Experimental studies were carried out on the reducibility of two different chromite ores using different reducing carbonaceous reducing agents in the temperature range 1173 to 1573 K. "Friable lumpy" ores and "hard lumpy" ores were used in the experiments. Petroleum coke, devolatilized coke, (DVC) and graphite were used as reducing agents. It was found that iron was practically completely reduced before the commencement of the reduction of chromium in the ore. The reduction of iron was controlled by diffusion. The activation energy for this process was estimated to be 130 kJ/mole. The reduction of chromium was controlled by either chemical reaction or nucleation. Rate of reduction was highest when raw petroleum coke was used as the reducing agent. The DVC was less effective compared to raw coke, whereas the rate of reduction was lowest when graphite was used as the reducing agent.

The reduction of chromite ore with carbon has been studied extensively in many laboratories. Inert gases have been used in these investigations to control the experimental conditions. However, little information is available in the literature on the influence of the gas flow rate on the rate of reduction. Experiments were carried out to study the influence of the flow rate of inert gas on the reducibility of chromite ore. The experiments showed that the rate of reduction increased with the increasing flow rate of argon up to an optimum flow rate. At higher flow rates, the rate of reduction decreased. The influence of the proportion of reductant on the extent of reduction depended on the rate of flow rate of inert gas. The experimental results are interpreted on the basis of a model that postulates that the mechanism of reduction changes with the flow rate of argon.

Extensive experimental investigations have been reported in the literature on the kinetics of reduction of chromite ore. The data obtained have been used for understanding the process of reduction in the submerged arc furnace during the production of ferrochromium. A major drawback of these studies is that these have been carried out on fine particles of ore and reductant usually ,100 mm in size. However, the ore and coke charged to the submerged arc furnace are usually about 10-75 mm cross-section. This is about three orders of magnitude larger than the samples usually studied in the laboratory. Since the size of the particles plays a significant role in determining the kinetics of reduction, experiments were carried out on the reduction of lumpy chromite ore of different sizes. Coke of different particles sizes was used as the reductant. The controlling mechanism of reduction is influenced by the size of the ore particle and also that of coke. It is also controlled by the temperature of reduction. At 1473 K, the reduction is controlled by diffusion for large ore particles, whereas it is controlled by chemical reaction for smaller particles. At 1373 K, chemical reaction is the controlling mechanism for both large and small ore particles. The relative size of the ore with respect to coke plays an important role in the kinetics of reduction, rather than the actual particle sizes.