Selective Phase Transformation Behavior of Titanium-bearing Electric Furnace Molten Slag during the Molten NaOH Treatment Process

Abstract

In this paper, selective phase transformation for titanium-bearing phase (Ti-bearing phase) and impurity phase in titanium-bearing electric arc furnace molten slag (Ti-bearing EAF slag) was effectively realized during the molten NaOH treatment process. The phase transformation mechanism based on thermodynamic calculation was investigated in detail by X-ray diffraction, X-ray photoelectron spectroscopy and Raman spectrum. It is indicated that the Ti-bearing phases in Ti-bearing EAF slag such as anosovite solid solution and Mg₂TiO₄ can be easily converted to Na₂TiO₃ with NaCl-type crystal structure, whilst the main impurity phase such as MgAl₂O₄ was apt to be decomposed by molten NaOH to form NaAlO₂ and MgO. In addition, with increasing of roasting temperature and time, as well as decreasing of Ti-bearing EAF slag/NaOH mass ratio (R_slag/NaOH), the formed Na₂TiO₃ could be partly changed to NaMO₂ (M=Mg, Ti, Fe) with α-NaFeO₂-type crystal structure, due to the coexisting metal ions like Mg²⁺ and Fe³⁺ in the slag be doped into or even substituted the Ti atoms of Na₂TiO₃ to form NaMO₂ (M=Ti, Fe, Mg).