A Note on the Occurrence of Yttrium and Rare Earth Elements in Coal Combustion Products

Abstract

There is an international need for a variety of lanthanide elements (rare earth elements, or REEs) in modern electronic and related components. This has led to a desire to broaden production from both previously productive locations and to expand production to new sources, possibly including coal-derived fly ash. The concentration of lanthanides in coal-combustion fly ash depends on a number of factors, one of the most important being the concentration of the elements in the feed coal. Unlike some elements, such as Zn and As, the REE concentration is largely not a function of element volatility. In this study, we review the concentrations of REEs in a power plant burning a variety of coals. Additionally, a power plant burning 2-3% tires in a cyclone boiler and a plant burning 30% pet coke were also investigated. In general, the Yttrium + REE concentrations do not systematically vary between electrostatic precipitator rows. However, the light REE/heavy REE ratio (LREE/HREE) generally decreases with a decrease in flue gas temperature. The element partitioning responsible for the LREE/HREE decrease is not fully understood.