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Akira Usui - One of the best experts on this subject based on the ideXlab platform.
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enrichment mechanisms of antimony and arsenic in marine Ferromanganese oxides insights from the structural similarity
Geochimica et Cosmochimica Acta, 2019Co-Authors: Soichiro Uesugi, Teruhiko Kashiwabara, Akira Usui, Takaaki Itai, Shitong Yang, Masato Tanaka, Yoshio TakahashiAbstract:Abstract Marine Ferromanganese crusts and nodules as potential mineral deposits have received increasing attention. However, much less knowledge is available concerning the incorporation and enrichment mechanisms for antimony (Sb) and arsenic (As) in marine Ferromanganese oxides. In this study, the surface complexations of Sb(V) and As(V) on synthetic ferrihydrite and Mn oxides (δ-MnO2 and birnessite) were investigated by a combination of adsorption experiments, extended X-ray absorption fine structure (EXAFS) analyses, and quantum chemical calculations. The speciation, distribution, and local structure of Sb and As in different types of natural marine Ferromanganese oxides were determined by X-ray absorption near edge structure (XANES) and EXAFS analyses to reveal the enrichment mechanisms for the two elements in Ferromanganese oxides at the molecular level. To the best of our knowledge, the Sb EXAFS analyses for different types of marine Ferromanganese oxides are herein reported for the first time. Results showed that Sb(V) is preferentially adsorbed on Mn oxides through energetically favorable bidentate–mononuclear complexation because of the structural similarity between the octahedron SbV(OH)6− and MnO6 unit, although bidentate–binuclear (corner-sharing) and bidentate–mononuclear (edge-sharing) complexes can be formed on ferrihydrite and Mn oxides for the adsorption of Sb(V). By contrast, tetrahedral AsVO43− is mostly adsorbed on ferrihydrite and Mn oxides with the formation of bidentate–binuclear complexes. In natural marine Ferromanganese oxides, Sb and As can be retained by Fe and Mn (oxyhydr)oxide components, and the disparate distribution of the two elements to Mn oxides may largely depend on the Mn/Fe ratio and constituent minerals. The larger enrichment factor of Sb than that of As in marine Ferromanganese oxides may result from their preferential attachment modes onto the Fe and Mn phases and different inhibition effects from coexisting anions in seawater. Compared with As, a part of Sb may be strongly associated with the lateral sites in Mn oxides via the formation of bidentate edge-sharing complexes, with which anions such as sulfate in seawater do not significantly compete. The findings from this study provide the molecular-scale insights into the enrichment processes and mechanisms of Sb and As in marine Ferromanganese oxides. Our study also helps elucidate the incorporation mechanisms and geochemical behaviors of other oxyanions in marine and surface environments.
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comparison of arsenate and molybdate speciation in hydrogenetic Ferromanganese nodules
Egyptian Computer Science Journal, 2019Co-Authors: Shitong Yang, Teruhiko Kashiwabara, Akira Usui, Soichiro Uesugi, Masato Tanaka, Minako Kurisu, Chihiro Miyamoto, Yoshio TakahashiAbstract:Marine Ferromanganese oxides contain a large amount of trace elements, such as arsenic (As) and molybdenum (Mo). However, the host phases of tetrahedral AsO43– and MoO42– oxyanions therein have not been clearly identified thus far. In this work, we explored the mineralogical components of hydrogenetic (HG) Ferromanganese nodules and compared the distribution behaviors of As and Mo. The X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS) analyses showed that the predominant manganese and iron phases were vernadite (δ-MnO2) and ferrihydrite, respectively. According to the sequential extraction examination, both As and Mo were associated with the iron (oxyhydr)oxide phases. However, the XAS analyses indicated that As was retained by the ferrihydrite phase via double corner-shared complexation, while Mo was preferentially adsorbed on δ-MnO2 via edge-shared complexation. The immobilization of As and Mo by HG Ferromanganese samples was attributed to specific chemical binding (ΔGchem) rather than Cou...
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continuous growth of hydrogenetic Ferromanganese crusts since 17 myr ago on takuyo daigo seamount nw pacific at water depths of 800 5500 m
Ore Geology Reviews, 2017Co-Authors: Akira Usui, Teruhiko Kashiwabara, Aya Sakaguchi, Keisuke Nishi, Hisaaki Sato, Yoshio Nakasato, Blair Thornton, Ayaka Tokumaru, Kyoko Yamaoka, Shingo KatoAbstract:Ferromanganese crusts cover all outcrops on Takuyo-Daigo seamount traversed during remotely operated underwater vehicle (ROV) dives, except in places covered by foraminifera sand. Takuyo-Daigo is a Cretaceous seamount located in the northwest Pacific Ocean. Geological and bathymetric mapping provide the framework for this study. Chemical and mineralogical analyses of the hydrogenetic Ferromanganese crusts show temporal and spatial variations typical of those found in previous studies. Outcrops from 800 to 5500 m water depths are covered with Ferromanganese crusts up to 105 mm thick. Beryllium isotope dating shows that the crusts have apparently been growing continuously at all water depths, even through the modern oxygen minimum zone (OMZ), contrary to some earlier models for deposition. Growth rates vary from 2.3 to 3.5 mm/Myr, with Fe or Mn fluxes of 0.07–0.11 g/cm2/Myr since the early-middle Miocene. Co/Mn ratios decrease with water depth while Fe/Mn and other metallic elements increase or show no change, based on the analysis of the uppermost crust surface. This is probably because Co is the most abundant redox-sensitive element derived from seawater that occurs in crusts.
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Chemical processes for the extreme enrichment of tellurium into marine Ferromanganese oxides
Geochimica et Cosmochimica Acta, 2014Co-Authors: Teruhiko Kashiwabara, Akira Usui, Yasuko Oishi, Aya Sakaguchi, Toshiki Sugiyama, Yoshio TakahashiAbstract:Abstract Tellurium, an element of growing economic importance, is extremely enriched in marine Ferromanganese oxides. We investigated the mechanism of this enrichment using a combination of spectroscopic analysis and adsorption/coprecipitation experiments. X-ray Absorption Near-Edge Structure (XANES) analysis showed that in adsorption/coprecipitation systems, Te(IV) was oxidized on δ-MnO 2 and not oxidized on ferrihydrite. Extended X-ray Absorption Fine Structure (EXAFS) analysis showed that both Te(IV) and Te(VI) were adsorbed on the surface of δ-MnO 2 and ferrihydrite via formation of inner-sphere complexes. In addition, Te(VI) can be structurally incorporated into the linkage of Fe octahedra through a coprecipitation process because of its molecular geometry that is similar to the Fe octahedron. The largest distribution coefficient obtained in the adsorption/coprecipitation experiments was for the Te(VI)/ferrihydrite coprecipitation system, and it was comparable to those calculated from the distribution between natural Ferromanganese oxides and seawater. Our XAFS and micro-focused X-ray fluorescence (μ-XRF) mapping of natural Ferromanganese oxides showed that Te was structurally incorporated as Te(VI) in Fe (oxyhydr)oxide phases. We conclude that the main process for the enrichment of Te in Ferromanganese oxides is structural incorporation of Te(VI) into Fe (oxyhydr)oxide phases through coprecipitation. This mechanism can explain the unique degree of enrichment of Te compared with other oxyanions, which are mainly enriched via adsorption on the surface of the solid structures. In particular, the great contrast in the distributions of Te and Se is caused by their oxidized species: (i) the similar geometry of the Te(VI) molecule to Fe octahedron, and (ii) quite soluble nature of Se(VI). Coexisting Mn oxide phases may promote structural incorporation of Te(VI) by oxidation of Te(IV), although the surface oxidation itself may not work as the critical enrichment process as in the case of some cations. This enrichment mechanism also means that Ferromanganese oxides mainly scavenge dominant Te(VI) species from seawater and do not affect its species distribution in seawater, as described in a previous model. The variation in Te abundances and the correlation of Te concentration with the growth rate of natural Ferromanganese oxides are consistent with the coprecipitation mechanism.
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tungsten species in natural Ferromanganese oxides related to its different behavior from molybdenum in oxic ocean
Geochimica et Cosmochimica Acta, 2013Co-Authors: Teruhiko Kashiwabara, Yoshio Takahashi, Tomoya Uruga, Matthew A Marcus, Hajime Tanida, Yasuko Terada, Akira UsuiAbstract:Abstract The tungsten (W) species in marine Ferromanganese oxides were investigated by wavelength dispersive XAFS method. We found that the W species are in distorted O h symmetry in natural Ferromanganese oxides. The host phase of W is suggested to be Mn oxides by μ-XRF mapping. We also found that the W species forms inner-sphere complexes in hexavalent state and distorted O h symmetry on synthetic ferrihydrite, goethite, hematite, and δ-MnO 2 . The molecular-scale information of W indicates that the negatively-charged WO 4 2− ion mainly adsorbs on the negatively-charged Mn oxides phase in natural Ferromanganese oxides due to the strong chemical interaction. In addition, preferential adsorption of lighter W isotopes is expected based on the molecular symmetry of the adsorbed species, implying the potential significance of the W isotope systems similar to Mo. Adsorption experiments of W on synthetic ferrihydrite and δ-MnO 2 were also conducted. At higher equilibrium concentration, W exhibits behaviors similar to Mo on δ-MnO 2 due to their formations of inner-sphere complexes. On the other hand, W shows a much larger adsorption on ferrihydrite than Mo. This is due to the formation of the inner- and outer-sphere complexes for W and Mo on ferrihydrite, respectively. Considering the lower equilibrium concentration such as in oxic seawater, however, the enrichment of W into natural Ferromanganese oxides larger than Mo may be controlled by the different stabilities of their inner-sphere complexes on the Mn oxides. These two factors, (i) the stability of inner-sphere complexes on the Mn oxides and (ii) the mode of attachment on ferrihydrite (inner- or outer-sphere complex), are the causes of the different behaviors of W and Mo on the surface of the Fe/Mn (oxyhydr)oxides.
Shingo Kato - One of the best experts on this subject based on the ideXlab platform.
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continuous growth of hydrogenetic Ferromanganese crusts since 17 myr ago on takuyo daigo seamount nw pacific at water depths of 800 5500 m
Ore Geology Reviews, 2017Co-Authors: Akira Usui, Teruhiko Kashiwabara, Aya Sakaguchi, Keisuke Nishi, Hisaaki Sato, Yoshio Nakasato, Blair Thornton, Ayaka Tokumaru, Kyoko Yamaoka, Shingo KatoAbstract:Ferromanganese crusts cover all outcrops on Takuyo-Daigo seamount traversed during remotely operated underwater vehicle (ROV) dives, except in places covered by foraminifera sand. Takuyo-Daigo is a Cretaceous seamount located in the northwest Pacific Ocean. Geological and bathymetric mapping provide the framework for this study. Chemical and mineralogical analyses of the hydrogenetic Ferromanganese crusts show temporal and spatial variations typical of those found in previous studies. Outcrops from 800 to 5500 m water depths are covered with Ferromanganese crusts up to 105 mm thick. Beryllium isotope dating shows that the crusts have apparently been growing continuously at all water depths, even through the modern oxygen minimum zone (OMZ), contrary to some earlier models for deposition. Growth rates vary from 2.3 to 3.5 mm/Myr, with Fe or Mn fluxes of 0.07–0.11 g/cm2/Myr since the early-middle Miocene. Co/Mn ratios decrease with water depth while Fe/Mn and other metallic elements increase or show no change, based on the analysis of the uppermost crust surface. This is probably because Co is the most abundant redox-sensitive element derived from seawater that occurs in crusts.
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molecular characterization of the microbial community in hydrogenetic Ferromanganese crusts of the takuyo daigo seamount northwest pacific
Fems Microbiology Letters, 2011Co-Authors: Shota Nitahara, Akira Usui, Shingo Kato, Tetsuro Urabe, Akihiko YamagishiAbstract:The abundance and phylogenetic diversity of the microbial community in the hydrogenetic Ferromanganese crust, sandy sediment and overlying seawater were investigated using a culture-independent molecular analysis based on the 16S rRNA gene. These samples were carefully collected from the Takuyo-Daigo Seamount, located in the northwest Pacific Ocean, by a remotely operated vehicle. Based on quantitative PCR analysis, Archaea occupy a significant portion of the prokaryotic communities in the Ferromanganese crust and the sediment samples, while Bacteria dominated in the seawater samples. Phylotypes belonging to Gammaproteobacteria and to Marine group I (MGI) Crenarchaeota were abundant in clone libraries constructed from the Ferromanganese crust and sediment samples, while those belonging to Alphaproteobacteria were abundant in that from the seawater sample. Comparative analysis indicates that over 80% of the total phylotype richness estimates for the crust community were unique as compared with the sediment and seawater communities. Phylotypes related to Nitrosospira belonging to the Betaproteobacteria and those related to Nitrosopumilus belonging to MGI Crenarchaeota were detected in the Ferromanganese crust, suggesting that these ammonia-oxidizing chemolithoautotrophs play a role as primary producers in the microbial ecosystem of hydrogenetic Ferromanganese crusts that was formed as precipitates from seawater.
Teruhiko Kashiwabara - One of the best experts on this subject based on the ideXlab platform.
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enrichment mechanisms of antimony and arsenic in marine Ferromanganese oxides insights from the structural similarity
Geochimica et Cosmochimica Acta, 2019Co-Authors: Soichiro Uesugi, Teruhiko Kashiwabara, Akira Usui, Takaaki Itai, Shitong Yang, Masato Tanaka, Yoshio TakahashiAbstract:Abstract Marine Ferromanganese crusts and nodules as potential mineral deposits have received increasing attention. However, much less knowledge is available concerning the incorporation and enrichment mechanisms for antimony (Sb) and arsenic (As) in marine Ferromanganese oxides. In this study, the surface complexations of Sb(V) and As(V) on synthetic ferrihydrite and Mn oxides (δ-MnO2 and birnessite) were investigated by a combination of adsorption experiments, extended X-ray absorption fine structure (EXAFS) analyses, and quantum chemical calculations. The speciation, distribution, and local structure of Sb and As in different types of natural marine Ferromanganese oxides were determined by X-ray absorption near edge structure (XANES) and EXAFS analyses to reveal the enrichment mechanisms for the two elements in Ferromanganese oxides at the molecular level. To the best of our knowledge, the Sb EXAFS analyses for different types of marine Ferromanganese oxides are herein reported for the first time. Results showed that Sb(V) is preferentially adsorbed on Mn oxides through energetically favorable bidentate–mononuclear complexation because of the structural similarity between the octahedron SbV(OH)6− and MnO6 unit, although bidentate–binuclear (corner-sharing) and bidentate–mononuclear (edge-sharing) complexes can be formed on ferrihydrite and Mn oxides for the adsorption of Sb(V). By contrast, tetrahedral AsVO43− is mostly adsorbed on ferrihydrite and Mn oxides with the formation of bidentate–binuclear complexes. In natural marine Ferromanganese oxides, Sb and As can be retained by Fe and Mn (oxyhydr)oxide components, and the disparate distribution of the two elements to Mn oxides may largely depend on the Mn/Fe ratio and constituent minerals. The larger enrichment factor of Sb than that of As in marine Ferromanganese oxides may result from their preferential attachment modes onto the Fe and Mn phases and different inhibition effects from coexisting anions in seawater. Compared with As, a part of Sb may be strongly associated with the lateral sites in Mn oxides via the formation of bidentate edge-sharing complexes, with which anions such as sulfate in seawater do not significantly compete. The findings from this study provide the molecular-scale insights into the enrichment processes and mechanisms of Sb and As in marine Ferromanganese oxides. Our study also helps elucidate the incorporation mechanisms and geochemical behaviors of other oxyanions in marine and surface environments.
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comparison of arsenate and molybdate speciation in hydrogenetic Ferromanganese nodules
Egyptian Computer Science Journal, 2019Co-Authors: Shitong Yang, Teruhiko Kashiwabara, Akira Usui, Soichiro Uesugi, Masato Tanaka, Minako Kurisu, Chihiro Miyamoto, Yoshio TakahashiAbstract:Marine Ferromanganese oxides contain a large amount of trace elements, such as arsenic (As) and molybdenum (Mo). However, the host phases of tetrahedral AsO43– and MoO42– oxyanions therein have not been clearly identified thus far. In this work, we explored the mineralogical components of hydrogenetic (HG) Ferromanganese nodules and compared the distribution behaviors of As and Mo. The X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS) analyses showed that the predominant manganese and iron phases were vernadite (δ-MnO2) and ferrihydrite, respectively. According to the sequential extraction examination, both As and Mo were associated with the iron (oxyhydr)oxide phases. However, the XAS analyses indicated that As was retained by the ferrihydrite phase via double corner-shared complexation, while Mo was preferentially adsorbed on δ-MnO2 via edge-shared complexation. The immobilization of As and Mo by HG Ferromanganese samples was attributed to specific chemical binding (ΔGchem) rather than Cou...
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continuous growth of hydrogenetic Ferromanganese crusts since 17 myr ago on takuyo daigo seamount nw pacific at water depths of 800 5500 m
Ore Geology Reviews, 2017Co-Authors: Akira Usui, Teruhiko Kashiwabara, Aya Sakaguchi, Keisuke Nishi, Hisaaki Sato, Yoshio Nakasato, Blair Thornton, Ayaka Tokumaru, Kyoko Yamaoka, Shingo KatoAbstract:Ferromanganese crusts cover all outcrops on Takuyo-Daigo seamount traversed during remotely operated underwater vehicle (ROV) dives, except in places covered by foraminifera sand. Takuyo-Daigo is a Cretaceous seamount located in the northwest Pacific Ocean. Geological and bathymetric mapping provide the framework for this study. Chemical and mineralogical analyses of the hydrogenetic Ferromanganese crusts show temporal and spatial variations typical of those found in previous studies. Outcrops from 800 to 5500 m water depths are covered with Ferromanganese crusts up to 105 mm thick. Beryllium isotope dating shows that the crusts have apparently been growing continuously at all water depths, even through the modern oxygen minimum zone (OMZ), contrary to some earlier models for deposition. Growth rates vary from 2.3 to 3.5 mm/Myr, with Fe or Mn fluxes of 0.07–0.11 g/cm2/Myr since the early-middle Miocene. Co/Mn ratios decrease with water depth while Fe/Mn and other metallic elements increase or show no change, based on the analysis of the uppermost crust surface. This is probably because Co is the most abundant redox-sensitive element derived from seawater that occurs in crusts.
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Chemical processes for the extreme enrichment of tellurium into marine Ferromanganese oxides
Geochimica et Cosmochimica Acta, 2014Co-Authors: Teruhiko Kashiwabara, Akira Usui, Yasuko Oishi, Aya Sakaguchi, Toshiki Sugiyama, Yoshio TakahashiAbstract:Abstract Tellurium, an element of growing economic importance, is extremely enriched in marine Ferromanganese oxides. We investigated the mechanism of this enrichment using a combination of spectroscopic analysis and adsorption/coprecipitation experiments. X-ray Absorption Near-Edge Structure (XANES) analysis showed that in adsorption/coprecipitation systems, Te(IV) was oxidized on δ-MnO 2 and not oxidized on ferrihydrite. Extended X-ray Absorption Fine Structure (EXAFS) analysis showed that both Te(IV) and Te(VI) were adsorbed on the surface of δ-MnO 2 and ferrihydrite via formation of inner-sphere complexes. In addition, Te(VI) can be structurally incorporated into the linkage of Fe octahedra through a coprecipitation process because of its molecular geometry that is similar to the Fe octahedron. The largest distribution coefficient obtained in the adsorption/coprecipitation experiments was for the Te(VI)/ferrihydrite coprecipitation system, and it was comparable to those calculated from the distribution between natural Ferromanganese oxides and seawater. Our XAFS and micro-focused X-ray fluorescence (μ-XRF) mapping of natural Ferromanganese oxides showed that Te was structurally incorporated as Te(VI) in Fe (oxyhydr)oxide phases. We conclude that the main process for the enrichment of Te in Ferromanganese oxides is structural incorporation of Te(VI) into Fe (oxyhydr)oxide phases through coprecipitation. This mechanism can explain the unique degree of enrichment of Te compared with other oxyanions, which are mainly enriched via adsorption on the surface of the solid structures. In particular, the great contrast in the distributions of Te and Se is caused by their oxidized species: (i) the similar geometry of the Te(VI) molecule to Fe octahedron, and (ii) quite soluble nature of Se(VI). Coexisting Mn oxide phases may promote structural incorporation of Te(VI) by oxidation of Te(IV), although the surface oxidation itself may not work as the critical enrichment process as in the case of some cations. This enrichment mechanism also means that Ferromanganese oxides mainly scavenge dominant Te(VI) species from seawater and do not affect its species distribution in seawater, as described in a previous model. The variation in Te abundances and the correlation of Te concentration with the growth rate of natural Ferromanganese oxides are consistent with the coprecipitation mechanism.
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tungsten species in natural Ferromanganese oxides related to its different behavior from molybdenum in oxic ocean
Geochimica et Cosmochimica Acta, 2013Co-Authors: Teruhiko Kashiwabara, Yoshio Takahashi, Tomoya Uruga, Matthew A Marcus, Hajime Tanida, Yasuko Terada, Akira UsuiAbstract:Abstract The tungsten (W) species in marine Ferromanganese oxides were investigated by wavelength dispersive XAFS method. We found that the W species are in distorted O h symmetry in natural Ferromanganese oxides. The host phase of W is suggested to be Mn oxides by μ-XRF mapping. We also found that the W species forms inner-sphere complexes in hexavalent state and distorted O h symmetry on synthetic ferrihydrite, goethite, hematite, and δ-MnO 2 . The molecular-scale information of W indicates that the negatively-charged WO 4 2− ion mainly adsorbs on the negatively-charged Mn oxides phase in natural Ferromanganese oxides due to the strong chemical interaction. In addition, preferential adsorption of lighter W isotopes is expected based on the molecular symmetry of the adsorbed species, implying the potential significance of the W isotope systems similar to Mo. Adsorption experiments of W on synthetic ferrihydrite and δ-MnO 2 were also conducted. At higher equilibrium concentration, W exhibits behaviors similar to Mo on δ-MnO 2 due to their formations of inner-sphere complexes. On the other hand, W shows a much larger adsorption on ferrihydrite than Mo. This is due to the formation of the inner- and outer-sphere complexes for W and Mo on ferrihydrite, respectively. Considering the lower equilibrium concentration such as in oxic seawater, however, the enrichment of W into natural Ferromanganese oxides larger than Mo may be controlled by the different stabilities of their inner-sphere complexes on the Mn oxides. These two factors, (i) the stability of inner-sphere complexes on the Mn oxides and (ii) the mode of attachment on ferrihydrite (inner- or outer-sphere complex), are the causes of the different behaviors of W and Mo on the surface of the Fe/Mn (oxyhydr)oxides.
Yoshio Takahashi - One of the best experts on this subject based on the ideXlab platform.
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enrichment mechanisms of antimony and arsenic in marine Ferromanganese oxides insights from the structural similarity
Geochimica et Cosmochimica Acta, 2019Co-Authors: Soichiro Uesugi, Teruhiko Kashiwabara, Akira Usui, Takaaki Itai, Shitong Yang, Masato Tanaka, Yoshio TakahashiAbstract:Abstract Marine Ferromanganese crusts and nodules as potential mineral deposits have received increasing attention. However, much less knowledge is available concerning the incorporation and enrichment mechanisms for antimony (Sb) and arsenic (As) in marine Ferromanganese oxides. In this study, the surface complexations of Sb(V) and As(V) on synthetic ferrihydrite and Mn oxides (δ-MnO2 and birnessite) were investigated by a combination of adsorption experiments, extended X-ray absorption fine structure (EXAFS) analyses, and quantum chemical calculations. The speciation, distribution, and local structure of Sb and As in different types of natural marine Ferromanganese oxides were determined by X-ray absorption near edge structure (XANES) and EXAFS analyses to reveal the enrichment mechanisms for the two elements in Ferromanganese oxides at the molecular level. To the best of our knowledge, the Sb EXAFS analyses for different types of marine Ferromanganese oxides are herein reported for the first time. Results showed that Sb(V) is preferentially adsorbed on Mn oxides through energetically favorable bidentate–mononuclear complexation because of the structural similarity between the octahedron SbV(OH)6− and MnO6 unit, although bidentate–binuclear (corner-sharing) and bidentate–mononuclear (edge-sharing) complexes can be formed on ferrihydrite and Mn oxides for the adsorption of Sb(V). By contrast, tetrahedral AsVO43− is mostly adsorbed on ferrihydrite and Mn oxides with the formation of bidentate–binuclear complexes. In natural marine Ferromanganese oxides, Sb and As can be retained by Fe and Mn (oxyhydr)oxide components, and the disparate distribution of the two elements to Mn oxides may largely depend on the Mn/Fe ratio and constituent minerals. The larger enrichment factor of Sb than that of As in marine Ferromanganese oxides may result from their preferential attachment modes onto the Fe and Mn phases and different inhibition effects from coexisting anions in seawater. Compared with As, a part of Sb may be strongly associated with the lateral sites in Mn oxides via the formation of bidentate edge-sharing complexes, with which anions such as sulfate in seawater do not significantly compete. The findings from this study provide the molecular-scale insights into the enrichment processes and mechanisms of Sb and As in marine Ferromanganese oxides. Our study also helps elucidate the incorporation mechanisms and geochemical behaviors of other oxyanions in marine and surface environments.
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comparison of arsenate and molybdate speciation in hydrogenetic Ferromanganese nodules
Egyptian Computer Science Journal, 2019Co-Authors: Shitong Yang, Teruhiko Kashiwabara, Akira Usui, Soichiro Uesugi, Masato Tanaka, Minako Kurisu, Chihiro Miyamoto, Yoshio TakahashiAbstract:Marine Ferromanganese oxides contain a large amount of trace elements, such as arsenic (As) and molybdenum (Mo). However, the host phases of tetrahedral AsO43– and MoO42– oxyanions therein have not been clearly identified thus far. In this work, we explored the mineralogical components of hydrogenetic (HG) Ferromanganese nodules and compared the distribution behaviors of As and Mo. The X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS) analyses showed that the predominant manganese and iron phases were vernadite (δ-MnO2) and ferrihydrite, respectively. According to the sequential extraction examination, both As and Mo were associated with the iron (oxyhydr)oxide phases. However, the XAS analyses indicated that As was retained by the ferrihydrite phase via double corner-shared complexation, while Mo was preferentially adsorbed on δ-MnO2 via edge-shared complexation. The immobilization of As and Mo by HG Ferromanganese samples was attributed to specific chemical binding (ΔGchem) rather than Cou...
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Chemical processes for the extreme enrichment of tellurium into marine Ferromanganese oxides
Geochimica et Cosmochimica Acta, 2014Co-Authors: Teruhiko Kashiwabara, Akira Usui, Yasuko Oishi, Aya Sakaguchi, Toshiki Sugiyama, Yoshio TakahashiAbstract:Abstract Tellurium, an element of growing economic importance, is extremely enriched in marine Ferromanganese oxides. We investigated the mechanism of this enrichment using a combination of spectroscopic analysis and adsorption/coprecipitation experiments. X-ray Absorption Near-Edge Structure (XANES) analysis showed that in adsorption/coprecipitation systems, Te(IV) was oxidized on δ-MnO 2 and not oxidized on ferrihydrite. Extended X-ray Absorption Fine Structure (EXAFS) analysis showed that both Te(IV) and Te(VI) were adsorbed on the surface of δ-MnO 2 and ferrihydrite via formation of inner-sphere complexes. In addition, Te(VI) can be structurally incorporated into the linkage of Fe octahedra through a coprecipitation process because of its molecular geometry that is similar to the Fe octahedron. The largest distribution coefficient obtained in the adsorption/coprecipitation experiments was for the Te(VI)/ferrihydrite coprecipitation system, and it was comparable to those calculated from the distribution between natural Ferromanganese oxides and seawater. Our XAFS and micro-focused X-ray fluorescence (μ-XRF) mapping of natural Ferromanganese oxides showed that Te was structurally incorporated as Te(VI) in Fe (oxyhydr)oxide phases. We conclude that the main process for the enrichment of Te in Ferromanganese oxides is structural incorporation of Te(VI) into Fe (oxyhydr)oxide phases through coprecipitation. This mechanism can explain the unique degree of enrichment of Te compared with other oxyanions, which are mainly enriched via adsorption on the surface of the solid structures. In particular, the great contrast in the distributions of Te and Se is caused by their oxidized species: (i) the similar geometry of the Te(VI) molecule to Fe octahedron, and (ii) quite soluble nature of Se(VI). Coexisting Mn oxide phases may promote structural incorporation of Te(VI) by oxidation of Te(IV), although the surface oxidation itself may not work as the critical enrichment process as in the case of some cations. This enrichment mechanism also means that Ferromanganese oxides mainly scavenge dominant Te(VI) species from seawater and do not affect its species distribution in seawater, as described in a previous model. The variation in Te abundances and the correlation of Te concentration with the growth rate of natural Ferromanganese oxides are consistent with the coprecipitation mechanism.
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tungsten species in natural Ferromanganese oxides related to its different behavior from molybdenum in oxic ocean
Geochimica et Cosmochimica Acta, 2013Co-Authors: Teruhiko Kashiwabara, Yoshio Takahashi, Tomoya Uruga, Matthew A Marcus, Hajime Tanida, Yasuko Terada, Akira UsuiAbstract:Abstract The tungsten (W) species in marine Ferromanganese oxides were investigated by wavelength dispersive XAFS method. We found that the W species are in distorted O h symmetry in natural Ferromanganese oxides. The host phase of W is suggested to be Mn oxides by μ-XRF mapping. We also found that the W species forms inner-sphere complexes in hexavalent state and distorted O h symmetry on synthetic ferrihydrite, goethite, hematite, and δ-MnO 2 . The molecular-scale information of W indicates that the negatively-charged WO 4 2− ion mainly adsorbs on the negatively-charged Mn oxides phase in natural Ferromanganese oxides due to the strong chemical interaction. In addition, preferential adsorption of lighter W isotopes is expected based on the molecular symmetry of the adsorbed species, implying the potential significance of the W isotope systems similar to Mo. Adsorption experiments of W on synthetic ferrihydrite and δ-MnO 2 were also conducted. At higher equilibrium concentration, W exhibits behaviors similar to Mo on δ-MnO 2 due to their formations of inner-sphere complexes. On the other hand, W shows a much larger adsorption on ferrihydrite than Mo. This is due to the formation of the inner- and outer-sphere complexes for W and Mo on ferrihydrite, respectively. Considering the lower equilibrium concentration such as in oxic seawater, however, the enrichment of W into natural Ferromanganese oxides larger than Mo may be controlled by the different stabilities of their inner-sphere complexes on the Mn oxides. These two factors, (i) the stability of inner-sphere complexes on the Mn oxides and (ii) the mode of attachment on ferrihydrite (inner- or outer-sphere complex), are the causes of the different behaviors of W and Mo on the surface of the Fe/Mn (oxyhydr)oxides.
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molecular scale mechanisms of distribution and isotopic fractionation of molybdenum between seawater and Ferromanganese oxides
Geochimica et Cosmochimica Acta, 2011Co-Authors: Teruhiko Kashiwabara, Masaharu Tanimizu, Yoshio Takahashi, Akira UsuiAbstract:Abstract The distribution of Mo between seawater and marine Ferromanganese oxides has great impacts on concentration and isotopic composition of Mo in modern oxic seawater. To reveal the adsorption chemistry of Mo to Ferromanganese oxides, we performed (i) detailed structural analyses of Mo surface complexes on δ-MnO2, ferrihydrite, and hydrogenetic Ferromanganese oxides by L3- and K-edge XAFS, and (ii) adsorption experiments of Mo to δ-MnO2 and ferrihydrite over a wide range of pHs, ionic strengths, and Mo concentrations. XAFS analyses revealed that Mo forms distorted octahedral (Oh) inner-sphere complexes on δ-MnO2 whereas it forms a tetrahedral (Td) outer-sphere complex on ferrihydrite. In the hydrogenetic Ferromanganese oxides, the dominant host phase of Mo was revealed to be δ-MnO2. These structural information are consistent with the macroscopic behaviors of Mo in adsorption experiments, and Mo concentration in modern oxic seawater can be explained by the equilibrium adsorption reaction on δ-MnO2. In addition, the large isotopic fractionation of Mo between seawater and Ferromanganese oxides detected in previous studies can be explained by the structural difference between MoO 4 2 - and adsorbed species on the δ-MnO2 phase in Ferromanganese oxides. In contrast, smaller fractionation of Mo isotopes on ferrihydrite is due to little change in the Mo local structures during its adsorption to ferrihydrite. The structures of Mo species adsorbed on crystalline Fe (oxyhydr)oxides, goethite, and hematite were also investigated at pH 8 and I = 0.70 M (NaNO3). Our XAFS analyses revealed that Mo forms inner-sphere complexes on both minerals: Td edge-sharing (46%) and Oh double corner-sharing (54%) for goethite, and Td double corner-sharing (14%) and Oh edge-sharing (86%) for hematite. These structural information, combined with those for amorphous ferrihydrite and δ-MnO2, show the excellent correlation with the magnitude of adsorptive isotopic fractionation of Mo reported in previous studies: the proportion of Oh species or their magnitude of distortion in Mo surface complexes become larger in the order of ferrihydrite Based on the comparison with previous reports for Mo surface species on various oxides, the chemical factors that affect Mo surface complex structures were also discussed. The hydrolysis constant of cation in oxides, log KOH (or the acidity of the oxide surfaces, PZC) is well correlated with the mode of attachment (inner- or outer-sphere) of Mo surface complexes. Furthermore, the symmetric change in Mo species from Td to Oh is suggested to be driven by the formation of inner-sphere complexes on specific sites of the oxide surfaces.
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molecular characterization of the microbial community in hydrogenetic Ferromanganese crusts of the takuyo daigo seamount northwest pacific
Fems Microbiology Letters, 2011Co-Authors: Shota Nitahara, Akira Usui, Shingo Kato, Tetsuro Urabe, Akihiko YamagishiAbstract:The abundance and phylogenetic diversity of the microbial community in the hydrogenetic Ferromanganese crust, sandy sediment and overlying seawater were investigated using a culture-independent molecular analysis based on the 16S rRNA gene. These samples were carefully collected from the Takuyo-Daigo Seamount, located in the northwest Pacific Ocean, by a remotely operated vehicle. Based on quantitative PCR analysis, Archaea occupy a significant portion of the prokaryotic communities in the Ferromanganese crust and the sediment samples, while Bacteria dominated in the seawater samples. Phylotypes belonging to Gammaproteobacteria and to Marine group I (MGI) Crenarchaeota were abundant in clone libraries constructed from the Ferromanganese crust and sediment samples, while those belonging to Alphaproteobacteria were abundant in that from the seawater sample. Comparative analysis indicates that over 80% of the total phylotype richness estimates for the crust community were unique as compared with the sediment and seawater communities. Phylotypes related to Nitrosospira belonging to the Betaproteobacteria and those related to Nitrosopumilus belonging to MGI Crenarchaeota were detected in the Ferromanganese crust, suggesting that these ammonia-oxidizing chemolithoautotrophs play a role as primary producers in the microbial ecosystem of hydrogenetic Ferromanganese crusts that was formed as precipitates from seawater.