Abstract

High-silica bauxite is not used to obtain sandy-grade alumina owing to its low alumina/silica ratio (μSi < 3). Acidic methods, such as the use of HCl and NH4HSO4, show promise for treating this raw material. The leaching of boehmite-kaolinite bauxite from the Severoonezhsk deposit mine (Arkhangelsk region, Russia) using a mixture of NH4HSO4 and H2SO4 was investigated for the first time. The bisulfate method, which combines the advantages of the acidic and alkaline methods, involves bauxite leaching, precipitation of ammonium alum, recrystallization for gibbsite precipitation, and calcination for alumina production. The effects of temperature (130–200 °C), liquid-to-solid ratio (8–12), and duration of leaching (5–90 min) on the degrees of extraction of Al, and rare earth elements (REEs) were evaluated. The extractions of Al, Fe, and Ga were found to be >90%, with most of the silica and titania remaining in the residue; moreover, a REEs extraction of 70%–80% was achieved. Residues obtained after leaching were studied by laser diffraction, XRD, XRF, and SEM to elucidate the leaching mechanism and the solubility of Al-containing minerals, such as boehmite (AlOOH), kaolinite (Al4[Si4O10](OH)8), and muscovite (KAl2[AlSi3O10](OH)2). The acquired data can be used to facilitate the development of an effective technology for the treatment of high-silica bauxite in Russia.