Kinetic study on microwave-enhanced direct reduction of titanomagnetite concentrate with coal

Titanomagnetite concentrate is one of the important titanium resources. The apparent activation energy (\({E}_{\mathrm{a}}\)) of the direct reduction of titanomagnetite concentrate was composed of two parts (average activation energy: \({\overline{E} }_{\mathrm{a}}={\overline{E} }_{\mathrm{a}-\mathrm{L}}+{E}_{\mathrm{a}-\mathrm{Step }1}\), where \({E}_{\mathrm{a}-\mathrm{L}}\) is the lattice energy of titanomagnetite concentrate, and \({E}_{\mathrm{a}-\mathrm{Step\ }1}\) is the activation energy of step 1 for the reduction of titanomagnetite concentrate in the route of Fe³⁺ \(\mathop{\longrightarrow}\limits^{\rm{Step}1}\) Fe²⁺ \(\mathop{\longrightarrow}\limits^{\rm{Step}2}\) Fe₂O²⁺ \(\mathop{\longrightarrow}\limits^{\rm{Step}3}\) Fe⁰). \({\overline{E} }_{\mathrm{a}}\) (583.43 kJ/mol), \({\overline{E} }_{\mathrm{a}-\mathrm{L}}\) (426.4 kJ/mol), and \({E}_{\mathrm{a}-\mathrm{Step}1}\) (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.