The mechanisms and consequences of inorganic reactions during the production of ferrous sulphate enriched bamboo biochars

Magnetic biochars are implicated in graphene micro-crystallite formation, soil redox processes and highly adsorbent chars. This study investigates the mechanisms of bamboo charring – when impregnated with FeSO₄·7H₂O – at 250, 350, 450 and 550 °C, using thermal and static techniques. Impregnation resulted in the oxidation of Fe²⁺ to mixed Fe³⁺/Fe²⁺ (magnetite) oxide forms during pyrolysis. A reaction sequence was proposed in which Fe-sulphates were incorporated with an ammonia catalyst. Sulphur became ubiquitous in both inorganic and organic forms, and additional minerals also formed. Stable aromatics and separation of holo-cellulosic and degraded lignin volatilisation phases were catalysed, and carboxylation was inhibited. Concentrations of C fluctuated more substantially, before stabilising at high HTTs. Pyrolysis temperatures of 450 °C and above appear to maximise stable C concentrations.These observations indicated that this treatment may yield agriculturally engineered chars with enhanced redox potential, more neutral pH, and a range of nutrients.