Effects of CaO, MgO, Al2O3 and SiO2 on the carbothermic reduction of synthetic FeCr2O4

Abstract

In order to optimize the current reduction process of chromite, a good knowledge of reduction mechanism involved is required. The basic component in chromite ore is FeCr₂O₄ with gangue component like MgO and Al₂O₃. In lack of clear and consistent explanation about the effect of addition on the reduction of FeCr₂O₄, investigation of synthetic FeCr₂O₄ with different kind and amount of additions was carried out at 1673K under isothermal mode. Kinetic mechanism was also studied by linear fitting of different kinetic equations. Combined with rate-controlling step, it could be concluded as follows. CaO could enhance the reduction because Ca²⁺ would replace Fe²⁺, thus facilitated the ion diffusion in solid phase. Al₂O₃ had a positive influence as well, since Al³⁺ could form a solid solution phase with Cr³⁺ and made Cr³⁺ reduced more easily. MgO would hinder the reduction due to formation of a more stable phase MgCr₂O₄. SiO₂ would also hamper the Cr metallization because there was a liquid phase formed when Cr³⁺ was reduced to divalent, which would impede the nucleation of reduction product.