolerant species and targeted efforts to chemically stabilize harmful PTEs. The presented approach may serve as a pivotal study for industrial areas with similar contamination levels. [Display omitted] • Ag, As, Cd, Pb, Sb, and Zn were dramatically enriched in a millennia-old Ag/Pb mine. • XANES analysis revealed that As was primarily associated with scorodite. • Soil-to-plant transfer of Cd was high in Malva sylvestris. • Olives surpassed the limits for Cd and Pb, thus, a consumption should be avoided. • Cancer risk of As exposure was unacceptably high, well beyond the 1 × 10-4 threshold. [ABSTRACT FROM AUTHOR]

Highlights: [•] Resting cells of Aliihoeflea sp. strain 2WW oxidize 200μg/L As(III) in 32h. [•] Goethite is 100-fold higher efficient in adsorbing 200μg/L As(V) than As(III). [•] The combined 2WW-goethite system is tested in buffer solution for As removal. [•] 2WW-goethite system remove 95% of the As(III) present, meeting World Health Organization limit adequately. [Copyright &y& Elsevier]

Highlights: [•] Schwertmannite is a better scavenger than goethite in identical sorbent:solute ratio. [•] Partial As(III) oxidation to As(V) by schwertmannite and goethite in anoxic media. [•] Arsenic-rich surface precipitates form on schwertmannite with decayed morphology. [•] Bidentate binuclear binding of both As(V) and mixed As(III)–As(V) on schwertmannite. [•] Dissolved ferrous iron has negligible control on As(III) uptake and redox stability. [Copyright &y& Elsevier]

Jarosite coprecipitation with hazardous oxyanions can attenuate the concentrations of these elements in acid mine drainage. However, jarosite can be easily transformed to goethite with changes in geochemical conditions. Consequently, the released oxyanions can greatly affect environments. The changes in the mineralogy and mobility of five oxyanions, namely AsO 4 , SeO 3 , SeO 4 , MoO 4 , and CrO 4 , which were coprecipitated with jarosite, are investigated herein during the mineral transformation. Our results show that the oxyanion species and the pH values greatly affect the mineral transformation and dissolution rates of jarosite-containing oxyanions. The transformation and dissolution rates of the jarosite samples at pH 8 are noticeably higher than those at pH 4. The X-ray diffraction results show that the CrO 4 and SeO 4 jarosites are as effectively transformed to goethite as the jarosite without oxyanions, while the SeO 3 and AsO 4 jarosites are least transformed, resulting in different sulfate and oxyanion concentrations in the solution. The oxyanions in jarosite are the main controlling factor in the mineral transformation and dissolution rates. In acid mine drainage, although CrO 4 is easily attenuated by the jarosite precipitation, it has the highest mobility during the goethite transformation. On the contrary, AsO 4 shows the opposite case. [Display omitted] • Oxyanions play important roles in the jarosite transformation and dissolution rates. • Jarosites with CrO 4 and SeO 4 are transformed to goethite at high pH. • Jarosite with AsO 4 shows the lowest transformation and dissolution rates. • In acid mine drainage, jarosite with AsO 4 has the least environmental effects. • CrO 4 in jarosite shows the highest mobility in AMD. [ABSTRACT FROM AUTHOR]

The redox process of electron shuttles like cysteine on iron minerals under aerobic conditions may largely determine the fate of arsenic (As) in soils, while the interfacial processes and underlying mechanisms are barely explored. This work systematically investigates the interfacial oxidation processes of As(III) on goethite induced by cysteine. Results show that the addition of cysteine significantly enhances the oxidation efficiency (~ 40%) of As(III) (C 0 : 10 mg/L) by goethite at pH 7 under aerobic conditions, which is 19.5 times of that without cysteine. cysteine induces Fe(III) reduction on the surface of goethite, and the generation absorbed Fe(II) species play an important role in As(III) oxidation. In particular, the further complexation of Fe(II) with cysteine is thermodynamically favorable for electron transfer, leading to an enhanced As(III) oxidation efficiency. The oxidation efficiency of As(III) in the goethite/cysteine system increases by increasing cysteine concentration and decreases by elevating pH conditions. In addition, evidence indicates that •O 2 - radicals account for approximately 80% of total oxidized As(III). Meanwhile, only 16% of As(III) oxidation can be attributed to the formed •OH radicals. This work provides new insight into the role of organic electron shuttling compounds in determining As cycling in soils. [Display omitted] • Cysteine induces As(III) oxidation by goethite under aerobic conditions. • Fe(III)/Fe(II) cycle of the goethite surface was involved in O 2 activation. • Cysteine complexed Fe(II) is thermodynamically favorable for electron transfer. • The • O 2 - and ⦁OH are the dominant ROS responsible for As(III) oxidation. [ABSTRACT FROM AUTHOR]