Dewatering fine coal is needed in many applications but has remained a great challenge. The hydrophobic-hydrophilic separation (HHS) method is a powerful technology to address this problem. However, organic solvents in solvent-coal slurries produced during HHS must be recovered for the method to be economically viable. Here, the experimental studies of recovering solvents from pentane-coal and hexane-coal slurries by combining liquid-solid filtration and in-situ vaporization and removing the solvent by a carrier gas (i.e., drying) are reported. The filtration behaviors are studied under different solid mass loading and filtration pressure. It is shown that using pressure filtration driven by 20 psig nitrogen, over 95% of solvents by mass in the slurries can be recovered, and filtration cakes can be formed in 60 s. The drying behavior was studied using nitrogen and steam at different temperatures and pressures. It is shown that residual solvents in filtration cakes can be reduced below 1400 ppm within 10 s by 15 psig steam superheated to 150C, while other parameter combinations are far less effective in removing solvents. Physical processes involved in drying and the structure of solvent-laden filtration cakes are analyzed in light of these results. / Master of Science / Coal particles below a certain size are discarded to waste tailing ponds as there is no economically viable method for processing them. However, a new process called hydrophobic-hydrophilic separation offers a solution to this problem. A hydrophobic solvent is used to displace water from a coal-water slurry, and it is then easier and cheaper to filter and dry this new coal-solvent slurry. In this work experimental studies of recovering solvents from pentane-coal and hexane-coal slurries by combining filtration and drying are reported. The filtration behaviors are studied under different solid mass loading and filtration pressures. It is shown that using pressure filtration driven by 20 psig nitrogen, over 95% of solvents by mass in the slurry can be recovered, and filtration cakes can be formed in 60 s. The drying behavior was studied using nitrogen and steam at different temperatures and pressures to evaporate any remaining solvents. It is shown that the remaining solvents in filtration cakes can be reduced below 1400 ppm within 10 s by using 15 psig steam superheated to 150C as a drying medium, while other parameter combinations are far less effective in removing solvents. Physical processes involved in drying and the structure of solvent-laden filtration cakes are analyzed in light of these results.

Froth flotation has long been regarded as the best available technology for ultrafine particles separation. However, froth flotation has extreme deficiencies for recovering ultrafine particles that are less than 30-50 μm in size for coal and 10-20 μm for minerals. Furthermore, dewatering of flotation products is difficult and costly using currently available technologies. Due to these problems, coal and mineral fines are either lost to tailings streams inadvertently or discarded purposely prior to flotation. In light of this, researchers at Virginia Tech have developed a process called hydrophobic-hydrophilic separation (HHS), which is based originally on a concept known as dewatering by displacement (DbD). The process uses non-polar solvents (usually short-chain alkanes) to selectively displace water from particle surfaces and to agglomerate fine coal particles. The resulting agglomerates are subsequently broken (or destabilized) mechanically in the next stage of the process, whereby hydrophobic particles are dispersed in the oil phase and water droplets entrapped within the agglomerates coalesce and exit by gravity along with the hydrophilic particles dispersed in them. In the present work, further laboratory-scale tests have been conducted on various coal samples with the objective of commercial deployment of the HHS process. Test work has also been conducted to explore the possibility of using this process for the recovery of ultrafine minerals such as copper and rare earth minerals. Ultrafine streams produced less than 10% ash and moisture consistently, while coarse coal feed had no observable degradation to the HHS process. Middling coal samples were upgraded to high-value coal products when micronized by grinding. All coal samples performed better with the HHS process than with flotation in terms of separation efficiency. High-grade rare earth mineral concentrates were produced with the HHS process ranging from 600-2100 ppm of total rare earth elements, depending on the method and reagent. Additionally, the HHS process produced copper concentrates assaying greater than 30% Cu for both artificial and real feed samples, as well as, between 10-20% Cu for waste samples, which all performed better than flotation. / Master of Science / Froth flotation has long been regarded as the best available technology for separating fine particles. Due to limitations in particle size with froth flotation, and high downstream dewatering costs, a new process has been developed called the hydrophobic-hydrophilic separation (HHS) process. This process was originally based on a concept known as dewatering by displacement (DbD) which was developed by researchers at Virginia Tech in 1995. The process uses hydrocarbon oils, like pentane or heptane, to selectively collect hydrophobic particles, such as coal, for which it was originally developed. In coal preparation plants, a common practice is to purposefully discard the ultrafine stream that flotation cannot recover and has an increased dewatering cost. The HHS process can effectively recovery this waste stream and produce highgrade salable product, with significantly reduced cost of dewatering. In the work presented, laboratory-scale tests have been conducted on various coal samples with the objective of commercial deployment of the HHS process. In this respect, several varying plant streams have been tested apart from the traditional discard stream. Additionally, test work has expanded into mineral commodities such as copper and rare earth minerals. In this work, salable high-value coal products were achievable with the HHS process. Ultrafine streams consistently produced less than 10% ash and moisture. Coarse coal feeds had no observable degradation to the HHS process and were able to produce single digit ash and moisture values. Middling coal samples were upgraded to high-value coal products when micronized by grinding. All coal samples performed better with the HHS process than with flotation in terms of separation efficiency. High-grade rare earth mineral concentrates were produced with the HHS process ranging from 600- 2100 ppm of total rare earth elements depending on the method and reagent. Additionally, the HHS process produced copper concentrates assaying greater than 30% Cu for an artificial and feed samples, as well as, between 10-20% Cu for waste samples, which all performed better than flotation.

This thesis pertains to the processing of ultra-fine mineral particles and low rank coal using the hydrophobic--hydrophilic separation (HHS) method. Several explorative experimental tests have been carried out to study the effect of the various physical and chemical parameters on the HHS process. In this study, the HHS process has been employed to upgrade a chalcopyrite ore. A systematic experimental study on the effects of various physical and chemical parameters such as particle size, reagent dosage and reaction time on the separation efficiencies have been performed. For this, a copper rougher concentrate (assaying 15.9 %Cu) was wet ground and treated with a reagent to selectively hydrophobize the copper-bearing mineral (chalcopyrite), leaving the siliceous gangue minerals hydrophilic. The slurry was subjected to a high-shear agitation to selectively agglomerate the chalcopyrite and to leave the siliceous gangue dispersed in aqueous phase. The agglomerates were then separated from dispersed gangue minerals by screening and the agglomerates dispersed in a hydrophobic liquid (n-pentane) to liberate the water trapped in the agglomerates. The chalcopyrite dispersed in the hydrophobic liquid was separated from the medium to obtain a concentrate substantially free of gangue minerals and moisture. The copper recoveries were substantially higher than those obtained by flotation. The HHS process was also tested on ultrafine mono-sized silica beads. The results were superior to those obtained by flotation, particularly with ultrafine particles. The HHS process has also been tested successfully for upgrading subbituminous coals. Low-rank coals are not as hydrophobic as high-rank coals such as bituminous and anthracite coals. In the present work, a low-rank coal from Wyoming was hydrophobized with appropriate reagents and subjected to the HHS in a similar manner as described for processing copper. The results showed that the HHS process reduced the moisture substantially and increased the heating value up to 50% without heating the coal. Laboratory-scale tests conducted under different conditions, e.g., particle size, reagent type, reaction time, and pretreatments, showed promising results. Implementation for the HHS process for upgrading low-rank coals should help reduce CO2 emissions by improving combustion efficiencies. / Master of Science