Iron-montmorillonite treated corn straw biochar: Interfacial chemical behavior and stability

In this study, corn straw biomass was co-pyrolyzed with a clay mineral (montmorillonite) in the presence of iron-bearing materials (FeCl₃, magnetite and iron acetylacetone) and the prepared iron-montmorillonite biochars were characterized for their interfacial behavior. The results showed that, by adding iron to the pyrolysis process, organometallic complexes such as Fe-O-C were generated on the surface of biochars. All the iron-montmorillonite biochars were also shown to enhance the oxidation resistance likely by the increased relative contents of CO and COOH from 0% and 3.7% to 6.5-8.4% and 5.5-6.3%, respectively, compared with the iron-absent biochar. The measured carbon recalcitrance index (R₅₀, bicohar) of iron-montmorillonite biochars in thermogravimetric analysis (TGA) also increased from 46.9% to 48.6-56.9%. Among the three types of added iron materials, magnetite showed the best performance in improving biochar stability. The study indicated that, when added together, montmorillonite and iron were effective in improving the stability of biochar, which displays an important environmental significance of carbon sequestration.