Process flowsheet for extraction of Fe, Al, Ti, Sc, and Ga values from red mud

Abstract

A comprehensive process flowsheet is investigated to recover metallic values from red mud with high-purity products such as alumina, silica, ferrous oxalate, titania, and Sc-Ga containing purified solution. The carbonated red mud leached in 1 M hydrochloric acid at 50 °C for 1 h dissolves 44.5% Al and 51% Si, followed by 2 M oxalic acid leaching at 90 °C for 2.5 h yielding 61% Fe and 46–48% Sc and Ga dissolution. High-purity ferrous oxalate product is retrieved from the leach solution, and the Sc and Ga ions report to the solution. Titanium enriched residue is baked with 1 mL/g sulfuric acid at 300 °C for 1 h, forming TiOSO4, Fe2(SO4)3, and Al2(SO4)3 phases, followed by water leaching. 64.5% Ti and ∼ 27% Fe dissolution is attained, and solution contains Fe (7.47 g/L), Ti (3.09 g/L), Al (2.44 g/L), Si (0.17 g/L), Sc (2 mg/L), and Ga (3 mg/L) ions. Thermal hydrolysis of solution recovers titania precipitate (96.9% purity), and the solution after hydrolysis contains Fe, Sc, and Ga values. The overall metal extraction (84% Fe, 79% Ti, 92% Al, 78% Sc, 89 % Ga) in the proposed flowsheet is higher compared to direct acid baking process (51% Fe, 65% Ti, 89% Al, 51% Sc, 48 % Ga). Products recovered include high-purity silica (4.8 wt%), alumina (9.3 wt%), Fe(II) oxalate (20.7 wt%), titania (8.9 wt%), and a final residue yield of 12.6 wt%. Microwave exposure at 2 kW for 7 min improves the dissolution of the Sc (84%) and Ti (85.5%). H2 reduction at 450 °C, 30 min converted hematite to magnetite and increased Fe dissolution to 90%. Red mud's mineralogical and composition modification by magnetic separation, reduction, and microwave exposure were ineffective to improve selective dissolution.