Abstract
Coal-derived power comprises over 39% of the world’s power production. Therefore, a mass volume of coal combustion byproducts are generated and shifted the extra burden onto the economy and environment. Circulating fluidized bed combustion (CFBC) has been found to be a clean and ultimate technology for Korea’s coal-fired power plants to have effective power generation from low-grade imported coal with reduced emissions. Efforts have been made to broaden the utilization of CFBC coal ash, and to promote sustainable development of CFBC technology. Investigations provided numerous evidences for coal ash to be a potential deposit for rare earths reclamation. However, the basic characteristics and the methods of rare earth mining from the CFBC bottom ash lack detailed understanding and are poorly reported. This study highlighted an insight of the CBFC bottom ash with respect to REEs concentration. Moreover, agents were tested as a means for leaching REEs from Samcheok CFBC bottom ash. The leaching tests were performed in relation to variations in concentration, time and temperature. The results were applied to identify suitable processes to leach REEs from the ash and clarify the potential valuation of CFBC bottom ash. The leaching conditions attained by ANOVA analysis for hydrochloric concentration, temperature, and time of 2 mol L−1, 80 °C, and 12 h, were found to provide a maximum extraction of yttrium, neodymium and dysprosium of 62.1%, 55.5% and 65.2%, respectively.
Highlights
Rare earth elements (REEs) comprise 15 elements, starting from the atomic number 57 (La) to 71 (Lu), of the periodic table encompassing scandium and yttrium
Several techniques for extraction and separation of individual REEs from waste coal ash have been summarized including physical [46] and chemical processes [47,48]. These processes generally start with the dissolution of rare earths using acid as the leaching agent, followed by separation of unwanted minerals from the leachate by filtration, and precipitation through solvent extraction, recovery of REEs/REOs by hydro metallurgy
This study investigated the acid leaching methods applied on Samcheok Circulating fluidized bed combustion (CFBC) bottom ash with a pulp density of 100 g L−1 under different conditions that targeted to enhance REE leaching efficiency and reduce the amount of reagent used
Summary
Rare earth elements (REEs) comprise 15 elements, starting from the atomic number 57 (La) to 71 (Lu), of the periodic table encompassing scandium and yttrium. Rare earth recovery from industrial waste, end-used REEs bearing products, and mining residues (bauxite residue, coal tailings) has been considered as potential alternative sources of REEs [18,19]. Several techniques for extraction and separation of individual REEs from waste coal ash have been summarized including physical [46] and chemical processes [47,48] These processes generally start with the dissolution of rare earths using acid as the leaching agent, followed by separation of unwanted minerals from the leachate by filtration, and precipitation through solvent extraction, recovery of REEs/REOs by hydro metallurgy. In Korea, there are limited resources of rare earths and at the same time having landfill (coal ash residues, municipal solid waste residues, etc.) problems To resolve these problems, efficient recycling technologies are required and adopted. The variables included the reagent type, reagent concentration, residence time, and temperature
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