At the Porto Vesme disposal site in southern Sardinia, Italy, about 30 million tonnes of bauxite residues from aluminium extraction using the Bayer process are stored. The mineralogical and geochemical features of these residues have recently been investigated, also to assess the economic viability of extracting rare earth elements (REEs) and other valuable elements, such Ga, Sc, V (Mameli et al., 2025; Schingaro et al., 2025). The samples mineralogy includes hematite, goethite, ilmenite, gibbsite, boehmite, bayerite, anatase, rutile, quartz, sodalite, cancrinite, andradite, calcite, dolomite, halite. Lanthanides-rich phosphate minerals as well as LREE ferrotitanates were sporadically observed. The samples chemistry provides Fe2O3, Al2O3, SiO2, Na2O, TiO2 and CaO in order of abundance but also relevant concentrations of Zr, Cr, Ce, V, Sr, Ni, Zn, Ga and Y. The REEs are enriched relative to the parent material with LREEs > HREEs+Y and Sc. Ce is the most abundant LREE and the chondrite normalized patterns show significant positive Ce anomalies. However identification of REE/ valuable elements bearing phases in bauxite residue is not a trivial task and necessitates investigation at the nanoscale. Preliminary results of TEM analyses have revealed the abundant presence of Fe-Ti oxides bearing Ca, Cr and LREE with laminar habit and lattice fringes spacing around 2.70 Å which can correspond with a ferrotitanate phase. EDS identification of the precise ferrrotitanate composition is difficult because of the LREE, Ti, and Cr intense and complex X-ray energy overlaps in the 4.5 to 6 keV spectral interval, especially when Ti has high concentration (Lacinska et al., 2021). However, detailed EDS analyses allowed the identification of a well defined peak for the Lα line of La (4.65 keV), slightly overlapped with Ti Kα line (4.52 keV). Ce was identified by the Ce Lβ line at 5.26 keV, given that Ce Lα line (4.84 keV) was usually hidden by the Ti Kβ line (4.93 keV). Cr was easily identified by its Cr Kα line (5.41 keV).
Nanoscale analysis of Red Muds from Portovesme (Sardinia) / Ouladmansour, A.; Millán, J. J.; Abad Martìnez, M. I.; Mesto, E.; Lacalamita, M.; Agrosì, G.; Mongelli, G.; Mameli, P.; Schingaro, E. - (2025), pp. 153-153. ( Congresso congiunto SIMP-SGI 2025 Geosciences and the Challenges of the 21st Century Padova (Italy) 16 -18 September 2025) [10.3301/absgi.2025.03].
Nanoscale analysis of Red Muds from Portovesme (Sardinia)
Mameli P.;
2025-01-01
Abstract
At the Porto Vesme disposal site in southern Sardinia, Italy, about 30 million tonnes of bauxite residues from aluminium extraction using the Bayer process are stored. The mineralogical and geochemical features of these residues have recently been investigated, also to assess the economic viability of extracting rare earth elements (REEs) and other valuable elements, such Ga, Sc, V (Mameli et al., 2025; Schingaro et al., 2025). The samples mineralogy includes hematite, goethite, ilmenite, gibbsite, boehmite, bayerite, anatase, rutile, quartz, sodalite, cancrinite, andradite, calcite, dolomite, halite. Lanthanides-rich phosphate minerals as well as LREE ferrotitanates were sporadically observed. The samples chemistry provides Fe2O3, Al2O3, SiO2, Na2O, TiO2 and CaO in order of abundance but also relevant concentrations of Zr, Cr, Ce, V, Sr, Ni, Zn, Ga and Y. The REEs are enriched relative to the parent material with LREEs > HREEs+Y and Sc. Ce is the most abundant LREE and the chondrite normalized patterns show significant positive Ce anomalies. However identification of REE/ valuable elements bearing phases in bauxite residue is not a trivial task and necessitates investigation at the nanoscale. Preliminary results of TEM analyses have revealed the abundant presence of Fe-Ti oxides bearing Ca, Cr and LREE with laminar habit and lattice fringes spacing around 2.70 Å which can correspond with a ferrotitanate phase. EDS identification of the precise ferrrotitanate composition is difficult because of the LREE, Ti, and Cr intense and complex X-ray energy overlaps in the 4.5 to 6 keV spectral interval, especially when Ti has high concentration (Lacinska et al., 2021). However, detailed EDS analyses allowed the identification of a well defined peak for the Lα line of La (4.65 keV), slightly overlapped with Ti Kα line (4.52 keV). Ce was identified by the Ce Lβ line at 5.26 keV, given that Ce Lα line (4.84 keV) was usually hidden by the Ti Kβ line (4.93 keV). Cr was easily identified by its Cr Kα line (5.41 keV).I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
