(763a) Leaching Rare Earth Elements (REEs) from Coal Ash By Mineral Acids

Yan Luo¹, Hanjing Tian¹ James Hower², and Maohong Fan³

¹Department of Chemical Engineering, West Virginia University, Morgantown, WV

²Center for Applied Energy Research, University of Kentucky, Lexington, KY

³Department of Chemical Engineering, University of Wyoming, Laramie, WY

KEYWORDS: REEs, leaching, coal ash, HCl, HNO₃

ABSTRACT

Rare earth elements (REEs), identified as “critical or near critical materials” by US-DOE, are playing a significant role in energy, car batteries, advanced magnets, metallurgy and military because of their magnetic, electronic catalytic and optical properties. REEs have been found in varying concentrations up to 1,000 parts per million (ppm) by weight in coal ash. As such, coal ash can be a potentially viable source for these strategic metals.

However, significant technical gaps present on the REEs releasing efficiency because of their structural imbedding into the “glassware” framework of coal ash. In this study, systematic study was performed to evaluate the performance of mineral acids HCl or HNO₃ for leaching REEs from four types of coal ashes obtained from various domestic location. ICP-MS analysis indicated the selected coal ashes have minimal 300 ppm. When leaching with HCl for three times, the REEs recovery yields reached 18, 45, 27 and 53%, respectively; and the REEs recovery yields reached respective 10, 28, 17 and 44 % when HNO₃ was utilized. Overall, the HCl showed better REEs leaching efficiencies than HNO₃. XRD analysis exhibited that the main components for the four coal ashes were quartz and silica-aluminate as well as other small amount of C, Fe, Mg, Ca, Al, Cu, and S salts. The structure and composition of the coal ash is the main reason leading to the various REEs recovery efficiency. The optimal leaching process will be performed further to maximize REEs recovery efficiency from coal ash.