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In a novel method of beneficiation of low-grade chromite ore, nuggets, 25 mm in diameter and 10 mm long, made of chromite ore and coke fines, are subjected to partial reduction. A significant degree of reduction of iron oxide is observed at temperatures of 1373-1523 K up to a reduction time of 240 min, and subsequent magnetic separation is found to enrich the low-grade chromite ore. In the kinetic studies performed on the partial reduction of chromite ore, nucleation and growth model NG1 (Avrami-Erofeev eq.; n=1) is found to be the rate-controlling regime. However, during the early phase of the reaction, particularly at lower temperature up to 1423 K, the nucleation and growth model NG2 (Avrami-Erofeev eq., n=2) predicts the reduction behaviour better. At higher conversion, particularly at a higher temperature of 1523 K, diffusion plays a significant role. The average apparent activation energy of reaction, based on the NG1 model over the entire reaction period, is estimated to be 38.52 kJ/mol. [ABSTRACT FROM AUTHOR]

A detailed investigation is made to study the effect of the presence of gangue materials like SiO, AlO and PO on the reducibility of iron ores in the blast furnace and sponge iron/DRI plants. The shatter index and abrasion index are found to improve marginally with increased content of the gangue materials, though the improvement is not significant. The rate of reduction decreases with time, and interfacial chemical reaction is identified as the rate-controlling resistance. The apparent activation energy is determined from the slope of the plot $${1-(1-f)^{0.5 }}$$ versus time, where f denotes the extent of reduction. At a high temperature (1373 K), a little deviation from linearity is observed, indicating greater contribution of diffusion. The apparent activation energy is found to vary between 125.82 and 149.49 kJ/mol for different composition of the nuggets. The presence of SiO and AlO is found to reduce the apparent activation energy, E, while the presence of PO increases the value of E. The average decrease in the apparent activation energy is found to be 1.63 and 1.33 kJ/mol per unit mass% increase in SiO and AlO, respectively, and the average increase in the apparent activation energy is 2.69 kJ/mol per unit mass% increase in PO. [ABSTRACT FROM AUTHOR]

An isothermal kinetic study of a novel technique for reducing agglomerated iron ore by volatiles released by pyrolysis of lean-grade non-coking coal was carried out at temperature from 1050 to 1200°C for 10-120 min. The reduced samples were characterized by scanning electron microscopy, energy-dispersive X-ray spectroscopy, and chemical analysis. A good degree of metallization and reduction was achieved. Gas diffusion through the solid was identified as the reaction-rate-controlling resistance; however, during the initial period, particularly at lower temperatures, resistance to interfacial chemical reaction was also significant, though not dominant. The apparent rate constant was observed to increase marginally with decreasing size of the particles constituting the nuggets. The apparent activation energy of reduction was estimated to be in the range from 49.640 to 51.220 kJ/mol and was not observed to be affected by the particle size. The sulfur and carbon contents in the reduced samples were also determined. [ABSTRACT FROM AUTHOR]