Imaging of mineral-enriched biochar by FTIR, Raman and SEM–EDX

Recent interest in biochar characterisation has been driven by its effectiveness as a soil additive, where it can act as a carbon sink, a detoxification agent, and as a means to improve crop yields, especially when prepared as a char–mineral composite. Optimising biochar performance, raw material selection and manufacturing conditions, demands an understanding of structure and chemistry in these complex materials that typically comprise numerous minerals and organic phases. This study presents techniques to successfully image these challenging materials using Fourier transform infrared (FTIR) spectroscopy and Raman spectroscopy. The FTIR and Raman results are presented with results from scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM–EDX), and X-ray photoelectron spectroscopy (XPS). We demonstrate that millimetre-scale organic phases are present in Acacia saligna biochar particles. Mineral enrichment of this biochar with bentonite-iron oxide generates new chemical phases, most likely through acid catalysed dehydration.