Kinetics Study on Reduction of CaWO4 by Si from 1423 K to 1523 K

Abstract

Abstract Investigation on reduction kinetics of scheelite(CaWO4) provides important fundamental knowledge to control and optimize process of Ferrotungsten manufacturing and direct reduction of scheelite in steelmaking. In this work, the isothermal reduction kinetics of CaWO4 powder by Si powder at 1,423 K, 1,473 K and 1,523 K, where all reactants and products are in solid state, was investigated by using X-ray diffraction quantitative analysis. Scanning electronic microscopy (SEM) attached with energy dispersive spectra (EDS) was also employed to investigate the microstructure of reaction interface. Both Jander model and Ginstling–Brounshtein model could describe kinetics of reduction of CaWO4 well, whereas 3D interfacial reaction model could not describe the kinetics of reduction of CaWO4. The rate determining step for reduction of CaWO4 could be diffusion of Si across product layer. The values of activation energies obtained by fitting kinetic data using Jander and Ginstling–Brounshtein model are as great as 379.93 kJ/mol and 387.16 kJ/mol respectively. The oxygen partial pressure during reduction has impact on the kinetics of reduction. The reduction was retarded by increase of oxygen partial pressure.