Experiments and kinetic modeling for reduction of ferric oxidebiochar composite pellets

Abstract

The reduction behavior, phase transformation and microstructure evolution of four ferric oxide-biochar composite pellets (RLC-pellet, PHC-pellet, MCC-pellet and PSC-pellet) were investigated by use of nonisothermal thermogravimetric, X-Ray diffraction (XRD) and Scanning electron microscopy (SEM) analysis. he apparent kinetic parameters of reduction process were estimated by fitting the experimental data to the three parallel nth order rate models. The results showed that ferric oxide-biochar composite pellet reduction process was divided into three stages of Fe2O3→Fe3O4, Fe3O4→FeO and FeO→Fe, where the first stage was independent to the next two stages. The sequence of reduction reactivity as to all samples was MCC-pellet > PHC-pellet > PSC-pellet > RLC-pellet. Meanwhile, increasing heating rate could efficiently improve the reduction reactivity. Through kinetic analysis, it was found that three parallel nth order rate models could well represent reduction process, and activation energies of three stages calculated by the model were 204.9-405.5 kJ/mol, 259.6-643.8 kJ/mol and 291.5-685.8 kJ/mol, respectively. The marked compensation effect was also presented between the activation energy and pre-exponential factor.