Browsing by Subject "Clay"
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Item 2015 Clay County Adolescent Sexual Health Report(2015) Teenwise MinnesotaItem 2016 Clay County Adolescent Sexual Health Report(2016) Healthy Youth Development - Prevention Research CenterItem 2017 Clay County Adolescent Sexual Health Report(2017) Healthy Youth Development - Prevention Research CenterItem 2018 Clay County Adolescent Sexual Health Report(2018) Healthy Youth Development - Prevention Research CenterItem 2019 Clay County Adolescent Sexual Health Report(2019) Healthy Youth Development - Prevention Research CenterItem 2020 Clay County Adolescent Sexual Health Report(2020) Healthy Youth Development - Prevention Research CenterItem 2021 Clay County Adolescent Sexual Health Report(2021) Healthy Youth Development - Prevention Research CenterItem 2022 Clay County Adolescent Sexual Health Report(2022) Healthy Youth Development - Prevention Research CenterItem 2023 Clay County Adolescent Sexual Health Report(2023) Healthy Youth Development - Prevention Research CenterItem Adsorption of Freshwater Dissolved Organic Matter to Clay and Polyethylene Particles(2019-08) Burrows, AlvinOrganic matter (OM), especially dissolved organic matter (DOM), plays several integral roles in aquatic systems. OM acts as a short-term sink of carbon and a food source for heterotrophs and shields biota from harmful UV radiation. It also facilitates the transport of nutrients, trace metals and pollutants in the environment. The uptake and transport of these compounds are related to the fate of the DOM to which they are bound. Suspended solids such as clays or microplastics can adsorb DOM into their interlayer spaces or onto their surfaces leading to: 1. Possible physical protection of OM that would have been mineralized or degraded by biota; 2. Increased transport of OM through the water column to the sediments (for sinking particles) or increased time for OM in the surface water (for less-dense microplastic particles); 3. Increased uptake by larger aquatic organisms. Increased particle-associated mobility (either by sinking through the water column or being transported at the surface via wind-driven processes) also increases associated nutrient, trace metal and pollutant transport, which in sufficient quantities, may perturb the aquatic system’s equilibrium and affect its chemistry. Microplastics, a new particle-type in aquatic systems, have been observed and documented in the world’s oceans since the 1970s, but their presence in the Laurentian Great Lakes was first recorded in 2013. The roles that microplastics and other particulates (both naturally occurring and anthropogenically impacted) play in aquatic environments need to be thoroughly studied so that a better understanding of their fate and environmental impact can be gained. The goal of this study was to qualitatively examine and compare the adsorption of open water Lake Superior DOM and DOM from a tributary stream to polyethylene microplastic spheres and to clays (kaolinite and montmorillonite). UV-VIS optical proxies were used to monitor changes in aromaticity (A254, SUVA) and molecular weight (E2:E3, S250-400, SR) within the remaining dissolved phase. Aromaticity proxies suggest that clays preferentially adsorbed aromatic species, while polyethylene had no significant effect on DOM composition. Changes in the amount of carbon remaining in the dissolved phase were measured using dissolved organic carbon (DOC) analysis while the amount adsorbed to the surface of the particulates was measured using elemental analysis (EA). DOC analysis did not show significant changes in the amount of dissolved organic carbon after sorption testing. EA was unable to provide a definitive answer for carbon adsorbed by polyethylene but suggests that kaolinite and montmorillonite adsorb similar amounts of carbon in both environments.Item Chemical and Hydrodynamic Effects in Polymer-Clay Flocculation: Anisotropic particulate size and surface morphology effects in varied and controlled hydrodynamic fields(2017-12) Wilkinson, NikolasPolymer-driven flocculation of suspended particles is a critical process for many applications, including composite materials synthesis, paper manufacturing, and water treatment. However, the role of solution physicochemical properties on the polymer-particle assembly dynamics is nontrivial, particularly for non-spherical, polydisperse particulates such as natural clays. Properties including ionic strength and pH affect both the individual particulate aggregates themselves, as well as the polymer – particle flocculation event. In this work, we study the effects of ionic strength and aggregate size and structure on the polymer behavior and flocculation performance with anisotropic bentonite clay particles using traditional jar tests. The final floc structure is largely informed by ionic-strength driven changes to the initial clay aggregate size and surface structure. With increasing bentonite aggregate size, a transition from a networked to a patched polymer − aggregate floc structure is observed, independent of ionic strength during flocculation. Additionally, the clay’s aggregate morphology is a more direct control parameter of optimal polymer dose and final turbidity (turbidity after 5 min sedimentation) than zeta potential for aqueous bentonite systems. Flocculation performance is the same when bentonite aggregate morphology is the same, regardless of a change in zeta potential. Likewise, when bentonite aggregate morphology changes, flocculation performance also changes, regardless of the identical zeta potential. Therefore, initial clay aggregate morphology controls the extent of polymer adsorption and optimal polymer dose, while initial clay aggregate size controls the internal floc structure. While traditional jar tests offer the advantages of experimental simplicity, speed, and mimic treatment geometries, there is limited homogeneity and control over hydrodynamics within the system. Taylor-Couette cells offer a much higher degree of hydrodynamic control and have been shown to improve several industrial processes due to the wide variety of hydrodynamic flow states accessible. Traditional designs, however, limit the ability to introduce new fluids into the annulus during device operation due to geometric confinement and complexity. As a key part of this thesis effort, a co- and counter-rotating Taylor-Couette cell with radial fluid injection has been constructed. The new inner cylinder design does not modify the critical Re for flow instabilities and can precisely inject a desired mass at a desired flow rate. Using the newly designed, modified Taylor-Couette cell, axial mass transport behavior is experimentally determined over two orders of magnitude of Reynolds number. Four different flow states, including laminar and turbulent Taylor vortex flows and laminar and turbulent wavy vortex flows, were studied. Using flow visualization techniques, the estimated dispersion coefficient was found to increase with increasing Re, and a single, unified regression is found for all vortices studied. In addition to mass transport, the vortex structures’ stability to radial injection is also quantified. A new dimensionless stability criterion, the ratio of injection to diffusion timescales, was utilized to capture the conditions under which vortex structures are stable to injection. Using the stability criterion, global and transitional stability regions are identified as a function of Reynolds number, Re. Overall, this thesis examines chemical and hydrodynamic effects in polymer flocculation with natural clays, and shows the importance of initial contaminant properties on flocculation performance. The initial contaminant properties affect both flocculation efficiency and resultant floc structure and are often not considered at treatment plants. Consideration of these properties potentially can improve process predictive capabilities, which improves process performance.Item Data supporting Inhibition of the Growth of Harmful Algal Bloom-forming Freshwater Cyanobacteria by Clay(2022-03-14) Yang, Judy Q; Tomaska, Katherine R; Wei, Guanju; tomas098@umn.edu; Tomaska, Katherine R; Yang Research Group: Environmental Transport LabThis dataset contains cell density measurements and confocal images of Microcystis Aeruginosa. The raw data from hand counting cells under a microscope with a hemocytometer is included, as well as the calculated cell density based on the hemocytometer measurements. The bacteria cells were grown in one of three growth conditions. Each growth condition was simulated in three different flasks. For each date, the cell densities of identical growth conditions were averaged. Cell densities for each date and growth condition were subsequently plotted with error bars to determine any trends. Additionally, data on the environmental conditions of cell growth are included on dates when the measurements were taken. The physical interactions between cyanobacteria and clay particles were visualized using a confocal laser scanning microscope (Nikon C2 plus). Each image is around 2048 by 2048 pixels at a resolution of 0.08 um/pixel. We used a 20X objective magnification. A sequence of images was taken at 10-second intervals for 5 minutes. The laser used for excitation has a wavelength of 488 nm (FITC) and the emission wavelength is 525 nm.Item Role of Water Chemistry on Balling(University of Minnesota Duluth, 2003-06-20) Iwasaki, Iwao; ;Green ball qualities are adversely affected by increased concentrations of Ca++ and Mg++ in process waters because of the replacement of Na+ in bentonite by the divalent cations through cation exchange reaction. Preliminary laboratory tests indicated that displacement of interstitial plant water in filter cakes with RO. water restored ball quality. A few preliminary pilot plant tests were performed to study the effect of removing ca++ and Mg++ ions from filter cakes during filtration by spray washing with softened water, and its effect on balling characteristics.Item Two-dimensional clay and graphene nanosheets for polymer nanocomposites and energy storage applications(2013-08) Qian, YuqiangClay and graphene nanosheets are attractive to materials scientists due to their unique structural and physical properties and potentially low cost. This thesis focuses on the surface modification and structure design of clay and graphene nanosheets, targeting special requirements in polymer nanocomposites and energy storage applications. The high aspect ratio and stiffness of clay and graphene nanosheets make them promising candidates to reinforce polymers. However, it is challenging to achieve a good dispersion of the nanosheets in a polymer matrix. It is demonstrated in this study that organic modifications of clay and graphene nanosheets lead to better filler dispersion in polymer matrices. A prepolymer route was developed to achieve clay exfoliation in a polyurethane-vermiculite system. However, the phase-separated structure of the polyurethane matrix was disrupted. Intragallery catalysis was adopted to promote the clay exfoliation during polymerization. With both catalytic and reactive groups on the clay modifier, the polyurethane-vermiculite nanocomposites showed a significant increase in modulus and improved barrier performance, compared to neat polyurethane. The toughening effect of graphene on thermosetting epoxies and unsaturated polyesters (UPs) was also investigated. Various types of graphene with different structures and surface functionalities were incorporated into the thermosetting resin by in situ polymerization. The toughening effect was observed for epoxy nanocomposites at loading levels of less than 0.1 wt%, and a peak of fracture toughness was observed at 0.02 or 0.04 wt% of graphene loadings for all epoxy-graphene systems. A microcrack-crazing mechanism was proposed to explain the fracture behavior of epoxy-graphene systems based on fractography observations. Similar peak behavior of fracture toughness was not observed in UP system. UP nanocomposites with modified graphene oxide showed better mechanical performance than those with unmodified graphene oxide, which was attributed to better graphene dispersion and a stronger UP-graphene interface. Graphene has also been extensively studied in energy storage applications, due to its high conductivity and surface area. In order to utilize the benefits of graphene, macroscopic graphene/V2O5 films and graphene aerogels were fabricated from the self-assembly of graphene materials. The unique 2D structure of graphene helped to maintain the integrated film morphology in graphene/V2O5 composites and the monolithic macroporous structure in graphene aerogels. Good conductivity was obtained by incorporation of graphene sheets in the structure, which results in good electrochemical performance as electrode materials for batteries or supercapacitors. The facile preparation methods allow good control of the composition and thus the properties of the macroscopic graphene nanostructures.