From Amorphous to Semi-Graphitic Carbon: Catalytic Transformations of Biochar in a Pilot Ferroalloy Furnace

The pilot-scale furnace experiment was designed to assess the influence of biocoke on ferromanganese production processes. The investigation focused on the transformation behaviour of organic carbonaceous materials within a pilot ferroalloy furnace, employing a comprehensive, multi-analytical approach that included micro-computed tomography (μCT), micro-Raman spectroscopy, and organic petrology. The results indicate that the degradation pathways of biocoke and its biogenic component (biochar) differ markedly across individual furnace zones and are strongly governed by temperature gradients as well as the material’s position within the charge bed.

Distinct signs of partial graphitisation were detected in both the conventional coke matrix and the biochar fraction, as evidenced by Raman spectroscopic analyses. While biochar is generally classified as a non-graphitizable carbon, localised development of semi-graphitic structures was identified, suggesting that catalytic graphitisation may occur under specific furnace conditions. This transformation is most likely promoted by the presence of molten and/or vaporised transition metals—particularly iron and manganese—at temperatures exceeding 1500 °C, which may act as effective catalysts for the reorganisation of amorphous carbon into more ordered, graphite-like structures.

Catalytic graphitisation proceeds via interaction between amorphous carbon and metallic nanoparticles, leading to the formation of a metastable carbide phase that subsequently decomposes into graphitic carbon. In contrast to conventional graphitisation routes, this mechanism represents a single-step process that does not require a distinct carbonisation stage. The migration of metal vapours and molten droplets through the porous charge bed likely generates localised microenvironments that are especially favourable for such transformations, particularly in the lower regions of the furnace.

Complementary Raman analyses, including comparisons with established reference materials, confirmed the anisotropic and graphitic nature of selected carbon domains. Importantly, organic petrology plays a key role in the assessment of the biochar graphitisation process, enabling the identification, spatial characterisation, and textural interpretation of carbon structural evolution at the microscale.

These observations not only advance the understanding of the thermal and chemical behaviour of biogenic carbon in metallurgical systems, but also highlight a promising pathway for enhancing carbon structure through in-situ catalytic mechanisms. Research on efficient catalytic graphitisation of biochar, together with its systematic evaluation using petrographic techniques, is currently being actively conducted and further developed at ITPE (Institute of Energy and Fuel Processing Technology).

Fig. 1 The exemplary photomicrograph presenting a locally graphitized biochar particle (polarized light + Lambda plate,oil immersion, x500 mag.)