Original Article

Kinetics of isothermal growth of Ulvöspinel (Fe_3-xTi_xO₄) in Ti-bearing blast furnace slag with Fe₂O₃ powder additive

Department of Physical Chemistry of Metallurgy, School of Metallurgical and Ecological Engineering, University of Science and Technology Beijing, Beijing 100083, PR China

^* e-mail: baijunyan@ustb.edu.cn

Received: 6 December 2023
Accepted: 25 February 2023

Abstract

Based on chemical composition and mineral composition of Ti-bearing BF slag, Fe₂O₃ is introduced to the Ti-bearing BF slag, a magnetic Ulvöspinel phase is formed after roasting, then enriched by magnetic separation. The effects of Fe₂O₃ dosage, holding temperature and holding time on the grain size and crystal area of Ulvöspinel in titanium bearing blast furnace slag were investigated by SEM-EDS analyses. The occurrence of Ca, Si, Fe, Ti and other elements in roasted slag were studied by EDS. The grain size and crystallization area of Ulvöspinel (>30 µm) in roasted slag under different conditions were counted by image plus pro 6.0 software. The growth kinetics of Ulvöspinel in isothermal process was described by Johnson-Mehl-Avrami-Kologoromov (JMAK) model, the apparent activation energy of Ulvöspinel growth was obtained. The results show that the mixed roasted slag of Ti-bearing BF slag and Fe₂O₃ is mainly composed of Ulvöspinel phase and calcium-silicon phase; Titanium mainly occurs in Ulvöspinel Fe_3-xTi_xO₄ (0 < x < 1), and only trace titanium exists in the calcium silicate phase; The growth of Ulvöspinel phase mainly includes two processes: crystal nucleus growth and Ostwald coarsening; The temperature of about 1073 K is favorable for the growth of Ulvöspinel. If the temperature is too high, low undercooling (ΔT = 1693–T_k) may lead to the slow the nucleation rate, and when the temperature is below 1073 K, the high viscosity slag leads to the slow dissolution of molten Ulvöspinel grains; when mass ratio 25% Fe₂O₃ to Ti-bearing BF slag, as holding time prolonging, the size and crystal area of Ulvöspinel (>30 µm) gradually increases, and the average size and area fraction of Ulvöspinel (>30 µm) is 56.67 µm and 78.79% after 120 min. After that, the growth of Ulvöspinel almost stopped. The growth process of Ulvöspinel can be described by JMAK equation, and its apparent activation energy is 550.39 kJ. mol⁻¹.