Browsing by Subject "Iron"

Now showing 1 - 14 of 14
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    Controlled electrochemical synthesis of giant magnetostrictive iron-gallium alloy thin films and nanowires.
    (2012-04) Reddy, Kotha Sai Madhukar
    Magnetostrictive Galfenol (Fe1-xGax, x = 10% - 40%) alloys have generated tremendous interest in recent times because of their potential as functional materials in various micro- and nano-electromechanical systems (MEMS/NEMS)-based transducers and sensors. Among the giant magnetostrictive alloys, Terfenol-D (Tb1-xDyxFe2) has the largest magnetostriction, but its brittle nature limits its applications. In contrast, the next best magnetostrictive alloy, Galfenol, is highly malleable and ductile while having the tensile strength of Iron. Electrochemistry is an economical route to fabricate 'very thick' films (upto several microns) or high-aspect ratio structures like nanowire arrays. However, the highly electropositive nature of gallium makes it very difficult to electrodeposit from aqueous solutions, similar in behavior to other non-ideal elements like molybdenum, phosphorus, tungsten etc. As a result, Fe1-xGax alloy plating has been severely plagued by non-repeatability in compositions from growth to growth, lack of uniformity in filling of pores when growing nanowires in nanoporous templates, undesired secondary hydrogen evolution reactions etc. In this study, a thorough understanding of the complex interplay between various deposition parameters (pH, overpotential, concentration, hydrodynamic conditions) was achieved, leading to an understanding of the deposition mechanism itself, thus allowing excellent control and ability to tune the alloy compositions. Arrays of nanowires were fabricated with alternating segments of the magnetostrictive alloy Fe1-xGax and Cu in nanoporous anodic aluminum oxide (AAO) templates. A novel rotating disk electrode-template (designed in-house) was used to optimize the nanowire length distributions by controlling the various aspects of electrodeposition like nucleation, kinetics and mass-transfer. Extensive structural characterization was done by X-ray diffraction (XRD), electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM), and magnetic characterization by vibrating sample magnetometry (VSM). Furthermore, of excellent promise in semiconductor spintronics, the feasibility of fabricating epitaxially nucleated Fe1-xGax thin films on GaAs having the desired (001) texture was demonstrated. Structural characterization using microdiffraction, high resolution ω - 2θ and rocking curve analysis revealed that the films grown on GaAs(001) are highly textured with <001> orientation along the substrate normal, and the texture improved further upon annealing at 300 °C for 2 hours in N2 environment. This was in contrast to films grown on polycrystalline brass substrates which exhibited undesired <011> texture out-of-plane. Rocking curve analysis on Fe1-xGax/GaAs structures further confirmed that the <001> texture in the Fe1-xGax thin film was indeed due to epitaxial nucleation and growth. A non-linear current-voltage plot was obtained for the Fe1-xGax/GaAs Schottky contacts, characteristic of tunneling injection, and showed improved behavior with annealing.
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    High-valent Iron Intermediates in Nonheme Iron Catalytic Systems Designed for Hydrocarbon Oxidations
    (2019-05) Kal, Subhasree
    Inspired by nonheme iron enzymes, synthetic chemists have developed iron complexes to catalyze hydrocarbon oxidation reactions. High-valent iron intermediates have been proposed to be the oxidant for both enzymes and synthetic catalysts. For future development of catalysts, it is critical to discover and understand pathways for forming high-valent iron oxidants that can perform difficult oxidative transformations such as alkane and aromatic hydroxylation. Additionally, understanding the pathways to generate iron-based oxidants in model synthetic systems can help in elucidating mechanisms of the enzymes. This thesis describes a new pathway to form reactive high-valent FeV oxidants by utilizing strong Lewis and Brϕnsted acids. The acids facilitate heterolytic cleavage of the O–O bond in FeIII–OOH intermediates generated from the reaction of nonheme FeII complexes and H2O2. This pathway converts an inefficient catalyst for cyclohexane hydroxylation into an efficient catalytic system, forming an FeV oxidant in the catalytic cycle that hydroxylates cyclohexane within seconds at -40 °C. This new oxidant can also perform benzene hydroxylation equally efficiently. FeIII(OTf)3 is one of the Lewis acids that does this chemistry, giving rise to the first synthetic example where a mononuclear FeIII–OOH intermediate is activated by a second iron(III) ion to form an FeV oxidant. This work introduces the idea that the second iron in diiron nonheme enzymes can also act as a Lewis acid to activate O2 and form high-valent iron oxidants like Q in sMMO, which oxidizes methane to methanol. In addition, this thesis explores the importance of ligand topology around the iron center by comparing the effect of Lewis acid on the reactivity of three different catalytic systems. The effect of ligand topology was also investigated in the case of FeV intermediates that were generated stoichiometrically via one-electron oxidation of two topological isomers of an FeIV compound. The properties of the isomeric FeV intermediates, and the effect of Lewis acid in each case were explored.
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    Interactions with Iron: Ferrous Iron Transport and Resistance in Shewanella oneidensis strain MR-1
    (2017-01) Bennett, Brittany
    All living cells have requirements for metals, largely for the catalytic functions of metalloenzymes and other metal-containing proteins. However, metals become toxic to cells at higher concentrations. Therefore, it is imperative that organisms maintain intracellular metal concentrations within a viable range. As such, cells have many means through which to import, export, store, and detoxify metals, in order to fine-tune the intracellular concentration and reduce the toxicity of each. Iron is one of the most-used metals in metalloproteins, due to both its abundance in the Earth’s crust and its redox flexibility. Easily reduced to the ferrous state (Fe2+) or oxidized to ferric state (Fe3+), iron is widely used in enzymes involved in electron transfer, such as cytochromes, or redox sensing, such as transcription factors. The importance of iron is underscored by the large number of cellular processes that have been discovered in all domains of life that regulate the concentration and usage of iron. Multiple transport systems, for example, mediate the influx and efflux of both Fe2+ and Fe3+. Additionally, the redox flexibility of iron and its midrange redox potentials make iron a potential substrate for anaerobic respiration. Shewanella oneidensis strain MR-1 is a dissimilatory metal-reducing bacterium that lives in the redox transition zones of aquatic sediments. S. oneidensis produces numerous cytochromes that allow it to respire a wide variety of substrates, including extracellular, insoluble Fe3+ compounds, which are reduced to Fe2+. Fe2+ is much more soluble than Fe3+ in physiologically relevant conditions; therefore, S. oneidensis must contend with increasing local concentrations of soluble Fe2+ as it continues to respire Fe3+. How S. oneidensis interacts with Fe2+ and resists Fe2+ toxicity is the subject of this thesis. The second and third chapters of this thesis describe two newly discovered Fe2+ transport proteins in S. oneidensis. The first, which has been named FeoE (ferrous iron export), is an Fe2+ exporter that reduces the intracellular Fe2+ concentration during Fe3+ respiration by S. oneidensis. FeoE belongs to the Cation Diffusion Facilitator superfamily of divalent metal efflux proteins, which includes transporters of Cd2+, Co2+, Cu2+, Fe2+, Ni2+, and Zn2+. Studies presented in this dissertation demonstrate that FeoE is exclusively an Fe2+ exporter. The transporter described in Chapter 3, which was named FicI (ferrous iron and cobalt importer), is an Fe2+ and Co2+ importer. FicI belongs to the Magnesium Transporter-E (MgtE) family of Mg2+ and Co2+ importers; this is the first discovery of an MgtE protein that imports Fe2+ and not Mg2+. FicI appears to represent a secondary Fe2+ importer active at higher Fe2+ concentrations. FicI doesn’t require nucleotide hydrolysis for Fe2+ import, unlike the primary Fe2+ importer FeoB, therefore allowing the cell to conserve energy under high Fe2+ conditions. The fourth chapter in this thesis concerns the ATP-dependent protease ClpXP. ClpXP has previously been found to be involved in various cellular functions in several bacterial species, including releasing stalled proteins from ribosomes and the regulation of sigma factors, which influence the transcription of large groups of genes. The work presented in Chapter 4 shows that ClpXP is needed for the resistance of S. oneidensis to higher concentrations of Fe2+, which does not appear to involve previously described functions of ClpXP. Data presented in Chapter 4 indicate that ClpXP may target metalloproteins during Fe2+ stress, a finding that implicates high Fe2+ concentrations in protein mismetallation and misfolding. Supplementary Tables S1 and S2 contain transposon screen and protein-trapping results, respectively, relevant to this chapter. The work in this thesis expands the knowledge of the ways in which S. oneidensis interacts with Fe2+, including its uptake and efflux, and presents a potential mode of Fe2+ toxicity under anoxic conditions. As iron is an essential metal to most living organisms, and as there are many microorganisms living in metal-rich environments, the work presented here is relevant both to the study of S. oneidensis and to microbiology in general. The protein families discussed here are highly conserved among many microorganisms, and their newly discovered functions in S. oneidensis are likely to apply in others as well. More broadly, this work presents several widely-conserved proteins that have been repurposed or given added functions to meet the needs of an organism in order for it to thrive in a particular environmental niche, which reflects the adaptive nature of evolution.
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    Iron-Nickel-Sulfur-Carbon System Under High Pressure, With Implications To Earth’S Mantle
    (2016-10) Zhang, Zhou
    Fe-Ni-S-C phases are accessory phases in the Earth’s mantle, but carry important geochemical and geophysical implications. According to their chemical behavior, Fe-Ni-S-C phases preferentially store siderophile and chalcophile elements (and potentially noble gases). Physically, Fe-Ni-S-C phases have distinctly higher densities, surface tensions, and electrical conductivities, and lower melting points than mantle silicates. Understanding the geochemical and geophysical impacts caused by Fe-Ni-S-C phases requires accurate quantification of the basic properties of Fe-Ni-S-C phases under mantle conditions. This PhD thesis uses both high-pressure experiments and thermodynamic calculations to constrain the melting temperatures and compositions of Fe-Ni-S-C phases in the Earth’s upper mantle mantle, and their potential for deep carbon storage. This study suggests that monosulfides in the upper mantle are mostly molten, even in significant portions of cratonic roots under continental geotherms. Incorporation of carbon depresses the monosulfide solidus by 50-100˚C. Experiments and calculations of reactions between Fe-Ni-S melts and silicates at mantle conditions suggest that Fe-Ni-S melts are Ni-rich (Ni/(Ni+Fe)~0.6) monosulfides ((Fe+Ni)/S~1 or Xs~0.5) under oxidized (FMQ -2 to FMQ) conditions at 2 GPa. With increasing depth in the mantle (thus decreasing fO2), Fe-Ni-S melts become increasingly Ni- and S-poor, characterized by Ni/(Ni+Fe)~0.4, (Fe+Ni)/S~3, and Xs~0。4 at 8 GPa, and Ni/(Ni+Fe)~0.2, Xs~0.05 and (Fe+Ni)/S~10 at 12 GPa. Carbon solubility in Fe-Ni-S melts determined by high-pressure experiments suggests that carbon solubility decreases exponentially with increasing Xs. Based on mantle Fe-Ni-S melt compositions, C-S relations in carbon-saturated melts, and the typical mantle P-T-fO2 profile and sulfur abundance (200 ppm), it is suggested that significant amounts (40-100%) of deep carbon could potentially be stored in Fe-Ni-S melts in the Earth’s reduced deep upper mantle.
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    Magnetic Anisotropies and Damping in Epitaxial Iron Thin Films
    (2021-08) Etheridge, James
    In the research presented in the following thesis, the magnetic properties of a setof Fe/InAs(001) heterostructures with thicknesses ranging from 1.4 nm to 39.0 nm are investigated through the use of ferromagnetic resonance, x-ray diffraction, and magnetometry. The magnetic anisotropy results are heavily dependent on Fe thickness. The ferromagnetic resonance data point to an anisotropic relaxation of the Fe film that induces a shear strain in the Fe lattice. The shear strain produces an extra term of magnetoelastic origins in the free energy density resulting in several interesting results including a rotation of the uniaxial easy axis. Several x-ray diffraction experiments were performed to confirm the anisotropic relaxation of the Fe film. The magnetic damping of the samples were also investigated, yielding results that were anisotropic. The cause of the damping results can most likely be attributed to two-magnon scattering.
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    Micronutrient interactions affecting the developing rat brain
    (2013-06) Bastian, Thomas William
    Micronutrient deficiencies affect billions of people worldwide and often coexist in developing countries due to consumption of diets lacking nutrient diversity. Thus, it is important to consider how micronutrients such as copper (Cu), iron (Fe), and iodine interact physiologically. Cu, Fe, and iodine/thyroid hormone (TH) deficiencies lead to similar brain development deficits, suggesting these micronutrient deficiencies share a common mechanism contributing to the observed derangements. Previous studies in rodents and humans indicate that Cu and Fe deficiencies during adolescence or adulthood lead to impaired TH status. However, prior to this thesis research, relationships between Fe or Cu deficiencies and thyroidal status had not been assessed in the most vulnerable population, the developing fetus/neonate. My first two studies showed that Fe deficiency lowers newborn rat circulating and brain TH concentrations and alters TH-regulated brain gene expression. In a third study, Fe deficiency exacerbated the effect of mild TH insufficiency on neonatal thyroidal status and brain TH-responsive gene expression. Together, these novel findings suggest that impaired neonatal thyroidal status may contribute to some of the brain developmental abnormalities associated with fetal/neonatal Fe deficiency. Fe deficiency also has significant impacts on the developing brain independent of effects on thyroid function. In humans, Fe deficiency often results in anemia, reduced blood oxygen carrying capacity. Decreased oxygen delivery to the brain can induce a compensatory increase in blood vessel outgrowth. My final study demonstrated, for the first time, that Fe deficiency anemia increases blood vessel growth in the neonatal rat brain. The functional contribution of increased vasculature to the developing Fe-deficient brain is unknown but could be adaptive, maladaptive, or both. In summary, my thesis research exploring micronutrient interactions during brain development has identified two novel potential contributors to the brain developmental derangements associated with Fe deficiency: impaired neonatal thyroid function and increased neonatal brain vasculature.
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    Mono- and Dinuclear Nonheme Iron Model Complexes: O-O Bond Activation, Structural Characterization and Reactivity Study
    (2015-05) Rohde, Gregory
    The structures and reactivities of mono- and dinuclear nonheme iron model complexes were investigated. In Chapters 2 and 3, O-O bond activation of H2O2 by the dinuclear complexes [(FeIII2(μ-O)(μ-OH)L2]3+ (1A) and [(FeIII2(μ-OH)2L2]4+ (2A), L = tris(3,5-di-methyl-4-methoxypyridyl-2-methyl)amine, to form the high-valent [(FeIV2(μ-O)(OH)(O)L2]3+ (3A) and [(FeIV2(μ-O)2L2]4+ (4A) was studied. H2O2 and H2O competed for binding to the Fe centers of 1A and 2A, and [H2O2] was rate limiting under the concentrations studied. The presence of base increased the H2O2 activation rate for 2A, but not for 1A. The H2O2 activation rates by 1A and 2A were comparable to that of the mononuclear nonheme iron complex [FeII(TMC)]2+ (TMC = tetramethylcyclam) (J. Am. Chem. Soc. 2010, 2134-2135) after accounting for water inhibition. A crystal structure of [(FeIV2(μ-O)2L2]4+ (4A), or diamond core, was solved and described the Fe2O2 core in more detail than the original EXAFS structural assignment. In addition, structures of other complexes with Fe2O2L2 cores in different oxidation and protonation states were also studied and compared to the Fe2O2 cores of the high-valent enzymes intermediates RNR-X and sMMO-Q. In Chapter 4, iron complexes supported by the TMC ligand were studied by X-ray crystallography. A second isomer of the [FeIV(O)(TMC)]2+ complex was found, and the mechanism of conversion to the original isomer was explored. Additionally, the crystal structure of (TMC)FeIII(μ-O)Sc(NCCH3)(OTf)4 complex was obtained and used to reassign the Fe oxidation state of the originally reported (TMC)FeIV(μ-O)Sc(OH)(OTf)4 complex.(Nat. Chem. 2010, 756-759) In Chapter 5, the hydrogen atom transfer (HAT) rates of a series of S = 2 mononuclear nonheme iron complexes, [FeIV(O)TMG2dien(X)]2+,+ (X = CH3CN, Cl-, Br-, N3-, CH3CO2- and CF3CO2-; TMG2dien = 1,1-bis{2-[N2-(1,1,3,3- tetramethylguanidino)]ethyl}amine), were reported. Substitution of CH3CN with carboxylate and halide anions cis to the oxo ligand increased the HAT oxidation rate by as much as 15 times. A series of S = 1 nonheme iron complexes, [FeIV(O)TPA(Y)]2+,+ (Y = CH3CN, Cl-, CH3CO2- and CF3CO2-; TPA = tris(pyridyl-2-methyl)amine), was also investigated to explore what effect spin state has on reactivity. The HAT rates were similar for the [FeIV(O)TPA(Y)]2+,+ series, while OAT rates were much faster for the [FeIV(O)TPA(CH3CN)]2+ species.
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    NCOA4 is Essential for HT22 Hippocampal Neuronal Cell Survival During Iron Deficiency
    (2020-06) Bengson, Emily
    Iron is essential for proper cell function and development, serving as a cofactor for many metalloproteins. However, mismanagement of cellular iron leads to increased reactive oxygen species (ROS), which ultimately leads to ferroptosis, a newly discovered form of regulated cell death, which is iron-dependent. Neurodegeneration has been associated with brain iron accumulation and, more recently, ferroptosis. NCOA4 manages the cellular labile iron pool by controlling the release of ferritin iron via ferritinophagy. The present studies examined the capacity of hippocampal cells in handling iron fluctuation, with particular focus on NCOA4 and ferritin. HT22 mouse hippocampal cells were treated with ferric ammonium citrate (FAC) and deferoxamine (Dfo) to produce cellular iron overload and deprivation, respectively. Ferroptosis was determined by measures of ferrostatin-1 effects and Ptgs2 mRNA. For ferritinophagy studies, Ncoa4 was silenced by siRNA transfections. Functional impacts of impaired ferritinophagy were assessed via CCK-8 cell viability assays and western and qPCR analyses of iron-related genes. HT22 cells were highly susceptible to cellular iron overload. FAC-treated cells featured acute morphological changes, decreased viability, and elevated Ptgs2 mRNA abundance. Iron effects were prevented by ferrostatin-1, indicating ferroptosis by cellular iron overload. Dfo alone had minimal impact on cell morphology and viability. NCOA4 protein, but not mRNA, levels were elevated by cellular iron restriction. Ferritin turnover by iron deficiency was impaired in NCOA4-depleted cells, presumably due to impaired ferritinophagy. Moreover, HT22 cells became sensitive to iron deficiency by loss of NCOA4. Our studies demonstrate iron can induce ferroptosis in HT22 neuronal cells. We also identify NCOA4-mediated ferritinophagy as an integral process for neuronal cell survival during iron deficiency.
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    Non-canonical pathways of HIF1-alpha regulation in ovarian cancer: implications for tumor angiogenesis and metastasis.
    (2011-10) Joshi, Hemant Prakash
    The high rates of mortality associated with epithelial ovarian cancer (EOC) are a direct consequence of its metastatic nature. Activation of angiogenesis is a significant factor in generation of metastases and is contingent upon the cellular response to hypoxia within the tumor microenvironment. Hypoxia-inducible factor 1 (HIF1) is a transcription factor composed of HIF1α and HIF1β subunits and is the master regulator of the hypoxic response. Hypoxia and HIF1 are therefore critical mediators of tumor angiogenesis and metastasis. Regulation of HIF1 is primarily at the level of protein. In normoxia, the HIF1α subunit is hydroxylated via an oxygen- and iron-dependent mechanism and targeted for destruction. In hypoxia, low oxygen levels preclude hydroxylation and HIF1α is stabilized, allowing for its association with constitutively expressed HIF1β to form bioactive HIF1. We have identified two novel mechanisms of HIF1α regulation that are oxygen-responsive in EOC cells (EOCCs). The first involves dynamins, a class of proteins involved in endocytic processes such as transferrin/iron uptake. Exposing EOCCs to hypoxic conditions results in lower levels of dynamin 2. Impairment of dynamin 2 activity in normoxia causes accumulation of HIF1α protein due to a rapid decrease in intracellular iron levels and HIF1α polyubiquitination. Treatment with a form of iron that is not dependent on dynamins for endocytosis reverses this effect. Conversely, overexpression of dynamin 2 in hypoxia results in suppression of HIF1α protein levels. A second novel mechanism of HIF1α control involves microRNAs (miRNAs), ~22 nucleotide, non-coding RNA molecules that repress translation of target mRNAs by binding their 3' untranslated regions (UTRs). Using microarray and qPCR analysis, we found that exposing EOCCs to hypoxia reduced levels of miR-199a-1, a miRNA that is located in an intron within the dynamin 2 gene and is predicted in silico to target the HIF1α 3' UTR. We further demonstrated that miR-199a-1 directly targets the HIF1α 3' UTR and overexpression of miR-199a-1 suppresses HIF1α protein levels and HIF1-driven gene expression. Moreover, cells stably overexpressing miR-199a-1 exhibit marked defects in migratory ability. We corroborated these findings in vivo by overexpressing miR-199a-1 in a mouse model of metastatic EOC and found significant reductions in tumor vessel density and tumor burden. Together, these findings provide insight into non-canonical, dynamin-dependent and miRNA-based mechanisms of HIF1 regulation that may have important implications in the progression of EOC.
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    PATHWAYS TO DEPRESSIVE SYMPTOMS AND INFLAMMATION FROM EARLY PSYCHOSOCIAL AND NUTRITIONAL ADVERSITY: A LONGITUDINAL STUDY OF CHILEAN YOUTH
    (2020-06) Reid, Brie
    Exposure to early life adversity (ELA) is thought to increase the risk of later psychopathology through alterations in immune system functioning, notably through increased inflammation. However, nutritional adversities such as iron deficiency may arise from and co-occur with ELA. Psychosocial adversity and nutritional adversities together may play a causal role in the development of psychosocial maladjustment via increases in circulating inflammatory factors. The present study investigates whether psychosocial ELA predicts iron status early in life and uses structural equation modeling to determine if ELA and iron status in infancy predict increased inflammation in adolescence and depressive symptoms in emerging adulthood. The study is a follow-up of infants from working-class communities in Santiago, Chile, who participated in a preventive trial of iron supplementation at six months of age. Anthropometrics, stressful life events, maternal depression, socioeconomic status, support for child development, and iron status were measured in the first year of life, five years, ten years, and adolescence. In adolescence, participants provided blood samples for inflammation assessments (CRP, WBC, neutrophil to lymphocyte ratio, and monocyte count). In emerging adulthood (21y), participants provided self-reported depressive symptoms. ELA in infancy predicted iron status in infancy and depressive symptoms in emerging adulthood. However, ELA did not directly predict increased inflammation in adolescence, and increased inflammation did not predict increased depressive symptoms. Iron status in infancy predicted increased monocyte count in adolescence, and ELA in infancy predicted higher levels of monocytes indirectly through iron status in infancy. These findings provide novel evidence of the association between postnatal ELA and iron status and suggest that ELA predicts depressive symptoms independent of inflammation in this population. These findings also provide evidence of a novel pathway by which early adversity and nutrition program the developing immune system.
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    Physiological Roles and Regulation of NCOA4 in Macrophages
    (2020-09) Guggisberg, Cole
    Phagocytosing macrophages are critical to systemic iron homeostasis owing to their capability to recycle iron from senescent RBCs and store iron under systemic distress. NCOA4 has recently been identified as a key regulator of ferritin, mediating its degradation via ferritinophagy. Yet, its function in macrophages remains unclear. The present studies employed a cell culture model of J774 macrophages, to examine the role and regulation of macrophage NCOA4 by iron status, red cell iron recycling, and inflammation. Macrophage NCOA4 is responsive to iron status and inversely related to ferritin abundance. By erythrophagocytosis, ferritin peaks at 12 hours with subsequent decrease at 24 hours which is NCOA4-dependent. Hepcidin activity repressed NCOA4 preventing the turnover of ferritin between 12 and 24 hours in erythrocyte laden macrophages. Macrophages were treated with LPS, which decreased both NCOA4 transcript and protein abundance. Altogether our studies demonstrate an active role of NCOA4-mediated ferritinophagy in macrophage iron homeostasis.
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    Potential Value Added Products from the Minnesota Ilmenite Deposits
    (University of Minnesota Duluth, 2002-10) Benner, Blair R; Niles, Harlan B
    As part of the University of Minnesota’s ongoing support for the development of ilmenite deposits located within the Duluth complex, the University’s Permanent Trust Fund sponsored a project by the Coleraine Minerals Research Laboratory to determine if valued added products could be produced from the ilmenite deposits and to determine if ilmenite recovery could be increased. A previous study sponsored by the Minerals Coordinating Committee indicated that using high pressure rolls in place of a rod mill to grind the ilmenite increases TiO2 recovery by about 10 percent. The major loss of TiO2 (about 25 %) was associated with the removal of magnetite by magnetic separation after spiral concentration. The objective of this program was to determine if the magnetic portion of the spiral concentrate could be upgraded to make a concentrate suitable for either blast furnace pellet feed or DRI feed. During upgrading of the magnetic portion, non-magnetic materials should contain the bulk of the ilmenite, and they would also be upgraded to determine the potential for additional ilmenite recovery. Initial liberation grinds and Davis tube tests on the spiral magnetic concentrate indicated that grinding and magnetic separation alone could not upgrade the material sufficiently. Standard silica flotation on the ground and magnetically separated material did not provide significant upgrading. The best concentrate produced contained 58.84 percent iron, 6.66 percent TiO2, and 5.74 percent silica. Perhaps this material could be used in the iron nugget process. Amine flotation, fatty acid flotation and WHIMS were used to recover TiO2 from the non-magnetic portion of the reground spiral magnetic concentrate. Only fatty acid flotation of the ilmenite showed any potential for recovering additional ilmenite at grade. Additional test work on the use of silicate depressants is needed. Elutriation tests on size fractions indicated that grinding to finer than 200 mesh is needed for liberation of the ilmenite from the silicate gangue. While the previous test work showed increased TiO2 recovery in the spiral nonmagnetic fraction, no work was conducted on upgrading that material to determine if the increased recovery could be carried through to a final concentrate. Therefore, bench scale electrostatic separator tests were run on the spiral non-magnetic fraction produced in the previous project. The electrostatic tests indicated that both grade and recovery could be obtained.
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    Supporting data for "Sulfur geochemistry impacts population oscillations of wild rice (Zizania palustris)"
    (2020-07-10) LaFond-Hudson, Sophia; Johnson, Nathan W; Pastor, John; Dewey, Brad; lafo0062@d.umn.edu; LaFond-Hudson, Sophia
    Wild rice populations decline with exposure to elevated sulfate due to production of sulfide in anoxic sediment. Using self-sustaining wild rice mesocosms, we collected data on the population response to sulfate, as well as iron and litter, which both may modify the production and availability of sulfide to plants. Wild rice also experiences natural population oscillations due to delays in release of nitrogen from decomposing litter. We use this data to investigate how sulfate-induced population declines interact with stable litter-driven population cycles. Population data was collected 2014-2019, and geochemical data (iron, sulfide, pH) was collected in 2019, after 5 years of of a factorial design treatment (sulfate, iron, litter).
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    Utilization of synchrotron radiation X-ray microscopy, micro-probe, and spectroscopy to characterize the carbon, sulfur, and iron speciation of particles from buoyant, deep-sea hydrothermal plumes in the Mid-Cayman Rise
    (2017-04) Kamermans, Brandi
    The purpose of this study was to investigate the geochemical inputs to rising hydrothermal vent plumes of the Mid-Cayman Rise. To assess processes that modulate hydrothermal fluxes to the deep ocean at the Mid-Cayman Rise, the speciation of Fe, S, and C was measured for particles and aggregates using: (1) microprobe S 1s and Fe 1s X-ray absorption near edge structure (XANES) spectroscopy, (2) microprobe X-ray fluorescence (XRF) chemical mapping, and (3) scanning transmission X-ray microscopy (STXM) based C 1s and Fe 2p XANES. The Mid-Cayman Rise is an ultraslow spreading center located in the Caribbean Sea. The Mid-Cayman Rise hosts two hydrothermal vents that produce geochemically diverse fluids: (1) Beebe, the deepest (5000 ± 50 meters) known high-temperature (398 oC) vent site with high iron and sulfur, and (2) Von Damm (2300 ± 50 meters) with fluids at 110 to 200 oC (Kinsey and German, 2013). My samples were collected with a newly developed instrument, called the SUPR (SUspended Particle Rosette) (Breier et al., 2014). The SUPR was developed for high-precision collection of deep-sea samples, and it also made it possible to collect samples for complementary research efforts. Carbon XANES of Von Damm fluids reveal the presence of biomolecules such as proteins, lipids, polysaccharides, and chitin in plume particles. Iron 2p imaging and XANES indicate that nanoparticulate Fe minerals are associated with particulate organic C (POC). Sulfur 1s XANES and chemical mapping data reveal the presence of sulfonate, sulfone, and ester sulfate, as well as elemental S, and indicate that microbial processes and chemical oxidation occur in the subsurface or in the near vent samples. In the Von Damm particles, a shift from strongly reduced to oxidized, including the appearance of intermediate S-bearing functionalities, suggests turbulent mixing of Von Damm fluids with seawater provide oxic and pH neutral conditions where chemical and biological interactions can occur. The Fe 1s XANES observations capture trends that suggest particles within the Von Damm and Beebe Vents could be sourced from chemical processes within the plume and physical entrainment processes from multiple sources.