Comparative Performance of Bio-Carbon and Petroleum Coke as Reductants in CaCl2 Assisted Direct Reduction of Chromite

CaCl2-assisted Direct Reduction of Chromite (DRC) is a potentially lower energy alternative to conventional chromite smelting to produce ferrochrome (FeCr). This study investigates the technical feasibility of substituting petroleum coke (PC) with bio-carbon (BC) as the reductant in DRC and quantifies its effects on reduction behavior, alloy characteristics, and residual phase evolution. Chromite pellets containing CaCl2 flux and either PC or BC were reduced under controlled conditions using thermogravimetric analysis and electric tube furnace experiments with continuous off-gas monitoring. Products were characterized using various methods including 3D X-ray microtomography, Scanning Electron Microscope (SEM)-based quantitative mineralogy, and Wavelength Dispersive Spectrometry using an Electron Probe Microanalyzer (WDS-EPMA). BC accelerated reduction kinetics relative to PC due to its devolatilization, which generated a microporous network and increased the reactive surface area. Correspondingly, peak CO flux occurred 8 min earlier with BC during vertical tube furnace tests. BC also produced finer FeCr alloys, with 15% of alloy volume below the initial reductant particle size compared with 3% for PC, reflecting enhanced alloy densification. Alloy compositions using both reductants met high-carbon FeCr specifications. BC use also promoted the formation of non-olivine and Cl-bearing slag phases, indicating that reductant type can influence the partitioning behavior of non-alloying elements within slag phases.