Kinetics of solid-state reduction of chromite overburden

The demand for alternative low-grade iron ores is on the rise due to the rapid depletion of high-grade natural iron ore resources and the increased need for steel usage in daily life. However, the use of low-grade iron ores is a constant clinical task for industry metallurgists. Direct smelting of low-grade ores consumes a substantial amount of energy due to the large volume of slag generated. This condition can be avoided by direct reduction followed by magnetic separation (to separate the high amount of gangue or refractory and metal parts) and smelting. Chromite overburden (COB) is a mine waste generated in chromite ore processing, and it mainly consists of iron, chromium, and nickel (<1wt%). In the present work, the isothermal and non-isothermal kinetics of the solid-state reduction of self-reduced pellets prepared using low-grade iron ore (COB) were thoroughly investigated via thermal analysis. The results showed that the reduction of pellets followed a first-order autocatalytic reaction control mechanism in the temperature range of 900–1100°C. The autocatalytic nature of the reduction reaction was due to the presence of nickel in the COB. The apparent activation energy obtained from the kinetics results showed that the solid-state reactions between COB and carbon were the rate-determining step in iron oxide reduction.