Distribution of REE in bauxite residues deposited in Corinth Gulf
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Date
2023-10-22
Authors
Ντούρος, Ευθύμιος Παναγιώτης
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Abstract
Bauxite residue (BR) is the solid waste of reddish-brown color produced from the metallurgical processing of bauxite for the recovery of aluminum hydroxides through the Bayer process. On a global scale, approximately 140 Mt of bauxite residue are produced annually, with over 2.7 × 10^9 t already stored as of 2011.
The red color of the bauxite residues is due to the presence of iron oxides (mainly hematite, Fe2O3), while it contains also aluminum, titanium and silica oxides and critical elements such as rare earth elements (REE). During the Bayer process, the REE are enriched in the bauxite residue compared to the original bauxite, with an enrichment factor of about two. In general, REE are considered valuable for recovery from the bauxite residue, as they are critical raw materials by many countries.
In Greece, the bauxite residue is produced by the aluminum production plant "Aluminium of Greece S.A." (ATE) in Aspra Spitia, Boeotia. The waste was disposed of in the Gulf of Antikyra in the northern and central part of the Corinthian Gulf through a submarine pipeline starting in the 1970s, with an annual disposal rate of 680,000 tons. It's estimated that over 20 million tons of the BR have been deposited in the Corinthian Gulf, covering up to 12% of its total area, till 2012 when the disposal in the Gulf has been ceased.
The thin layers of bauxite residue mixed with recent sediments within the Corinth Gulf were studied using petrographic and geochemical methods to determine its petrological and chemical characteristics, focusing on the qualitative and quantitative features of the rare earth elements. Various techniques were employed, including optical observation of polished block sections under white light, X-ray fluorescence (XRF) and X-ray diffraction (XRD) analysis, inductively coupled plasma mass spectrometry (ICP-MS), and scanning electron microscopy-energy-dispersive X-ray spectroscopy (SEM-EDS). Mapping of the bauxite’s residue dispersion in the research area, including the Gulf of Antikyra and the central basin of the Corinthian Gulf, was also conducted.
Rare earth elements contained in the bauxite residue range between 484 and 771 mg/kg. Through statistical analysis, positive correlations were observed between rare earth elements and iron (Fe2O3) and titanium (TiO2) oxides, indicating their coexistence in common mineral phases.
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Keywords
Bauxite residues, Rare earth elements, Corinth Gulf