This study presents the results of concentrations of rare earth elements and yttrium (REY ), uranium (U), and thorium (Th) in ashes from combustion/co-combustion of biomass (20%, 40%, and 60% share) from the agri-food industry (pomace from apples, walnut shells, and sunflower husks) and hard coal. The study primarily focuses on ashes from the co-combustion of biomass and hard coal, in terms of their potential use for the recovery of rare earth elements (REE ), and the identification of the sources of these elements in the ashes. Research methods such as ICP-MS (inductively coupled plasma mass spectrometry), XRD (X-ray diffraction), and SEM -EDS (scanning electron microscopy with quantitative X-ray microanalysis) were used. The total average content of REY in ash from biomass combustion is 3.55–120.5 mg/kg, and in ash from co-combustion, it is from 187.3 to 73.5 mg/kg. The concentration of critical REE in biomass combustion ash is in the range 1.0–38.7 mg/kg, and in cocombustion ash it is 23.3–60.7 mg/kg. In hard-coal ash, the average concentration of REY and critical REY was determined at the level of 175 and 45.3 mg/kg, respectively. In all samples of the tested ashes, a higher concentration of Th (0.2–14.8 mg/kg) was found in comparison to U (0.1–6 mg/kg). In ashes from biomass and hard-coal combustion/co-combustion, the range of the prospective coefficient (Coutl) is 0.66–0.82 and 0.8–0.85, respectively, which may suggest a potential source for REE recovery. On the basis of SEM -EDS studies, yttrium was found in particles of ashes from biomass combustion, which is mainly bound to carbonates. The carriers of REY , U, and Th in ashes from biomass and hard-coal co-combustion are phosphates (monazite and xenotime), and probably the vitreous aluminosilicate substance.

In this paper cation arrangement in two samples of aluminoceladonite, emerald‑green and dark-green were studied by Mössbauer, Raman and X-ray photoelectron spectroscopies. The X-ray photoelectron spectroscopy (XPS) spectra obtained in the region of the Si2p, Al2p, Fe2p, K2p, and O1s core levels provided information, for the first time highlighting a route to identify the position of Si, Al, K, and Fe cations in a structure of layered silicates. The XPS analysis showed the presence of Al in tetrahedral and octahedral coordination while the K2p line indicated the possibility of K+ substitution by other cations in interlayer sites. Mössbauer spectroscopy provided information about crystal chemistry with respect to the local electronic and geometric environment around the Fe atom and to distortions of the polyhedra. It turned out that iron was located mostly in the cis-octahedra position wherein about 75% of iron appeared in the form of Fe ³⁺. The most preferred cation combinations around Fe corresponded to 3Fe ³⁺ ions and MgFe ²⁺Fe ³⁺/2MgFe ³⁺. Raman spectroscopy illustrated aluminium substitution in silicon and iron positions wherein the concentration of the aluminium determined the degree of structural distortion within the layered system. These isomorphic substitutions implied a typical band arrangement in the hydroxyl region, which has not been observed in celadonites so far.