Browsing by Author "Li, Biao"

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    Discrimination of Six Flotation Kinetic Models Used in the Conventional Flotation and Carrier Flotation of -74 μm Coal Fines
    Bu, Xiangning; Wang, Xuexia; Zhou, Shaoqi; Li, Biao; Zhan, Hanhui; Xie, Guangyuan (2020-06-16)
    In this study, experimental results of conventional flotation and carrier flotation were characterized by six commonly used flotation kinetic models. Two statistical criteria (coefficient of determination, R-2, and root mean square error, RMSE) were used for comparison of fitting performance of different models. All kinetic models tested gave good levels of goodness of fit, but the second-order model with rectangular distribution (model 6) provided the best fitting performance for the experimental data of conventional flotation and carrier flotation. On this basis, two parameters, that is, modified flotation rate constant (K-m) and selectivity index (SI), were used to evaluate the difference in flotation separation selectivity between conventional flotation and carrier flotation. Comparisons of K-m and SI values indicated that carrier flotation significantly improved the flotation rate constant of combustible materials and flotation separation selectivity of ultrafine coal (-74 mu m). In addition, measurements of average bubble size and water recovery indicated that both the coalescence of bubbles and the drainage of liquid in the froth were promoted when coarse coal particles (contact angle >90 degrees) were employed as the carrier to assist the flotation recovery of ultrafine particles, which in turn favored the inhibition effect of the entrainment of gangue materials in carrier flotation compared to conventional flotation.
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    Grinding Behaviors of Components in Heterogeneous Breakage of Coals of Different Ash Contents in a Ball-and-Race Mill
    Duan, Jin; Lu, Qichang; Zhao, Zhenyang; Wang, Xin; Zhang, Yuxin; Wang, Jue; Li, Biao; Xie, Weining; Sun, Xiaolu; Zhu, Xiangnan (MDPI, 2020-03-03)
    Coals used for power plants normally have different ash contents, and the breakage of coals by the ball-and-race mill or roller mill is an energy-intensive process. Grinding phenomena in mill of power plants is complex, and it is also not the same with ideal grinding tests in labs. The interaction among various coals would result in changes of grinding behaviors and energy consumption characterization if compared with those of single breakage. In this study, anthracite and bituminous coal of different ash contents were selected to be heterogeneously ground. Quantitation of components in products was realized using the relation between sulfur content of the mixture and mass yield of one component in the mixture. Product fineness t10 of the component was determined, and split energy was calculated on the premise of specific energy balance and energy-size reduction model by a genetic algorithm. Experimental results indicate that breakage rate and product fineness t10 of the mixture decrease with the increase of hard anthracite content in the mixture. Unlike the single breakage, t10 of anthracite in heterogeneous grinding is improved dramatically, and bituminous coal shows the opposite trend. The interaction between components results in the decrease of the specific energy of the mixture if compared with the mass average one of components in single breakage. Breakage resistance of hard anthracite decreases due to the addition of soft bituminous coal, and grinding energy efficiency of anthracite is also improved compared with that of single grinding.
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    Hydrophobic-Hydrophilic Separation Process for the Recovery of Ultrafine Particles
    Li, Biao (Virginia Tech, 2019-11-20)
    The demands for copper and rare earth elements (REEs) in the U.S. will keep rising due to their applications in green energy technologies. Meanwhile, copper production in the U.S. has been declining over the past five years due to the depletion of high-grade ore deposits. The situation for REEs is worse; there is no domestic supply chain of REEs in the U.S. since the demise of Molycorp, Inc. in 2016. Studies have shown that the rejected materials from copper and coal processing plants contain significant amounts of valuable metals. As such, this rejected material can be considered as potential secondary sources for extracting copper and REEs, which may help combat future supply risks for the supply of copper and REEs in the U.S. However, the valuable mineral particles in these resources are ultrafine in size, which poses considerable challenges to the most widely used fine particle beneficiation technique, i.e., froth flotation. A novel technology called the Hydrophobic-Hydrophilic Separation (HHS) process, developed at Virginia Tech, has been successfully applied to recover fine coal in previous research. The results of research into the HHS process showed that the process has no lower particle size limit, similar to solvent extraction. Therefore, the primary objective of this research is to explore the feasibility of using the new process to recover ultrafine particles of coal, copper minerals, and rare earth minerals (REMs) associated with coal byproducts. In the present work, a series of laboratory-scale oil agglomeration and HHS tests have been carried out on coal with the objectives of assisting the HHS tests in pilot-scale, and the scale-up of the process. The knowledge gained from this study was successfully applied to solving the problems encountered in the pilot-scale tests. Additionally, a new and more efficient equipment known as the Morganizer has been designed and constructed to break up the agglomerates in oil phase as a means to remove entrained gangue minerals and water. The effectiveness of the new Morganizers has been demonstrated in laboratory-scale HHS tests, which may potentially result in the reduction of capital costs in commercializing the HHS process. Furthermore, the prospect of using the HHS process for processing high-sulfur coals has been explored. The results of this study showed that the HHS process can be used to increase the production of cleaner coal from waste streams. Application of the HHS process was further extended to recover the micron-sized REMs from a thickener underflow sample from the LW coal preparation plant, Kentucky. The results showed that the HHS process was far superior to the forced-air flotation process. In one test conducted during the earlier stages of the present study, a concentrate assaying 17,590 ppm total REEs was obtained from a 300 ppm feed. In this test, the Morganizer was not used to upgrade the rougher concentrate due to the lack of proper understanding of the fundamental mechanisms involved in converting oil-in-water (o/w) Pickering emulsions to water-in-oil (w/o) Pickering emulsions. Many of the studies has, therefore, been focused on the studies of phase inversion mechanisms. The results showed that phase inversion requires that i) the oil contact angles (θo) of the particles be increased above 90o, ii) the phase volume of oil (ϕo) be increased, and iii) the o/w emulsion be subjected to a high-shear agitation. It has been found that the first criterion can be readily met by using a hydrophobicity-enhancing agent. These findings were applied to produce high-grade REM concentrates from an artificial mixture of micron-sized monazite and silica. Based on the improved understanding of phase inversion, a modified HHS process has been developed to recover ultrafine particles of copper minerals. After successfully demonstrating the efficacy and effectiveness of this process on a series of artificial copper ore samples, the modified HHS process was used to produce high-grade copper concentrates from a series of cleaner scavenger tails obtained from operating plants.