Comprehensive utilization of Titanium-bearing Blast Furnace Slag by H2SO4 Roasting and Stepwise Precipitation

Abstract

Titanium-bearing blast furnace slag (Ti-BFS) is an industrial solid waste rich in titanium, magnesium and aluminum. However, it is difficult to utilize Ti, Mg and Al from Ti-BFS for the strong stability and poor reaction activity of Ti-BFS. A comprehensive utilization route of Ti, Mg and Al from Ti-BFS was proposed. Ti-BFS was firstly roasted with H₂SO₄ to realizes the conversion of Ti, Mg and Al to their corresponding sulphates. The sulphates were leached by dilute H₂SO₄ solution to extraction Ti, Mg and Al from roasted Ti-BFS. The roasting conditions were optimized as follows, sulfuric acid concentration of 85%(mass), temperature of 200 °C, acid-slag ratio of 5.5, particle size of Ti-BFS <75 μm, and reaction time of 1 h. The extraction rates of titanium, aluminum, and magnesium reached 82.42%, 88.78% and 90.53%, respectively. The leachate was hydrolyzed at 102 °C for 5 h with a titanium hydrolysis ratio of 96%. After filtration and calcination, TiO₂ with a purity of 97 %(mass) was obtained. Al in the leachate was converted to NH₄Al(SO₄)₂·12H₂O by the neutralization of ammonia water at pH = 4.5. Al₂O₃ was obtained by the calcination of NH₄Al(SO₄)₂·12H₂O. The residual solution can be used to prepare products of magnesium sulfate. In the proposed process, Ti, Mg and Al were extracted from Ti-BFS and utilized comprehensively to prepare valuable products. The leaching behavior of roasted Ti-BFS with water was also studied. It followed the unreacted shrinking core model. The apparent activation energy was 26.07 kJ·mol⁻¹ . This research not only provides a viable method for recovering valuable metals in Ti-BFS, but also provides a strategy to comprehensive utilize the valuable elements in Ti-BFS.