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The interaction between organic phosphorus (OP) and iron oxide significantly influences the phosphorus cycle in the natural environment. In shallow lakes, intense oxidation-reduction fluctuations constantly alter the existing form of iron oxides, but little is known about their impact on the adsorption and fractionation of OP molecules. In this study, electrospray ionization coupled with Fourier transform ion cyclotron resonance mass spectrometry (ESI-FT-ICR MS) was used to investigate the fractionation of OP from alkali-extracted sediment induced by crystalline goethite and amorphous ferrihydrite adsorption at a molecular scale. The results showed that ferrihydrite and goethite both exhibited high OP adsorption, and the adsorption amount decreased as the pH increased. The adsorption kinetics matched the pseudo-second-order equation. The ESI-FT-ICR MS analysis showed that 91 P-containing formulas were detected in the alkaline-extracted sediment solution. Ferrihydrite and goethite adsorbed 51 and 24 P-containing formulas, respectively, with adsorption rates of 56.0 % and 26.4 %. Ferrihydrite could adsorb more OP compounds than goethite, but no obvious molecular species selectivity was observed during the adsorption. The P-containing compounds, including unsaturated hydrocarbons-, lignin/carboxyl-rich alicyclic molecule (CRAM)-, tannin-, and carbohydrate-like molecular compounds, were more suitable for iron oxide adsorption. The double bond equivalence (DBE) is a valuable parameter that indicates OP fractionation during adsorption, and P-containing compounds with lower DBE values such as lipid- and protein-like molecular were prone to remain in the solution after adsorption. These research results provide insights into the biogeochemical cycling process of P in the natural environment. [Display omitted] • Ferrihydrite adsorbed more OP from alkali-extracted sediment than goethite. • No molecular species selectivity difference in OP adsorption by iron oxides. • Lipid-like and protein-like OP molecules are almost not adsorbed by iron oxides. • DBE is a valuable parameter that indicates the OP fractionation during adsorption. [ABSTRACT FROM AUTHOR]

[Display omitted] • Iron ooids from the Eocene Transylvanian Basin intermix with nummulites. • Ooid cortex and nucleus are made of goethite. Nummulites preserve calcareous shell. • Iron ooids were transported in places of nummulite accumulation. The middle Eocene ironstone of the Transylvanian Basin, Romania, provides new insight into the genesis and paleoenvironmental significance of ferruginous ooids. An horizon at the base of the Căpuş Formation in north-western Romania, well known for the spectacular nummulite banks there exposed, documents a peculiar association of large foraminifera within a matrix dominated by millimetric Fe-ooids. These red-brownish Fe-ooids are well evident through the whitish colour of the carbonatic host matrix. An integrated analysis of the ooids, carried out by Environmental Scanning Electron Microscopy, Micro-X-ray Diffraction and Raman spectroscopy, allowed its detailed chemical and mineralogical characterization. Ooids are mostly composed of continuous concentric cortical layers of goethite interlayered by a few thin layers of phosphatic phases, whereas nuclei are made of ferruginous grains. No evidence of biological activity was detected in the cortex of the ooids to support a bio-mediated genesis. The occurrence of this ironstone testifies the existence of ferruginous bottom waters in the Eocene tropical/sub-tropical shallow-marine settings of the central Neotethyan Realm. The limited extension of the iron source area suggests that also local (e.g., not global) events could have been able to trigger iron ooidal deposition throughout the Phanerozoic. [ABSTRACT FROM AUTHOR]

Rice is one of the most important staple food crops; however, it is prone to cadmium (Cd) accumulation, which has negative health effects. Therefore, methods to reduce Cd uptake by rice are necessary. At present, there is limited research on the effects of co-application of silicon (Si) and goethite in mitigating Cd stress in rice. Furthermore, the specific mechanisms underlying the effects of their combined application on iron plaque formation in rice roots remain unclear. Therefore, this study analyzed the effects of the combined application of Si and goethite on the biomass, physiological stress indicators, Cd concentration, and iron plaques of rice using hydroponic experiments. The results revealed that co-treatment with both Si and goethite increased the plant height and dry weight, superoxide dismutase and catalase activities, photosynthetic pigment concentration, and root activity. Moreover, this treatment decreased the malondialdehyde concentration, repaired epidermal cells, reduced the Cd concentration in the roots by 57.2 %, and increased the number of iron plaques and Cd concentration by 150.9 % and 266.2 % in the amorphous and crystalline fractions, respectively. The Cd/Fe ratio in amorphous iron plaques also increased. Our findings suggest that goethite serves as a raw material for iron plaque formation, while Si enhances the oxidation capacity of rice roots. The application of a combination of Si and goethite increases the quantity and quality of iron plaques, enhancing its Cd fixation capacity. This study provides theoretical evidence for the effective inhibition of Cd uptake by iron plaques in rice, providing insights into methods for the remediation of Cd contamination. [Display omitted] • Silicon and goethite can alleviate cadmium stress in rice. • Silicon and goethite promote the formation of iron plaque and enhance its quality. • Iron plaques are an effective barrier to prevent the accumulation of cadmium in rice. • Combined application of silicon and goethite reduced Cd content in rice by 50 %. [ABSTRACT FROM AUTHOR]

Dissimilatory iron-reducing bacteria (DIRB) affect the geochemical cycling of redox-sensitive pollutants in anaerobic environments by controlling the transformation of Fe morphology. The anaerobic oxidation of antimonite (Sb(III)) driven by DIRB and Fe(III) oxyhydroxides interactions has been previously reported. However, the oxidative species and mechanisms involved remain unclear. In this study, both biotic phenomenon and abiotic verification experiments were conducted to explore the formed oxidative intermediates and related processes that lead to anaerobic Sb(III) oxidation accompanied during dissimilatory iron reduction. Sb(V) up to 2.59 μmol L−1 combined with total Fe(II) increased to 188.79 μmol L−1 when both Shewanella oneidensis MR-1 and goethite were present. In contrast, no Sb(III) oxidation or Fe(III) reduction occurred in the presence of MR-1 or goethite alone. Negative open circuit potential (OCP) shifts further demonstrated the generation of interfacial electron transfer (ET) between biogenic Fe(II) and goethite. Based on spectrophotometry, electron spin resonance (ESR) test and quenching experiments, the active ET production labile Fe(III) was confirmed to oxidize 94.12% of the Sb(III), while the contribution of other radicals was elucidated. Accordingly, we proposed that labile Fe(III) was the main oxidative species during anaerobic Sb(III) oxidation in the presence of DIRB and that the toxicity of antimony (Sb) in the environment was reduced. Considering the prevalence of DIRB and Fe(III) oxyhydroxides in natural environments, our findings provide a new perspective on the transformation of redox sensitive substances and build an eco-friendly bioremediation strategy for treating toxic metalloid pollution. [Display omitted] • MR-1 and goethite are indispensable for Sb(III) oxidation under anoxic conditions. • The interfacial electron transfer rate increases with the microbial driven-Fe(II). • Electron transfer process plays a pivotal role in anaerobic Sb(III) oxidation. • Labile Fe(III) is the commanding oxidative species underlie Sb(III) oxidation. [ABSTRACT FROM AUTHOR]

The Fe(II)/Fe(III) cycle is an important driving force for dissolution and transformation of jarosite. Divalent heavy metals usually coexist with jarosite; however, their effects on Fe(II)-induced jarosite transformation and different repartitioning behavior during mineral dissolution-recrystallization are still unclear. Here, we investigated Fe(II)-induced (1 mM Fe(II)) jarosite conversion in the presence of Cd(II), Mn(II), Co(II), Ni(II) and Pb(II) (denoted as Me(II), 1 mM), respectively, under anaerobic condition at neutral pH. The results showed that all co-existing Me(II) retarded Fe(II)-induced jarosite dissolution. In the Fe(II)-only system, jarosite first rapidly transformed to lepidocrocite (an intermediate product) and then slowly to goethite; lepidocrocite was the main product. In Fe(II)–Cd(II), -Mn(II), and -Pb(II) systems, coexisting Cd(II), Mn(II) and Pb(II) retarded the above process and lepidocrocite was still the dominant conversion product. In Fe(II)–Co(II) system, coexisting Co(II) promoted lepidocrocite transformation into goethite. In Fe(II)–Ni(II) system, jarosite appeared to be directly converted into goethite, although small amounts of lepidocrocite were detected in the final product. In all treatments, the appearance or accumulation of lepidocrocite may be also related to the re-adsorption of released sulfate. By the end of reaction, 6.0 %, 4.0 %, 76.0 % 11.3 % and 19.2 % of total Cd(II), Mn(II), Pb(II) Co(II) and Ni(II) were adsorbed on the surface of solid products. Up to 49.6 %, 44.3 %, and 21.6 % of Co(II), Ni(II), and Pb(II) incorporated into solid product, with the reaction indicating that the dynamic process of Fe(II) interaction with goethite may promote the continuous incorporation of Co(II), Ni(II), and Pb(II). [Display omitted] • The coexisting divalent metals retarded Fe(II)-induced jarosite dissolution. • In treatments with Cd(II), Mn(II) and Pb(II), lepidocrocite was dominant product. • In treatments with Co(II) and Ni(II), the main converted product was goethite. • Released sulfate may play an important role in the accumulation of lepidocrocite. • Fe(II) induced continuous incorporation of Co(II), Ni(II) and Pb(II) into goethite. [ABSTRACT FROM AUTHOR]

The development of most effective reduction catalysts is an essential for promoting the sustainability by minimizing the waste and safeguard the environment. Herein, we prepared palladium-cobalt bimetallic nanoparticles modified on goethite nanorods (PdCo/α-FeOOH) as a catalyst for the catalytic degradation of various organic pollutants under mild reaction conditions. The structure and morphology of synthesized catalysts were tested by XRD, FT-IR, BET, SEM, TEM, HR-TEM and XPS techniques. The ultra-small PdCo bimetallic NPs (2.95 ± 0.5 nm) synthesized onto the surface of α-FeOOH nanorod were confirmed by HR-TEM analysis. The prepared catalysts were played an important role in the reduction of toxic nitrocompounds such as (4-nitrophenol (4-NP), 4-nitroaniline (4-NA), 4-(4-nitrophenyl)morpholine (4-NM) and 4-(2-fluoro-4-nitrophenyl)morpholine (4-FNM)) and rhodamine B (RhB) dye. The PdCo/α-FeOOH nanocatalyst displayed a greater rate constant (∼1.5 min and k app = 2.631 min−1) compared to their respective mono-metallic counterparts (Pd/α-FeOOH and Co/α-FeOOH). The reusability results indicated that >97 % of conversion for 4-NP, and RhB dye over 10 consecutive reaction cycles in the batch method. Furthermore, the continuous flow reactor with PdCo/α-FeOOH catalyst was constructed, and it showed the ability to eliminate > 99 % of both 4-NP and RhB dye and maintained a degradation rate of >98 % for 20 consecutive recycles. The superior catalytic activity of the PdCo/α-FeOOH catalyst compared to other mono-metallic catalysts could be attributed to their particle size and synergistic effect. This study has the potential to facilitate the utilization of the synthesized bimetallic nanostructure in a wider range of other wastewater treatments. [Display omitted] [ABSTRACT FROM AUTHOR]

Cadmium (Cd) contamination in paddy soils poses a serious threat to agricultural production and human health. In this study, cysteine was selected as the leaching agent for remediating Cd-contaminated paddy soils because of its effective, low cost and ecofriendly characteristics. Microcosmic simulation experiment was using to investigate the fate of Cd and elucidate the transformation mechanism of Cd in the key components of paddy soil under cysteine leaching. Results showed that the total Cd removal rate of paddy soils reached 46.8–87.4% under the optimal conditions. This was mainly attributed to the decrease of exchangeable fraction (F1), carbonate bound fraction (F2), iron/manganese-bound fraction (F3) and organic matter bound fraction (F4) of Cd. After cysteine leaching, soil fertility was promoted due to the increase in nitrate nitrogen (NN), ammonia nitrogen (AN), available phosphorus (AP) and organic matter (OM). pH, CaCO 3 , available potassium (AK), NN, AP, amorphous iron oxides (Fe o) were the main contributors to Cd fractionation transformation. The desorption of Cd from ferrihydrite (Fh) and goethite (Gt) surfaces is hypothesized to stem from dual mechanisms: the dissolution due to the low solution pH and the reducibility of cysteine, which facilitated the conversion of Fh and Gt to hematite (Hm). And the -SH complexation also ascribed to the activation of Cd bound by Fe-OH in Fh and Gt and oxygen-containing functional groups in humic acid (Ha). For chlorite (Ch), the primary driver for Cd desorption was identified as an ion-exchange process, whereby electrostatically adsorbed Cd2+ were replaced by H+ produced by cysteine protonation. [Display omitted] • The key influencing parameters of reduce remediation of Cd polluted paddy soil by cysteine leaching were investigated. • The removal of Cd mainly attributed to the decrease of F1, F2, F3, and F4 fractions. • Cd was desorbed from Fh and Gt owing to the low solution pH and reducibility of cysteine. • The -SH complexation caused the activation of Cd bound by Fe-OH in Fh and Gt and the oxygen functional groups in Ha. • Cd desorption in chlorite was achieved by ion exchange between electrostatically adsorbed Cd and H+ of cysteine solution. [ABSTRACT FROM AUTHOR]

Uranium (U) pollution in soil resulted by human activities is a critical environmental issue. Goethite and humic acid (HA), as predominant soil constituents, significantly influence the migration and transformation of uranium in soil, but effects of combining them together on the sequestration and immobilization of U at different mineralization condition are still rare. To simulate the ability of different combinations of HA and goethite to limit the migration of uranium (VI) in the soil environment, the humic acid-modified goethite (OPHG, TSHG) were synthesized by one-pot and two steps synthesis methods in this study. After modified by HA, the specific surface area of materials increased from 29.67 m2/g to 121.53 m2/g and 39.89 m2/g respectively. The effects of dosage, contact time, pH, initial concentration and temperature on the removal of U(VI) by goethite and modified goethite were investigated. The results showed the maximum difference of them reached 41.59% and 15.69 mg/g for reaction 60 min at pH=4.5. The equilibrium adsorption data fit to the pseudo-second-order kinetics and Langmuir models, and the maximum adsorption capacities increased from 64.63 mg/g to 92.04 mg/g. The analyses results indicated that OPHG remove U(VI) mainly through the formation of ≡ FeO UO 2 OH between Fe−O and uranyl ions, as well as the complexation of carboxyl and hydroxyl groups on HA molecules with uranium to form the HA-Goethite-U(VI) ternary complexes FeOHAUO 2. These results are benefited for understanding the effects of HA and goethite on immobilization uranium in soil and would be used to predict and remediate the polluted soil. [Display omitted] • Synthesized modified goethite in different ways to simulate the combination of humic acid and goethite in soil (OPHG, TSHG). • OPHG presented better removal efficiency than goethite and TSHG for the increased specific surface area. • The mechanism of uranium capture by modified goethite is mainly through the surface complexation reaction. [ABSTRACT FROM AUTHOR]

A novel tribo-testing method using a pin-on-plate tribometer was developed to test and visualize the coefficient of friction over surfaces with oxides present to examine low adhesion issues. Tribo-test data was recorded each pass over test surfaces showing how friction changes with mechanical action. Trackside environmental monitoring and railhead swabbing was performed to investigate the physical and chemical environment of the railhead. Iron oxides were both synthesized on and deposited on rail steel substrates to simulate 'wet-rail' conditions. Powdered oxide layers of magnetite, haematite, goethite and lepidocrocite were deposited on rail steel substrates to investigate individual oxides. Composition was analysed using X-ray diffraction and scanning electron microscopy before testing. Magnetite, Haematite and Lepidocrocite were formed when water alone was applied to the surfaces. Low friction was observed on oxidized sample surfaces only outside high roughness, oxide pitted, areas, but these conditions were shown to be difficult to achieve and transient. [ABSTRACT FROM AUTHOR]

Macroporous strong acidic resin (D001) is restricted in Pb(II) removal from water due to the interference of common environmental cations. A novel modified D001 (nFeOOH@D001) was developed by loading nanoscale α-FeOOH (nFeOOH) with a facile ethanol-dispersion-impregnation method to improve Pb(II) removal from aqueous solution. Solid-phase analysis showed that α-FeOOH of 10–100 nm was evenly loaded onto D001. The nFeOOH@D001 maintained the electrostatic adsorption ability of D001, and obtained the complexation adsorption capacity of nFeOOH. The nFeOOH@D001 therefore achieved a 20.2% higher Pb(II) removal rate of 74.5% as compared to the D001 of 54.3%. Under the competition of Ca2+ and Mg2+ ions, the nFeOOH@D001 showed better selectivity for Pb(II) through the complexation of hydroxyl and ferrite groups on nFeOOH. The pseudo-first order kinetics and Langmuir-adsorption models well fitted the Pb(II) removal data, indicating a chemistry and monolayer adsorption process. This process depended on pH and achieved a Pb(II) removal over 65% within a pH range of 3–7. During cyclic test, used nFeOOH@D001 could be refreshed with acetic acid as eluent. Spent nFeOOH@D001 could be remodified with nFeOOH by the above impregnation method after stripping iron oxides with hydrochloric acid. The regenerated nFeOOH@D001 obtained a regeneration rate of 97.6% as compared to virginal nFeOOH@D001. The results demonstrated that the introduction of nFeOOH could effectively improve the performance of D001 for Pb(II) removal from water. [Display omitted] • Nanoscale goethite-modified resin (nFeOOH@D001) was prepared with ethanol-dispersion-impregnation. • α-FeOOH of 10–100 nm on D001 provided additional adsorption sites to compensate for its occupation. • Hydroxyl and ferrite groups on nFeOOH removed Pb(II) by complexation. • nFeOOH@D001 had higher Pb(II) selectivity as compared to D001. • nFeOOH@D001 exhibited excellent stability and reusability. [ABSTRACT FROM AUTHOR]

The dual-functional heterogeneous Fenton catalyst Cu/Ti co-doped iron-based Fenton catalyst (Cu/Ti -Fe 3 O 4 @FeOOH, FCT) were successfully prepared by precipitation oxidation method and characterized by XRD, XPS and XAFS. The prepared Cu/Ti co-doped Fe 3 O 4 @FeOOH nanoparticles consisted of goethite nanorods and magnetite rod octahedral particles, with Cu and Ti replacing Fe in the catalyst crystal structure, leading to the formation of the goethite structure. The heterogeneous Fenton catalyst FCT exhibited excellent degradation activity for cyanide in wastewater and showed different reaction mechanisms at varying pH levels. When treating 100 mL of 12 mg L−1 NaCN solution, complete degradation occurred within 40 min at 30 °C and pH ranging from 6.5 to 12.5 without external energy. Compared to Fe 3 O 4 , FCT shows superior degradation activity for cyanide. The surface Cu(Ⅰ) facilitated the electron transfer and significantly improved the catalytic activity of the catalyst. Additionally, the magnetic properties of the Ti-doped catalyst samples were greatly enhanced compared to the Cu@FeOOH catalyst doped with Cu, making them favorable for recycling and reuse. FCT maintains 100% degradation of cyanogen after three cycles, indicating its excellent stability. Furthermore, electron spin resonance spectroscopy, free radical quenching experiments and fluorescence probe techniques using terephthalic acid (TA) and benzoic acid (BA) confirmed that the presence of •OH and FeⅣ=O reactive species was responsible for the catalysts exhibiting different mechanisms at different pH conditions. Compared with other heterogeneous Fenton catalysts, FCT exhibits intentional degradation activity for cyanide-containing wastewater under different acid-base conditions, which greatly broadened the pH range of the heterogeneous Fenton reaction. [Display omitted] • 100% degradation of cyanide wastewater by Cu/Ti co-doped Fe 3 O 4 @FeOOH. • Cu and Ti replace Fe in situ within the magnetite and gothite lattices. • Cu/Ti co-doped Fe 3 O 4 @FeOOH is suitable for a wide pH range. • The catalyst exhibits dual reaction mechanisms in varying pH conditions. • Cu/Ti co-doped Fe3O4@FeOOH's strong magnetism enables effortless recovery and reuse. [ABSTRACT FROM AUTHOR]

Methylene Blue (MB) was adsorbed from aqueous solution using Baobab (Adansonia digitata L.) fruit pod and its goethite modified form. Adsorbents were characterized using Fourier Transform-Infra Red (FTIR) spectroscopy and Scanning Electron Microscopy (SEM). Batch experiments were conducted at room temperature (26.8 °C) and the adsorption data were fitted using Langmuir, Freundlich, Temkin and Dubinin- Radushkevich isotherms. Also, kinetic data was fitted using Pseudo-first order, pseudo-second order, Elovich and intra-particle diffusion models. Goethite modified baobab (GMB) appeared to have a coarse microporous surface with smoother surface and larger pore volumes compared to unmodified baobab (UB). The -C=O band was observed at 1631 and 1636 cm-1 for UB and GMB. The -OH band was observed at 3447.00 cm-1 and 3442 cm-1 for UB and GMB respectively. Langmuir model was suitable for describing the adsorption data of UB with R² of 0.9293 while Temkin model was best for fitting adsorption data of MB on GMB with R² of 0.9691. However, maximum adsorption capacity was obtained with Freundlich adsorption isotherm (15.4253 and 43.1301 mg/g for UB and GMB respectively). The maximum biosorption were 8.98 mg/g and 9.86 mg/g for UB and GMB respectively at pH 10. Pseudo-second-order kinetic model best fitted the kinetic data with R² values of 0.9968 and 0.9993 for UB and GMB, ΔH° values were 83.123 KJ/mol and 361.094 KJ/mol for UB and GMB, while ΔS° values were 3.084 J/mol/ K and 1.765 J/mol/K for UB and GMB respectively. GMB adsorbed more of MB than UB and the process was endothermic. [ABSTRACT FROM AUTHOR]

The goethite biochar composite (GBC) is synthesized by co-precipitating iron oxide onto biochar prepared from cotton stalks and used for As(III) adsorption such as adsorption isotherms, kinetics, and the impact of initial concentration, initial pH, contact time, humic acid and ionic strength. The coating was characterized by SEM-EDS, FTIR and XRD analysis. Batch sorption were conducted to evaluate the possibility of GBC as a potential adsorbent for the removal of As(III). The results indicated that the optimum pH using the BC and GBC were determined to be 3.0 for As(III) removal, and GBC has higher adsorption capacity for As(III) than raw biochar. On the basis of the Langmuir and Freundlich model, for GBC and BC, the maximum adsorption capacity of As(III) obtained by the experiment was 30.7706 mg / g and 9.20883 mg / g. According to our kinetic experiments, GBC adsorbed As(III) very quickly and reached equilibrium in 120 minutes. Adsorption kinetics experimental data accords with pseudo second-order kinetic model. This study shows that goethite coating can enhance arsenic adsorption capacity of cotton stalk biochar, leading to a new natural adsorbent with low cost and high sorption capacity, with possible application in arsenic remediation. [ABSTRACT FROM AUTHOR]

Gatifloxacin (GAT) is a new generation fluoroquinolone antibiotic and its adsorption onto iron minerals influenced by coexisting trace elements [e.g., Cu(II)] has not been well investigated. To evaluate the adsorption behavior of GAT and Cu(II) onto goethite and hematite, the complexation constants of GAT with Cu(II) were determined using potentiometric titration, and the effects of Cu(II) concentration and solution pH on GAT adsorption were investigated using batch experiments. It was observed that GAT adsorption was negatively correlated with molar concentration ratio of Cu(II) to GAT. In our experimental pH range (i.e., 3.0–10.8), the calculated main species involved in GAT adsorption were Cu(GAT±)2+ and Cu(GAT±)22+ under acidic to neutral conditions, and formation of Cu(GAT−)2(s) facilitated the removal of GAT from solution under alkaline condition. The adsorption data were well fitted by the Freundlich model and showed high nonlinearity. In adsorption onto goethite, the primary interactions shifted from electrostatic repulsion to formation of goethite–Cu(II)–GAT ternary surface complexes with increase of GAT concentration. For hematite, electrostatic repulsion was the main inhibiting mechanism and became stronger with increase of Cu(II) concentration. Our findings suggest that it is necessary to consider the complexation between GAT and coexisting metal cations in evaluating its transport in soils rich in different iron minerals. [ABSTRACT FROM AUTHOR]

Heavy metal pollution caused by acid mine drainage (AMD) is a global environmental concern. The processes of migration and transformation of heavy metals carried by AMD are more complicated in karst areas where carbonate rocks are widely distributed. Water, suspended particulate matter (SPM), and sediments are the crucial media in which heavy metals migrate and it is important to elucidate the geochemical behavior of AMD heavy metals in these environments. This study tracked AMD heavy metals from release to migration and transformation in a natural river system in a karst mining area. AMD directly impacted the hydrochemical composition of the karst water environment, but the carbonate rock naturally neutralized the acidity of the AMD. AMD heavy metal concentrations decreased gradually after the tributaries from the mining area entered the main river, with the metals tending to accumulate in SPM and sediments. The forms in which heavy metals were present were influenced by pH and their relative concentrations. Raman spectroscopy and transmission electron microscopy of sediments from the mining area suggested that the presence of an iron phase plays an important role in the fate of AMD-derived heavy metals. It is, therefore, necessary to elucidate the mechanisms of iron phase precipitation from sediments in order to control AMD-derived heavy metals in karst mining areas. This study improves our understanding of the geochemical behavior of heavy metals in karst environments and provides direction for the prevention and control of AMD in affected areas. [Display omitted] • Mechanisms of heavy metals migration in karst mining areas are elucidated. • Heavy metals migrate mainly in suspended particulate matter and sediments. • Goethite and jarosite are the dominant Fe phases in sediments. • Iron phase precipitation is central to the control of acid mine drainage pollution. [ABSTRACT FROM AUTHOR]

In this study, we developed prediction models for the adsorption of divalent and trivalent oxyanions on goethite based on machine learning algorithms. After verifying the reliability of the models, the importance of goethite specific surface area (SSA) and the average oxyanion adsorption capacities of goethite with different SSAs were calculated by shapley additive explanations (SHAP) importance analysis and partial dependence (PD) analysis. Despite there were differences in the feature importance of divalent and trivalent oxyanions, the contribution of goethite's SSA to the adsorption amount ranked the fourth based on SHAP importance, indicating SSA played the important role in oxyanion adsorption. Meanwhile, the PD values of SSA and the optimized complexation constants from surface complexation modeling (SCM) both indicated a non-monotonic relationship between the goethite with different SSA and its oxyanions binding capacity. When the total site concentration and crystal face composition were used as the machine learning model input features, the SHAP importance values of crystal faces and the PD decomposition results indicated that the (001) face showed the crucial influence on oxyanions adsorption amount. These findings demonstrated the important role of crystal face composition in goethite's adsorption ability, and provided a theoretical explanation for the variations of oxyanions adsorption amount on different SSA goethite. [Display omitted] • Machine learning models were developed to predict adsorption percentage of oxyanions. • Oxyanions with different valent should be modeled separately. • SHAP values revealed the important role of SSA in oxyanion adsorption. • PD values and SCM results showed non-linear SSA-oxyanion adsorption ability relation. • The (001) face played an important role in the oxyanion adsorption. [ABSTRACT FROM AUTHOR]

Perfluorooctanoic acid (PFOA) has been widely utilized, leading to serious contamination. Iron (hydr)oxide transformation was varied in media. Whereas, dynamic transformation effect was extensively unclear. Here, iron (hydr)oxide dynamic transformation-induced PFOA transport and attenuation was investigated by emphasizing initial goethite (α -FeOOH) and associated minerals content and groundwater type based on the multi-process attenuation model. Results revealed that groundwater type did not affect the PFOA attenuation pathway. However, it controlled the iron (hydr)oxide dynamic transformation differences. PFOA transport behavior (retardation factor R from 2.61 to 1.91) was significantly affected by iron (hydr)oxide dynamic transformation. Iron (hydr)oxide transformation induced the greatest PFOA transport risk (R = 1.91, attenuation rate λ = 0.0001 min−1) in SO 4 2− environment, where complex α -FeOOH, Fe 3 O 4 , and β -Fe 2 O 3 ·H 2 O transformed to simplex β -FeOOH, leading to instantaneous (K d) and kinetic (α) two-site sorption fraction change. Furthermore, the associated mineral Fe 3 O 4 of goethite was crucial in PFOA attenuation (λ from 0.0001 to 0.0002 min−1). Fe 3 O 4 released Fe2+ and the oxidation of Fe2+ to Fe3+ provided electrons, facilitating the formation of F–(CF 2) 7 –COO· radicals, which played a key role in the following cycle attenuation process. This study provides a theoretical basis for understanding the interaction mechanism of PFOA and iron (hydr)oxide dynamic transformation under groundwater differences. [Display omitted] • Associated mineral Fe 3 O 4 (releasing Fe2+) of goethite plays a key role in PFOA attenuation. • Groundwater type control iron (hydr)oxide dynamic transformation differences. • PFOA transport behavior is significantly affected by iron (hydr)oxide dynamic transformation. • Iron (hydr)oxide transformation induces the greatest PFOA transport risk in SO 4 2− groundwater. • SO 4 2− environment-induce α -FeOOH, Fe 3 O 4 , and β -Fe 2 O 3 ·H 2 O transform to β -FeOOH. [ABSTRACT FROM AUTHOR]

The increased applications and production of graphene oxide (GO) make the necessity to study information on the interaction of GO with minerals. In this work, adsorption and desorption were used to study the reversibility of interaction between GO and goethite/kaolinite. Result showed that the pH value, ionic strength, and temperature had significant effects on the adsorption and desorption behavior of GO. Interaction force was stronger between GO and goethite than that of kaolinite. The interaction may be attributed to the electrostatic, hydrogen-bonding, and Lewis acid base interactions. The irreversible interaction between GO and minerals may be a main mechanism for the observed desorption hysteresis. These results are important for evaluating the fate and health risk of GO in the environment. Image 1 • Adsorption and desorption of GO on cationic goethite and anionic kaolinite minerals was studied. • PH value, ionic strength, and temperature influence the adsorption and desorption behavior of GO. • Part of interaction between GO and minerals was irreversible. [ABSTRACT FROM AUTHOR]

Abstract The surface catalysis of goethite on the Cr(VI) reduction by tartaric acid was examined together with its adsorption characteristics towards the two reactants. The results showed the adsorption of tartaric acid by goethite was favorable at low pH and adsorption isotherm could be properly described by Langmuir model. The adsorption kinetic curves for both reactants obeyed the pseudo second-order rate model (R2 >0.99). The FTIR spectrum suggested the formation of bidentate binuclear surface complexes between tartaric acid and goethite. At pH 4.50, the reduction percentage of 0.1 mM Cr(VI) by 1.0 mM tartaric acid alone was about 12% after 72 h, while which was increased to 100% in the presence of goethite within 24 h. Kinetic results revealed the Cr(VI) reduction only occurred between the adsorbed tartaric acid and the aqueous Cr(VI) since the Cr(VI) adsorption was completely inhibited under the examined conditions. Meanwhile, the catalysis of aqueous Fe(III) released from the goethite surfaces was excluded due to its low concentration (<5 μ M). With the initial concentration of tartaric acid decreased to 0.1 mM, Cr(VI) reduction could be completed within 4 h, confirmed by the XPS result that only Cr(III) species existed on the goethite surfaces. In this case, electron transfer was suggested to occur directly between the two adsorbed reactants or goethite was believed to serve as an ideal channel to allow electron excited from the adsorbed tartaric acid to transfer to the adsorbed Cr(VI). The findings above were helpful for us to understand the Cr(VI) reduction by organic compounds in soils with rich contents of Fe-oxides. Highlights • Bidentate binuclear surface complexes between tartaric acid and goethite was suggested. • Aqueous Cr(VI) could be reduced to Cr(III) by adsorbed tartaric acid on the goethite surfaces. • The catalysis of aqueous Fe(III) did not operate in the overall reaction. • Three mechanisms were proposed for goethite-catalyzed Cr(VI) reduction by tartaric acid. [ABSTRACT FROM AUTHOR]

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Abstract Iron oxides are important pedogenic Cr(III)-bearing phases which experience high-temperature alteration via fire-induced heating of surface soil. In this study, we examine if heating-induced alteration of Cr(III)-substituted Fe oxides can potentially facilitate rapid high-temperature oxidation of solid-phase Cr(III) to hazardous Cr(VI). Synthetic Cr(III)-substituted ferrihydrite, goethite and hematite were heated up to 800 °C for 2 h. Corresponding heating experiments were also conducted on an unpolluted Ferrosol-type soil, which had a total Cr content of 220 mg kg−1, initially undetectable Cr(VI) and Fe speciation comprising a mixture of hematite, goethite and ferrihydrite (according to Fe K-edge EXAFS spectroscopy). Up to ∼50% of the initial Cr(III) was oxidised to Cr(VI) during heating of Cr(III)-substituted ferrihydrite and hematite, with the greatest extent of Cr(VI) formation occurring at 200–400 °C. In contrast, heating of Cr(III)-substituted goethite resulted in up to ∼100% of Cr(III) oxidizing to Cr(VI) as the temperature approached 800 °C. In the Ferrosol-type soil, heating at ≥400 °C also resulted in large amounts of Cr(VI) formation, with a maximum total Cr(VI) concentration of 77 mg kg−1 forming at 600 °C (equating to oxidation of ∼35% of the soil's total Cr content). A relatively large portion (31–42%) of the total Cr(VI) which formed during heating of the soil was exchangeable, implying a high level of potential mobility and bioaccessibility. Overall, the results show that Cr(VI) forms rapidly via the oxidation of Fe oxide-bound Cr(III) at temperatures which occur in surface soils during fires. On this basis and given the frequency and extent of wild-fires around the world, we propose that fire-induced oxidation of Fe oxide-bound Cr(III) may represent a globally-significant pathway for the natural formation of hazardous Cr(VI) in surface soil. Graphical abstract Image 1 Highlights • Heating drives oxidation of Cr(III) substituted within Fe oxides to Cr(VI). • Fire-induced heating of unpolluted soil can drive hazardous Cr(VI) formation. • A large portion of newly-formed Cr(VI) is likely to be readily mobile. • Fire-induced Cr(III) oxidation may be an important pathway for Cr(VI) formation. Fire-induced oxidation of Fe oxide-bound Cr(III) may represent a largely unexplored, yet globally-significant pathway for the natural formation of hazardous Cr(VI) in soil. [ABSTRACT FROM AUTHOR]

Abstract Multi-walled carbon nanotubes (MWCNTs) are increasing used in commercial applications and may be released into the environment with anionic surfactants, such as sodium dodecylbenzenesulfonate (SDBS), in sewer discharge. Little research has examined the transport, retention, and remobilization of MWCNTs in the presence or absence of SDBS in porous media with controlled chemical heterogeneity, and batch and column scale studies were therefore undertaken to address this gap in knowledge. The adsorption isotherms of SDBS on quartz sand (QS), goethite coated quartz sand (GQS), and MWCNTs were determined. Adsorption of SDBS (MWCNTs » GQS > QS) decreased zeta potentials for these materials, and produced a charge reversal for goethite. Transport of MWCNTs (5 mg L−1) dramatically decreased with an increase in the fraction of GQS from 0 to 0.1 in the absence of SDBS. Conversely, co-injection of SDBS (10 and 50 mg L−1) and MWCNTs radically increased the transport of MWCNTs when the GQS fraction was 0, 0.1, and 0.3, especially at a higher SDBS concentration, and altered the shape of retention profile. Mathematical modeling revealed that competitive blocking was not the dominant mechanism for the SDBS enhancement of MWCNT transport. Rather, SDBS sorption increased MWCNT transport by increasing electrostatic and/or steric interactions, or creating reversible interactions on rough surfaces. Sequential injection of pulses of MWCNTs and SDBS in sand (0.1 GQS fraction) indicated that SDBS could mobilize some of retained MWCNTs from the top to deeper sand layers, but only a small amount of released MWCNTs were recovered in the effluent. SDBS therefore had a much smaller influence on MWCNT transport in sequential injection than in co-injection, presumably because of a greater energy barrier to MWCNT release than retention. This research sheds novel insight on the roles of competitive blocking, chemical heterogeneity and nanoscale roughness, and injection sequence on MWCNT retention and release. Graphical abstract Image 1 Highlights • Both breakthrough curves and retention profiles were determined and simulated. • Co-injection of SDBS and MWCNTs radically increased the transport of MWCNTs. • Competitive blocking was not the dominant mechanism for SDBS and MWCNT transport. • SDBS had a much smaller influence on MWCNT transport in the sequential injection. • SDBS altered the shape of the retention profile of MWCNT. Experimental and modeling studies demonstrated that SDBS had a much smaller influence on MWCNT transport in sequential injection than in co-injection experiments. [ABSTRACT FROM AUTHOR]

Abstract In this study, iron is removed from aqueous solution using a fluidized-bed crystallizer. Homogeneous oxyhydroxide pellets (FeOOH) were recovered at various value of pH, surface loading (L), and initial ferrous concentration to assess the treatability of iron-containing water. The optimal conditions for treating initial ferrous concentrations of 100–300 mg/L were L = 0.6 kg/m2/h (with 29 m/h of upflow velocity), a bed expansion of 50% and pH = 6.5 yielding the total iron removal (TR) of more than 99% and a corresponding iron crystallization ratio (CR) of 85%. X-ray diffractometry (XRD) revealed that the pellets consisted of a mixture of goethite (α-FeOOH) and lepidocrocite (γ-FeOOH). Scanning electron microscopy (SEM) yielded images of pellets of up to 1 mm in diameter, which were assembled from FeOOH flakes with thicknessess of 0.2–0.4 µm. Graphical abstract Image, graphical abstract [ABSTRACT FROM AUTHOR]

Copyright of Tecnologia em Metalurgia, Materiais e Mineração is the property of Associacao Brasileira de Metalurgia e Materiais and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Abstract Soil is a heterogeneous porous media that is comprised of a variety of organo-mineral aggregates. Sorption of heavy metals onto these composite solids is a key process that controls heavy metal mobility and fate in the natural environment. Pollution from a combination of heavy metals is common in soil, therefore, understanding the competitive binding behavior of metal ions to organo-mineral composites is important in order to predict metal mobility and fate. In this study, batch experiments were paired with spectroscopic studies to probe the sorption characteristics of ternary Cd Ni Cu sorbates to a binary organo-goethite composite made with Bacillus cereus cells. Scanning electron microscopy shows that goethite nano-sized crystals are closely associated with the bacterial surfaces. Sorption experiments show a larger adsorptivity and affinity for Cu than Cd/Ni on goethite and B. cereus, and the goethite– B. cereus composite. X-ray photoelectron spectroscopy reveals that carboxylate and phosphate functional moieties present on the bacterial cell walls are primarily responsible for metal sorption to the goethite– B. cereus composite. Synchrotron-based X-ray fluorescence shows that Cu and Ni are predominately associated with the bacterial fraction of the goethite– B. cereus composite, whereas Cd is mainly associated with the goethite fraction. The findings of this research have important implications for predicting the mobility and fate of heavy metals in soil multi-component systems. Graphical abstract Image 1 Highlights • Larger adsorptivity & affinity for Cu than Cd and Ni on goethite-bacteria composite. • Competitive sorption among Cu, Cd and Ni is weaker on composite than on goethite. • Cu and Ni are mainly bound to the bacterial fraction of the binary composite. • Cd is sorbed mainly on the goethite fraction of the binary composite. Cd, Ni and Cu ions compete for similar binding sites on the end-member goethite and B. cereus , but due to different binding affinities, Cu and Ni are mainly bound to the bacterial fraction whereas Cd is predominately sorbed on the goethite fraction of the binary bacteria–mineral composite. [ABSTRACT FROM AUTHOR]

Phosphorus (P) removal from freshwater bodies to ultra-low concentrations is fundamental to prevent eutrophication, while its recovery is necessary to close the P usage cycle. Iron oxide-based adsorbents seem promising candidates, being abundant, cheap, and easy to synthesize compounds, with good affinity for P. Affinity is the key parameter when targeting ultra-low concentrations. Also, adsorbent regeneration and re-use is fundamental for the economic viability, hence the adsorbent stability is important. Goethite, (α-FeOOH), is one of the most stable iron (Fe3+) (hydr)oxide species, with higher affinity, but lower adsorption capacity (per kg) compared to other species. Doping could change goethite surface properties, to boost the adsorption capacity, while preserving the high stability and affinity for P. In this work, pure goethite was compared to goethite doped (5%at.) with different elements of different preferential oxidation states: Zn2+, Mn3+, and Zr4+. Doping was successfully achieved for all elements, albeit Zr showed a lower Fe substitution than targeted. Zn doping increased the goethite point of zero charge and adsorption capacity (per mass and per surface area), preserving the high affinity, while Mn- and Zr- doping displayed a decrease in all the parameters. These could be explained with surface protonation as a charge compensation mechanism in Zn2+-for-Fe3+ substitution. The regeneration test showed improved P recovery for Zr- and Zn-doped goethite. All samples remained stable throughout the whole process. This work provides promising insights on doping as a strategy to manipulate iron oxides surface properties and for developing a highly performing and long-lasting goethite-based adsorbent. [Display omitted] • Three different elements with different oxidation states were used as dopants for goethite: Zn2+, Mn3+, Zr4+. • Zn-doped goethite showed the highest point of zero charge and P adsorption. • Zr doping of goethite, which has never been attempted before, was successful. • Mn- and Zr-doped goethite displayed a decrease in P adsorption performances. • Charge compensation mechanism during doping interesting for adsorbent development. [ABSTRACT FROM AUTHOR]

Solid fuels are added during the pelletizing process in order to reduce the natural gas consumption in the firing process and to obtain better temperature distribution inside the pellets for its induration. The purpose of this research was to evaluate the effect of the amount of carbon added to mixtures containing different types of pellet feed on the mechanical strength. The pellet mixtures were prepared with different dosages of anthracite (1, 1.2 and 1.4% of fixed carbon) and two different sorts of pellet feed. The mixing, pelletizing and firing stages were done on a pilot scale, and the fired pellets were subjected to the mechanical properties evaluation and microstructural analyses. It was found that when increasing the amount of anthracite, the compression and tumbler strength of the fired pellets decreased, which seemed to be related to the formation of a large number of pores and magnetite in the core of the pellets. When a larger amount of porous hematite and goethite were used in the pellet feed, larger quantities of magnetite were found in the microstructure of the pellets. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Adsorption of 4- n -nonylphenol on goethite and hematite follows Langmuir isotherm model. • Pseudo-second order kinetics were found to explain the kinetics of adsorption. • Maximum absorption was achieved at the first 24 h, at pH close to the pKa of 4- n -nonylphenol. Abstract The adsorption of 4- n -Nonylphenol (4- n -NP), a persistent emerging contaminant, onto the surface of hematite and goethite was studied using Attenuated Total Reflectance (ATR)-FTIR spectroscopy. The adsorption kinetics for hematite and goethite show that equilibrium was reached in less than 24 h, with the fastest kinetics to saturation achieved on hematite. Adsorption isotherms studies show that Langmuir model bests fits the data, with the highest adsorption capacity observed in goethite, with a calculated 4- n -NP maximum adsorption that was 3 times more than that of hematite. This higher maximum capacity on the surface of goethite was attributed to the presence of more OH species on the surface of goethite than on hematite. When the pH was varied, maximum adsorption was achieved close to pKa of 4- n -NP, with maximumvalues matching those acquired from adsorption isotherms and kinetic studies. [ABSTRACT FROM AUTHOR]

Topsoil contamination near the Stanisław Siedlecki Polish Polar Station (PPS), Hornsund, Svalbard, has been assessed using magnetic methods supplemented by chemical analyses and microscopic observations. Analysis of magnetic parameters has enabled to evaluate the concentration, magnetic mineralogy, and grain-size distribution of anthropogenic magnetic particles. Heavy-metal contamination near the PPS originates primarily from local sources. Anthropogenic spherical, magnetite-like particles were found near the station, whereas uncontaminated topsoil is devoid of such particles. Magnetic studies indicate that magnetite and goethite are the primary magnetic phases, with magnetite levels being higher in polluted area. Magnetic fraction of contaminated topsoil includes a mixture of single-domain and multi-domain grains, while uncontaminated topsoil contains smaller grains. Results show a clear correspondence between Pollution Load Index and magnetic susceptibility anomalies, and that the areal extent of PPS impact on the environment has not expanded significantly since 2004 (although a new contamination source, the scrap yard, is now present). A comparison of magnetic susceptibility measurements with metal analyses indicates that magnetic methods can be used as a rapid, inexpensive, non-invasive, and sensitive tool for the evaluation of topsoil contamination. [ABSTRACT FROM AUTHOR]

Graphene oxide (GO) may strongly interact with toxic metal ions and mineral particles upon release into the soil environment. We evaluated the mutual effects between GO and Ni (Ni(II)) with regard to their adsorption and co-adsorption on two minerals (goethite and hematite) in aqueous phase. Results indicated that GO and Ni could mutually facilitate the adsorption of each other on both goethite and hematite over a wide pH range. Addition of Ni promoted GO co-adsorption mainly due to the increased positive charge of minerals and cation–π interactions, while the presence of GO enhanced Ni co-adsorption predominantly due to neutralization of positive charge and strong interaction with oxygen-containing functional groups on adsorbed GO. Increasing adsorption of GO and Ni on minerals as they coexist may thus reduce their mobility in soil. Extended X-ray absorption fine structure (EXAFS) spectroscopy data revealed that GO altered the microstructure of Ni on minerals, i.e., Ni formed edge-sharing surface species (at R Ni-Fe ∼3.2 Å) without GO, while a GO-bridging ternary surface complexes (at R Ni-C ∼2.49 Å and R Ni-Fe ∼4.23 Å) was formed with GO. These findings improved the understanding of potential fate and toxicity of GO as well as the partitioning processes of Ni ions in aquatic and soil environments. [ABSTRACT FROM AUTHOR]

9,10-Anthraquinone-2,6-disulfonic acid (AQDS) is commonly used as a model species to examine the influence of quinones on different biogeochemical cycles. The reduced form of this quinone, AH2DS, can donate electrons to the toxic metal species Cr(VI), leading to the precipitation of less soluble Cr(III) phases. Due to the environmental abundance of Fe(III) (oxyhydr)oxides, such as goethite (α-FeOOH), it is important to study the role of these mineral phases on the electron transfer reaction between AH2DS and Cr(VI). In this study, this electron transfer reaction is examined in the presence and absence of goethite at three different ratios of AH2DS/Cr(VI). Ultraviolet-visible spectroscopy is used to qualitatively assess the oxidation state of AQDS during reactions with goethite. Iron K-edge and Cr K-edge X-ray absorption spectroscopy are used to examine the role of goethite in electron transfer and identify Cr(III) phases that form. Goethite inhibits the extent of Cr(VI) reduction to Cr(III), most notably at the highest ratio of AH2DS/Cr(VI) investigated. Production of semiquinone radical species may limit electron transfer and decrease the yields of Fe(II) and Cr(III), both in the presence and absence of goethite. Understanding abiotic electron transfer reactions that occur in systems with multiple redox active species is important to determine the contribution of abiotic redox reactions to Fe biogeochemical cycling in natural soils. [ABSTRACT FROM AUTHOR]

It is of great scientific and practical importance to explore the mechanisms of accelerated degradation of Hexachlorobenzene (HCB) in soil. Both iron oxide and dithionite may promote the reductive dechlorination of HCB, but their effects on the microbial community and the biotic and abiotic mechanisms behind it remain unclear. This study investigated the effects of goethite, dithionite, and their interaction on microbial community composition and structure, and their potential contribution to HCB dechlorination in a paddy soil to reveal the underlying mechanism. The results showed that goethite addition alone did not significantly affect HCB dechlorination because the studied soil lacked iron-reducing bacteria. In contrast, dithionite addition significantly decreased the HCB contents by 44.0–54.9%, while the coexistence of dithionite and goethite further decreased the HCB content by 57.9–69.3%. Random Forest analysis suggested that indicator taxa (Paenibacillus , Acidothermus , Haliagium , G12-WMSP1, and Frankia), Pseudomonas , richness and Shannon's index of microbial community, and immobilized Fe content were dominant driving factors for HCB dechlorination. The dithionite addition, either with or without goethite, accelerated HCB anaerobic dechlorination by increasing microbial diversity and richness as well as the relative abundance of the above specific bacterial genera. When goethite and dithionite coexist, sulfidation of goethite with dithionite could remarkably increase FeS formation and then further promote HCB dechlorination rates. Overall, our results suggested that the combined application of goethite and dithionite could be a practicable strategy for the remediation of HCB contaminated soil. [Display omitted] • POPs are an important environmental issue for their high toxicity and persistence. • Goethite did not affect HCB dechlorination with few iron-reducing bacteria. • Dithionite addition accelerated HCB dechlorination by influencing soil microbes. • Sulfidation of goethite with dithionite increased FeS and promoted HCB dechlorination. [ABSTRACT FROM AUTHOR]

Chalcopyrite flotation is selectively depressed by oxidation treatment. The presence of ferric oxyhydroxide on the surface of chalcopyrite after oxidation treatment is a key factor in depressing chalcopyrite flotation. However, there is no concrete evidence that ferric oxyhydroxide has a depressing effect. In addition, the effectiveness of this depressing effect could be enhanced by directly applying ferric oxyhydroxide nanoparticles. This study investigated the effect of goethite (α-FeOOH) nanoparticles on the surface properties and flotation behavior of chalcopyrite. α-FeOOH nanoparticles were produced through chemical precipitation followed by hydrothermal treatment. The crystalline structure of irregular rice grain-shaped α-FeOOH nanoparticles was confirmed by the X-ray diffraction pattern and scanning electron microscope image. Micro-flotation experiments showed that chalcopyrite recovery decreased significantly from 93 % to 13 % when 30 mg/L α-FeOOH nanoparticles was used. This flotation result demonstrated the potential of α-FeOOH nanoparticles as a nanodepressant for the flotation of chalcopyrite. These nanoparticles physically adsorbed on the chalcopyrite surface and rendered its surface hydrophilic, thereby reducing the chalcopyrite flotation recovery. The attractive electrostatic force between the positively charged α-FeOOH nanoparticles and the negatively charged chalcopyrite surface is likely responsible for the adsorption of α-FeOOH nanoparticles on chalcopyrite. [Display omitted] The effect of goethite nanoparticles (Nps) on the flotation of chalcopyrite is studied. Goethite (α-FeOOH) Nps deplete the flotation recovery of chalcopyrite. α-FeOOH Nps alter the surface hydrophobicity of chalcopyrite. α-FeOOH Nps and chalcopyrite have opposite charges and are attracted electrostatically. [ABSTRACT FROM AUTHOR]

Garnet-bearing aluminous gneisses in the Vasil’kovka area of the Orekhov-Pavlograd zone of the Ukrainian Shield were studied using the THERIAK-DOMINO, THERMOCALC, and WINTWQ software and mineral geothermobarometry methods. The stability fields of parageneses formed at the initial, peak, and post-peak metamorphic stages have been estimated: T = 500-650 °C and P > 7 kbar, T = 800-850 °C and P - 8 kbar, and T = 600-670 °C and P = 4.0-5.5 kbar, respectively. A “clockwise” PT path has been established. Based on the aluminous gneiss, the age of metamorphism is determined as Paleoproterozoic (2014 ± 11 Ma). Unique regularly oriented acicular goethite microinclusions were described in garnet. In contrast to other known oriented Ti-bearing mineral inclusions in garnet, these goethite inclusions suggest not only extremely high P and T values (necessary for the formation of oriented Ti-bearing inclusions) but also a high oxygen fugacity. The obtained data broaden the concepts of the ways and conditions of formation of regularly oriented mineral phases in garnet. [ABSTRACT FROM AUTHOR]

Phytoplankton-derived dissolved organic matter (PDOM) and macrophyte-derived dissolved organic matter (MDOM) exist ubiquitously in eutrophic freshwater lakes. To understand the heterogeneous roles of individual fluorescent DOM components in the adsorption of antibiotics onto sediment minerals, the adsorptive fractionation of DOM on goethite (α–FeOOH) and its interaction with sulfamethazine (SMT) were investigated using fluorescence excitation-emission matrix combined with parallel factor analysis (EEM–PARAFAC). The affinity sequence for goethite of the 4 fluorescent PARAFAC components followed the order of: tryptophan- > tyrosine- > long emission wavelength (LEW) humic- > and short emission wavelength (SEW) humic-like component. This sequence indicated the preferential adsorption of protein-like substances. Meanwhile, tyrosine-like components can strongly form complexes with SMT with a large binding constant, followed by tryptophan- and SEW humic-like components. However, LEW humic-like component did not effectively react with SMT. The main mechanism of fluorescence quenching between DOM and SMT was static quenching. The result indicated that protein-like substances in DOM were favorable to SMT adsorption by acting as a bridge to form complexes with both goethite surface and SMT molecules, whereas humic-like substances played secondary roles in the DOM–goethite–SMT ternary system. Due to its higher content of protein-like substances, PDOM improved the SMT adsorption on goethite more than MDOM. Therefore, the abundant DOM released from phytoplankton and macrophytes affected the transport of antibiotics to sediments and might eventually change their bioavailability and toxicity to organisms. [ABSTRACT FROM AUTHOR]

Abstracts In this research, dielectric barrier discharge plasma was developed to cooperate with goethite for removing caffeine in aqueous solution. Goethite was characterized by X-ray diffraction and scanning electron microscopy. The effects of input power, initial concentration and catalysts concentration on the removal efficiency of caffeine were evaluated. Furthermore, the degradation pathways of caffeine were also discussed preliminarily. In the case of caffeine concentration at 50 mg L −1 , the degradation efficiency of caffeine was improved from 41% to 94% after 24 min on the conditions of input power of 75 W by combining goethite catalysts (2.5 g L −1 ), while the energy efficiency could be enhanced 1.6–2.3 times compared to the single DBD reactor. The reaction mechanism experiments demonstrated that attack by hydroxyl radical and ozone was the main degradation process of caffeine in aqueous solution. These studies also provided a theoretical and practical basis for the application of DBD-goethite in treatment of caffeine from water. [ABSTRACT FROM AUTHOR]

Arsenic (As) in soils is often adsorbed on Fe-(hydro)oxides surface, rendering them more resistant to dissolution, which is undesirable for phytoremediation of As-contaminated soils. Arsenic hyperaccumulator Pteris vittata prefers to grow in calcareous soils where available Fe and As are low. To elucidate its mechanisms of acquiring Fe and As from insoluble sources in soils, we investigated dissolution of goethite with pre-adsorbed arsenate (AsV; As-goethite) in presence of four organic ligands, including two root exudates (oxalate and phytate, dominant in P. vittata ) and two microbial siderophores (PG12-siderophore and desferrioxamine B). Their presence increased As solubilization from As-goethite from 0.03 to 0.27–5.33 mg L −1 compared to the control. The siderophore/phytate bi-ligand treatment released 7.42 mg L −1 soluble Fe, which was 1.2-fold that of the sum of siderophore and phytate, showing a synergy in promoting As-goethite dissolution. In the ligand-mineral-plant system, siderophore/phytate was most effective in releasing As and Fe from As-goethite. Moreover, the continuous plant uptake induced more As-goethite dissolution. The continued release of As and Fe significantly enhanced their plant uptake (from 0.01 to 0.43 mg plant −1 As and 2.7–14.8 mg plant −1 Fe) and plant growth (from 1.2 to 3.1 g plant −1 fw) in P. vittata . Since microbial siderophores and root exudates often coexist in soil rhizosphere, their synergy in enhancing dissolution of insoluble As-Fe minerals may play an important role in efficient phytoremediation of As-contaminated soils. [ABSTRACT FROM AUTHOR]

Properties of Fe-rich abandoned mine drainage (AMD) precipitates on mercury removal were accomplishedby fixed bed adsorption system. Puregoethite was synthetized as a reference material.Characteristicexamination tests revealed the AMD precipitates primarily consist of poorly crystallized nanoparticulate goethite. Fixed bed adsorption tests demonstrate itowns mercury removal capacity of about 175.6μg/g. Furthermore, a predominant oxidized mercury fraction of about 65-70% was also observed. Properties responsible for the reaction mechanism were analyzed preliminarily. Previously proposed aggregation-based growth pathway was helpful to understand the crystal formation process, during which point defects, dislocations and planar defects on the surface were produced. In this study, they were considered as active sites for the elemental mercury oxidation reactions. Based on the active sites and the effect of gas components on mercury removal obtained in the tests, Eley-Rideal chemisorptions mechanism was proposed to explain the reactions. [ABSTRACT FROM AUTHOR]

In this work, Pd nanoparticles was precipitated over iron oxide that prepared through two basic approaches to look for better dispersion of Pd nanoparticles and robust catalyst for carbon monoxide oxidation. The first involves direct precipitation of iron oxide using sodium hydroxide, and the second involves hydrothermal treatment after precipitation. The catalysts were characterized by many techniques such as, FTIR, XRD, N 2 adsorption-desorption, H 2 -TPR and TEM images. The catalytic activity of the prepared catalysts was tested in CO oxidation reaction. The XRD showed that, α-FeOOH crystalline structure is formed. While, TEM images showed that, α-FeOOH has nanorods structure with different dimensions. The TPR experiment indicated that the reducibility of Pd/FeOOH catalyst was much more enhanced. The results also demonstrate that, as compared with the direct precipitation approach, the hydrothermal treatment after precipitation approach of iron oxide enable better dispersion of Pd nanoparticles as well as hinder the growth of large Pd crystallites which are important to produce outstanding catalysts for carbon monoxide oxidation. [ABSTRACT FROM AUTHOR]

Environmental mobility of C 60 fullerene can be significantly affected in the presence of naturally abundant α-FeOOH. However, α-FeOOH vary significantly in sizes, shapes and associated properties that can greatly influence the fate and transport of C 60 fullerene in environmental media. Therefore, colloidal hetero-association between well crystallized low aspect (L Asp ) α-FeOOH and nC 60 fullerene may differ substantially to weakly crystallized high-aspect (H Asp ) counterpart. In contrast to L Asp α-FeOOH, inherent crystal defects and surface charge generation in H Asp α-FeOOH facilitated strong Coulombic attraction and aggregation with fullerene in acidic pH. However, L Asp α-FeOOH demonstrated subtle entropic depletion mediated interaction with fullerene prevalent in hard rods. Humic acid (HA) encapsulation of H Asp α-FeOOH substantially blocked fullerene attachment. Minute enhancement in colloidal stability was detected for HA-coated H Asp α-FeOOH and fullerene mixture to HA-coated H Asp α-FeOOH alone. To investigate the interfacial assembly of α-FeOOH with fullerene “ in situ” differential interference contrast (DIC) microscopic investigations were employed. This study showed significantly different interface behavior of the binary mixtures of fullerene and H Asp α-FeOOH NPs, and L Asp particles. On air-water interface, bare H Asp α-FeOOH displayed liquid crystalline packing. However, addition of fullerene to H Asp α-FeOOH suspension at pH5 produced closed-loop polygonal and circular ring structures. Head-to-tail alignment of magnetic dipoles as well as fullerene hydrophobicity facilitated such assembly formation. “ Ex situ ” AFM investigation revealed further the presence of magnetically derived ring structure which asserts that the formed “ in situ ” ensembles were not transient, hence, may abate fullerene transport through environmental interfaces. Barring hydrophobicity assisted attachment of fullerene to L Asp α-FeOOHs, the absence of any close-packed structures may unlikely abate fullerene transport as envisaged in case of H Asp α-FeOOH. Thus, aspect ratio variation and associated material properties of naturally abundant α-FeOOH may significantly impact fullerene transport through environmental media. [ABSTRACT FROM AUTHOR]

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

Excessive application of fertilizers has caused a high load of phosphorus (P) in the North China Plain. The fate of P and its effects on aquatic ecosystems depend on its chemical speciation in soils. However, few studies systematically investigated the transport and retardation of different P species in the fluvo-aquic soil. In this study, the transport of inorganic P (orthophosphate, PO 4), organic P (phytic acid, PA) and particulate P (hydroxyapatite nanoparticles, nHAP) in the fluvo-aquic soil were investigated by column experiments, and their retardation from major soil components such as kaolin, CaCO 3 , Al 2 O 3 , and goethite (GT) was also investigated by monitoring breakthrough curves and fitting transport models. The transport of P species in fluvo-aquic soil followed the order of PO 4 > PA > nHAP. A high fraction of increased clay and mineral particle-associated P (P-E) was observed for PO 4 and PA; while significant Ca-associated P (P-Ca) for nHAP. Under the experimental conditions, both CaCO 3 and GT were the most influential factors for PO 4 , PA, and nHAP retention. Goethite strongly inhibited PO 4 transport due to its high PO 4 adsorption capacity, while CaCO 3 strongly inhibited PA transport due to its strong association with PA under alkaline conditions. Both CaCO 3 and GT can severely inhibit nHAP transport due to the favorable electrostatic conditions as well as the Ca2+ bridging effect. These results indicated that CaCO 3 played a key role in regulating the retention of organic P and particulate P in the calcareous soil, and also suggested the important role of Fe (hydr)oxides in controlling the transport of inorganic P, which could out-compete that of CaCO 3. [Display omitted] • Transport ability of P species in fluvo-aquic soil followed the order of PO 4 > PA > nHAP. • P-E fraction was the major fraction for the retained PO 4 and PA, while P-Ca for nHAP. • CaCO 3 and goethite were the most influential controlling factors for PO 4 , PA, and nHAP transport. • CaCO 3 had a greater inhibition impact on PA and nHAP transport while goethite significantly inhibited PO 4 transport. [ABSTRACT FROM AUTHOR]

One of the leading causes of As release from streambed sediments into freshwater systems is competition with phosphate. Among important sources of P to the fluvial ecosystems are wastewater treatment plants (WWTP), estimated to account for 25–45% of all P in surface waters. In this paper, long-term effects of discharged phosphorus from a small WWTP on the arsenic mobility were studied in an As-enriched fluvial system (approx. 240 mg/kg) in central Czech Republic. After 7 years of elevated P (≤7.7 mg/L) in the stream water, the total As decreased by 25% and the total P increased by 40% in the sediments downstream (at a distance of 66 m). The results of the chemical extractions and mineralogical analyses indicated that the changes in the concentration were mostly due to the sorption processes in the Fe (oxyhydr)oxides (goethite and hematite). In the downstream samples, the As in these phases decreased two-fold, and P was significantly enriched by 45–140%. Phosphorus was also found precipitated as newly formed Ca phosphates. The stream water monitoring indicated that the discharged P was either sequestered when the levels of dissolved P were high (>2.3 mg/L) or released from the downstream sediments when these levels were low (<∼1.5 mg/L). Meanwhile, As was continuously mobilized from the downstream sediments likely due to (i) the ongoing As desorption from the exterior parts of the Fe (oxyhydr)oxides at high aqueous P levels and (ii) the dissolution of As-bearing Ca phosphates at low dissolved P levels. These findings clearly demonstrate that point sources of P to streams and rivers, such as WWTP, may result in the permanent and long-term release of As from contaminated streambed sediments. [Display omitted] • Effluent may permanently and over long-time release As from sediments. • Elevated P (≤7.7 mg/L) in the stream water causes a decrease in bound As. • Discharged phosphate adsorbs and precipitates as Ca phosphates. • Phosphate competes with As for sorption sites on Fe (oxyhydr)oxides. [ABSTRACT FROM AUTHOR]

Goethite is a commonly found iron (hydr)oxide in soils and sediments that has been proven to possess abundant defects in structures. However, the underlying impact of these defects in goethite on arsenic immobilization remains unclear. In this study, goethite samples with abundant, moderate, and sparse defects were synthesized to evaluate their arsenic adsorption capacities. The characteristics of the defects in goethite were investigated by extended X-ray absorption fine structure (EXAFS), high angle annular dark field-scanning transmission electron microscopy-energy dispersion spectrum (HAADF-STEM-EDS) mapping, vibrating-sample magnetometry (VSM), and electron spin resonance (ESR). The characterization analysis revealed that the defects in as-synthesized goethite primarily existed in the form of Fe vacancies. Batch experiments demonstrated that the adsorption capacities of defect-rich goethite for As(V) and As(III) removal were 10.2 and 22.1 times larger than those of defect-poor goethite, respectively. The origin of the impact of Fe defects on arsenic immobilization was theoretically elucidated using density functional theory (DFT) calculations. The enhanced adsorption of goethite was attributed to the improvement of the arsenic affinity due to the Fe vacancy defect, thus considerably promoting arsenic immobilization. The findings of this study provide important insight into the migration and fate of arsenic in naturally occurring iron (hydr)oxides. [Display omitted] • Goethite samples with tunable defects were synthesized by a precipitation method. • The defect characteristics of goethite were carefully examined. • Fe vacancy was the primary defect type existed in the defective goethite samples. • Fe vacancy defect significantly promoted the arsenic immobilization on goethite. • The enhanced arsenic adsorption was attributed to an increase in affinity. [ABSTRACT FROM AUTHOR]

In this study, the efficiency of electrocoagulation (EC) with iron electrodes was applied to remove two phosphonates, 1-hydroxyethylidene-1, 1-diphosphonic acid (HEDP) and nitrilotris(methylene) triphosphonic acid (NTMP) from concentrates. This work provides a detailed description of the experimental procedure and results on phosphonate removal and recovery from different electrolytes, including synthetic and real reverse osmosis (RO) membrane concentrates. This research showed high selectivity of EC, removing 100% and 80% of the NTMP and the HEDP respectively, confirming no competition with sulfates, nitrates, or silica. When experimenting with other electrolytes, calcium showed to be critical in enhancing the flocculation process, while calcium carbonate precipitation contributed to capturing the phosphonates from the concentrate. The produced iron oxide (sludge) was confirmed as goethite and akaganéite, and finally transformed into hematite, indicating the oxidation from Fe2+ to Fe3+ during the EC process. After the iron precipitate collection, an alkaline wash of the sludge was enough to recover 100% of the initial phosphorus from the NTMP phosphonate. However, further research is needed to optimize the recovery procedure and to improve the results with the HEDP. 70 and 140 A·m−2 current densities were optimal to bring HEDP and NTMP concentrations down to 32 μM (1 mg·L−1) in only 30 and 10 min respectively. In these conditions, the operational costs, 1.10 and 0.03 €·m−3 of treated concentrate, were estimated for HEDP and NTMP respectively. Even when EC has been widely studied for phosphate removal, this technique has been barely applied to treat concentrates containing phosphonate-based antiscalants. EC opens new possibilities for phosphonates and phosphorus to be removed and recovered respectively from membrane and other concentrates. [Display omitted] • Electrocoagulation technique was tested to remove phosphonates from concentrates. • Calcium has a key role in the coagulation process and the adsorption of phosphorus. • Phosphorus removal was identical when treating real and synthetic concentrates. • Analysis of the flocs revealed main presence of hematite and calcium carbonate precipitation. • Optimal operating costs were found below μM phosphorus concentration. [ABSTRACT FROM AUTHOR]

Atmospheric mineral dust can influence climate and biogeochemical cycles. An important component of mineral dust is ferric oxide minerals (hematite and goethite) which have been shown to influence strongly the optical properties of dust plumes and thus affect the radiative forcing of global dust. Here we report on the iron mineralogy of dust-source samples from the Bodélé Depression (Chad, north-central Africa), which is estimated to be Earth’s most prolific dust producer and may be a key contributor to the global radiative budget of the atmosphere as well as to long-range nutrient transport to the Amazon Basin. By using a combination of magnetic property measurements, Mössbauer spectroscopy, reflectance spectroscopy, chemical analysis, and scanning electron microscopy, we document the abundance and relative amounts of goethite, hematite, and magnetite in dust-source samples from the Bodélé Depression. The partition between hematite and goethite is important to know to improve models for the radiative effects of ferric oxide minerals in mineral dust aerosols. The combination of methods shows (1) the dominance of goethite over hematite in the source sediments, (2) the abundance and occurrences of their nanosize components, and (3) the ubiquity of magnetite, albeit in small amounts. Dominant goethite and subordinate hematite together compose about 2% of yellow-reddish dust-source sediments from the Bodélé Depression and contribute strongly to diminution of reflectance in bulk samples. These observations imply that dust plumes from the Bodélé Depression that are derived from goethite-dominated sediments strongly absorb solar radiation. The presence of ubiquitous magnetite (0.002–0.57 wt%) is also noteworthy for its potentially higher solubility relative to ferric oxide and for its small sizes, including PM < 0.1 μm. For all examined samples, the average iron apportionment is estimated at about 33% in ferric oxide minerals, 1.4% in magnetite, and 65% in ferric silicates. Structural iron in clay minerals may account for much of the iron in the ferric silicates. We estimate that the mean ferric oxides flux exported from the Bodélé Depression is 0.9 Tg/yr with greater than 50% exported as ferric oxide nanoparticles (<0.1 μm). The high surface-to-volume ratios of ferric oxide nanoparticles once entrained into dust plumes may facilitate increased atmospheric chemical and physical processing and affect iron solubility and bioavailability to marine and terrestrial ecosystems. [ABSTRACT FROM AUTHOR]

The decolorization of Orange II by an electro-enhanced goethite (α-FeOOH) activating peroxydisulfate (PDS) process (EC/α-FeOOH/PDS process) is reported in this study. Sulfate radicals was produced by activating PDS with Fe(II), which was generated continuously from the cathodic reduction of Fe(III) on α-FeOOH surface. The decolorization of Orange II showed little dependence on the initial pH. The comparison of Orange II decolorization under different systems was investigated. The surface properties of α-FeOOH before and after reaction were investigated by X-ray Photoelectron Spectroscopy (XPS). The radical species generated in EC/α-FeOOH/PDS process were determined by Electron Paramagnetic Resonance (EPR). On the basis of the results, the mechanism of Orange II decolorization in EC/α-FeOOH /PDS process was proposed. The catalyst α-FeOOH maintained its high activity during repeated batch experiments. Response surface methodology (RSM) based on Box–Behnken statistical experiment design (BBD) was applied to analyze the experimental variables. The response surface methodology models were derived from the experimental results and the response surface plots of the pseudo-first-order decolorization rate constant were developed accordingly. [ABSTRACT FROM AUTHOR]