Partitioning of Rare Earth Elements (REEs) from Coal to Coal Fly Ash in Different Thermal Power Stations (TPSs) of India

Abstract

Rare earth elements (REEs) have been a topic of profound interest for several decades especially in the present age of electronic and digital revolution. India has the world’s richest beach sands with REEs, yet it imports some strategic REEs to fulfil its demand. It’s high time to explore alternative sources to meet its demand and coal ash from Thermal Power Stations (TPS) can be a very good alternative resource. In the present study, coal and coal fly ash (CFA) from seven Indian TPSs have been evaluated for estimation of REEs and variations in minerals compositions. Mineralogy of the samples is estimated using X-Ray diffraction (XRD) technique. Coal samples mostly consist of quartz and kaolinite however phase transformations of minerals occurred due to high temperature treatment during combustion. CFA mostly contains quartz and mullite. REEs have been determined by Inductively Coupled Plasma-Atomic Emission Spectrometry (ICP-AES) and considerable occurrence of any specific REE is not observed. Among the studied TPSs, Pr has the highest concentration among REEs in ash, reaching up to 63 ppm. The Outlook Coefficient (C_out) of REEs is in the range of 0.3 - 4.5 and 0.1 - 1.2 for coal and CFA respectively. In this research paper, Enrichment Coefficient (Δ_e) has been introduced to see the enrichment of REE in CFA with respect to the mother coal and a graph of Δ_e vs glassy phase has been plotted to observe the partitioning of REEs. Occurrence of Light REEs is more prominent than Heavy REEs.