Chapter 1 Dynamic Processes Occurring at the Cr^III_aq – Manganite (γ-MnOOH) Interface: Simultaneous Adsorption, Microprecipitation, Oxidation/Reduction and Dissolution The complex interaction between Cr^III_aq and manganite (γ-MnOOH) was systematically studied at room temperature over a pH range of 3 to 6, and within a concentration range of 10⁻⁴ to 10⁻² M CrOH²⁺_aq. Solution compositional changes during batch reactions were characterized by ICP and UVvis. The manganites were characterized before and after reaction with XPS, SEM, high-resolution FESEM, and EDS analysis. Fluid-cell AFM was used to follow these metal-mineral interactions in situ. The reactions are characterized by 1) sorption of Cr^III and the surface-catalyzed microprecipitation of Cr^III-hydroxy hydrate on manganite surfaces, 2) the acidic dissolution of the manganite, and 3) the simultaneous reductive dissolution of manganite coupled with the oxidation of Cr^III_aq to highly toxic Cr^VI_aq. Cr^III-hydroxy hydrate was shown to precipitate on the manganite surface while still undersaturated in bulk solution. The rate of manganite dissolution increased with decreasing pH due both to faster acid-promoted and Mn-reduction- promoted dissolution. Due to direct redox coupling with Mn reduction, Cr oxidation was most rapid in the lower pH range. Neither Mn^II nor Cr^VI were ever detected on manganite surfaces, even at the maximum rate of their generation. At the highest pHs of this study, Cr^III_aq was effectively removed from solution to form Cr^III-hydroxy hydrate on manganite surfaces and in the bulk solution, and manganite dissolution and Cr^VI_aq generation were minimized. All interface reactions described above were heterogeneous across the manganite surfaces. This heterogeneity is a direct result of the heterogeneous semiconducting nature of natural manganite crystals, and is also an expression of the proximity effect, whereby redox processes on semiconducting surfaces are not limited to next nearest neighbor sites. Chapter 2 Comparison of the Reactivity of Various Mn-Oxides with Cr^III_aq: Microscopic and Spectroscopic Observations of Dissolution, Cr-sorption and Cr and Mn Redox Interactions The interaction between Cr^III_aq and seven different Mn-oxides (6 monomineralic, 1 synthetic) have been observed in pH ~4.4 HNO₃ and pH ~4.4 ~10⁴ M Cr^III_aq solutions. For each mineral-solution interaction, the aqueous chemical concentrations (e.g. [Mn]_aq, [Cr]_aq, [Cr^VI_aq]) were measured with time. Reacted samples were examined by XPS to determine if, and to what extent, the surface chemical states of Cr, Mn and O had changed. Microscopic observations of the reacted surfaces were obtained using AFM and high-resolution, low-voltage FESEM. The solubility of the Mn-oxides in the acidic, non-Cr bearing solutions varied inversely with the average Mn valence, but did not show systematic behavior with respect to the mineral structure type (e.g. tunnel, layer, framework). This trend was interpreted as resulting from the relative ability of an adsorbed proton to polarize surface Mn-O bonds, with the polarizability being in the order Mn²⁺-O > Mn³⁺-O > Mn⁴⁺-O. For samples reacted with Cr^III_aq, the rate and extent of reductive dissolution was always greater than for acidic dissolution during the initial time period. The measured ratios of the [Mn]_aq : [Cr^VI]_aq were approximately in agreement with the values expected from the proposed stoichiometric reactions. Cr-uptake was observed to occur in undersaturated solutions as a result of adsorption, absorption and surface catalyzed precipitation. The chromium as detected by XPS was predominately Cr^III, however pyrolusite contained both Cr^III and Cr^VI. Previous studies have implicated a chromium surface precipitate to be responsible for the cessation of the Cr^III_aq oxidation reaction. Our surface sensitive FESEM and AFM observations tend to suggest that Cr-uptake is by isolated site binding, very small (<30 nm) surface clusters or monolayer scale films. Cr-uptake was followed by slow Cr-release on several of the solids (particularly the layered solids) after a substantial portion of the total aqueous Cr had been converted to Cr^VI_aq. The oxidizing ability of the different Mn-oxides for Cr^III_aq is evaluated with regards to the energy level of the redox couple (i.e. the redox potential) as compared with the Fermi energy level of the Mn-oxide. Although these energies were calculated rather than directly measured, the results indicate that electrons originating from adsorbed Cr^III ions may be transferred into the conduction band or more likely, into available surface states. The presence of an initial limited quantity of electron accepting surface states likely explains the observation of a rapid initial Cr^III-oxidation followed by much slower oxidation. The Mn-oxides that exhibited the greatest and longest lasting Cr^III-oxidizing power were the Mn-oxides containing Mn⁺, and in particular those containing Mn³⁺ and Mn⁺. It is believed that the combined presence of a reducible Mn ion (e.g. Mn³⁺) and a highly soluble Mn⁺ ion facilitates a sustained Cr^III-oxidation reaction because fresh surface is exposed during the reaction. / Ph. D.

Lead sorption efficiencies (sorption per surface area) were measured for a number of natural and synthetic Mn and Fe-oxides using a flow through reactor. The Mn-oxide phases examined included synthetic birnessite, natural and synthetic cryptomelane, and natural and synthetic pyrolusite; the Fe-oxides studied were synthetic akaganeite, synthetic ferrihydrite, natural and synthetic goethite, and natural and synthetic hematite. The sorption flow study experiments were conducted with 10 ppm Pb with an ionic strength of either 0.01 M NaNO3 or 0.01 M KNO3 both at pH 5.5. The experimental effluent solution was analyzed using aqueous spectroscopic methods and the reacted solids were analyzed using microscopy (field emission scanning electron microscopy, FE-SEM), structure analysis (powder X-ray diffraction, XRD), bulk chemical spectroscopy (energy dispersive spectroscopy, EDS), and surface sensitive spectroscopy (X-ray photoelectron spectroscopy, XPS). Overall, the synthetic Mn-oxides did have higher sorption efficiencies than the natural Mn-oxides, which in turn were higher than the natural and synthetic Fe-oxides. Only natural pyrolusite had a sorption efficiency as low as the Fe-oxides. Most of the natural and synthetic Fe-oxides examined in this study removed about the same amount of Pb from solution once normalized to surface area, although synthetic akaganeite and hematite were significantly less reactive than the rest. The observed efficiency of Mn-oxides for Pb sorption is directly related to internal reactive sites in the structures that contain them (birnessite and cryptomelane, in the case of this study). Comparisons of solution data to XPS data indicated that Pb went into the interlayer of the birnessite, which was supported by XRD; similarly some Pb may go into the tunnels of the cryptomelane structure. Layer structures such as birnessite have the highest Pb sorption efficiency, while the 2 x 2 tunnel structure of cryptomelane has lower efficiencies than birnessite, but higher efficiencies than other Mn- or Fe-oxide structures without internal reactive sites. / Ph. D.

Manganese(II) and (III) complexes of potentially bidentate and tridentate Schiff base ligands have been prepared. The ligands were prepared from substituted salicylaldehyde or pyridine-2-carboxaldehyde and amines with hydrocarbon or alkylpyridyl substituents. The electrochemistry and the oxygenation kinetics of these and similar tetradentate, pentadentate, and hexadentate complexes have been studied. The electrochemistry of the majority of the complexes involves the Mn(III)/Mn(II) couple. However, varying the solvent shows that electron transfer is often accompanied by slow changes in the number of solvent molecules coordinated to the metal or changes in the actual denticity of the ligand. Activation energies and entropies for the reactions with 0₂ show that a large number of parameters influence the rate of reaction. Primary among these is competition between 0₂, solvent molecules, and donor atoms from the ligands for coordination sites on the metal. However, the reactions were all (with one exception) found to be first order in both complex and 0₂, implying that the slow step is formation of a Mn(III)-superoxo complex. The exception was with complexes of the tetradentate Mn(SALC_n) type, where a simple rate law could not be fitted. This was explained by either steric hindrance or polymerization of the complex due to the flexibility imparted by the long polymethylene chain in the tetradentate ligand. / Ph. D.

Understanding and establishing reaction mechanisms is an important area in heterogeneous catalysis. This dissertation describes the use of in situ laser Raman spectroscopy combined with kinetic measurements and dynamic experiments to determine the mechanism of catalytic reactions. Two cases involving ozone reactions on manganese oxide catalysts were treated. Manganese oxide was chosen because it is the most active of the transition metal oxides for ozone decomposition and because it is a well-known catalyst for complete oxidation reactions. The first case studied was that of the ozone decomposition reaction on a supported manganese oxide catalyst. An adsorbed species with a Raman signal at 884 cm-1 was observed and assigned to a peroxide species based on results of in situ Raman spectroscopy, 18O isotopic substitution measurements, and ab initio MO calculations. The reaction pathway of ozone decomposition was elucidated with carefully designed isotopic experiments. The reaction sequence was found to involve two irreversible, kinetically significant steps: 1) dissociative adsorption of ozone to form a peroxide species and an atomic oxygen species, and 2) desorption of the peroxide intermediate. The kinetic behavior of the peroxide species and the overall decomposition reaction were investigated to test the validity of the proposed sequence. The transient kinetics were found to be consistent with the steady state kinetics, and both were well represented by the two-step sequence, indicating that the proposed reaction sequence accurately described the mechanism of decomposition. The surface was found to be non-uniform, with activation energies that varied linearly with coverage. At zero surface coverage the activation energy for ozone adsorption was found to be 6.2 kJ mol-1, while that for desorption of the peroxide species was found to be 69.0 kJ mol-1. The second case investigated was that of ethanol oxidation using ozone on alumina and silica supported manganese oxide catalysts. Ethanol was found to react with ozone at lower temperatures than with oxygen, and also with a lower activation energy. The reaction kinetics was found to be well described by a power law equation with the reaction orders on ozone and ethanol being 0.89 and 0.81 respectively. The oxidation reactivity was found to be closely related to that of ozone decomposition, suggesting an important role of ozone decomposition in the reaction mechanism. In situ laser Raman spectroscopic studies showed the existence of adsorbed ethoxide species on the catalyst surface under reaction conditions, however, at a much lower concentration than when oxygen alone was used as the oxidant. Transient experiments provided direct evidence that surface peroxide (an adsorbed species due to ozone) and surface ethoxide (an adsorbed species due to ethanol) reacted with each other on the catalyst surface. / Ph. D.

The possible effects of pipe materials on drinking water quality have been analyzed in the distribution system of the water treatment plant of "La La Concepciónâ " in Tegucigalpa, Honduras. "La La Concepciónâ " is a surface water reservoir experiencing biogeochemical cycling of manganese. Black water problems have been reported in the distribution system since 1998. An evaluation of the potential influence that PVC and iron pipes could have on the concentration of iron and manganese in drinking water, the effects caused by the presence of manganese in PVC and iron pipe surfaces, and residual chlorine and Pb concentrations in the distribution system was performed. The sampled neighborhoods received an intermittent service. Water was suspended for 8 hours every day due to water quantity problems in the city. Water and pipe samples were obtained for PVC and galvanized iron pipes because these constitute the majority of the infrastructure used for distribution systems in Honduras. Thermodynamic and kinetic conditions for possible manganese oxidation by chlorine and dissolved oxygen in the distribution system were also evaluated. As expected, total Fe concentrations were greater for first flush conditions from the iron pipe. Water samples obtained from the PVC pipe showed higher total Mn concentrations and more black color than those obtained from the iron pipe for both first flush and continuous flow conditions. Residual chlorine decayed relatively fast along the sampled section of the distribution system. Pb concentrations were detected on water samples obtained from PVC for first flush and continuous flow and on iron pipe for first flush. Preliminary experiments showed that manganese-oxidizing and -reducing bacteria were present in the walls of both PVC and iron pipes. Higher numbers of colony-forming microorganisms were recovered from iron (30-fold more) compared to PVC pipe sections. However, the majority of isolates from the PVC biofilm (8 of 10, 80 %) were capable of Mn-oxidation while only 35 % (11 of 31) of isolates from the iron biofilm sample demonstrated Mn-oxidation. This research demonstrates the importance of the different interactions between water and the infrastructure used for its supply in producing safe drinking water. / Master of Science

The National Research Council recently called for a more interdisciplinary approach to drinking water research to address the critical issue of global drinking water supplies. Hypolimnetic oxygenation systems (HOₓ) are being increasingly used to improve water quality in stratified reservoirs by increasing dissolved oxygen (O₂) concentrations and subsequently suppressing the release of soluble species such as iron (Fe) and manganese (Mn) from the sediment into the water. However, while the influence of HOx on the water column has been established, little work has been done on how oxygenation affects sediment O₂ uptake (i.e., sediment oxygen demand) and other sediment-water fluxes. In response to the growing need for alternative approaches for improving water quality, we conducted highly interdisciplinary research to evaluate how O₂, Fe, and Mn cycling at the sediment-water interface is influenced by both natural and HOx-induced variations in water column dynamics, chemical redox processes, and microbial activity within the sediment, all of which may govern sediment-water fluxes. Studies were performed in an alpine lake in Switzerland and in an HOₓ-equipped drinking-water-supply reservoir in Virginia. This research was based on in situ field campaigns paired with laboratory experiments, microbial analyses, and computer simulation to elucidate variable sediment O₂ uptake and corresponding Fe and Mn cycling. This work is unique in that sediment-water fluxes were assessed using in situ data from both sides of the sediment-water interface. Results show that sediment O₂ uptake flux is strongly controlled by both wind- and HOₓ-induced dynamic forcing. Our findings reveal that Fe and Mn fluxes were suppressed from the bulk hypolimnion via biogeochemical cycling in the oxic benthic region. Results also indicate that the sediment microbial community structure may directly respond to HOₓ-induced variation in sediment O₂ availability. Additionally, based on an analysis of the robustness of several commonly used methods for flux calculations, we show that flux estimates are not strongly dependent on the method chosen for analysis. Ultimately, by emphasizing the highly transient nature of sediment O₂ uptake, this research will aid in accurate characterization of various sediment-water fluxes and corresponding water quality. Our results will also directly contribute to the optimization of HOₓ operations and lake and reservoir management. / Ph. D.

Including porosity introduces absorption into the previously developed scattering analysis for elastic spheres. Acoustic propagation in porous media has two distinct compressional modes, one in which the fluid and the structure move in phase with each other and the other in which they move in opposite phase. Expressions for the complex wavenumbers of both waves are derived, using the parameters for manganese nodules. A modal analysis with a pressure boundary condition indicates that the first kind of compressional wave is lightly attenuated and carries most of the energy of the coupled system. The second compressional wave is highly attenuated and effectively loses all of its energy in the first centimeter of the nodule. This second wave is very important for consideration of nodule-scale dimensions since it represents the dominant loss mechanism. A method was developed to form a single effective compressional wave attenuation for both compressional waves by employing a pressure and velocity boundary condition at the surface of the nodule and using a spatially integrated intensity match. An effective wave attenuation is generated for the compressional wave in the non-porous elastic model which accounts for porous attenuation and which is based on a parameter defined as travel distance L. If L is assumed to be proportional to nodule radius, the attenuation is approximated as constant for the frequency range of interest and is independent of nodule radius. An effective attenuation is predicted. The shear attenuation is found to exhibit a frequency squared form dependence for manganese nodules. However, shear attenuation is very small for ideal nodules and is negligible compared to the compressional loss. The elastic model of the nodule was numerically altered to accommodate complex wavenumbers in shear and compression. Four distinct regions of attenuation are observed in individual reflectivity, R_θ, versus ka plots and discussed. The importance of including attenuation is readily apparent from observing the transformation of the elastic non-porous results. Scattering experiments were performed on manganese nodules and experimental individual reflectivity versus ka plots were generated. Good agreement is found for the spherical Atlantic nodules using values in the third region of attenuation. From these experiments, an estimation of attenuation is made and compared with the theoretical prediction. The influence of attenuation on individual scattering and multiple scattering is investigated. Attenuation tends to shift the major bottom reflectivity, C_R, peak toward lower ka values. This affects the prediction of the acoustic response of manganese nodule deposits. / Master of Science

Yes / To interpret nitrogen sintering of chromium and manganese steels without the formation of deleterious oxides, but with manganese and carbon modifying the local microclimate, the role of the volatile Mn and carbothermic reactions were considered. Reduction of Cr2O3 by Mn vapour is always favourable. CO is an effective reducing agent, however, whereas at atmospheric pressure it will reduce FeO at ~730°C, temperatures some 500 and 700°C higher, i.e. above those for conventional sintering, are necessary for reducing Cr2O3 and MnO, respectively. Accordingly partial pressures must be considered and the sintering process is modelled at a conglomerate of several surface oxidised alloy particles surrounding a pore with graphite present and a tortuous access to the nitrogen-rich atmosphere containing some water vapour and oxygen. The relevant partial pressures were calculated and reduction reactions become thermodynamically favourable from ~200°C. Kinetics, however, dictates availability of CO and the relevant reactions are the water-gas, C + H2O = CO + H2 from ~500°C and the Boudouard, C + CO2 = 2CO, from ~700°C. Discussion of sintering mechanisms is extended to processing in semi-closed containers, also possessing specific microclimates.

The demand for Lithium-ion batteries (LIBs) has been growing exponentially in recent years due to the proliferation of electric vehicles (EV). A large amount of lithium-ion batteries are expected to reach their end-of-life (EOL) within five to seven years. The improper disposal of EOL lithium-ion batteries generates enormous amounts of flammable and explosive hazardous waste. Therefore, cost-effectively recycling LIBs becomes urgent needs. Lithium nickel cobalt manganese oxides (NCM) are one of the most essential cathode materials for EV applications due to their long cycle life, high capacity, and low cost. In 2008, 18.9% of Lithium-ion batteries used NCM cathode material worldwide while this number increased to 31% six years later. An environment–friendly and low-cost direct recycling process for NCM has been developed in this project. The goal of this project is to recycle the EOL NCM and yield battery-grade NCM with equivalent electrochemical performance compared to virgin materials. In order to achieve this goal, four different heat treatment conditions are investigated during the direct recycling process. From the experimental results, the charge and discharge capacities of the recycled material are stable (between 151-155 mAh/g) which is similar to that of the commercial MTI NCM when sintered at 850 °C for 12 hours in the air. In addition, the cycling performance of recycled NCM is better than the commercial MTI NCM up to 100 cycles. / Master of Science / The demand for Lithium-ion batteries has been growing exponentially in recent years due to the proliferation of electric vehicles. A large amount of lithium-ion batteries are expected to reach their end-of-life within five to seven years. The improper disposal of end-of-life lithium-ion batteries generates enormous amounts of flammable and explosive hazardous waste. Therefore, cost-effectively recycling Lithium-ion batteries becomes urgent needs. Lithium nickel cobalt manganese oxides are one of the most essential cathode materials for electric vehicles applications due to their long cycle life, high capacity, and low cost. In 2008, 18.9% of Lithium-ion batteries used Lithium nickel cobalt manganese oxides cathode material worldwide while this number increased to 31% six years later. An environment–friendly and low-cost direct recycling process for Lithium nickel cobalt manganese oxides material has been developed in this project. The goal of this project is to recycle the end-of-life manganese oxides cathode material. In order to achieve this goal, four different heat treatment conditions are investigated during the direct recycling process. From the experimental results, the cycling performance of recycled NCM is better than the commercial MTI NCM.

The oxidation of soluble manganese (Mn(II)) to insoluble manganese dioxide (MnO_x(s)) is fairly well understood; however, the role of ferric hydroxide/oxides (Fe(OH)₃_(s)) in catalyzing the oxidation of Mn(II) by oxidants such as free chlorine (HOCI) is one specific aspect of manganese removal via oxidation that requires further investigation. Data collected in this study indicate that the rate of Mn(II) oxidation may be beneficially catalyzed by the presence of previously formed Fe(OH)₃_(s) particles. The mechanistic means by which this enhanced oxidation is accomplished was the focal point of this research. Specifically, the research objectives were as follows: (1) To study all possible Mn(ID) removal mechanisms for a typical groundwater system to determine the necessary experimental conditions required to isolate the study of Mn(II) oxidation in the presence of ferric hydroxides/oxides (Fe(OH)₃_(s)). (2) To investigate the means by which ferric hydroxides/oxides (Fe(OH)₃_(s)) may enhance the removal of Mn(II) during water treatment by interacting with HOCI; and (3) To develop an engineered system that captures the observed catalyzing effect iron oxides have on Mn(II) oxidation by HOCI citing key system design parameters. To complete these objectives a combination of batch and continuous flow bench-scale experiments were utilized. Batch study results indicated that the primary Mn(II) removal mechanism was a combination of adsorption and oxidation, specifically, adsorption of Mn(II) onto the iron oxide surface where Mn(II) is subsequently oxidized. A continuous flow system was developed to utilize this removal mechanism under water treatment plant conditions to improve the efficiency of iron and manganese removal. The results from experimentation with the continuous flow system indicated the following: ∙ Sufficient free chlorine residual in effluent insures consistent system performance, ∙ Initial iron oxide concentration within reactor system must have adequate adsorption capacity for initial adsorption-oxidation step to occur, ∙ Removal efficiency and reactor stability increase with the accumulation of manganese oxides, and ∙ Solution pH and reactor hydraulics affect system performance significantly. The results suggest that this technology has the potential to change the look of conventional groundwater treatment systems that practice iron and manganese removal. / Master of Science