Toward Green Ferroalloys: Replacement of Fossil Reductants in the Pre-reduction Process of Chromite by Bio-Based Alternatives

The production of ferrochrome via carbothermic reduction in submerged arc furnaces is an energy-intensive process relying on the usage of coal and coke as reducing agents. The pre-reduction of chromite in a rotary kiln is currently carried out to decrease the specific electric energy consumption in the smelting furnace. However, as fossil reductants are still needed for reduction, CO2 is emitted. The usage of bio-based carbon with a faster carbon cycle compared to fossil reductants could be an option to decrease the specific CO2 footprint of Ferrochrome production. In this paper, the pre-reduction of chromite was investigated using various bio-based reducing agents and lignite coke as a fossil reference. Isothermal reduction trials were conducted at 1000, 1150, and 1300 degrees C and different holding times. While at lower temperatures the pre-reduction was insufficient, the bio-based reducing agents yield a degree of reaction between 61.0% and 65.4% at 1300 degrees C reaction times of 360 min. The highest degree of reaction is reached using coconut charcoal, followed by corn, olive, and bamboo charcoal. Coke results in the lowest degree of reaction with 51.9%. While the bio-based reducing agents performed similar after long reaction times, significant deviations were observed for shorter reaction times. X-ray diffraction was carried out to investigate the obtained product, which showed that the pre-reduction was mostly due to the formation of carbides, while the intensity of metals in the sample was rather low.