Browsing by Subject "Bentonite"

Now showing 1 - 5 of 5
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    Chemical and Hydrodynamic Effects in Polymer-Clay Flocculation: Anisotropic particulate size and surface morphology effects in varied and controlled hydrodynamic fields
    (2017-12) Wilkinson, Nikolas
    Polymer-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.
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    Green Ball Characterization
    (University of Minnesota Duluth, 2005-09-13) Kiesel, Richard F
    The objective of this research project was to correlate the physical quality of green balls with their behavior in the elastic region of the deformation curve under load. An understanding of the parameters that are key to the production of these quality standards will help to improve the quality of their products. Green ball quality is accepted by the industry as one of these key parameters. A procedure to further characterize green balls and develop a relationship to current quality assessment procedures will provide insight to the physical attributes and integrity of the green balls. A digital force gauge and compression test stand interlocked with PC based software was used to collect data and develop the relationship with the deformation of the green ball. Data on both wet and dried green balls were collected on varied bentonite additions and green ball moisture concentrations. The slope of the deformation curve, in the elastic region, was studied with regards to the green ball drop number, moisture content, wet strength and dry strength. The deformation behavior of the green balls is indirectly proportional to the slope of the deformation curve. As the elasticity of the green ball increases, the dry drop number, wet drop number and dry compressive strength is reduced. Although no significantly strong relationships are present, it is believed that the relationships to green ball quality, by collecting sufficient data over a period of time, can be significant.
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    Investigation of Papermill Sludge as a Taconite Binder
    (University of Minnesota Duluth, 1989-03-16) Goetzman, Harold E;
    Bentonite has been used by the taconite industry since commercialization of the process in the early 1950's. Although many alternate binders have been tested, including organic materials, bentonite still remains the preferred binder. Bentonite has the unique qualities that promote stable green balling conditions and provides acceptable strengths during drying, preheating, and contributes to the fired pellet strength at an acceptable cost. The incentive to consider other binders is based on such factors as improving the metallurgical properties of the pellets, decreasing their silica content, and lower overall costs. The USBM conducted a number of small scale tests using papermill sludge and other additives in place of bentonite as a binder for taconite pellets. Their balling tests indicated that acceptable green-ball strength could be achieved with papermill sludge. The fired pellet evaluations, however, were based on muffle furnace tests which do not accurately predict the fired pellet quality. Although the fired pellet data were also encouraging it was recognized that pot-grate tests were needed to obtain more definitive test data that could be directly related to commercial practice. Subsequently, the USBM recommended that the IRRRB fund an extension of the program to include pot-grate tests to verify the fired pellet quality obtained in the muffle furnace work. A test program was prepared by the Coleraine Research Laboratory of the Natural Resources Research Institute (NRRI) in cooperation with Dr. J. Nigro and Dr. L. Haas, USBM, and Mr. S. Dickinson, IRRRB. The contract proposal was submitted to the IRRRB January 27, 1988. The contract included evaluation of concentrate and sludge filtering and blending aspects, green-ball quality, and fired pellet quality based on pot-grate tests. This report presents data on all three aspects as stated in the contract and conclusions regarding future efforts in this area.
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    Role of Water Chemistry on Balling
    (University of Minnesota Duluth, 2000-06) 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. Several approaches were considered and some of the approaches were tested for remedying the adverse effects, namely, displacing moisture water by softened water by washing in filtration, increased use of bentonite, and such additives as Na2C03, NaHC03, NaOH, (NH4)2C03, EDTA, modified starch, and molasses. The use of NaOH and Na2C03 were quite effective in restoring the ball quality, particularly, when a combination of a modified starch and Na OH was used. It becomes of interest to investigate the mechanism that leads to the beneficial effects of these additives, so that some other additives, besides Na+containing salts, may be suggested.
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    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.