Proceeding Paper Development of Rare Earth Elements Separation Processes from Coal Fly Ash † Aggelos Tsachouridis * , Francis Pavloudakis and Nikolas Kiratzis *   Citation: Tsachouridis, A.; Pavloudakis, F.; Kiratzis, N. Development of Rare Earth Elements Separation Processes from Coal Fly Ash. Mater. Proc. 2021, 5, 69. https://doi.org/10.3390/ materproc2021005069 Academic Editor: Anthimos Xenidis Published: 9 December 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). Department of Mineral Resources Engineering, University of Western Macedonia, 50100 Kozani, Greece; f.pavloudakis@gmail.com * Correspondence: aggtsax@yahoo.gr (A.T.); nkiratzis@uowm.gr (N.K.) † Presented at the International Conference on Raw Materials and Circular Economy, Athens, Greece, 5–9 September 2021. Abstract: Rare Earth Elements and Yttrium (REY) constitute an important family of metals, with a wide range of applications and a massive impact on global industry. Studies have verified that the REY exist at significant concentrations in coal fly (CFA) and bottom ash (CBA). In the present contribution, the feasibility of CFA and CBA from the thermal power plant of PPC Meliti, Florina as a possible REY source is examined. Results are presented on the chemical and mineralogical analysis of the samples along with characterization of the initial material. Size separation results are also presented, as the first step in a subsequent beneficiation process for potential REY recovery. Keywords: Rare Earths; Yttrium; fly ash; beneficiation; size separation 1. Introduction Rare Earth Elements are essential raw materials for a wide variety of industrial products—from electric and hybrid vehicles to tablets and next generation mobile phones and from photovoltaic panels and wind turbines to space technology and weapon systems. Reliable and unhindered access to certain raw materials is a growing concern within the EU and across the globe. In order to address this challenge, in 2011, the EU Commission created the first CRM (Critical Raw Materials) list so as to classify these materials according to their industrial demand, their supply risk and their impact on the European Green Deal. The recent revised assessment of 2020 includes 83 individual raw materials, amongst which the REY (grouped as Heavy REY and Light REY) play a predominant role. More specifically, based on the combination of their supply risk for key technologies and their economic importance, the REY are classified as critical raw materials, having the highest supply risk amongst all 83 raw materials listed, with a relative medium economic importance [1]. The classification of the REY into Heavy and Light is based on their atomic number, with the L.REY being the elements from La to Sm (Atomic number 57 → 62) and the H.REY from Eu to Lu (Atomic Number 63 → 71) [2]. Another classification, according to Seredin and Dai [3], categorizes these elements as Critical (Nd, Eu, Tb, Dy, Y, Er), Uncritical (La, Pr, Sm, Gd) and Excessive (Ce, Ho, Tm, Yb, Lu). Based on this characterization, the above authors indicated that each potential source should ideally have a high concentration of Critical REY and a small concentration of Excessive REY (especially Ce, which is the most abundant in nature). In order to further characterize the material under investigation, the Outlook Coefficient and the Critical Percentage indexes have been introduced and described by the equations below: Coutlook = ( Nd + Eu + Tb + Dy + Er + Y)/ ∑ REY (Ce + Ho + Tm + Yb + Lu)/ ∑ REY (1) Critical % = ( Nd + Eu + Tb + Dy + Er + Y) ∑ REY × 100. (2) Mater. Proc. 2021, 5, 69. https://doi.org/10.3390/materproc2021005069 https://www.mdpi.com/journal/materproc