Platon N. Gamaletsos

This study provides a comprehensive database of sulfur isotope values from Greece, including samples of C3 and C4 plants and terrestrial and aquatic animal bones. This comprehensive analytical approach examines sulfur isotopes—along with carbon and nitrogen—in modern plants, terrestrial mammals, and fish bones (fresh and marine reservoirs) from Greece. The results show a clear offset in δ³⁴S values between terrestrial and aquatic animals, influenced by their dietary sources from marine or freshwater environments. This δ³⁴S offset and the clear difference between S-C-N isotopes permits the reconstruction of the dietary habits of domesticated herbivores and demonstrates differences in husbandry practices and animal movements. Additionally, the combination of sulfur and nitrogen values allows the reconstruction of the diet of omnivores, revealing the type of protein consumed. Finally, this isotopic dataset will provide an essential backbone for future archaeological, ecological, and forensic studies.

To tackle the challenge of bauxite residue (BR), generated during the alumina production, as well as to recover some of its metal content, three combinatory H₂-based processes were utilized. Firstly, Greek BR was mixed with NaOH to produce water soluble Na-aluminates and was roasted under pure H₂ gas in order to reduce the Fe⁺³ content. Then the first process combined water leaching and magnetic separation, the second water leaching and melting and the last included wet magnetic separation. The water media resulted in the dissolution of Na-aluminate phases and the production of Al, Na-ion rich leachates. From these, pregnant leaching solutions recovery of Al was 78%, 84% and for the third case it reached 91%. Concerning Na recovery, it could reach 94%. Both melting process and magnetic separation aimed for Fe recovery from the material. The former case however still needs to be optimized, here its concept is introduced. The magnetic fraction, after the dry magnetic separation, varied in Fe content from 31.57 wt.% to 38.50 wt.%, while after the wet magnetic separation it reached 31.85 wt.%.

Eudialyte-group minerals (EGM) attract global interest as potential resources for high-field-strength elements (e.g. Zr, Nb, Ta, and rare-earth elements), i.e. critical materials for modern technologies. They are particularly valued for their relative enrichment in the most critical lanthanides, i.e. Nd and heavy rare earth elements (Gd–Lu). However, rare earth element (REE) substitution mechanisms into the EGM structure are still poorly understood. Light and heavyREEmay occupy different sites and there may be ordering and/or defect clustering in the structure. This study uses X-ray absorption spectroscopy to determine the structural state ofREEin EGM from prospective eudialyte-bearing complexes. YttriumK-edge and NdL₃-edge spectra were collected as proxies for heavy and lightREE, respectively, and compared to natural and syntheticREE-bearing standards. Extended X-ray absorption fine structure data yield best fits for Y in six-fold coordination with Y–O distances of 2.24–2.32 Å, and a second coordination sphere comprising Fe, Na, Ca, Si and O at radial distances of 3.6–3.8 Å. These findings are consistent with dominant Y³⁺substitution for Ca²⁺on the octahedralM1 site in all the samples studied, and exclude preferential substitution of Y³⁺onto the smaller octahedralZsite or the large low-symmetryN4 site.Using lattice strain theory, we constructed relative partitioning models to predict site preferences of lanthanides we have not measured directly. The models predict that allREEare favoured on the Ca-dominantM1 site and that preferential partitioning of heavy over lightREEincreases in EGM containing significant Mn in theM1-octahedral rings (oneillite subgroup). Thus, the flatREEprofiles that make EGM such attractive exploration targets are not due to preferential partitioning of light and heavyREEonto different sites. Instead, local ordering of Mn- and Ca-occupiedM1 sites may influence the capacity of EGM to accommodate heavyREE.