Application of Geochemical Modeling in Rare Earth Elements Leaching of Coal Combustion and Secondary Residues

Abstract

Geochemical modeling offers the opportunity to predict the extraction behavior of rare earth elements (REEs) from secondary resources, as well as to mechanistically confirm the governing reactions that control leachability and speciation. In this chapter, several studies on the extraction and recovery of REEs from coal combustion residues and mining wastes, where geochemical modeling was utilized, are reviewed. The motivation of each study is discussed and compared, the methodologies utilized in each study are summarized and contrasted, and the main results obtained in these studies are described. Elements of interest for recovery from secondary resources, due to their economic value and relative scarcity, include light (e.g., Nd), middle (e.g., Tb) and heavy (e.g., Er) REEs, in addition to scandium and yttrium. Furthermore, the role that geochemical modeling has to play in environmental studies cannot be overemphasized, and is topic of discussion throughout. Future studies on the geochemical modeling of REEs will likely investigate the leaching kinetics and the long-term stability of REEs in waste storage sites, especially as the capability of geochemical modeling software and the comprehensiveness of thermodynamic databases expand to include the needed tools and data for these types of studies.