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The abiotic oxidation of As(III) is simultaneously mediated by the oxidation of Fe(II) in microaerobic environment, but the role of Fe minerals in the Fe(II)-mediated As(III) oxidation have been neglected. This work mimicked the microaerobic environment and examined the mechanisms of Fe(II) mediated the As(III) oxidation in the presence of Fe minerals using a variety of iron minerals (lepidocrocite, goethite, etc.). The results indicated the Fe(II) and As(III) oxidation rate were improved with Fe minerals, while As(III) oxidation efficiency increased by 1.3–1.8 times in comparison to that without minerals. Fe(II) mediated the As(III) oxidation happened on Fe minerals surface in the presence of Fe minerals. The As(III) oxidation efficiency increased with increasing Fe mineral concentrations (from 0.5 to 2 g L−1) but decreased with increasing pH values. Reactive oxygen species (ROS) that play a crucial role in As(III) oxidation were Fe(IV) and ·O 2 −, accounting for 42.7%–47.9% and 24.1%–29.8%, respectively. The Fe minerals facilitated the oxidation of As(III) by ROS and stimulated the release of ROS through the adsorbed-Fe(II) oxidation, both of which favored As(III) oxidation. This work highlighted the potential mechanisms of Fe minerals in promoting Fe(II) mediated the As(III) oxidation in microaerobic environment, especially in terms of As(III) oxidation efficiency, shedding a valuable insight on optimization of arsenic contaminated wastewater treatment processes. [Display omitted] • Fe minerals increase As(III) oxidation rate and efficiency. • Fe(II) oxidation mediate abiotic As(III) oxidation. • Fe(IV) and ·O 2 − are dominant ROS for As(III) oxidation. • Fe minerals stimulate ROS generation through adsorbed-Fe (II) oxidation. • Fe minerals promote the reaction between As(III) and ROS. [ABSTRACT FROM AUTHOR]

The adsorption of heavy metals on iron oxides generally increases with pH and is almost complete at neutral to slightly alkaline pH. However, almost complete adsorption on a linear scale does not imply sufficient removal of the heavy metals in terms of their toxicity. Here, we elucidated the chemical reactions that determine the solid–liquid partitioning of Pb(II) and Cd(II) on goethite at high pH. While the removal of both heavy metals was almost complete on a linear scale above pH 7 for Pb(II) and pH 9 for Cd(II), the dissolved metal concentrations decreased on a logarithmic scale with pH, reaching minima at around pH 10 for Pb(II) and pH 10–11 for Cd(II), and then they increased with pH thereafter. The XAFS spectra of Pb(II)- or Cd(II)-adsorbed goethite prepared at pH > 11 were almost the same as those at neutral pH, suggesting that removal of the heavy metals from solution was achieved by a single adsorption reaction over the entire pH range. Based on the observed macroscopic and microscopic adsorption behaviors at high pH, a robust surface complexation model was developed to predict the solid–liquid partitioning of divalent heavy metals over the entire pH range. [Display omitted] • The adsorption of Pb and Cd on goethite at high pH was studied experimentally. • The adsorption reached to maxima at pH 10 for Pb and pH 10–11 for Cd. • The speciation of Pb and Cd on goethite did not change with pH. • A single surface complexation reaction could reproduce the adsorption at high pH. • A robust model was developed to predict any divalent heavy metals on goethite. [ABSTRACT FROM AUTHOR]

Microbially mediated Fe(II) oxidation has a great potential for attenuating arsenic (As) mobility in an anoxic groundwaters. Green rust (GR), a common Fe(II)-bearing phase in such environments, could be easily oxidized into Fe (oxyhydr)oxides through microbial activity. This study focused on Acidovorax sp. strain BoFeN1, an anaerobic nitrate-reducing Fe(II)-oxidizing (NRFO) bacterium, to promote the transformation of GR. In biotic GR transformation experiments, magnetite formation occurred at [As] ini = 5 mg/L while lepidocrocite and goethite were formed at [As] ini = 10 mg/L. In the absence of bacterium, the GR persisted throughout the 120-h experiment. Meanwhile, with the addition of strain BoFeN1, the final aqueous As concentration significantly decreased from 0.237 to 0.004 mg/L (C 0 = 5 mg/L) and from 1.457 to 0.096 mg/L (C 0 = 10 mg/L) at 120 h. It was indicated that strain BoFeN1 played a crucial role in promoting the GR transformation and enhancing As immobilization. Further investigations revealed that the role of strain BoFeN1 extended beyond Fe-oxidation. With nitrite (the intermediate of nitrate bioreduction) as oxidizer, lepidocrocite/goethite were formed in the chemical-oxidation system, excluding magnetite. In the Bio - [As] ini = 5 mg/L, the occurrence of lepidocrocite via the bio-oxidation of Fe(II) in GR at 24 h, along with the metabolism of strain BoFeN1 reducing nitrate accompanied with H+ consumption, it should be reasonably deduced that the alkaline micro-environment of periplasm induced by strain BoFeN1 were vital for the transformation of lepidocrocite to magnetite triggered by trace Fe(II). However, in the Bio - [As] ini = 10 mg/L, more As adsorbed on GR inhibiting the adsorption of bacterium, so the alkaline micro-environment had no obvious effect on such transformation. This study helps to understand the interdependence between GR and anaerobic NRFO bacterium, and provides a new perspective for more effective As remediation strategies in anoxic groundwaters. [Display omitted] • Acidovorax sp. strain BoFeN1 promoted the transformation of GR in presence of As and increased As immobilization. • Bacterium adsorbed on GR to oxidize Fe(II) in GR forming lepidocrocite during the transformation of GR to magnetite. • The alkaline micro-environment induced by strain BoFeN1 was vital for the transformation of GR to magnetite. [ABSTRACT FROM AUTHOR]

In urbanized areas, extracellular DNA (exDNA) is suspected of carrying genes with undesirable traits like virulence genes (VGs) or antibiotic resistance genes (ARGs), which can spread through horizontal gene transfer (HGT). Hence, it is crucial to develop novel approaches for the mitigation of exDNA in the environment. Our research explores the role of goethite, a common iron mineral with high adsorption capabilities, in exDNA adsorption processes. We compare well-crystalline, semi-crystalline, and nano goethites with varying particle sizes to achieve various specific surface areas (SSAs) (18.7–161.6 m2/g) and porosities. We conducted batch adsorption experiments using DNA molecules of varying chain lengths (DNA sizes: <11 Kb, <6 Kb, and <3 Kb) and assessed the impact of Ca2+ and biomacromolecules on the adsorption efficacy and mechanisms. Results show that porosity and pore structure significantly influence DNA adsorption capacity. Goethite with well-developed meso- and macroporosity demonstrated enhanced DNA adsorption. The accumulation of DNA on the goethite interface led to substantial aggregation in the system, thus the formation of DNA-goethite conjugates, indicating the bridging between mineral particles. DNA chain length, the presence of Ca2+, and the biomacromolecule matrix also affected the adsorption capacity and mechanism. Interactions between DNA and positively charged biomacromolecules or Ca2+ led to DNA compaction, allowing greater DNA accumulation in pores. However, a high concentration of biomacromolecules led to the saturation of the goethite surface, inhibiting DNA adsorption. AFM imaging of goethite particles after adsorption suggested the formation of the DNA multilayer. The study advances understanding of the environmental behavior of exDNA and its interaction with iron oxyhydroxides, offering insights into developing more effective methods for ARGs removal in wastewater treatment plants. By manipulating the textural properties of goethite, it's possible to enhance exDNA removal, potentially reducing the spread of biocontamination in urban and industrial environments. [Display omitted] • DNA molecules tend to accumulate inside the meso- and macro-pores of gothite. • The DNA adsorption capacity and diffusion rate depend on the molecule size. • Ca2+ invokes DNA condensation, thus increasing DNA adsorption. • Low concentration of bacterial lysate biomass increases DNA adsorption capacity. • Gothite – DNA interaction may govern the fate of ARGs contamination. [ABSTRACT FROM AUTHOR]

Iron (hydr)oxides and humic acid (HA) are important active components in soils and usually coexist in the environment. The effects of HA on the adsorption and subsequent immobilization of phosphate on iron (hydr)oxide surface are of great importance in studies of soil fertility and eutrophication. In this study, two types of goethite with different particle sizes were prepared to investigate the phosphate adsorption behaviors and complexation mechanisms in the absence or presence of HA by combining multiple characterization and modeling studies. The adsorption capacity of micro- (M-Goe) and nano-sized goethite (N-Goe) for phosphate was 2.02 and 2.04 μmol/m2, which decreased by ∼25% and ∼45% in the presence of 100 and 200 mg/L HA, respectively. Moreover, an increase in equilibrium phosphate concentration significantly decreased the adsorption amount of goethite for HA. Charge distribution-multisite surface complexation (CD-MUSIC) and natural organic matter-charge distribution (NOM-CD) modeling identified five phosphate complexes and their corresponding affinity constants (log K P). Among these phosphate complexes, FeOPO 2 OH, (FeO) 2 PO 2 , and (FeO) 2 POOH species were predominant complexes on the surface of both M-Goe and N-Goe across a wide range of pH and initial phosphate concentrations. The presence of HA had little effect on the coordination mode and log K P of phosphate on goethite surface. These results and the obtained model parameters shed new lights on the interfacial reactivity of phosphate at the goethite-water interface in the presence of HA, and may facilitate further prediction of the environmental fate of phosphate in soils and sediments. [Display omitted] • Competition of HA impedes phosphate adsorption and promotes phosphate availability. • The complete parameters of CD-MUSIC and NOM-CD model were proposed. • Five phosphate complexes and their corresponding log K P were identified. • FeOPO 2 OH, (FeO) 2 PO 2 and (FeO) 2 POOH are predominant species on goethite surfaces. • HA has little effect on the coordination mode and log K P of phosphate on goethite. [ABSTRACT FROM AUTHOR]

Calcium (Ca2+) and phosphorous (PO 4 3−) significantly influence the form and effectiveness of nitrogen (N), however, the precise mechanisms governing the adsorption of ammonium nitrogen (NH 4 +-N) and nitrate nitrogen (NO 3 −-N) are still lacking. This study employed batch adsorption experiments, charge distribution and multi-site complexation (CD-MUSIC) models and density functional theory (DFT) calculations to elucidate the mechanism by which Ca2+ and PO 4 3− affect the adsorption of NH 4 +-N and NO 3 −-N on the goethite (GT) surface. The results showed that the adsorption of NH 4 +-N on the GT exhibited an initial increase followed by a decrease as pH increased, peaking at a pH of 8.5. Conversely, the adsorption of NO 3 −-N decreased with rising pH. According to the CD-MUSIC model, Ca2+ minimally affected the NH 4 +-N adsorption on the GT but enhanced NO 3 −-N adsorption via electrostatic interaction, promoting the adsorption of ≡FeOH-NO 3 − and ≡Fe 3 O-NO 3 − species. Similarly, PO 4 3− inhibited the adsorption of ≡FeOH-NO 3 − and ≡Fe 3 O-NO 3 − species. However, PO 4 3− boosted NH 4 +-N adsorption by facilitating the formation of ≡Fe 3 O-NH 4 + via electrostatic interaction and site competition. DFT calculations indicates that although bidentate phosphate (BP) was beneficial to stabilize NH 4 +-N than monodentate phosphate (SP), SP-NH 4 + was the main adsorption configuration at pH 5.5–9.5 owing the prevalence of SP on the GT surface under site competition of NH 4 +-N. The results of CD-MUSIC model and DFT calculation were verified mutually, and provide novel insights into the mechanisms underlying N fixation and migration in soil. [Display omitted] • Coexisting ions significantly contribute to the N-adsorbed speciation. • Ca2+ enhanced NO 3 −-N adsorption via ≡Fe 3 O-NO 3 − formation via electrostatic interaction. • Electrostatic interactions and site competition affect NH 4 +-N adsorbed by BP and SP. • BP has a stronger stabilizing effect on NH 4 +-N than SP. [ABSTRACT FROM AUTHOR]

Bisphenol A (BPA) in seawater tends to be deposited in coastal sediments. However, its degradation under tidal oscillations has not been explored comprehensively. Hydroxyl radicals (·OH) can be generated through Fe cycling under redox oscillations, which have a strong oxidizing capacity. This study focused on the contribution of Fe-mediated production of ·OH in BPA degradation under darkness. The removal of BPA was investigated by reoxygenating six natural coastal sediments, and three redox cycles were applied to prove the sustainability of the process. The importance of low reactivity Fe(II) in the production of ·OH was investigated, specifically, Fe(II) with carbonate and Fe(II) within goethite, hematite and magnetite. The degradation efficiency of BPA during reoxygenation of sediments was 76.78–94.82%, and the contribution of ·OH ranged from 36.74% to 74.51%. The path coefficient of ·OH on BPA degradation reached 0.6985 and the indirect effect of low reactivity Fe(II) on BPA degradation by mediating ·OH production reached 0.5240 obtained via partial least squares path modeling (PLS-PM). This study emphasizes the importance of low reactivity Fe(II) in ·OH production and provides a new perspective for the role of tidal-induced ·OH on the fate of refractory organic pollutants under darkness. [Display omitted] • Redox oscillations of coastal sediments promoted the production of ·OH. • The tidal-induced production of ·OH was rhythmic and sustainable in three cycles. • Fe(II) low reactivity could serve as an electron pool to facilitate ·OH production. • Fe(II) within the Fe NaAC and Fe AAO fraction could regenerate reactive Fe(II). • The contribution of ·OH in BPA degradation was 36.74–74.51 %. [ABSTRACT FROM AUTHOR]

Aquifer storage and recovery (ASR) is a promising approach for managing water resources that enhances water quality through biogeochemical reactions occurring within aquifers. Iron (hydr)oxides, which are the predominant metallic oxides in soil, play a crucial role in degrading dissolved organic carbon (DOC), primarily through a process known as dissimilatory iron reduction (DIR). However, the efficiency of this reaction varies depending on the mineralogy and composition of the aquifer, and this understanding is essential for adequate water quality in ASR. The objective of this study is to investigate the impact of iron (hydr)oxide on acetate, as an organic carbon source, attenuation during the ASR. To achieve this, three sets of laboratory sediment columns were prepared, each containing a different type of iron (hydr)oxide minerals: ferrihydrite, goethite, and hematite. Following an acclimation period of 28 days to simulate the microcosm within an aquifer, the columns were continuously supplied with the simulated river water spiked with acetate (DOC 40–60 mg L−1), and the acetate concentration in the effluent was monitored. The result revealed that the column containing ferrihydrite achieved 97% acetate attenuation through DIR with anoxic conditions (DO < 0.1 mg L−1), while the goethite and hematite columns exhibited limited attenuation rates of 40 and 50%, respectively. Furthermore, the efficiency of acetate attenuation in the ferrihydrite columns increased with the content of ferrihydrite but experienced a rapidly declined at higher contents (3–4%), possibly due to the partial conversion of ferrihydrite to goethite as a result of the interaction between ferrihydrite and the Fe(II) produced during DIR. Additionally, an analysis of the microbial community demonstrated that microorganisms known to possess the ability to reduce iron (hydr)oxides under anaerobic conditions were abundant in the ferrihydrite columns. [Display omitted] • DOC attenuation during the ASR was investigated with iron mineralogy and contents. • Ferrihydrite is the most efficient iron mineral for DOC attenuation via DIR. • At high ferrihydrite contents (>3%), efficiency declines due to Fe(II) intervention. • Ferrihydrite transforms into goethite upon the injection of DOC-reach surface water. • Findings could be beneficial for selecting optimal sites for ASR application. [ABSTRACT FROM AUTHOR]

In this study, the potential of bioleaching to extract valuable metals from industrial by-products, specifically basic oxygen steelmaking dust (BOS-D) and goethite was investigated. These materials are typically discarded due to their high zinc content and lack of efficient regeneration processes. By using Acidithiobacillus ferrooxidans , successful bioleaching of various metals, including heavy metals, critical metals, and rare earth elements was achieved. The Taguchi orthogonal array design was used to optimise the bioleaching process, considering four variables at three different levels. After 14 days, the highest metal extraction for the BOS-D (11.2 mg Zn/g, 3.2 mg Mn/g, 1.6 mg Al/g, 0.0013 mg Y/g, and 0.0026 mg Ce/g) was achieved at 1% solid concentration, 1% energy source concentration, 1% inoculum concentration, and pH 1.5. For goethite, the optimal conditions were 1% solid concentration, 4% energy source concentration, 10% inoculum concentration, and pH 2 resulting in a extraction of 26.6 mg Zn/g, 2.1 mg/g Mn, 1.8 mg Al/g, 0.01 mg Co/g, 0.0022 mg Y/g. These findings are significant, as they demonstrate the potential to extract valuable metals from previously discarded industrial by-products. The extraction of such metals can have substantial economic and environmental implications, while simultaneously reducing waste in the metallurgical industry. Furthermore, the preservation of initial concentration of iron in both BOS-D and goethite residues represents a significant step towards implementing more sustainable industrial practices. [Display omitted] • Bioaching was evaluated using Taguchi L9 orthogonal array design for metallurgical by-products. • Optimum condition to leach selected metals form BOS-D and goethite was defined. • The most influencing parameters were found as solid concentration followed by pH. [ABSTRACT FROM AUTHOR]

Understanding the distribution of PFOS isomers between the aqueous phase and goethite is crucial, since it is an abundant sorbent and thus may have a large influence on the mobility of PFOS. This study was conducted to understand the effects of pH, humic acid (HA), fulvic acid (FA) and sulfate on sorption of PFOS isomers. The results will increase the understanding about what parameters may control the fate and transport of PFOS in surface and ground water. The study was conducted by adding PFOS spiked water to a goethite slurry with different aqueous chemistry. Levels of total PFOS and PFOS isomers were quantified using an Ultra-Performance Liquid Chromatograph coupled to a triple quadrupole mass spectrometer. Results showed that sorption of PFOS was mainly dependent on pH; sorption decreased as pH increased. Presence of HA increased log K d from 1.29 to 2.03, 1.76 to 1.92 and 1.51 to 1.96 at pH 5.50–7.50 for 3-/4-/4-PFOS, 6-/2-PFOS and L-PFOS, respectively. Changes in the aqueous chemistry also affected the behaviour of PFOS as the addition of Na 2 SO 4 enhanced the sorption of PFOS. Results showed that L-PFOS was more readily sorbed to goethite at pH < 4.35 both in the presence and in the absence of humic or fulvic acids. At pH > 4.5 the 3-/4-/5-PFOS isomer group was more associated to goethite. Besides electrostatic interactions, which controlled the sorption of PFOS, this study indicate that the presence of dissolved humic substances in the aqueous phase enhances the sorption via hydrophobic mechanisms. • Sorption of PFOS isomers to goethite was mainly depending on pH; sorption was controlled by electrostatic mechanisms. • Presence of HA or FA enhanced sorption to goethite both via hydrophobic and electrostatic mechanisms. • L-PFOS was more readily sorbed to goethite at pH < 4.35, both in the presence and in the absence of humic substances. • At a pH above 4.5 the 3-/4-/5-PFOS isomer group was more sorbed to the solid phase compared to the other isomers. [ABSTRACT FROM AUTHOR]

Abstract The coprecipitation of organic matter (OM) and minerals is a relatively common phenomenon in soil, and it has a significant influence on the surface properties and reactivity of minerals. In turn, the fate of pollutants in soil is greatly affected by the organic-mineral composites. In this study, goethite-fulvic acid (Ge-FA) composites with varying FA mass ratios in the range of 0–15% were synthesized by coprecipitation. The sample properties were studied using XRD, FTIR, SEM-EDS and N 2 gas adsorption techniques. The influence of Ge-FA on the mobility of Pb/Cd in soil was investigated. The crystal forms of Ge-FA changed from goethite (FA≤4%) to hematite (FA≥5%), and the FA affected the Fe O bond vibrations. These results demonstrated that FA was successfully introduced into the iron oxide. Ge-FA changed from a filamental morphology to an aggregate as the FA ratio increased. The coprecipitation resulted in blockages of iron oxides, thereby decreasing the specific surface area and pore volume. The adsorption amount of Pb(II) on Ge-FA increased as the FA ratio increased, but no significant change was observed for Cd(II). With the application of Ge-FA, the exchangeable concentrations of Pb and Cd in contaminated soil decreased by 42.4%–93.6% and 15.8%–43.7%, respectively. The exchangeable and carbonate bound fractions of Pb and Cd decreased and were transformed into the Fe Mn bound and residual fractions. Graphical abstract Image 1 Highlights • Ge-FA has a different crystal structure and stability than goethite and fulvic acid. • Fulvic acid can enhance the adsorption capacity of goethite by coprecipitation. • Ge-FA has an obvious immobilization effect on Pb and Cd in soil. [ABSTRACT FROM AUTHOR]

Abstract Nowadays non-steroidal anti-inflammatory drugs (NSAIDs) are often detected in surface water and groundwater. In this study, effects of environmental factors, i.e., solution pH, ionic strength, temperature and surface-bound organic acids, on bonding of three typical NSAIDs (ketoprofen, naproxen and diclofenac) onto goethite were systematically investigated. Column chromatography, batch experiments, attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy and surface complexation modeling were used to probe the adsorption mechanisms. Bonding of three NSAIDs onto goethite was totally reversible, ionic strength-dependent and endothermic (adsorption enthalpy 2.86–9.75 kJ/mol). These evidences supported H-bonding mechanism, which was further explained by ATR-FTIR observation and a triple planes model. Surface-bound organic acids (phthalic acid, trimellitic acid and pyromellitic acid) by inner-sphere complexation with goethite were hard to be desorbed. Surface-bound phthalic acid increased the uptake of NSAIDs but surface-bound trimellitic acid and pyromellitic acid reduced their adsorption. The reason is that the adsorbed phthalic acid can result in a more hydrophobic surface while adsorbed trimellitic acid and pyromellitic acid increased the surface negative charge and polarity. Finally, adsorption of NSAIDs onto goethite with/without surface-bound organic acids was well described by a free energy model, in which contributions of interactions (e.g., H-bonding and van der Waals) were evaluated. Highlights • H-bonding dominates the adsorption of three NSAIDs onto goethite. • Adsorption is totally reversible, ionic strength-dependent and endothermic. • Organic acids affect the adsorption of NSAIDs by changing surface properties. • Contributions of adsorption mechanisms by goethite-organic acids were evaluated. [ABSTRACT FROM AUTHOR]

Abstract Adsorption of a diverse set of chemicals onto goethite was evaluated by column chromatography. The pH of the effluents was 4.7–5.2. Van der Waals forces dominate the exothermic adsorption of 8 nonpolar compounds (e.g., PAHs and chlorobenzenes). H-bonding is responsible for the adsorption of 32 monocarboxylic acids (i.e., benzoic acids, naphthoic acids and acidic pharmaceuticals) and their adsorption tends to be endothermic. Steric effects significantly decreased the bonding of monocarboxylic acids with ortho-substitutions. Exothermic adsorption of 10 monophenols is controlled by weak H-bonding. Bonding of these 50 solutes onto goethite is totally reversible. In contrast, inner-sphere complexation of phthalic acid and chlortetracycline with goethite occurred according to their low desorption ratio (1.1%–54.4%). Polyparameter linear free energy relationship (PP-LFER) models were established to provide acceptable fitting results of the goethite-solute distribution coefficients (RMSE = 0.32 and 0.30 at 25 °C and 5 °C, respectively). It is worthy to note that steric effects must be considered to get a better prediction for compounds with ortho-substitutions. Graphical abstract Image 1 Highlights • Adsorption of 50 investigated compounds onto goethite was reversible. • H-bonding of monocarboxylic acids was endothermic. • Weak adsorption of monophenols and nonpolar compounds was exothermic. • Distribution coefficients (K d) were fitted by pp-LFER models. [ABSTRACT FROM AUTHOR]

Abstract Oxalic acid potentially enhances pump-and-treat for groundwater As remediation by accelerating mobilization. This study examines how oxalic acid mobilizes As from Fe(III)-oxide coated sand under hydrodynamic conditions. Four columns were packed with metal-substituted ferrihydrite or goethite to 1% Fe, presorbed to 50% As surface coverage, and reacted with pH = 2.2 artificial groundwater amended with 10 mM oxalic acid at 1 m day−1. Arsenic elution was affected by both As and Fe speciation. Although the As(V) columns experienced faster substrate dissolution, As(V) elution was delayed by re-adsorption, whereas As(III) elution was rapid due to pH decrease that prevented re-adsorption. Cr-ferrihydrite and Ni-goethite dissolved both effectively initially but then diverged. The Cr-ferrihydrite columns experienced continuous stoichiometric Fe and Cr release, and As release could be sustained. The Ni-goethite columns initially experienced nonstoichiometric Fe and Ni release, and As release was extensive. Such release, however, was not sustained. We hypothesized that Ni-goethite contained sites with distinct reactivity, and oxalic acid targeted readily-dissolved, sorption-dense sites. Our data indicate that oxalic acid-enhanced pump-and-treat methods would be easier to apply to aquifers dominated by As(III), requiring less amendment to be injected; such oxalic acid-enhanced methods remove reactive sediment Fe and As, potentially preventing future groundwater contamination. Graphical abstract Image 1 Highlights • We study oxalic acid promoted metal release from As presorbed Fe oxide coated sand. • Cr and Ni substituted ferrihydrite and goethite were used. • The effect of substrate dissolution was isolated from other As release mechanisms. • As(V) elution was retarded, whereas As(III) elution was rapid due to pH decrease. • Unlike Cr-ferrihydrite, metal release from Ni-goethite could not be sustained. [ABSTRACT FROM AUTHOR]

A photochemical system combining iron (hydr)oxides and oxalate (Ox) shows application prospects in wastewater treatment due to the abundance of reactive oxygen species (ROS) generation. Nevertheless, it is a challenge to the investigate photochemical activity of iron (hydr)oxides/Ox systems with varying structural properties. Herein, the photochemical behaviors of Ox on goethite (Gt) surface from the view of structural dependent activity, containment degradation, and ROS generation were explored in detail. Results confirmed that bidentate mononuclear was formed on Gt surface after complexing Ox. Combined with density functional theory calculation and pH time evolution during aniline degradation, the photochemical activity of the Gt/Ox system fell in between that of ferrihydrite/Ox and hematite/Ox systems. After irradiating 120 min visible light, 96.5% aniline was degraded by 1.0 mM Ox and 0.2 g/L Gt. The amount of •OH in vis/Gt/Ox system could be up to 309.3 μM and its generation was closely associated with Fe(II) while slightly affected by the generated H 2 O 2. Moreover, as revealed by high-performance liquid chromatography with mass spectrometric and Ecological Structure Activity Relationships software, the toxicity of the intermediates of aniline degradation in the vis/Gt/Ox system towards fish and green algae increased first but then declined accompanied by the generation of non-toxic ring-opening products at the end of reaction. According to the findings in the presented study, it could be concluded that vis/Gt/Ox is a promising approach to wiping out aniline wastewater. [Display omitted] • The structural dependent activity of Ox on Gt surface is studied. • Ox adsorption and detachment on Gt surface are investigated by in-situ ATR-FITR. • The dissolved O 2 is activated by CO 2 •− radicals and Fe(II) to generate ROS. • •OH generation is closely associated with Fe(II) rather than the intermediate H 2 O 2. • The toxicity of aniline degradation intermediates is firstly evaluated by ECOSAR. [ABSTRACT FROM AUTHOR]

In the environment, simultaneous presence of arsenic (As) of different oxidation states is common, which hampers our understanding of As behavior. In the current study, the pH dependency of arsenite (As(III)) and arsenate (As(V)) adsorption to goethite under the influence of calcium (Ca 2+ ) (as a major cation) and phosphate (PO 4 3− ) (as a major anion) was studied, and the reliability of the CD-MUSIC model prediction was tested. The results show that the presence of the major ions led in general to a weaker and more complicated pH dependency of As adsorption. Calcium promoted As(V) adsorption especially at high pH, which can reverse the direction of the pH dependency. The presence of Ca 2+ can even decrease As(III) adsorption when As(V) and/or PO 4 3− are present. Phosphate competed strongly with both As(III) and As(V) in their adsorption, especially at intermediate and low pH. In the multi-component system, As(III) adsorbs weaker than As(V) over the environmental relevant pH range, therefore it is often the dominant As species in solution and soluble As(III) concentration generally decreases with increasing pH. In the same pH range, As(V) adsorption shows a complicated pH dependency. Soluble As(V) reaches a minimum around pH 6 at high concentration of major bivalent cations (e.g. Ca 2+ ), whereas soluble As(V) will decrease with pH at low bivalent cation concentrations. The experimental results can be reliably predicted and explained with the CD-MUSIC model. The outcome of this study can provide understanding needed in the risk assessment and remediation of As contaminated soils and water. [ABSTRACT FROM AUTHOR]

The accurate modeling of heavy metal adsorption in complex systems is fundamental for risk assessments in soils and associated environments. Bacteria-iron (hydr)oxide associations in soils and sediments play a critical role in heavy metal immobilization. The reduced adsorption of heavy metals on these composites have been widely reported using the component additivity (CA) method. However, there is a lack of a mechanism model to account for these deviations. In this study, we established models for Cd adsorption on goethite- Pseudomonas putida composites at 1:1 and 5:1 mass ratios. Cadmium adsorption on the 5:1 composite was consistent with the additivity method. However, the CA method over predicted Cd adsorption by approximately 8% on the 1:1 composite at high Cd concentration. The deviation was corrected by adding the site blockage reactions between P. putida and goethite. Both CA and “CA-site masking” models for Cd adsorption onto the composites were in line with the ITC data. These results indicate that CA method in simulating Cd adsorption on bacteria-iron oxides composites is limited to low bacterial and Cd concentrations. Therefore the interfacial complexation reactions that occur between iron (hydr)oxides and bacteria should be taken into account when high concentrations of bacteria and heavy metals are present. [ABSTRACT FROM AUTHOR]

Different environmental conditions such as pH and dissolved elements of mine stream induce precipitation of different minerals and their associated microbial community may vary. Therefore, mine precipitates from various environmental conditions were collected and their associated microbiota were analyzed through metagenomic DNA sequencing. Various Fe and Mn minerals including ferrihydrite, schwertmannite, goethite, birnessite, and Mn-substituted δ-FeOOH (δ-(Fe 1-x , Mn x )OOH) were found in the different environmental conditions. The Fe and Mn minerals were enriched with toxic metal(loid)s including As, Cd, Ni and Zn, indicating they can act as scavengers of toxic metal(loid)s in mine streams. Under acidic conditions, Acidobacteria was dominant phylum and Gallionella (Fe oxidizing bacteria) was the predominant genus in these Fe rich environments. Manganese oxidizing bacteria, Hyphomicrobium , was found in birnessite forming environments. Leptolyngbya within Cyanobacteria was found in Fe and Mn oxidizing environments, and might contribute to Fe and Mn oxidation through the production of molecular oxygen. The potential interaction of microbial community with minerals in mine sites can be traced by analysis of microbial community in different Fe and Mn mineral forming environments. Iron and Mn minerals contribute to the removal of toxic metal(loid)s from mine water. Therefore, the understanding characteristics of mine precipitates and their associated microbes helps to develop strategies for the management of contaminated mine water. [ABSTRACT FROM AUTHOR]

The photochemical behavior of goethite has been one of the most important topics in the field of environmental science due to it plays a significant role in the removal and transformation process of numerous pollutants. However, the interfacial electron transfer process of goethite is not clear. Using a nanosecond laser flash photolysis spectrometer, we report the transient spectroscopic observations of interfacial electron-transfer reactions in goethite dispersion under UV irradiation. Excitation of goethite generated conduction-band electron (e cb − ) and hole (h + ). The conduction band electron (e cb − ) reacted with an electron acceptor, methylviologen dichloride hydrate (MV 2+ ), forming reduced methylviologen (MV + ) with a second-order rate constant of (2.6 ± 0.3) × 10 9 L mol −1 s −1 . The concentration of MV + was strongly influenced by MV 2+ initial concentration and pH values. The flat band potential of goethite was calculated to be E fb (goethite, pH = 7) = 0.24 V (vs NHE). Oxygen did not react with conduction band electron of goethite. The present study provides a reliable method to investigate the photo-induced interfacial charge transfer of goethite. [ABSTRACT FROM AUTHOR]

We have compared the elimination of 5-bromosalicylic acid (BSA) in the systems of goethite (α-FeOOH)/H 2 O 2 and lepidocrocite (γ-FeOOH)/H 2 O 2. The results demonstrated that BSA (10 mg L−1) could be successfully adsorbed on α- and γ-FeOOH (0.5 g L−1) and then effectively degraded after the addition of H 2 O 2 (14.7 mM). BSA adsorption on both α- and γ-FeOOH followed pseudo-second order adsorption kinetic models, with γ-FeOOH having greater adsorption ability than α-FeOOH. In the α-FeOOH/H 2 O 2 system, BSA degradation was well fitted with the pseudo-second order kinetics, whereas the oxidation in γ-FeOOH/H 2 O 2 system had a two-stage pseudo-first order kinetics. Electron paramagnetic resonance (EPR) results for these two systems revealed the presence of •OH and •OOH, and further tests with radical captures demonstrated their dominance in degrading BSA. Based on the electronic structure analysis, electrons were more easily transferred from the H 2 O 2 molecule to the Fe atoms of α-FeOOH, explaining the density functional theory (DFT) calculation results, which showed that α-FeOOH performed better in catalyzing the decomposition of H 2 O 2. However, the free radicals are more likely to desorb from γ-FeOOH, which made the γ-FeOOH/H 2 O 2 system more efficient in degrading BSA. [Display omitted] • Adsorption and catalytic performance of α- and γ-FeOOH was compared. • γ-FeOOH performed better in BSA removal, but relatively poor in mineralization. • Potential energy reduced more when H 2 O 2 cracked on α-FeOOH. • The energy barriers of radical desorption was lower for γ-FeOOH. • Higher electronic conductivity of α-FeOOH lead to a better hybridization with H 2 O 2. [ABSTRACT FROM AUTHOR]

Copper is a trace element essential for living creatures, but copper content in soil should be controlled, as it is toxic. The physical-chemical-biological features of Cu in soil have a significant correlation with the Fe(II)/Cu(II) interaction in soil. Of significant interest to the current study is the effect of Fe(II)/Cu(II) interaction conducted on goethite under anaerobic conditions stimulated by HS01 (a dissimilatory iron reduction (DIR) microbial). The following four treatments were designed: HS01 with α-FeOOH and Cu(II) (T1), HS01 with α-FeOOH (T2), HS01 with Cu(II) (T3), and α-FeOOH with Cu(II) (T4). HS01 presents a negligible impact on copper species transformation (T3), whereas the presence of α-FeOOH significantly enhanced copper aging contributing to the DIR effect (T1). Moreover, the violent reaction between adsorbed Fe(II) and Cu(II) leads to the decreased concentration of the active Fe(II) species (T1), further inhibiting reactions between Fe(II) and iron (hydr)oxides and decelerating the phase transformation of iron (hydr)oxides (T1). From this study, the effects of the Fe(II)/Cu(II) interaction on goethite under anaerobic conditions by HS01 are presented in three aspects: (1) the accelerating effect of copper aging, (2) the reductive transformation of copper, and (3) the inhibition effect of the phase transformation of iron (hydr)oxides. [ABSTRACT FROM AUTHOR]

The Sukinda ultramafic complex in Odisha has the largest chromite reserve in India. Sediment derived from ultramafic rocks has been enriched with various metals. Further, mining activities enhance the influx of metals into sediment by dumping mine overburden and tailings in the open area. Metal concentration in sediment is found in order of Cr Total (Cr) > Mn > Ni > Co > Zn > Cu with average concentration 26,778 mg/kg, 3098 mg/kg, 1813 mg/kg, 184 mg/kg, 116 mg/kg and 44 mg/kg respectively. Concentration of Cr(VI) varies from 5.25 to 26.47 mg/L with an average of 12.27 mg/L. Based on various pollution indices, it is confirmed that the area is severely contaminated. Nano-scale goethite, kaolinite, clinochlore and chromite have been identified and have high concentration of Cr, Co and Ni. Goethite has shown maximum metal retention potential as deciphered by high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). The HAADF-STEM mapping and principal component analysis indicate that Cr and Co mostly derived from chromite whereas Ni and Zn are derived from serpentine. Later, these metals co-precipitate and/or adsorbed onto the goethite and clay minerals. Fractionation study of metals confirms that Cu is the most mobile element followed by Zn. However, at low pH condition Ni is mobilized and likely to be bioavailable. Though Cr mostly occurs in residual fraction but as its concentration is very high, a small proportion of exchangeable fraction contributes significantly in terms of its bioavailability. Thus bioavailable Cr can pose severe threat to the environment in the Sukinda ultramafic complex. [ABSTRACT FROM AUTHOR]

The adsorption of diclofenac (DCF), one of the widely used non-steroidal anti-inflammatory drugs, onto the surface of goethite was investigated with batch experiments. The adsorption at different pH values (5.3, 7.4, and 10.0) were well fitted with the pseudo-second-order model. The results showed that the adsorption of DCF onto goethite was strongly depended on solution pH. The amount of adsorbed DCF decreased with increasing pH duo to electrostatic repulsive interactions. Fourier transform infrared (FTIR) results indicated that carboxyl group ( COOH) might be involved in the adsorption, and DCF formed bidentate chelate and bridging bidentate complexes on the surface of goethite. [ABSTRACT FROM AUTHOR]

Arsenite (As(III)) is toxic in drinking water, which becomes an environmental concern worldwide. This work was to synthesize porous hematite through the calcination of natural goethite concentrate for As(III) adsorption, including adsorption kinetics, isotherms and the influence of pH and temperature. The calcination was performed at 300 °C for 180 min, producing porous hematite with large amount of micropores. The maximum adsorption capacity of As(III) on porous hematite was achieved at pH 6.0 and 25 °C, about 14.46 mg g −1 , compared with 2.965 mg g −1 on the original goethite concentrate. The improvement might be attributed to the formation of micropores and thus the increase in the surface area. Also, it was found that the adsorption was strongly pH dependent and reduced with increasing temperature. It is indicated that the low-cost porous hematite has great potential in As(III) removal from contaminated water. [ABSTRACT FROM AUTHOR]

Soil acidification in southern China increases the environmental risk posed by heavy metals, especially cadmium (Cd), and has been accelerated by anthropic activities. Long-term fertilizer use increases the quantity of phosphate (P) in soils, which affects the biogeochemistry of heavy metals in soil environments. In this study, various analytical methods were used to investigate the critical mechanisms controlling P(V)–Cd(II) interactions with goethite (α-FeOOH, a typical iron oxide widely distributed in red soil areas) with added P(V)/Cd(II) in different molar ratios (to simulate the annual P fertilizer surplus). After excluding pH interference by using organic buffers, Cd(II) adsorption processes on α-FeOOH were found to be enhanced by the presence of P(V), whereas the Cd(II) adsorption type changed from single inner-sphere complexation to both inner- and outer-sphere complexation. The results of a zeta potential analysis, X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM) and X-ray photoelectron spectroscopy (XPS) showed different dominant mechanisms underlying the promotion of Cd(II) adsorption by P(V) at different P(V)/Cd(II) molar ratios. Electrostatic adsorption and the formation of ternary complexes were proven to be the critical mechanisms controlling the reactivity of Cd(II), where coprecipitation occurs at high P(V)/Cd(II) molar ratios and considerably enhances the fixation of Cd(II) and P(V). The mechanism for Cd(II) and P(V) coadsorption onto α-FeOOH under stable pH conditions was found to include both competitive and synergistic effects, and the results in this study show that more attention should be given to the impact of anthropic activities on the reactivity of heavy metals in the soil environment, especially farmland. [Display omitted] • Cd(II) stabilized onto α-FeOOH enhanced by P(V) through coadsorption. • Cd(II) formed outer-sphere complexes with P(V) on α-FeOOH. • Cd(II) regulated by electrostatic adsorption and formation of surface complexes. • Fe–P–Cd ternary complexes were proved by HRTEM-EDS and XPS analysis. [ABSTRACT FROM AUTHOR]

In this work, zero-valent iron (ZVI) combined with anaerobic bacteria was used in the remediation of Cd(II)-polluted soil under the mediation of sulfate (SO 4 2−). Owing to hydrogen-autotrophic sulfate reduction, serious corrosion occurred on sulfate-mediated biotic ZVI in terms of solid phase characterization as massive corrosive products (e.g., goethite, magnetite and green rust) were formed, which were crucial in the immobilization of Cd(II). Thus, this integrated system achieved a 4.9-fold increase in aqueous Cd(II) removal and converted more than 53% of easily available Cd(II)-fractions (acid-extractable and reducible) to stable forms (oxidizable and residual) based on the sequential extraction results as compared to the sulfate-mediated ZVI system. Increasing SO 4 2− concentration and ZVI dosage both demonstrated positive correlation to Cd(II) immobilization, which further reflected that hydrogenotrophic desulfuration acted an essential role in improving Cd(II) immobilization. It indicated that hydrogenotrophic desulfuration could accelerate iron corrosion and promote reactive mineral formation through biomineralization, as well as generate cadmium sulfide precipitates (CdS) to achieve excellent immobilization performance for Cd(II). Besides, this reaction was favorable under neutral pH condition. Our results highlighted the promoted effect of hydrogen-autotrophic desulfuration on ZVI corrosion to immobilize Cd(II) and offered a practicable technique in Cd(II)-polluted soil remediation. [Display omitted] • Sulfate-mediated biotic ZVI system was established to remediated Cd(II)-polluted soil. • Hydrogenotrophic desulfuration promoted iron corrosion and active mineral formation. • Significantly enhanced Cd(II) immobilization was achieved by sulfate-mediated biotic ZVI. [ABSTRACT FROM AUTHOR]

The iron mineral-catalyzed degradation of cephalosporin antibiotics with H 2 O 2 occurs ubiquitously in nature. Despite numerous studies, the effects of environmental conditions on reactive species production and degradation processes of cephalosporins remain unclear. Here, we report the iron mineral of goethite as the efficient and heterogenous catalyst for the degradation of cefradine (CRD) via H 2 O 2 activation under different conditions involving pH and visible light irradiation. Results show that the CRD removal rate is highly dependent on pH and visible light irradiation. Interestingly, when the pH ranges from 4.0 to 7.0, the degradation intermediates of CRD under dark are the same as under visible light conditions in the goethite/H 2 O 2 system. And, the ratio of CRD degradation rate constant (k Light / k Dark) reaches a maximum at pH 5.0, suggesting that CRD existing as zwitterion species is preferable for its removal with photoassistance. The mechanism investigation reveals that both •OH and ≡[FeIVO]2+ oxidants are generated during the reaction process, and •OH is the major oxidant at acidic pH, while ≡[FeIVO]2+ is more likely to be formed with photoassistance at near-neutral pH. According to UPLC–MS/MS analysis, CRD degradation likely happens via hydrogen atom abstraction from cyclohexadienyl by •OH, thioether and olefin oxidation by ≡[FeIVO]2+, and FeIII-catalyzed hydrolytic cleavage of β-lactam ring. These findings highlight the vital roles of pH and photoassistance in the heterogeneously activated H 2 O 2 with goethite for CRD degradation. [Display omitted] • The degradation rate of cefradine by goethite/H 2 O 2 system highly depends on pH and visible light irradiation. • Cefradine degradation intermediates under dark are the same as under visible light in goethite/H 2 O 2 system at pH 4.0–7.0. • Photo-assisted effect reaches a maximum when cefradine exists as zwitterions at pH 5.0 in goethite/H 2 O 2 system. • Both •OH and ≡[FeIVO]2+ are the oxidants under dark and visible light conditions in goethite/H 2 O 2 system at pH 4.0–7.0. • Three degradation pathways of cefradine in goethite/H 2 O 2 system were found, i.e. H abstraction, oxidation, and hydrolysis. [ABSTRACT FROM AUTHOR]

Adsorption of natural organic matter (NOM) to mineral surfaces is an important process determining the environmental fate and biogeochemical cycling of many elements. Natural organic matter consists of a heterogeneous mixture of soft and flexible organic molecules. Upon adsorption, size fractionation may occur, as well as changes in molecular conformation. Although very important, these phenomena have been omitted in existing adsorption models. Filling this gap, a novel framework for NOM adsorption to metal (hydr)oxides is presented. Humic acid (HA) was used as an analog for studying experimentally the NOM adsorption to goethite and its size fractionation as a function of pH, ionic strength, and surface loading. Size fractionation was evaluated for adsorption isotherms collected at pH 4 and 6, showing HA molecules of low molar mass were preferentially adsorbed. This phenomenon was incorporated into the new model. Consistent description of the HA adsorption data over the entire range of pH (3–11), ionic strength (2–100 mM), and surface loading (0.1–3 mg m−2) indicated that the spatial distribution of HA molecules adsorbed in the interface is a trade-off between maximizing the interaction of the HA ligands with the oxide surface and minimizing the electrostatic repulsion between HA particles as a result of interfacial crowding. Our advanced consistent framework is able to quantify changes in molar mass and molecular conformation, thereby significantly contributing to an improved understanding of the competitive power of HA for interacting on oxides with other adsorbed small organic acids as well as environmentally important oxyanions, such as phosphate, arsenate, and others. [Display omitted] • A novel model framework for interaction of organic matter and oxides is presented. • Size fractionation and particle conformational change are key parameters. • Size fractionation depends on pH, ionic strength, and surface loading. • Conformational change of adsorbed organic matter is driven by electrostatic forces. [ABSTRACT FROM AUTHOR]

Iron oxyhydroxides (FeOOH) are common crystalline forms of iron which play an important role in catalysis through a series of reduction-oxidation reactions. In this paper, Ce substituted goethite (Ce 0.1 Fe 0.9 OOH) was prepared by isomorphous substitution method, characterized by XRD, SEM, TEM-EDS, FTIR, and used for the catalytic ozonation of sulfamethazine (SMT). The results showed that the catalyst can significantly enhance the mineralization of SMT, and more than 42.1% SMT were mineralized in the presence of the catalyst, which is 1.74 times higher than ozonation alone. Moreover, with addition of catalyst, more ozone was dissolved into solution. The solution pH decreased due to small-molecule organic acids formation. The catalytic activity decreased slightly during the repeated batch experiments, due to the corrosion of the catalyst and the adsorption of the residual intermediates on the catalyst surface. [ABSTRACT FROM AUTHOR]

Arsenic (As) contamination has become a worldwide environmental problem: arsenite (As(Ⅲ)) especially has posed a major threat to human health. Here, we report the first three isolates of anaerobic As(Ⅴ)-reducing bacterial strains (strains JQ, DJ-3 and DJ-4) from a soil sample containing 48.7% of total As in the form of As(III) collected in Chifeng, Inner Mongolia, China. Strains JQ, DJ-3 and DJ-4 were phylogenetically closely related to Bacillus , Desulfitobacterium and Exiguobacterium , respectively. Among these strains, JQ and DJ-3 have the arsC gene, DJ-4 possesses the arrA gene. The three strains could all resist and reduce high concentrations of As(Ⅴ) under anoxic conditions. The order of resistance to As(Ⅴ) was DJ-3 > JQ > DJ-4. Strain DJ-3 not only possesses the strongest resistance to As(Ⅴ) but could also reduce 53% of the As(Ⅴ) to As(III) in the treatment of 60 mM As(Ⅴ) in 5 d. All three strains could release As from goethite; strain DJ-4 has the highest ability to promote the release of As (90.5%) from goethite. These results suggested that strains JQ, DJ-3 and DJ-4 may play an important role in the mobilization and transformation of As in soil. [ABSTRACT FROM AUTHOR]

Aromatic organoarsenical roxarsone (ROX) is a common additive for livestock feed. This arsenic containing pollutant could be discharged into the environment through agricultural application of animal manure, and pose potential threats to both humans and the wider environment. In this study, the influence of pH, competing anions and metal ions on the adsorption and desorption of ROX on goethite were investigated in order to understand their mobility in the environment. Both hydroxide ions and phosphate are common substances in the environment, and both are potential competing anions for ROX. Our results showed the addition of phosphate desorbed more ROX than the addition of hydroxide ions. As pH increased, the effect of phosphate did not show much difference to that of hydroxide ion. The results indicate that the presence of phosphate will greatly increase the mobility of ROX at low pH. Six common metal ions, including Zn 2+ , Cu 2+ , Fe 3+ , Mn 2+ , Mg 2+ , and Ca 2+ , were tested and all spiked metal ions enhanced the stability of ROX adsorption on the surface of goethite, and led to less desorption when phosphate was added. The results demonstrate that metal ions may form complex/surface precipitation with ROX to enhance its adsorption. The effect from Fe 3+ , Zn 2+ and Cu 2+ was more pronounced than other metal ions, which might result from the fact that these three metal ions tend to associate with hydroxide ions and decrease the pH. The results of this research may shed light on the environmental fate and transportation of aromatic organoarsenicals in soil. [ABSTRACT FROM AUTHOR]

The effects of Fe(II) on the sorption and precipitation of Sb(V) on soils and goethite were investigated using batch experiments and X-ray photoelectron spectroscopy (XPS) in this study. The sorption capacity of Sb(V) were much higher in anoxic soil than oxic soil. Typically, dissolved Fe(II) concentration in anoxic soils decreased significantly with increasing Sb(V), which may be suggestive of Fe–Sb precipitation. The elevated concentrations of Fe(II) (1 mM) enhanced the sorption capacity of Sb(V) on goethite significantly. However, synchrotron radiation X-ray diffraction showed no new characteristic peak, indicating that this Fe–Sb precipitate might be poor crystallinity or amorphous. Moreover, Sb(III) was detected in anoxic soil, and the reduction of Sb(V) to Sb (III) improved the sorption capacity of Sb in anoxic soil because of the low solubility and migration of Sb(III). Nevertheless, Fe–Sb co-precipitation and Sb(V) reduction to Sb(III) might contribute simultaneously to the increased sorption capacity of Sb(V) on anoxic soils. This research could improve our current understanding of soil Sb chemistry in paddy and wetland soils. [ABSTRACT FROM AUTHOR]

Polyferric sulphate has been widely used for emergent control on incidental release of heavy metals such as Cd to surface water, causing precipitation of Cd-loaded polyferric flocs to the sediment. To date, little is known about whether the dissolution of the flocs in the presence of dissimilatory iron reducing bacteria (DIRB) can occur and how the dissolution influences the fate of Fe and Cd in the sediment. Here, we demonstrated that Shewanella oneidensis MR-1, as representative DIRB, has the ability to reduce the flocs, resulting in the release of Fe 2+ and Cd 2+ to the solution. Batch experiment results showed that the concentrations of Fe 2+ and Cd 2+ reached the maximum values at 48 h and then decreased over the remaining incubation time. The characterizations on the solid phase by the scanning electron microscopy coupled with energy dispersive spectrometer, X-ray diffraction, and X-ray photoelectron spectroscopy technologies revealed the formation of iron minerals such as goethite and magnetite as a consequence of microbial Fe(III) reduction. The newly formed iron minerals played a significant role in re-immobilizing Cd by sorption. These results imply that microbial reduction of polyferric flocs is an important contributor to the transport and transformation of metals in the sediment–water interface. [ABSTRACT FROM AUTHOR]

In order to find out the truth of influence of solution chemistry on the oxidation efficiency of a goethite-catalyzed Fenton-like reaction, the amount of hydroxyl radicals ( OH) was quantified by using coumarin as its trapping agent to produce the only fluorescent derivative 7-hydroxycoumarin (7-HC), because OH was the reactive species responsible for the oxidation activity of Fenton reactions. The concentration of OH achieved maximum at solution pH of 3 and decreased with an increase of solution pH value. However, considerable amount of OH can also generate at near neutral pH (i.e. pH 6 and 7). The concentration of OH was increased both with increasing of goethite and H 2 O 2 dosages, but H 2 O 2 could compete with coumarin to scavenge OH to reduce the formation of 7-HC when the concentration of H 2 O 2 was too high. Anions inhibited OH generation followed an order of H 2 PO 4 − > SO 4 2− > Cl − > NO 3 − > ClO 4 − . Higher concentrations of Cl − and SO 4 2− resulted in greater inhibition of OH generation. Results of this study demonstrated that the influence of solution chemistry on the oxidation efficiency of the goethite-catalyzed Fenton-like reaction was greatly attributed to the effect of solution chemistry on the amount of OH formed in the process of reaction. [ABSTRACT FROM AUTHOR]

In modern agricultural practice, the land use pattern has been changing due to economic reasons and related policies, which significantly affects the basic physical and chemical properties of soils, thereby influencing the speciation and distribution of heavy metals (HMs) in soils. In this study, we selected three typical types of land use patterns (vegetable field, paddy field and forest field) in Shaoguan City, Guangdong Province, to analyze the content and distribution of HMs, screen the sensitive physicochemical properties, and predict the phytoavailability of HMs under different land use patterns with the multi-surface model (MSM). The forest field had relatively lower levels of labile and free HM ions than both paddy and vegetable fields, which may be attributed to the lower HM content in forest field. The modeling results revealed that organic matter (OM) is the primary carrier of HMs, accounting for 0.19%–97.92% of labile HMs. The sensitivity of soil physicochemical properties to free HM ions followed the order of pH > SOM > goethite > clay. Besides, the conversion of paddy field into vegetable or forest field increased the environmental risk of HMs. Our results may help better decision making in agricultural restructuring to reduce the risk of HM-contaminated soils, as well as give a demonstration for the application of the MSM in predicting the phytoavailability of HMs as a powerful technique. [Display omitted] • Free heavy metals on three land use patterns were studied by multi-surface model. • The sensitive physicochemical properties of soil were screened. • Forest field was found to have lower levels of labile and free heavy metals ions. • Conversion of paddy field into other fields increased the environmental risk. [ABSTRACT FROM AUTHOR]

Iron oxide-lignin composites (GLS) were prepared based on the significant role of Fe-OM in the environmental behaviour of heavy metals and lignin binding with iron oxide preferentially in soil. GLS was applied in Cd/Pb immobilization and the stability under acid rain was investigated. The results show that the iron oxide appeared weakly crystalline or amorphous similar to 2-line ferrihydrite after the addition of lignin. Agglomerates of nanoparticles with higher adsorption capacity were observed for GLS. The mobility factor (MF) of Cd/Pb in the soil decreased rapidly after adding GLS. At the 3% dosage, the MF of Cd and Pb in the soil was decreased by 58.94% and 78.15% respectively, which was approximately 5 times that of goethite (GE). The mobile and exchangeable Cd/Pb were converted to organic, amorphous Fe oxide-bound and residue fractions. Under acid rain conditions, MF continues to decline for the GLS group, increasing the organic and amorphous Fe oxide-bound fractions, while for control group (CK) and GE, the trend was the opposite. Lignin could inhibit iron oxide dissolution and stabilize the combination of Cd/Pb and iron oxides in soil. The better stability performance of GLS for Cd/Pb may be related to the higher adsorption capacity and microstructural difference after iron oxide combined with lignin. [Display omitted] • Iron oxide-lignin composites (GLS) show a higher adsorption capacity than goethite. • The mobility of Cd/Pb was decreased significantly after GLS application. • The stability of iron oxide was enhanced after combining with lignin. • GLS application consistently reduces the Cd/Pb leaching under acid rain conditions. [ABSTRACT FROM AUTHOR]

Previous studies have addressed the occurrence of Acid Rock Drainage (ARD) affecting La Silva stream due to the generation of large dumps of Middle Ordovician black shales during the construction of a highway close to El Bierzo (León, Spain). This ARD was characterized by sulphated acid waters with high concentration of heavy metals and anomalies in dissolved thorium (Th) and uranium (U). In the present study, we analyse in depth black shales and water, streambed sediments and precipitates of La Silva stream and its tributaries using different petrographic, mineralogical and geochemical approaches. Black shales, with average Th and U contents of 20 and 3 μg/g respectively contain disseminated detritic micro-grains of high weathering-resistant minerals, such as monazite and xenotime, that present smaller amounts of yttrium and rare earth elements (REY) and other elements as Ca, U, Th, Si and F. Results of the affected waters by ARD show an enrichment in dissolved Th, U and REY of several orders of magnitude with respect to natural waters. Sampled precipitates were mainly schwertmannite (Fe 8 O 8 (OH) 8-2x (SO 4) x O 16 •nH 2 O) and goethite (α–Fe3+O(OH)) that showed an enrichment of Th (up to 798 μg/g) and REY, due to the presence of dissolved anionic species (e.g. T h ( S O 4) 3 2 − , REY ( S O 4) 3 2 − ) that enables their adsorption. Furthermore, these black shales show a clear enrichment in REE (Rare Earth Elements) with respect to NASC (North American Shales Composite) normalized REE patterns. Likewise, normalized REE patterns of stream waters and precipitates clearly show convex curvatures in middle-REE (MREE) with respect to light- and something less than heavy-REE, indicating the trend towards MREE enrichment. These findings are essential to evaluate the impact of ARD of Mid Ordovician shales in the surrounding environment, and to start considering these site as potential source of REE and critical raw materials, activating a Circular Economy. [Display omitted] • Th, U and REY in rock, Acid Rock Drainage (ARD), precipitates and fluvial sediments. • The shales contained disseminated detritic micro-grains of monazite and xenotime with smaller amounts of Th, U and REY. • The oxidative dissolution of pyrite from Middle Ordovician shales generated ARD. • A low pH and sulphated waters, Th, U and REY can be dissolved as sulphated ionic complexes. • Th, heavy metals and REY retention in schwertmannite and goethite. [ABSTRACT FROM AUTHOR]

The viable and degradation potential of the strains which adhered to soil minerals are essential for eliminating organic pollutants from soil. Herein, the interaction (growth, biofilm formation and survive) of Arthrobacter sp. DNS10, an atrazine degrading strain, with three kinds of typical soil minerals, such as montmorillonite, kaolinite and goethite, as well as the atrazine degradation gene (trz N) expression of the strain in the minerals system were studied. The results showed that montmorillonite had significant promotion effect on the growth of strain DNS10, followed by kaolinite, but goethite significantly inhibited the growth of strain DNS10. In contrast, goethite notably promoted the biofilm formation and there was less biofilm detected in montmorillonite containing system. The percentage of the survival bacteria in the biofilm that formed on montmorillonite, kaolinite and goethite was 53.8%, 40.8% and 28.2%. In addition, there were more reactive oxygen species (ROS) were detected in the cells that exposed to goethite than those of the cells exposed to kaolinite and montmorillonite. These results suggest that the electrostatic repulsion between kaolinite/montmorillonite and strain DNS10 prevents them from contacting each other and facilitates bacterial growth by allowing the strain to obtain more nutrients. Oppositely, the needle-like morphology of goethite might damage the strain DNS10 cell when they were combined by electrostatic attraction, and the goethite induced ROS also aggravate the cytotoxicity of goethite on strain DNS10. In addition, the relative transcription of trz N in the cells contacted with montmorillonite, kaolinite and goethite was 0.94-, 0.27- and 0.20- fold of the no mineral exposure treatment. Briefly, this research suggests that the minerals with different structure and/or physicochemical characteristics might cause various trend for the biofilm formation and degradation potential of the bacteria. [Display omitted] • Growth, biofilm formation and trz N transcription of DNS10 exposed to three minerals were studied. • Montmorillonite promote DNS10 growth but had no effect on biofilm due to electrostatic repulsion. • Goethite inhibits DNS10 survival due to needle-like morphology and over-produced ROS. • Goethite obviously inhibited trz N transcription of DNS10 than Mont. and kaolin. • Dead DNS10 cells also could form biofilm in the three tested minerals system. [ABSTRACT FROM AUTHOR]

The geochemical processes of polyphosphates (poly-Ps) are important for phosphorus (P) management and environmental protection. Water-soluble ammonium polyphosphate (APP) containing various P species has been increasingly used as an alternative P-fertilizer. The various P species coexistence and the chelation of poly-Ps with mental would trigger the P's competitive adsorption and affect the APP's adsorption intensity on goethite, compared to single orthophosphate (P 1). P adsorption behaviors of APP1 with two P species and APP2 with seven P species on goethite were investigated via batch experiments in comparison to the traditional P-fertilizer of mono-ammonium phosphate (MAP). Coadsorption of P 1 and pyrophosphate (P 2) on goethite was investigated by molecular dynamics (MD) simulation. The more Fe3+ dissolved from goethite as a bridge due to the chelation of poly-Ps in APP and contributed to the stronger APP adsorption on goethite compared with MAP. Ion chromatography and spectral analysis showed P 1 and P 2 in APP were mainly adsorbed by goethite via mainly forming bidentate complexes. The goethite preferentially adsorbed P 1 at lower APP concentration but increased the poly-Ps' adsorption at higher APP concentration. MD simulation showed that electrostatic interaction and hydrogen bonds played a key role in water-phosphates-goethite systems. The P 1 pre-adsorbed on goethite could be replaced by P 2 at high P 2 concentration. The results develop new insights regarding the selective adsorption of various P species coexistence in goethite-rich environments. [Display omitted] • APP adsorption on goethite (Gt) increased with an increasing number of P species. • Gt co-adsorbed P species with low molecular weight (MW) in APP at low P concentration. • P species with high MW contributed to adsorption of APP on Gt at high P concentration. • Pyrophosphate (P 2) could replace orthophosphate (P 1) pre-adsorbed on Gt. • Hydrogen bonds played a key role in the water-phosphates-goethite adsorption systems. [ABSTRACT FROM AUTHOR]

Iron oxides play an important role in the transport and transformation of organic phosphorus in aquatic environments. However, the effect of different types of iron oxide on the environmental fate of organic phosphorus has remained unclear. In this study, the photodegradation of the organic phosphorus compound adenosine triphosphate (ATP) via the activity of crystalline (goethite) and amorphous (ferrihydrite) iron oxides was investigated. It was found that ATP was photodegraded by goethite, resulting in the release of dissolved inorganic phosphate under simulated sunlight irradiation. The concentration of ATP on goethite decreased by 75% after 6 h of simulated sunlight irradiation, while the concentration of ATP on ferrihydrite decreased by only 22%. ATR-FTIR spectroscopy revealed that the intensity of the peaks for the P–O and P O stretching vibrations in the goethite−ATP complex decreased significantly more after simulated sunlight irradiation than did those for the ferrihydrite treatment. Combined with the higher TOC/TOC 0 values for the goethite treatment, the results indicate that a more vigorous photochemical reaction took place in the presence of goethite than with ferrihydrite. Reactive oxygen species analysis also showed that hydroxyl and superoxide anion radicals were generated when goethite was exposed to simulated sunlight irradiation, while ferrihydrite did not exhibit this ability. Overall, this study highlights that the type of iron oxide is an important factor in the transformation of organic phosphorus in aquatic environments. [Display omitted] • Transformation of organic phosphorus after adsorption was investigated. • Organic phosphorus adsorbed on goethite underwent photodegradation. • •OH and O 2 •− generated on the gothite, but not ferrihydrite. • Iron minerals mediated the environmental fate of organic phosphorus. [ABSTRACT FROM AUTHOR]

Studying the adsorption-desorption kinetics of ions and molecules is crucial to understand the mobility of nutrients and pollutants in the environment. This article reports the adsorption-desorption kinetics of phosphate on goethite, as measured by ATR-FTIR spectroscopy at pH 4.5, 7.0 and 9.5. The system phosphate-goethite has become a model system to test new experimental setups and theories to understand the behavior of pollutants with phosphonic or phosphinic moieties such as glyphosate or glufosinate. One of the main difficulties in the analysis of ATR-FTIR spectra in adsorption-desorption kinetics is to calibrate the equipment to convert absorbance vs. t curves into adsorption vs. t curves, and thus the methodology to achieve a good calibration using spectroscopic data in combination with adsorption isotherms is clearly described. The time evolution of the different surface species was monitored simultaneously during adsorption and desorption at different pH, showing the advantages of this spectroscopy over traditional adsorption methods that only quantify total adsorption. Results were analysed in terms of a simple adsorption-desorption model that takes into account transport, attachment, detachment and surface transformation of the adsorbed species. The same rate parameters at a given pH could predict well the adsorption-desorption kinetics of the two formed surface species and the corresponding adsorption isotherm, giving new insights into the dynamics of phosphate on the surface of goethite. It was found that phosphate desorbed faster from goethite at low pH than at high pH, which is counterintuitive, but has good practical and environmental applications. [Display omitted] • The time evolution of different phosphate species was monitored simultaneously during adsorption on goethite. • The dynamics of surface speciation of phosphate allows understanding the adsorption mechanism. • Surface species at low pH desorbs faster than at high pH at the investigated loadings. [ABSTRACT FROM AUTHOR]

The aggregation and transport of biochar colloids (BCs) in the soil and groundwater are critical for applying biochar in the field and assessing long-term environmental risk. This research aimed to study the influence of dissolved organic matter (DOM) with different molecular weights (including humic acid, HA; bovine serum albumin, BSA; deoxyribonucleic acid, DNA) and three minerals (including kaolinite, goethite, and hematite) on the aggregation and transport behaviors of BCs. The adsorption of DOM on the surface of BCs increased the stability, inhibited aggregation, and promoted the transport of BCs. As the molecular weight of DOM increased, the thicknesses of the adsorption layer of HA, BSA, and DNA on BCs surface were 2.2 nm, 5.3 nm, and 5.6 nm, respectively, resulting in increasing steric hindrance and improving the stability and mobility of BCs. Kaolinite also significantly enhanced the stability and mobility of BCs by increasing the electrostatic repulsion. Goethite and hematite quickly combined with BCs through electrostatic attraction, resulting in stronger aggregation and retention of BCs. Compared to hematite, goethite provided more adsorption sites for BCs due to its needle-like shape, so goethite caused a larger heteroaggregation rate. Overall, the presence of DOM with different molecular weights and the minerals with varying surface charges in the soil environment had a significant and distinct impact on the stability, aggregation, and transport of BCs, which advances the knowledge of colloidal biochar fate in the soil and groundwater. [Display omitted] • DOM enhanced biochar colloids stability and transport by steric hindrance. • As the molecular weight of DOM increased, the steric hindrance between biochar colloids became stronger. • Different minerals affected biochar colloids aggregation and transport by various electrostatic interaction. • Goethite provided more adsorption sites for biochar colloids than hematite. [ABSTRACT FROM AUTHOR]

Goethite, hematite, ferrihydrite, and other iron oxides bind through various sorption reactions with humic substances (HS) in soils creating nano-, micro-, and macro-aggregates with a specific nature and stability. Long residence times of soil organic matter (SOM) have been attributed to iron-humic substance (Fe-HS) complexes due to physical protection and chemical stabilization at the organic–mineral interface. Humic acids (HA) and fulvic acids (FA) contain many acidic functional groups that interact with Fe oxides through different mechanisms. Due to the numerous interactions between mineral Fe and natural SOM, much research has led into a better identification and definition of HS. In this review, we first focus on the surface colloidal properties of Fe oxides and their reactivity toward HS. These minerals can be efficiently identified by usual techniques, such as XRD, FTIR spectroscopy, XAS, Mössbauer, diffuse reflectance spectroscopies (DRS), HRTEM, ATM, NanoSIMS. Second, we present the recent state of art regarding the adsorption/precipitation of HS onto iron mineral surfaces and their effects on binding metalloid and trace elements. Finally, we consider future research directions based on recent scientific literature, with particular focus on the ability of Fe nano-particles to increase Fe bioavailability, improve carbon sequestration, reduce greenhouse gas emissions, and decrease the impact of persistent organic and inorganic pollutants. The methodology in this field has rapidly developed over the last decade. However, new procedures to estimate the nature of Fe-HA bonds will be important contributions in clarifying the role of natural iron oxides in soil for carbon stabilization. [Display omitted] • Surface properties of Fe oxides, and their reactivity toward HS are examined. • A metal binding mechanism between Fe and HS is resumed. • HS impacts on chemical and oxidative/reductive reactivity of iron oxide is reviewed. • Stabilization mechanism of HA with Fe oxides is related with longer turnover of SOM. • Fe-HS is associated with transport and bioavailability of persistent organic pollutants. [ABSTRACT FROM AUTHOR]

Fe (oxyhydr)oxides are the main components that accumulate heavy metals (HMs) in the acid mine drainage (AMD) sediments, but how the aging pH and time of AMD solution affects the Fe mineralogy and HMs speciation remains ambiguous. Herein, we determined the impacts of aging pH and time on the Fe mineralogy and chemical fractions of HMs in the sediments from Dabaoshan mining area using mineral characterizations, chemical extraction, and AMD solution incubation. For the natural AMD sediments, jarosite and goethite are the major Fe (oxyhydr)oxides in sample S1 with solution pH 2.68, while schwertmannite is dominant in sample S2 with solution pH 6.78, co-existing minor ferrihydrite. With increasing the AMD solution pH, the total contents of HMs (expect for As) and the reducible fraction of HMs (expect for Pb) in the sediments both increase. The HMs of Mn, Zn, Ni, and Cd are mainly associated with Fe (oxyhydr)oxides, while Pb possibly exists as Pb-bearing minerals (e.g., PbSO 4) in the sediments. The oxidizable fraction of all HMs is negligible in both sediments. When the AMD solution of S1 was aged at different pHs, schwertmannite is dominant initially at all pHs, with a higher crystallinity being at a lower pH. With increasing aging time, the pre-formed schwertmannite transforms to goethite and jarosite at pH ≤ 3, while it keeps stable at pH 5 and 7 due to the accumulation of more HMs. These new insights are essential to assess the mobility and availability of HMs in the AMD-affected areas. [Display omitted] • Schwertmannite, goethite, and jarosite are the main Fe minerals in AMD sediments. • Schwertmannite transforms to goethite and jarosite at pH ≤ 3 with aging. • Natural schwertmannite is more stable at higher pH due to the presence of more HMs. • The HMs (expect for Pb) are primarily immobilized by Fe minerals. • Pb most likely exists as Pb-bearing minerals (e.g., PbSO 4). [ABSTRACT FROM AUTHOR]