Irkutsk National Research Technical University (Irkutsk, Russia)
М. P. Kuzmin, Associate Professor of the Department of Metallurgy of Non-Ferrous Metals, Candidate of Technical Sciences, Associate Professor, mike12008@yandex.ru
А. S. Kuzmina, Associate Professor of the Department of Radio Electronics and Telecommunication Systems, Candidate of Physical and Mathematical Sciences, kuzmina.istu@gmail.com
М. Yu. Kuzmina, Associate Professor of the Department of Metallurgy of Non-Ferrous Metals, Candidate of Chemical Sciences, Associate Professor, kuzmina.my@yandex.ru
Red mud, a large-tonnage high-alkaline waste from alumina production, is also a valuable technogenic raw material for scandium, gallium, and rare earth metals. The extraction of these metals is challenging because they do not form independent minerals but are dispersed within the crystal lattice of alumogoethite and alumohematite. This study presents a thermodynamic analysis of the stability of these carrier minerals in the temperature range of 298–1500 K. For the first time, the standard enthalpy of formation (ΔH°, 298) and standard Gibbs energy (ΔG°, 298) of alumogoethite with the composition (Fe0.6Al0.4)O(OH) were calculated as –733.2 and –734.9 kJ/mol, respectively. It is shown that at T > 870 K, alumogoethite becomes thermodynamically unstable and decomposes, releasing scandium, which transforms into highly stable Sc2O3. The difference in the Gibbs energies of formation between Sc2O3 and alumogoethite reaches 1165 kJ/mol, creating an exceptionally strong driving force for the migration of scandium into its own oxide phase. For gallium and yttrium, the onset temperatures of migration were determined to be 950–980 K and 1050–1080 K, respectively; a correlation between the ionic radius of M3+ and the migration temperature was established (coefficient of determination R2 = 0.94). Based on the obtained data, a temperature-staged processing scheme for red mud is proposed, enabling the sequential extraction of scandium (85–92%), gallium (60–75%), and the concentration of rare earth metals in the residue for subsequent acid leaching.
The work was carried out with the financial support of the Russian Science Foundation (grant No. 25-23-00924, https://rscf.ru/project/25-23-00924/).
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