Thermogravimetric study on carbothermic reduction of chromite ore under non-isothermal conditions

Abstract

In this paper, the reduction of chromite ore by coke was investigated by means of thermogravimetric analysis under non-isothermal conditions (from room temperature to 1823 K). The fractional reduced samples were examined by SEM/EDS and X-ray diffraction analyses. The experimental results showed that the reduction of iron in the chromite ore started before that of chromium in the ore, and the reduction of chromium and iron in the ore overlapped to some degree. Chromium iron carbide (Cr,Fe)₇C₃, was found to be the intermediate phase during the reduction, and a chromium gradient was found in the spinel phase of the fractional reduced sample at 1673 K. A four-stage reduction process was proposed: one stage involving the reduction of iron in the chromite ore and three stages involving the reduction of chromium in the ore. The activity aspects of component FeCr₂O₄ and component MgCr₂O₄ in the chromite ore were considered. The difficulty in the reduction of the chromite ore is attributed to the fact that, as the reduction proceeds, the activity of the component MgCr₂O₄ in the fractional reduced ore will decrease to a very low level, which makes further reduction very difficult.

Keywords:

• Thermogravimetric analysis
• Chromite ore
• Carbothermic reduction
• Direct alloying