Green rusts (GRs), a group of layered Fe(II)-Fe(III) hydroxide salts, have been observed to be effective reductants for degrading organic and inorganic contaminants under suboxic conditions. Furthermore, the addition of a transition metal to GRs can produce high-activity modified green rusts (HMGRs) that demonstrate higher degradation rates. Methods of modifying GRs to obtain high reactivity for degradation of PCE and nitrate were developed and reduction kinetics of PCE and nitrate by HMGRs were characterized in this study. First, the most promising HMGRs were developed through screening tests. GRs modified with Pt, Cu, Ag, or Pb were found to be effective in improving degradation rates of PCE. GR-F(Pt) and GR-F(Cu) were chosen because they showed high reactivity and produced non-chlorinated by-products. Pt and Cu showed the capability of improving reduction kinetics of nitrate by GRs. GR-F(Pt) and GR-F(Cu) were selected for further study. Second, degradation of PCE by GR-F(Cu) and GR-F(Pt) was characterized using a batch reactor system. The reaction kinetics of PCE degradation by GR-F(Cu) and GR-F(Pt) was strongly dependent on pH over the range of pH 7.5-11, with the fastest rate at pH 11. Increasing concentrations of Cu(II) over the range of 0 to 5 mM resulted in improving the reduction kinetics by a factor of more than 400, although the rate at 7.5 mM of Cu(II) was unexpectedly lower than that at 5 mM. Surface saturation behavior was observed in the rates of dechlorination of PCE by GR-F(Cu). Finally, nitrate reduction by GR-F(Cu) and GR-F(Pt) was further studied to determine the effects on degradation rates of pH, Cu(II) addition, and initial nitrate concentration. A reaction model with four sequential steps was proposed to describe the process of nitrate being reduced to ammonium and GR being oxidized to magnetite. The reaction rates of nitrate reduction by GR-F(Cu) and GR-F(Pt) was highest at pH 9. The reaction rates of GR-NO3 were improved by three orders of magnitude when Cu(II) was added in the range of 0 to 2.5 mM, while reaction rate decreased at concentrations above 2.5 mM. Saturation behavior was also observed in nitrate reduction by GR-F(Cu).

Green rusts (GRs), a group of layered Fe(II)-Fe(III) hydroxide salts, have been observed to be effective reductants for degrading organic and inorganic contaminants under suboxic conditions. Furthermore, the addition of a transition metal to GRs can produce high-activity modified green rusts (HMGRs) that demonstrate higher degradation rates. Methods of modifying GRs to obtain high reactivity for degradation of PCE and nitrate were developed and reduction kinetics of PCE and nitrate by HMGRs were characterized in this study. First, the most promising HMGRs were developed through screening tests. GRs modified with Pt, Cu, Ag, or Pb were found to be effective in improving degradation rates of PCE. GR-F(Pt) and GR-F(Cu) were chosen because they showed high reactivity and produced non-chlorinated by-products. Pt and Cu showed the capability of improving reduction kinetics of nitrate by GRs. GR-F(Pt) and GR-F(Cu) were selected for further study. Second, degradation of PCE by GR-F(Cu) and GR-F(Pt) was characterized using a batch reactor system. The reaction kinetics of PCE degradation by GR-F(Cu) and GR-F(Pt) was strongly dependent on pH over the range of pH 7.5-11, with the fastest rate at pH 11. Increasing concentrations of Cu(II) over the range of 0 to 5 mM resulted in improving the reduction kinetics by a factor of more than 400, although the rate at 7.5 mM of Cu(II) was unexpectedly lower than that at 5 mM. Surface saturation behavior was observed in the rates of dechlorination of PCE by GR-F(Cu). Finally, nitrate reduction by GR-F(Cu) and GR-F(Pt) was further studied to determine the effects on degradation rates of pH, Cu(II) addition, and initial nitrate concentration. A reaction model with four sequential steps was proposed to describe the process of nitrate being reduced to ammonium and GR being oxidized to magnetite. The reaction rates of nitrate reduction by GR-F(Cu) and GR-F(Pt) was highest at pH 9. The reaction rates of GR-NO3 were improved by three orders of magnitude when Cu(II) was added in the range of 0 to 2.5 mM, while reaction rate decreased at concentrations above 2.5 mM. Saturation behavior was also observed in nitrate reduction by GR-F(Cu).

Perchloroethylene (PCE) is a toxic contaminant that has been introduced into the environment over many years through industrial and agricultural wastes. Research has been done in the past to investigate PCE degradation by zero-valent iron (ZVI), green rust (GR) and a mixture of both. The combination of ZVI and green rust has been reported to be more effective for degrading PCE than either of them alone. Forming green rust electrochemically has the potential for depositing GR more effectively on the surface of ZVI where it will be able to more easily transfer electrons from ZVI to contaminants such as PCE. Therefore, the goal of this research was to determine the feasibility of electrochemically depositing green rust on zero-valent iron and to characterize it in terms of its composition, crystal properties and amount produced. XRD analysis was conducted to determine composition and crystal properties and a procedure was developed to measure the amount produced. Equipment was constructed to deposit green rust electrochemically onto ZVI. A chain of experiments with varying voltage, pH, time and amounts of ZVI were conducted to determine feasible experimental conditions for GR formation. Then, a method was developed to accurately measure the amount of surface oxides of iron deposited on the zero-valent iron substrate. This method was tested and found useful for measuring iron in: i) standard solutions of soluble iron with different concentrations of reagents; ii) suspensions with solid iron hydroxides by themselves; and iii) suspensions with solid iron hydroxides and ZVI. Electrochemical experiments were conducted and the amounts of iron hydroxides deposited on the ZVI surface were measured. XRD analysis of the deposits on the surface was conducted and the patterns of XRD-peaks were compared to that of type 2 – sulfate green rust.

Perchloroethylene (PCE) is a toxic contaminant that has been introduced into the environment over many years through industrial and agricultural wastes. Research has been done in the past to investigate PCE degradation by zero-valent iron (ZVI), green rust (GR) and a mixture of both. The combination of ZVI and green rust has been reported to be more effective for degrading PCE than either of them alone. Forming green rust electrochemically has the potential for depositing GR more effectively on the surface of ZVI where it will be able to more easily transfer electrons from ZVI to contaminants such as PCE. Therefore, the goal of this research was to determine the feasibility of electrochemically depositing green rust on zero-valent iron and to characterize it in terms of its composition, crystal properties and amount produced. XRD analysis was conducted to determine composition and crystal properties and a procedure was developed to measure the amount produced. Equipment was constructed to deposit green rust electrochemically onto ZVI. A chain of experiments with varying voltage, pH, time and amounts of ZVI were conducted to determine feasible experimental conditions for GR formation. Then, a method was developed to accurately measure the amount of surface oxides of iron deposited on the zero-valent iron substrate. This method was tested and found useful for measuring iron in: i) standard solutions of soluble iron with different concentrations of reagents; ii) suspensions with solid iron hydroxides by themselves; and iii) suspensions with solid iron hydroxides and ZVI. Electrochemical experiments were conducted and the amounts of iron hydroxides deposited on the ZVI surface were measured. XRD analysis of the deposits on the surface was conducted and the patterns of XRD-peaks were compared to that of type 2 – sulfate green rust.

Iron chemistry plays an important role in our world. At the nanoscale, iron oxide nanoparticles (nanomagnetite) have many inherent physical or chemical characteristics that drive potential solutions to real-world problems; appropriation of nanomagnetite’s properties as a “scaffold” for chemistry would further enhance its effectiveness in applications. In an effort to make use of nanomagnetite’s physical properties, a new “Sulfide Green Rust” (sGR) has been synthesized from magnetic iron nanoparticles. The material is crystalline, reactive due to high iron(II) content, and dissolves in the aqueous phase. Nanomagnetite’s magnetic properties were also observed to persist after sGR synthesis. X-ray absorption spectroscopy (XAS) confirmed the synthesis of this new FeS2-like material. The crystallinity, composition, and various physical characteristics were examined using a host of techniques including X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), Mössbauer spectroscopy, CRYO-TEM, Raman spectroscopy, and ultraviolet-to-visible (UV-Vis) spectroscopy. To demonstrate its use, the material was then subjected to a test of its reactive potential, namely water remediation of an orange dye contaminant. Iron serves a function at the macroscale as well regarding water treatment, since iron coagulation-filtration is the industry standard for arsenic treatment. Determining a technology’s merit as a solution goes beyond technical concern, however, as environmental and economic aspects also play important roles. Life Cycle Analysis, or LCA, methodology works to holistically compare each of these facets from cradle to grave. To address the current arsenic drinking water requirements at a case setting in Hungary, the LCA technique was applied on two example arsenic removal technologies, both coagulation-filtration and adsorption. 9 out of 10 considered impact categories tended to favour coagulation-filtration in this small municipality study, however realistic variations in water chemistry and product characteristics led to some overlap of their environmental impact. Electricity did not have a large direct impact, regeneration of the adsorption technology was very costly, and adsorption’s hazardous waste was not reduced compared to coagulation-filtration. Coagulation-filtration is also the cheaper of the two technologies; its highest cost is that of waste disposal, while the highest single expense modeled is that of adsorption media cost.

Le but de ce travail était de mieux comprendre les mécanismes mis en jeu lors de la corrosion marine des structures en acier. Ces mécanismes impliquant l’influence de micro-organismes vivants, et notamment des bactéries sulfurogènes, l’étude a couplé des méthodes physico-chimiques à des techniques de microbiologie et de biologie moléculaire. Dans un premier temps, un système modèle de laboratoire a été élaboré afin d’étudier en détail les interactions entre les bactéries sulfato-réductrices (BSR) et le principal produit de la corrosion électrochimique des aciers en milieu marin, à savoir la rouille verte sulfatée RV(SO42-). Nous avons ainsi pu reproduire une partie des mécanismes mis en jeu, en montrant que les BSR pouvaient se développer en consommant les ions SO42- issus de la rouille verte et générer ainsi la mackinawite FeS observée sur sites. Dans un deuxième temps, l’évolution de la couche composite « rouille/biofilm » se formant sur acier en milieu marin a été suivie pour des temps courts d’immersion, allant de 1 semaine à deux mois. Le suivi simultané des données microbiologiques et physicochimiques a permis de montrer que l’influence des BSR ne se faisait pratiquement pas sentir à ce stade. Cependant, le développement préférentiel de bactéries associées au fer et au soufre au sein de la couche de rouille a pu être mis en évidence. Par ailleurs, très localement, le processus influencé par les BSR a été détecté. Enfin, une étude électrochimique en solutions désaérées simulant l’eau de mer a été confrontée aux résultats de l’analyse physico-chimique et microbiologique d’un coupon immergé 11 ans en milieu portuaire. L’ensemble des résultats montrent que RV(SO42-) se forme également lorsque des conditions anoxiques sont établies à la surface du métal. La formation de RV(SO42-) entre cependant en compétition avec celle de FeS et Fe3O4 suite aux modifications du milieu que peuvent engendrer les micro-organismes. A ces temps d’immersion long, l’influence des bactéries semblent néanmoins s’amoindrir, les micro-organismes tendant à s’éloigner des strates internes de la couche de rouille et donc du métal pour coloniser des zones externes plus riches en substances nutritives. / The aim of this study was to understand the mechanisms involved in marine corrosion of steel structures. These mechanisms are known to be influenced by micro-organisms, in particular by the sulphide-producing bacteria. It was then necessary to couple physico-chemical investigations with techniques of microbiology and molecular biology. In the first part of this work, a laboratory model was designed so as to study the interactions between sulphate-reducing bacteria (SRB) and the main product of the electrochemical corrosion process of iron in seawater, the sulphated green rust, GR(SO42-). We demonstrated that SRB could grow using only the SO42- ions coming from the green rust, thus generating mackinawite FeS as observed in real marine corrosion cases. In the second part, the evolution of the “rust/biofilm” layer that forms on steel in natural seawater was followed for short immersion times, from 1 week to 2 months. The simultaneous monitoring of microbiological and physico-chemical data showed that the influence of SRB was negligible at those early stages. However, the preferential growth of bacteria associated with iron and sulphur could be detected. Moreover, the process influenced by SRB could be detected locally in one case. Finally, in the third part of this work, an electrochemical study of carbon steel in deaerated seawater-like solutions was compared to the results of the physico-chemical and microbiological characterisation of a steel coupon left 11 years in a harbour site. All the results showed that GR(SO42-) was also forming when anoxic conditions were met at the steel surface. The formation of GR(SO42-) however competes with that of FeS and Fe3O4 due to the modifications of the environment induced by micro-organisms. For such long immersion periods, the influence of bacteria seems to decrease. The micro-organisms tend to move away from the inner parts of the rust layer, and then from the metal, to settle the outer parts where more nutrients are available.

The current proposed method for the long-term management of intermediate and high level radioactive waste in the UK is via geological disposal. It is known that redox sensitive elements such as uranium and neptunium will significantly contribute to the total waste inventory. Recently, studies have indicated that both U and Np can be stabilised by interaction with minerals. Over long periods of time (1000’s -10,000’s years) steel canisters that encase radioactive waste in geodisposal systems will undergo anaerobic corrosion, potentially leading to the release of radionuclides, including U and Np. Anaerobic corrosion will also result in the formation of a number of oxide phases, including iron (oxyhydr)oxides e.g. magnetite and green rust. The interaction of U and Np with such forming iron (oxyhydr)oxides may lead to the sequestering of radionuclides in the environment through a range of processes such as adsorption to a mineral surface and incorporation into a mineral structure. Therefore the interactions between iron (oxyhydr)oxides and radionuclides are important to determine their fate if potentially released within the wider environment. In this study, the fate of U(VI) and Np(V) when in contact with a range of iron (oxyhydr)oxides was considered. These systems were selected to help understand the detailed mechanisms that may occur between radionuclides and iron (oxyhydr)oxides. XRD and TEM were used to characterise mineralogy, whilst acid digestions determined the distribution of U within the mineral phase. Synchrotron based XAS was used to determine oxidation state, site geometry and local bonding environment of the radionuclides associated with the mineral phases. The data suggests that: U(V) is stabilised and incorporated in octahedral coordination into both the magnetite and green rust structure in a uranate-like coordination; with increasing U concentration mineral formation favours uraninite and Fe(III) (oxyhydr)oxides; the limit of U incorporation into magnetite is 0.45 mol % U ± 0.23; Np(V) is reduced to Np(IV) on the iron (oxyhydr)oxide surface forming a bidentate binuclear complex; and that upon reoxidation, Np(IV) is partially reoxidised back to Np(V) but not released back into solution. These results highlight the significance in understanding the mechanisms when both Np and U are in contact with iron (oxyhydr)oxides which can contribute towards site environmental clean-up and waste management in the nuclear industry.

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.

Les rouilles vertes sont des hydroxysels mixtes Fe(II)-Fe(III) présents dans les sols hydromorphes sous forme de fougérite. Elles sont connues pour être capable de réduire des polluants organiques et métalliques. Les rouilles vertes peuvent être produites à partir de la bioréduction de lépidocrocite [gamma]-FeOOH par Shewanella putrefaciens, une bactérie ferriréductrice. En vue de comprendre leur formation dans l'environnement et d'utiliser leur réactivité dans la mise en place, à terme, d'un système de dépollution des sols et des eaux (colonne de sable), nous avons étudié leur formation dans un système en batch en présence d'une phase siliceuse (sable et acide silicique) et en présence de polymères organiques synthétiques (polyacrylate PAA et polyacrylamide PAM) afin de mimer la présence des corps bactériens. La silice est les polymères apparaissent comme de bons agents stabilisateurs, favorables à la formation des rouilles vertes. Les rouilles vertes formées en présence de ces agents stabilisateurs conservent leur capacité réductrice vis-à-vis d'un polluant organique, le rouge de méthyle et d'un polluant métallique, le mercure Hg2+. Nous avons ensuite transposé notre système en batch dans une colonne de sable + lépidocrocite [gamma]-FeOOH, soumise à un régime hydrodynamique. Nous avons réussi à former et à caractériser une rouille verte comme minéral secondaire de la bioréduction de la lépidocrocite par Shewanella putrefaciens / Green rusts are mixed species Fe(II)-Fe(III) present in hydromorphic soils as fougerite. They are capable to reduce organic and metallic pollutants. Green rusts may be produced from the bioreduction of lepidocrocite [gamma]-FeOOH by Shewanella putrefaciens, a dissimilatory iron reducing bacteria. In order to understand their formation routes in the environment and eventually, use their reactivity in a system for soil and water remediation (sand column), we studied their formation in a batch system with silica phase (quartz sand and silicic acid) and with two organic polymers (PAA polyacrylate and polyacrylamide PAM).The silica polymers appear to be good stabilizers, favorable to the formation of green rusts. Green rusts formed in the presence of the stabilizing agents retain their reductive capacity toward an organic pollutant, methyl red and a metallic pollutant, mercury Hg2+. Then, we have transposed our system in a flow through column of sand + lepidocrocite [gamma]-FeOOH. The carbonate green rust was formed and identified as secondary mineral of lepidocrocite bioreduction by Shewanella putrefaciens

Les travaux présentés dans ce mémoire sont consacrés à l'étude des processus d'adsorption des anions phosphate par la rouille verte ferrique carbonatée et la ferrihydrite. L'objectif final vise une application au traitement des eaux usées en milieu rural. La synthèse des deux oxydes de fer a été réalisée et leurs propriétés physico-chimiques caractérisées. Un intérêt particulier a été consacré à comparer les propriétés structurales de la rouille verte ferrique en fonction de différents paramètres de synthèse. Une étude approfondie des propriétés physico-chimiques de surface de la ferrihydrite par spectroscopie de photoélectrons X a quant à elle été réalisée. La réactivité de ces deux oxydes a ensuite été abordée en mode discontinu où l'équation cinétique du pseudo-second ordre et le modèle d'isotherme de Freundlich offrent les meilleurs ajustements. L'influence de divers paramètres a été prise en compte comme le pH, la force ionique, etc. Le mode continu a été envisagé sur un matériau de filtration constitué de l'oxyde de fer déposé sur de la pouzzolane. La méthode de fabrication ainsi que les conditions optimales de préparation du matériau de filtration ont été déterminées. Les mécanismes d'adsorption en condition de flux hydrodynamique ont alors mis en évidence des phénomènes advectifs, diffusifs et une régionalisation de l'eau régissant l'adsorption au sein de la colonne. Des informations telles que les capacités d'adsorption ou l'influence du débit sur le processus d'adsorption ont pu être également obtenues. Une expérience préliminaire sur une eau usée prétraitée met finalement en évidence une quantité adsorbée particulièrement intéressante pour une application industrielle potentielle / The Ph.D. work, presented in this manuscript, is devoted to evaluating phosphate adsorption process on carbonate ferric green rust and ferrihydrite. The main objective concerns an application for the treatment of waste water in rural areas. Both iron oxides are first synthesized and their physico-chemical properties characterized. The ferric green rust structural properties differences as a function of synthesis parameters such as aging period and addition of hydrogen peroxide solution is of particular interest. A detailed study of surface physico-chemical properties by X Photoelectron Spectroscopy is carried out in the case of ferrihydrite. The reactivity of these two iron oxides is then evaluated in batch experiments. Adsorption process follows the pseudo-second order kinetic equation and Freundlich isotherm model which give the best adjustments of experimental data. The influence of various parameters such as pH, ionic strength, etc on phosphate adsorption is also taken into account. Column experiments are afterwards carried out by using filtration material constituted of iron oxide deposited onto pozzolana. The optimal conditions to prepare this filtration material are naturally predetermined. Phosphate adsorption in hydrodynamic mode is characterized by advective and diffusive mechanisms and water regionalization which govern the adsorption process in the column. Moreover, phosphate adsorption capacity and flow rate influence on adsorption process are obtained. Finally, a preliminary experiment on a pre-treated waste water finally shows that the filtration material is potentially interesting for an industrial application