Wang J.,Center for Advanced Separation Technologies |
Yoon R.-H.,Center for Advanced Separation Technologies |
Morris J.,Virginia Polytechnic Institute and State University
International Journal of Mineral Processing | Year: 2013
Surface forces have been measured in situ between gold surfaces hydrophobized by self-assembly of xanthates from aqueous solutions using an atomic force microscope (AFM). The measurements conducted in potassium amyl xanthate (KAX) and potassium ethyl xanthate (KEX) solutions showed long-range hydrophobic forces, with the force curves showing no evidence for nanobubbles on the surfaces. The strongest hydrophobic force was observed at contact angle above 90 and in pure water, with a decay length of 29.5 nm. Both the contact angle and hydrophobic force increased with increasing xanthate concentration. At an excessively high concentration, the hydrophobic force diminished substantially. When the xanthate solution was replaced with pure water, however, a strong hydrophobic force reappeared, suggesting that the presence of residual xanthate ions in solution is detrimental to obtaining a strong and long-range hydrophobic force. This finding is consistent with the observation that hydrophobic force becomes weaker in the presence of NaCl in solution. © 2013 Elsevier B.V.
Funded in part by a U.S. Department of Energy National Energy Technology Laboratory grant, Virginia Tech engineers will test HHS technology, a patented process that takes advantage of properties of water-friendly and water-repellent materials to extract rare earth elements from coal waste, according to Roe-Hoan Yoon, a University Distinguished Professor and the Nicholas T. Camicia Professor of Mining and Materials Engineering. The effort is led by principal investigator Rick Honaker, a professor and chair of the University of Kentucky's Department of Engineering, who received his undergraduate and graduate engineering degrees at Virginia Tech. Researchers from West Virginia University and representatives from five corporate partners are also part of the team. The pilot effort is important because rare earth materials, used to create powerful permanent magnets in products as common as computer hard drives to electric motors, are in increasingly short supply, particularly heavy rare earth elements, researchers said. The best known source of the heavy rare earths is the clay from the Jiangxi Province, South China. But those resources are expected to be exhausted within 20 years, while recent studies showed that coal may be an excellent source of higher value heavy rare earth elements. "The majority of rare earths is produced in China as byproducts," said Yoon, who is the director of the Center for Advanced Separation Technologies at Virginia Tech. "With the recent closure of the rare earth mine in California, the U.S. relies more heavily on imports. It will be good for the country if we can develop an advanced separation technology to extract the critical materials from coal as byproducts, particularly the high-value rare earths essential for advanced manufacturing industries." The issue of domestic production affects matters concerning development of renewable energy resources and national security, the researchers said. "Domestic supply of rare earth materials is critical for the U.S. manufacturing industry," said U.S. Rep. Morgan Griffith, who represents Virginia's 9th district in the U.S. House of Representatives. "As the nation moves toward electric-drive vehicles, wind farming, and other sustainable energy measures, it is important to develop a reliable source of essential materials. In addition, we will develop new, cleaner applications for coal and coal byproducts to revitalize the mining industry." The U.S. has 10.9 million tons of rare earth resources in coal deposits located in just five western and four eastern states, including Kentucky, West Virginia and Virginia, according to the U.S. Geological Survey Coal Quality Database. Gerald Luttrell, the E. Morgan Massey Professor of Mining and Materials Engineering, will work with Yoon to execute Virginia Tech's part in the project, which involves a patented process called hydrophobic-hydrophilic separation (HHS). In addition to the academic partners, the team will also work with Arch Coal, Blackhawk Mining, Bowie Refining, Eriez Manufacturing and Minerals Refining Company. If the currently funded Phase I project is successful, researchers will seek $6 million in Phase II funding that will involve construction and testing of a mobile facility to be tested at different coal cleaning facilities in the central Appalachian coal field. Explore further: Commercial-scale test of new technology to recover coal from sludge successful
Park S.,Center for Advanced Separation Technologies |
Soni G.,Center for Advanced Separation Technologies |
Huang K.,Center for Advanced Separation Technologies |
Do H.,Center for Advanced Separation Technologies |
Yoon R.-H.,Center for Advanced Separation Technologies
IMPC 2014 - 27th International Mineral Processing Congress | Year: 2014
In a flotation froth (and foam), air bubbles become larger due to coalescence, causing bubble size to increase, bubble surface area to decrease, and hence casing less hydrophobic particles to drop off to the pulp phase below. Thus, bubble coarsening provides an important mechanism by which product grades are increased. On the other hand, excessive bubble coarsening results in low recoveries. In the present work, a model describing the process of bubbles becoming coarser in a foam as they rise to the top by deriving a mathematical relation between the Plateau border area, which controls film drainage rate, and the lamella film thickness, which controls bubble-coalescence rate. The model has been derived by assuming that liquid drainage rate increases due to slip at the air/water interface, and that the critical rupture thickness is determined by the capillary waves created by thermal motion. The model developed in the present work can predict the bubble size ratio between the top and bottom of a foam as functions of aeration rate, foam height, and surface tension (frother dosage). The model predictions are in good agreement with the changes in bubble sizes measured using a high-speed camera.