Browsing by Author "Honaker, Ricky Quay"

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    Development and Testing of a Mobile Pilot Plant for the Advancement and Scale-up of the  Hydrophobic-Hydrophilic Separation Process
    Sechrist, Chad Michael (Virginia Tech, 2024-06-03)
    Fine particle separation is a grand challenge in the mining and mineral processing industry. The industry standard process, froth flotation, is extremely robust and adaptable; however, it is inefficient for particles less than 20 microns. Owing to this limitation, some mining sectors, such as coal, opt to discard the ultrafine particles to waste impoundments as the costs to recover and dewater these materials are prohibitive. The Hydrophilic Hydrophobic Process (HHS) is one alternative to flotation that uses a recyclable solvent, rather than air bubbles, to selectively recover fine hydrophobic particles. Prior laboratory, proof-of-concept, and demonstration-scale testing has shown that the HHS process is extremely efficient, having no effective size limitation. The purpose of this research was to continue the development and improvement of the HHS process, through the design, construction, and testing of a mobile pilot plant. The pilot plant would in turn be used to demonstrate the robustness of the HHS process through a systemic study of multiple coal sources and ranks. In addition, the pilot plant would serve as a testbed for inquiry-based process intensification, the development and evaluation of design criteria for the various unit operation. Through the course of this research, a 50 lb./hr. (product rate) pilot plant was constructed and commissioned. Initial investigations focused on the shakedown and design of key unit operations, including the agglomeration and de-emulsification (i.e. Morganizing) steps. Studies showed that the initial design of these units, namely pump induced mixing in agglomeration and packed bed emulsification in the Morganizer, were not adequate to meet production demands, and as such, these stages were redesigned after appropriate fundamental evaluations. After implementing the design changes, the pilot plant was successfully operated over a 7-month period, routinely producing bituminous products with less than6% ash and less than 10% moisture as well as anthracite products with less than 3% ash and less than 4% moisture. This study also evaluated a new approach to de-emulsification using a jig based Morganizer in place of the standard oscillating column Morganizer. The jig utilizes a pulsing mechanism to move liquid to break up agglomerates versus the mechanical disk stack. Preliminary results showed that the jig Morganizer was comparable to the oscillating unit at more than half the size. This new design provides a pathway for reduced cost, footprint, and improved scalability. Lastly, this study evaluated both the HHS process and dual-scan X-ray based particle sorting as means of increasing the REE content of coal-based materials. Data from a pilot-scale x-ray sorter showed the unit was capable of preconcentrating REEs to over 300 ppm, while data from the HHS similarly showed the process was capable of REE recoveries of 85-90% and of preconcentrating REEs above 300 ppm. Altogether, these results indicate That both of these technologies are capable of efficiently and cost effectively preconcentrate REEs from wastes streams at operating coal preparation plants.
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    Development of the selective-shear coagulation process for ultrafine coal cleaning
    Honaker, Ricky Quay (Virginia Polytechnic Institute and State University, 1988)
    In order to produce coal containing less than 2% ash using a physical cleaning process, the coal must initially be ground to liberate the mineral matter. The result is a micronized feed material that cannot be efficiently treated using the commercial methods currently available. Therefore, an advanced physical cleaning technique for ultrafine coal, called"selective-shear coagulation", is presently being investigated. The process utilizes high shear conditions to overcome the strong electrostatic repulsive force between particles. The attractive hydrophobic interaction and van der Waals forces control the coagulation of the coal particles. The effects of various chemical parameters, such as pH and ion concentration, were studied. An optimum pH range was established for tap water and distilled water media. The presence of multivalent cations in the system increased coal recovery, but decreased selectivity. Physical parameters of the selective coagulation process, such as particle size, percent solids, and specific energy input, were studied. It was found that separation efficiency improved with decreasing particle size. An optimum feed percent solids was found by maximizing separation efficiency. In the case of distilled water, test results revealed that additional specific energy provided by mechanical agitation was required to induce coagulation after grinding. However, additional mixing was found unnecessary in the case of tap water. A continuous selective-shear coagulation process using an elutriation column as the separator was designed and characterized. A steady-state population balance model of the elutriation column was developed. The predictions were found to be in good agreement with experimental results.
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    A fundamental study of the selective hydrophobic coagulation process
    Honaker, Ricky Quay (Virginia Tech, 1992-07-05)
    It has been found that naturally hydrophobic carbonaceous materials such as coal and graphite can be selectively coagulated and separated from hydrophilic impurities without the use of oily agglomerants, flocculants or electrolytes. The coagulation occurs at ζ-potentials significantly higher than those predicted by the classical DLVO theory, suggesting that it is driven by a hydrophobic interaction energy. Thus, the process is referred to as the selective hydrophobic coagulation (SHe) process. The fundamental development of this process is the focus of this study. In this study, the energy barriers for the coagulation of two different coal samples and a graphite sample have been calculated using the extended DLVO theory, which incorporates the hydrophobic interaction energy in addition to the dispersion and the electrostatic energies. Stability diagrams have been developed from the data, which show that the maximum ζ-potential at which a given coal can coagulate decreases as surface hydrophobicity decreases. For the coagulation of minerals present in coal, the classical DLVO theory has been used for the energy barrier calculations. The results of these calculations provide an excellent correlation with the results from a series of SHC tests conducted with run-of-mine coal. The strength of the coal aggregates have also been investigated by measuring the coagula size distributions under different hydrodynamic conditions. The coagula size distributions were measured using an in-situ particle size analyzer. These results have been used along with models for coagulation rate and breakage rate to determine strength characteristics of the aggregates and to verify the primary parameters controlling the aggregate size. The study found that the coal and graphite aggregates incurred a substantial reduction in size when a small amount of mechanical agitation was applied. Based on this outcome, quiescent continuous processes have been successfully designed and developed to separate the coagulated hydrophobic particles from the dispersed hydrophilic particles.