During a study aiming to recover strategic elements and minerals from coal fly ash and bottom ash (RAREASH and CHARPHITE projects funded, respectively, by the 2nd ERA-MIN and 3rd ERA-MIN Programs of the European Union Commission), it was found that in coal fly ash and bottom ash from Romania and Poland, several morphotypes did not fit into the general fly ash classifications, unless grouped together as "undifferentiated inorganics". However, the combination of reflected light optical microscopy under oil immersion, scanning electron microscopy, and X-ray microanalysis (SEM/EDS) showed that many of these morphotypes not only have distinctive petrographic patterns but are also characterized by a chemical assemblage dominated by Ca, Mg, and P. In this paper, a survey of the literature is presented together with several detailed studies of samples from the RAREASH and CHARPHITE projects from which the following nomenclature are proposed: "calcispheres" for spongy Ca-rich morphotypes, "calcimagnesiaspheres" for (Ca + Mg)-rich morphotypes with visible MgO nodules and/or periclase (MgO) exsolved from Ca aluminate-silicate glass, and "magnesiaspheres" divided into "magnesiaferrospheres" for (Mg + Fe)-rich morphotypes with magnesioferrite, and "magnesiaoxyspheres" for magnesiaspheres mainly composed of (Mg + Fe)-rich amorphous material with visible MgO nodules and/or periclase.

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Coal ash char concentrates from four countries (Portugal, Poland, Romania, and South Africa) were prepared, characterised, and graphitized under the scope of the Charphite project (Third ERA-MIN Joint Call (2015) on the Sustainable Supply of Raw Materials in Europe). Coal ash chars may be a secondary raw material to produce synthetic graphite and could be an alternative to natural graphite, which is a commodity with a high supply risk. The char concentrates and the graphitized material derived from the char concentrates were characterised using proximate analysis, X-ray fluorescence, X-ray diffraction (structural), Raman microspectroscopy, solid-state nuclear magnetic resonance, scanning electron microscopy, and petrographic analyses to determine if the graphitization of the char was successful, and which char properties enhanced or hindered graphitization. Char concentrates with a lower proportion of anisotropic particles and a higher proportion of mixed porous particles showed greater degrees of graphitization. It is curious to see that embedded Al2O3 minerals, such as glass and clay, influenced graphitization, as they most likely acted as catalysts for crystal growth in the basal direction. However, the graphitized samples, as a whole, do not compare well against a reference natural graphite sample despite some particles in select char concentrates appearing to be graphitized following graphitization.

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The increasing demand for rare earth elements (REEs), which is associated with their economic importance and the supply risk, has motivated the research for alternative secondary sources of these elements. Coal and coal combustion ash have been pointed out as promising REE raw materials. This research seeks to understand REE fractionation, from feed coals to ashes, considering seasonal variations, and to assess the trends within the ash fractions that can be used for further beneficiation processes. Colombian commercial feed coals, combustion ashes, and their respective fractions were sampled from a Portuguese power plant and were characterized via petrographical, mineralogical, and chemical analyses. The total REE concentrations in the feed coals studied range between 6.97 and 23.15 ppm, while, in the ashes, they vary from 159.9 to 266.6 ppm. Fly ash (FA) from electrostatic precipitator (ESP) presented higher concentrations than the bottom (BA) and economizer (ECO) ashes. Furthermore, REEs and the LREE/HREE ratio increased slightly towards the back rows of the ESP. In the feed coals, the REEs are significantly correlated with ash, and they occur in micrometric phosphate minerals intermixed with clays. In the ashes, the REEs were mostly detected in micrometric particles, with P and Al-Si as the major components. The results from the fractioned samples show that the REEs were enriched in the fine (<25 µm) and nonmagnetic fractions of the ESP FA. A single trial combining sieving and magnetic separation enabled the attainment of a REE recovery of 53%, and a final enrichment factor of 1.25. Coal combustion ashes and their respective size fractions are promising REE raw materials; however, the REE oxide concentrations are below the economical cutoff of 1000 ppm.