Chromite ores prereduced to various stages of reduction were reduced by carbon at 1550 and 1600°C in the presence of molten slag of CaO-MgO-Al2O3-SiO2 system.
Chromium became liable to dissolve in the form of Cr2+ rather than Cr3+ in slag during the smelting reduction of chromite ores prereduced at 1200°C or above, even when the ores had higher iron content. This seemed to be mainly attributed to the fact that the dissociation oxygen pressure of chromite was decreased by preferential reduction of iron oxide in prereduction stage.
Metal produced in prereduction stage melted and flowed out to liquid droplets in the vicinity of chromite grain during the smelting reduction. As a result, indentations and pores were formed on the surface and inside of chromite grain, respectively.
The rate of smelting reduction increased with increasing the degree of reduction in prereduction stage. This seemed to be attributed to the increases in number and size of the indentations and pores as well as the change of oxidation state of chromium from Cr3+ to Cr2+.
