Xiao-dong Lv, You-ling Hou, Yun-tao Xin, Wei Lv, Xue-wei Lv
High-quality upgraded titanium slag obtained through semi-molten reduction with the addition of Na2CO3 is important for the fluidizing chlorination process to produce TiO2 pigments. The key is the effect of Na2CO3 on the reduction behavior of iron. Therefore, the effects of Na2CO3 on reduction mechanism and kinetics of iron during deep reduction of ilmenite concentrate were studied. The results indicated that the metallization ratio of the reduced sample increased with increasing temperature, time, and dose of Na2CO3. The addition of Na2CO3 significantly accelerated the reduction of iron in the ilmenite concentrate and promoted the growth of iron particles. However, the addition of Na2CO3 produced sodium iron titanates; thus, the metallization ratio of the sample decreased with an increase in the temperature and time when the temperature was above 1200 °C and the time was more than 30 min. When the doses of Na2CO3 were 0, 3, and 6 wt.%, the reduction of iron was controlled by the interfacial chemical reaction, both the interfacial chemical reaction and diffusion, and diffusion, respectively, and the apparent activation energies were 134.91, 64.89, and 120.82 kJ/mol, respectively.
, where 
is the lattice energy of titanomagnetite concentrate, and 
is the activation energy of step 1 for the reduction of titanomagnetite concentrate in the route of .jpg){kind=small}
. Ea (583.43 kJ/mol), 
(426.4 kJ/mol), and 
(157.0 kJ/mol) were calculated by the model-free methods based on thermogravimetry and Dmol3 module. Combined with the analysis of activation energy fluctuation and the shifting trend of related mechanism functions, the reduction kinetic system with three main characteristics, namely nucleation, diffusion and concentration fluctuation, was established. In addition, the scanning electron microscopy comparison analysis of the samples from microwave reduction and conventional reduction shows that microwave heating could realize the microstructure Ti–Fe separation and reduce the lattice energy of the titanomagnetite concentrate, thus enhancing the reduction process by 7.68% from the perspective of activation energy.
. The processing map and instability map constructed at a strain of 0.9 show that the suitable window for hot working with a true strain of 0.9 is in the temperature range of 970–1150 °C and strain rate range of 0.01–0.25 s-1, as well as at the temperature of 1150 °C and strain rate range of 0.25–10 s-1. The instability phenomenon appears in the process interval of 850–1096 C and 0.22–10 s-1.
