Cr(VI) removal by Fe-biochar composite derived from co-pyrolysis of rubber tree waste and steel sludge

Abstract

Global industrialization has led to an increase in waste generation, necessitating the development of sustainable management strategies. Pyrolysis can convert waste into valuable products such as biochar and syngas. This study investigates the co-pyrolysis of rubber tree waste (RT) and pipe sludge (PS) to produce Fe-biochar, which was utilized as a reactive medium for formic acid (FA)-mediated Cr(VI) removal. Pyrolysis was performed at varying RT-to-PS mass ratios, and the physicochemical properties of the resulting Fe-biochars were analyzed. Syngas monitoring and biocrude composition analysis were scrutinized to experimentally assess the catalytic effects of PS on the pyrogenic product formation. The Cr(VI) removal performance of the composite was explored in de-ionized water (DIW) and groundwater (GW) conditions, while computational fluid dynamics (CFD) modeling was employed to evaluate its field-scale applicability. The results demonstrate that PS played a key role in enhancing syngas (CO) production, which simultaneously limited biocrude formation. Fe-biochar produced at 800 °C exhibited the highest Cr(VI) removal efficiency due to its well-defined porous structure and the presence of redox-active Fe phases (Fe0 and FeO). The biochar showed higher Cr(VI) removal in GW than in DIW, attributed to formation of Fe-SO42− complexes, which enhanced redox reactions with Cr(VI). CFD modeling demonstrated the potential of Fe-biochar for field-scale GW remediation, highlighting the importance of optimized formic acid (FA) injection in Cr(VI) removal. These findings signify that the co-pyrolysis of RT and PS offers an eco-friendly waste management approach, while providing an effective medium for remediating water pollution.