Abstract
The effect of sodium and calcium salts on the carbothermic reduction of chromium ores has been studied. Among the additives such as chlorides, carbonates, fluorides and borates, the borates was found to have the strongest promoting effect on the reduction.
The rate of reduction increased remarkably with an increase in the amount of added borates, but their addition of more than 1 wt% was less effective. The effect was much more significant in the reduction step of MgCr2O4 component of chromite than that of the FeCr2O4 component. It was found that the borates facilitated the diffusion of ionic species particularly in Al2O3-containing chromite and the grain growth of metal produced.
Na2B4O7 slightly promoted the Boudouard reaction, but CaB4O7 retarded it. Based on the effect of CaB4O7, it was examined which of the Boudouard reaction or the reduction of chromite with CO gas mainly controlled the carbothermic reduction of synthetic chromites and chromium ores. The results were in good agreement with those from the kinetic analyses in the previous paper.
