Assessment of biocoke behaviour in a ferromanganese smelting pilot furnace: A petrographic approach

This study presents a pioneering investigation into the behaviour of biocoke, particularly its biogenic component (biochar), during ferromanganese production. Employing μCT scanning, micro-Raman spectrometry, and organic petrology, the research explores the transformation of organic matter throughout different zones of a pilot ferroalloy furnace. The results reveal that the degradation of biocoke and its biocomponent varies significantly depending on the relevant position within the furnace and the temperature conditions. Notably, the biocoke with a 20 % charcoal addition maintained structural integrity and functioned effectively as a reducing agent, contrary to concerns about premature gasification due to the high reactivity of biochar. Microscopic analysis confirmed the presence of partially preserved biochar even at the furnace's lowest levels, indicating active participation in the reduction process. Furthermore, the study provides compelling evidence of partial graphitisation within both the coke matrix and the biogenic component, most likely facilitated by catalytic effects from molten and/or vaporised metals such as iron and manganese at temperatures exceeding 1500 °C. The occurrence of semi-graphitic structures was confirmed by Raman spectroscopy. The work also advocates for a distinct classification of organic inerts of biomass origin, acknowledging their unique gasification and thermal behaviours. This classification should be refined through broader studies involving diverse biochar sources and interlaboratory comparisons. The findings validate the viability of biocoke as a sustainable and economically feasible reductant in ferroalloy production, as demonstrated through the Biocoke4FAI research project.