京都大学 / 0048 / 新制・課程博士 / 博士(地球環境学) / 甲第18435号 / 地環博第117号 / 新制||地環||23(附属図書館) / 31293 / 京都大学大学院地球環境学舎地球環境学専攻 / (主査)教授 勝見 武, 教授 高岡 昌輝, 准教授 乾 徹 / 学位規則第4条第1項該当 / Doctor of Global Environmental Studies / Kyoto University / DFAM

Iron (Fe) oxy-hydroxides such as ferrihydrite (Fh) are ubiquitous in surface environments. Because of their high surface area and high reactive surface, they can immobilize environmental contaminants and nutrients (e.g., oxyanions) through adsorption. Ferrihydrite is metastable and eventually transforms to hematite (Hm), goethite (Gt), and lepidocrocite (Lp). Although the Fh formation and transformation and oxyanion adsorption on its surface have been separately studied, the coupled interaction of these processes is only partly understood. The impact of oxyanion surface complexes on the rate and pathway of Fh transformation was studied. Results show that AsO43- and SO42- inner-sphere complexes decrease the rate of Fh transformation and induce the formation of Hm. In contrast, NO3- outer-sphere complexes promote the formation of Gt. We then investigated the impact of oxyanion (AsO43- and PO43-) surface loading on the rate and pathway of Fh transformation. The results show that the rate of Fh transformation decreases, and more Hm forms with increasing the oxyanion surface loading. Cryogenic transmission electron microscopy (Cryo-TEM) was also used to study the effect of oxyanion surface complexes (NO3- and PO43-) on the nucleation and growth of Gt and Hm during Fh transformation. Our results show that Gt first was formed from Fh dissolution and then grew by oriented attachment. In contrast, Hm formed after the aggregation of Fh particles. We propose that NO3- outer-sphere complexes hydrate the surface and promote the Gt formation through a dissolution/crystallization pathway, while PO43- inner-sphere complexes dehydrate the surface and induce more Hm through an aggregation pathway. In the final project, we investigated the formation of Fh from Fe oxy-hydroxide clusters. The results showed that increasing pH increased the size and structural order of particles that resemble 2-line Fh. Also, the particle size of aged samples at pHs 1.5 and 2.5 increased with time, and they transformed to Gt and Lp. In this work, we develop new ways to study the formation and transformation of Fh. These methods and information can be used to develop further studies towards a comprehensive understanding of Fh formation and transformation in other environmental conditions, such as redox systems. / Doctor of Philosophy / Iron (Fe) oxy-hydroxides nanoparticles are composed of Fe, oxygen (O), and water (H2O). One of the most famous Fe nanoparticles is ferrihydrite (Fh), which is commonly found in soils, sediments, and water. Ferrihydrite surface is positively charged and adsorbs negatively charged ions such as oxyanions, which are important contaminants (e.g., arsenate; AsO43- and sulfate; SO42) and nutrients (e.g., phosphate; PO43- and nitrate; NO3-) in drinking water in the US and around the world. The structure of Fh is not stable, and it transforms to other Fe oxy-hydroxides such as goethite (Gt), hematite (Hm), and lepidocrocite (Lp). Pre-adsorbed oxyanions may release during Fh transformation and impact water and soil quality. Additionally, oxyanion adsorption may affect the formation and transformation of Fh, which is not fully understood. In this work, we investigate how oxyanions change the rate and pathway of Fh transformation. The results show that the strong binding of AsO43- and SO42- slows down the rate of Fh transformation and favors the formation of Hm as opposed to Gt. While weak adsorption of NO3- promotes the formation of more Gt. We also study the transformation of Fh in the presence of different oxyanions (AsO43- and PO43-) concentrations. The results show that the rate at which Fh transforms to Gt and Hm decreases, and more Hm forms with increasing the concentration of oxyanions on the Fh surface. Interestingly, results also show that weekly bounded NO3- and SO42- could be released to the solution phase, while strongly adsorbed AsO43- and PO43- could remain on the surface during the ferrihydrite transformation. We also used an imaging technique (Cryogenic transmission electron microscopy; Cryo-TEM) to study the effect of oxyanion surface complexes (NO3- and PO43-) on the formation and growth of Gt and Hm during the Fh transformation. The results show that Gt first was formed from Fh and then grew to larger particles. In contrast, for the formation of Hm, Fh particles first aggregate, form larger particles, and then transform to Hm. In the final project, we investigate the formation of Fh from Fe oxy-hydroxide cluster precursors. Results show that Fe oxy-hydroxide clusters can be the potential precursors for forming Fh during the rapid hydrolysis of Fe(III) solutions. However, when these precursors are aged, they do not form Fh and transform to Gt and Lp, which have stable structures. In this work, we develop new ways to study the formation and transformation of Fh, which will have implications for understanding how and when contaminant remobilization will occur during Fh formation and transformation.

The complex interactions at the interfaces of minerals, microbes, and metals drive the cycling of iron and the fate and transport of metal(loid)s in contaminated systems. The former uranium mine near Ronneburg, Germany is one such system, where slightly acidic mine drainage crossing a steep redox gradient (groundwater outflow into a stream) forms and transforms iron (oxy)hydroxide nanoparticles. These particles interact with toxic metal(loid)s in water and sediments. Iron oxidizing and reducing bacteria also play a role in these processes. Biogeochemical reactions are influenced by nanoscale properties, and thus it is critical to probe environmental samples with appropriate techniques such as analytical transmission electron microscopy (TEM). This dissertation presents two studies on the iron (oxy)hydroxide mineral nanoparticles found in the Ronneburg mine drainage system. The first study uses TEM in conjunction with bulk analytical techniques to demonstrate the complexity of iron (oxy)hydroxide transformations at the steep redox gradient, and the partitioning of metal(loid)s within those mineral phases. An important result was the identification of Zn-bearing green rust platelets in the anoxic outflow water. Green rust minerals have only been identified in nature a handful of times, and we believe this work to be only the second to examine naturally occurring green rust using high resolution TEM (HR-TEM). Downstream of the outflow, aggregates of poorly crystalline iron oxide spheroids co-precipitated with amorphous silica formed and settled to the stream bed, where they aged to form nanoparticulate goethite and sequestered metals such as As and Zn. However, significant concentrations of Zn and Ni remained in the dissolved/nano (< 0.1 um) water fraction and continued downstream. The second study demonstrates that natural green rust nanoparticles and their synthetic analogs can be complex polycrystalline phases composed of crystallites only a few nanometers in size, and often include nano-regions of amorphous material. In addition to the typical pseudo-hexagonal platelet morphology, green rust nanorods were synthesized, which has not previously been reported. This work has important implications for the reactivity of green rust with biogeochemical interfaces in natural, anthropogenic, and industrial systems. A third study, presented in the appendix, characterizes the bacterial community at the Ronneburg mine drainage site and highlights iron oxidizers such as Gallionella sp., in particular those that form stalks of iron oxide nanoparticles. These biogenic stalks also contribute to the uptake of metal contaminants in water and sediments. The science of iron cycling is complex. It requires field-based exploration to enrich the contributions made by experimental, laboratory and modeling studies. This dissertation adds another chapter in the search for filling in missing pieces of this interconnected system. / Ph. D.

L’étude des formations de fer rubané (BIF) permet de comprendre les conditions des océans de et de l’atmosphère terrestres au cours de l’Archéen et du début du Protérozoïque. L’objectif de cette thèse est de fournir une analyse minéralogique et géochimique détaillée de BIFs de deux localités distinctes, séparées par la frontière Archéen-Protérozoïque. Une attention particulière est portée à la minéralogie de leurs carbonates et oxydes de fer. Les BIFs de 2,7 Ga de la formation Manjeri, Zimbabwe et de 2,4 Ga du Groupe Itabira, Brésil, ont dans les deux cas été précipités par mélange de fluides hydrothermaux marins oxygénés. Ceci est démontré par la présence d’inclusions de nano-hématite dans les lames de chert (Itabira et Manjeri) et de dolomite (Itabira seulement), qui sont interprétées comme la phase minérale la plus ancienne dans les échantillons. En outre, la microscopie électronique à transmission à faisceau d’ions focalisé (FIB-TEM) révèle la présence de plaquettes de nano ferrihydrite dans les BIF dolomitiques (carbonate d’itabirite). La dolomite est interprétée comme étant une phase primaire précipitée à des températures plus élevées (~100°C) de fluides hydrothermaux riches en CO2. Des anomalies positives en Eu dans les deux formations indiquent une composante hydrothermale, susceptible d’être la source du fer réduit. Les changements de faciès dans les deux unités sont le résultat de transgression/régression; et des évènements hydrothermaux post dépôt masquent les conditions primaires. Les carbonates riches en fer dans les deux faciès ont différentes origines: diagénétiques (Itabira) et hydrothermales post dépôt (Manjeri). Toutefois, les carbonates riches en fer des deux formations ont des valeurs négatives de ∂13C, ce qui indique qu’au moins une partie du carbone dans les carbonates est d’origine organique.Des analyses en balance de Curie dans le carbonate d’itabirite révèlent que la maghémite est le produit de transformation de la ferrihydrite lorsque de la dolomite se décompose à ~790°C. La maghémite a une température de Curie comprise entre 320 et 350°C et est stable jusqu’à une température de 925°C. Les analyses en FIB-TEM sur le processus de martitisation ont révélé deux mécanismes possibles à partir de deux échantillons de martite provenant respectivement du Brésil et d’Inde. En fonction de la cause de la martitisation, que nous avons déterminé être soit la déformation soit l’hydrothermalisme, la martitisation se produit respectivement par l’intermédiaire de:1. La réorganisation de défauts ponctuels, pour former des jumeaux. Ces défauts sont causés par les vacances dans la structure spinelle de la maghémite, dues à la suppression des ions Fe3+ en excès au cours de l’oxydation de la magnétite. C’est dans ce jumelage que le mécanisme de martitisation se produit.2. La migration des joints de grains par l’hématite au détriment de la magnétite, qui est due à la présence de fluide le long des interfaces du cristal. La maghémite se forme en raison de l’excès de Fe3+ produit pendant la martitisation de la magnétite, qui se déplace vers la surface des cristaux de magnétite. / It is the study of banded iron formations (BIFs) that provides understanding into the conditions of the Earth’s oceans and atmosphere during the Archean and Early Proterozoic. The aim of this thesis is to provide a detailed mineralogical and geochemical understand of BIFs from two separate localities separated by the Archean Proterozoic boundary. Close attention is paid to their carbonate and iron oxide mineralogy.The BIFs of the 2.7 Ga Manjeri Formation, Zimbabwe and 2.4 Ga Itabira Group, Brazil were both precipitated from oxygenated mixed marine-hydrothermal fluids. This is demonstrated by the presence of nano-hematite inclusions in the chert (Itabira and Manjeri) and dolomite (Itabira only) laminae, which is interpreted as the oldest mineral phase within the samples. Additionally, focused ion beam transmission electron microscopy (FIB-TEM) reveals the presence of nano ferrihydrite platelets within the dolomitic BIFs (carbonate itabirite). The dolomite is interpreted to be a primary phase precipitated at higher temperatures (~100°C) from CO2-rich hydrothermal fluids. Positive Eu anomalies in both formations indicate a hydrothermal component, likely to be the source of the reduced iron. Facies changes in both units are the result of transgression/regression and post depositional hydrothermal events mask primary conditions. Iron-rich carbonates in both facies have different origins; diagenetic (Itabira) and post depositional hydrothermal (Manjeri). However, the iron-rich carbonates of both formations have negative ∂13C values, indicating that at least part of the carbon in the carbonates is of organic origin. Curie Balance analyses into the carbonate itabirite reveals that maghemite is the transformation product of the ferrihydrite when dolomite decomposes at ~790°C. The maghemite has a Curie temperature between 320 and 350°C and is stable up to temperatures of 925°C.FIB-TEM investigations into the martitisation process revealed two possible mechanisms from two martite samples, from Brazil and India. Depending of the cause of the martitisation, here found to be deformation and hydrothermalism, the martitisation occurs respectively via either: 1. Ordering of point defects caused by vacancies in the spinel structure of maghemite, due to the removal of excess Fe3+ ions during the oxidation of magnetite, to form twins. It is in this twinning that the martitisation mechanism occurs.2. Grain boundary migration by hematite at the expense of magnetite is due to the presence of fluid along the crystal interfaces, where maghemite forms due to excess Fe3+ produced during martitisation of the magnetite, moving towards the surface of the magnetite crystals.

Material science is an interdisciplinary area of research, which in part, designs and characterizes new materials. Research is concerned with synthesis, structure, properties, and performance of materials. Discoveries in materials science have significant impact on future technologies, especially in nano-scale applications where the physical properties of nanomaterials are significantly different than their bulk counterparts. The work presented here discusses the use of ferritin, a hollow sphere-like biomolecule, which forms metal oxo-hydride nanoparticles inside its protein shell for uses as a bio-inorganic material.Ferritin is capable of forming and sequestering 8 nm metal-oxide nanoparticles within its 2 nm thick protein shell. A variety of metal-oxide nanoparticles have been synthesized inside ferritin. The work herein focuses on three distinct areas:1) Ferritin's light harvesting properties: namely band gaps. Discrepancies in the band gap energies for ferritin's native ferrihydrite mineral and non-native minerals have been previously reported. Through the use of optical absorption spectroscopy, I resolved the types of band gaps as well as the energy of these band gaps. I show that metal oxides in ferritin are indirect band gap semiconductors which also contain a direct transition. Modifications to the ferrihydrite mineral's band gaps are measured as a result of co-depositing anions into ferritin during iron loading. I demonstrate that these band gaps can be used to photocatalytically reduce gold ions in solution with titanium oxide nanoparticles in ferritin. 2) A new method for manganese mineral synthesis inside ferritin: Comproportionation between permanganate and Mn(II) forms new manganese oxide minerals inside ferritin that are different than traditional manganese oxide mineral synthesis. This reaction creates a MnO2, Mn2O3, or Mn3O4 mineral inside ferritin, depending on the synthesis conditions. 3) Ferritin as an energetic material: Ferritin is capable of sequestering various metals and anions into its interior. Perchlorate, an energetic anion, is sequestered through a co-deposition process during iron loading and is tested with energetic binding materials. Peroxide, which can be used as an oxidant, is also shown to be sequestered within apoferritin and combined with an aluminum based fuel for solid rocket propellants.

Diffuse Layer Modeling was used to describe single and multi-solute adsorption of Pb(II), Cu(II), Zn(II) and Cd(II) to ferrihydrite and As(V), V(V) Si and Ca(II) on granular ferric hydroxide, a commercially available iron oxide. Macroscopic data were used in conjunction with x-ray adsorption spectroscopy (XAS) data to evaluate the diffuse layer surface complexation model (DLM) for predicting sorption over a range of conditions. A self-consistent database was created for each of the adsorbents. The DLM provided excellent fits to the single solute data for the ferrihydrite system with the incorporation of spectroscopic evidence. Little competition was seen in the bisolute systems, except under very high coverages. While the DLM captured the lack of competition under low and medium coverages, competitive effects were not adequately modeled by the updated DLM for high coverages. Challenges remain in adequately describing metal removal when sorption may not be the primary mechanism of removal. The capabilities of the DLM were then evaluated for describing and predicting multisolute sorption to granular ferric hydroxide (GFH). The model can adequately describe anion competition, but the electrostatic effects due to outer sphere sorption were overpredicted, leading to an inadequate model fit for As(V) and Ca²⁺ systems. Despite the limitations of the DLM, it may be an appropriate compromise between goodness of fit and number of parameters for future integration into dynamic transport models and thermodynamic databases. / text

At the Idbäcken combined heat and power (CHP) plant waste wood is combusted. The flue gas from the combustion is condensed and heavy metals and other toxic species ends up in the condensate water. Since the condensate water in this way contains many toxic substances it needs to be treated before it is sent to the recipient Kilaån (the Baltic Sea). Arsenic (As) is one substance that needs to be removed, and this thesis aims to find the optimal conditions for As removal by using precipitation with iron(III) chloride (FeCl3). When FeCl3 comes in contact with water it forms ferrihydrite, an efficient sorbent due to its high specific area. The adsorption of As to ferrihydrite is dependent on different variables; pH, Fe(III) dosage, competitive ions et cetera. Lab-scale experiments have shown that a pH value between 3 and 8 is required for efficient As removal. Concerning the Fe(III) dosage further experiments are needed in order to tell what dosage that is the optimal in this case. Further, the removal of metals has also been studied. A comparison between two chemicals (TMT 15 and MP 7) used for metal removal has been made, which showed that TMT 15 is to prefer for metal removal. Also, it was found that efficient removal of metals require pH &gt; 5, preferably in the slightly alkaline pH range.

Nanotechnology is blossoming into one of the premiere technologies of this century, but the key to its progress lies in developing more efficient nanosynthesis methods. Variations in synthetic technique, however, can cause variations in size, structure, and surface characteristics, thereby altering the physical properties and functionality of the particles. Careful structural characterizations are thus essential for understanding the properties and appropriate applications for particles produced by new synthetic techniques.In this work, a new ‘solvent-deficient’ method is presented for the synthesis of an unprecedentedly wide range of metal oxide nanomaterials including at least one metal oxide from each group in Groups 3-4, 6-15, and the Lanthanides. XRD, BET, and TEM structural characterizations as well as chemical purity analyses of the products are given. The intermediates associated with the method are also investigated, allowing the reaction parameters to be rationalized and culminating in a proposed mechanism for the reaction. Several of the reaction intermediates are themselves useful products, expanding the range of this already versatile method. Optimized synthesis parameters as well as structural characterizations are presented for one such intermediate product, the iron oxyhydroxide called ferrihydrite.The Al2O3 nanoparticles produced by the new method show promise in catalyst support applications, and the synthesis and structural analysis (XRD, X-ray PDF, 27Al NMR, TG/DTA-MS) of these nanoparticles is provided. The XRD, PDF, and NMR analyses reveal that the initial boehmite-like phase transforms to the catalytically useful gamma-Al2O3 phase at unusually low temperatures (300-400°C), but boehmite-like local structure defects remain which heal slowly with increasing temperature up to 800°C. The ‘pure’ gamma-Al2O3 may still contain randomized, non-cubic, local structure distortions, and it transforms directly to alpha-Al2O3 at ~1050°C. To rationalize the local structure and the absence of the delta- and theta-Al2O3 phases during the alpha-phase transition, relationships between the many Al2O3 phases are presented via innovative symmetry-mode analyses, revealing a potential quazi-topotactic mechanism for the gamma-to-alpha transition.To stabilize the gamma-Al2O3 phase to higher temperatures for catalyst applications, 3 wt% of a lanthanum dopant was added via a new, 1-pot process based on the new solvent-deficient method. This process is described and X-ray PDF, TEM, 27Al NMR, and EXAFS analyses of the La-doped gamma-Al2O3 nanoparticles reveal that the dopant resides as isolated, adsorbed atoms on the gamma-Al2O3 surface. The first coordination shell of the isolated La is increasingly La2O3-like as calcination temperature increases but changes drastically to be more LaAlO3-like after the alpha-phase transition, which is delayed ~100°C by the La dopant. Combining the EXAFS, PDF, NMR, and symmetry-mode analyses, we provide new insight into the mechanism of stabilization provided by the La dopant.

No description available.

It is the study of banded iron formations (BIFs) that provides understanding into the conditions of the Earth's oceans and atmosphere during the Archean and Early Proterozoic. The aim of this thesis is to provide a detailed mineralogical and geochemical understand of BIFs from two separate localities separated by the Archean Proterozoic boundary. Close attention is paid to their carbonate and iron oxide mineralogy.The BIFs of the 2.7 Ga Manjeri Formation, Zimbabwe and 2.4 Ga Itabira Group, Brazil were both precipitated from oxygenated mixed marine-hydrothermal fluids. This is demonstrated by the presence of nano-hematite inclusions in the chert (Itabira and Manjeri) and dolomite (Itabira only) laminae, which is interpreted as the oldest mineral phase within the samples. Additionally, focused ion beam transmission electron microscopy (FIB-TEM) reveals the presence of nano ferrihydrite platelets within the dolomitic BIFs (carbonate itabirite). The dolomite is interpreted to be a primary phase precipitated at higher temperatures (~100°C) from CO2-rich hydrothermal fluids. Positive Eu anomalies in both formations indicate a hydrothermal component, likely to be the source of the reduced iron. Facies changes in both units are the result of transgression/regression and post depositional hydrothermal events mask primary conditions. Iron-rich carbonates in both facies have different origins; diagenetic (Itabira) and post depositional hydrothermal (Manjeri). However, the iron-rich carbonates of both formations have negative ∂13C values, indicating that at least part of the carbon in the carbonates is of organic origin. Curie Balance analyses into the carbonate itabirite reveals that maghemite is the transformation product of the ferrihydrite when dolomite decomposes at ~790°C. The maghemite has a Curie temperature between 320 and 350°C and is stable up to temperatures of 925°C.FIB-TEM investigations into the martitisation process revealed two possible mechanisms from two martite samples, from Brazil and India. Depending of the cause of the martitisation, here found to be deformation and hydrothermalism, the martitisation occurs respectively via either: 1. Ordering of point defects caused by vacancies in the spinel structure of maghemite, due to the removal of excess Fe3+ ions during the oxidation of magnetite, to form twins. It is in this twinning that the martitisation mechanism occurs.2. Grain boundary migration by hematite at the expense of magnetite is due to the presence of fluid along the crystal interfaces, where maghemite forms due to excess Fe3+ produced during martitisation of the magnetite, moving towards the surface of the magnetite crystals.