Efficient pre-reduction of chromite ore with biochar under microwave irradiation

Abstract

Pre-reduction of chromite ore is crucial for producing ferrochromium alloy by submerged arc furnace (SAF) smelting. In this study, an efficient method for low-temperature pre-reduction of chromite ore using biochar under microwave irradiation was explored to produce good burden for subsequent SAF smelting. The thermodynamic analysis proved the feasibility of the easy decomposition of the main phase in the ore, FeCr2O4 to Cr2O3, and finally to ferrochromium, mainly (Fe,Cr)7C3, in the commonly examined temperature range for pre-reduction. The characterizations of electromagnetic properties, microwave absorption capabilities, and temperature rising behaviors of the main raw materials and their mixtures showed that microwave heating could greatly improve the carbothermic reduction of chromite ore. Under the condition of C/O molar ratio of 1.2, addition of 2 wt% Na2B4O7, pre-reduction temperature of 1100 °C, and dwell time of 3 h, the chromite ore-biochar composite briquettes had efficient pre-reduction, producing pre-reduced briquettes with (Fe,Cr)7C3 as the main alloy phase. The iron and chromium metallization degrees (ηFe and ηCr) reached 98.1% and 86.8%, respectively. Compared with the conventional pre-reduction, they were increased by 15.9% and 51.7%, respectively. The results proved the feasibility of using microwave for efficent pre-reduction of chromite ore.