Coupled Fenton oxidation and photocatalytic pretreatment: A novel strategy for reducing AAEMs in biomass to enhance coal co-combustion performance

The high content of alkali and alkaline earth metals (AAEMs) in biomass fuels exacerbates slagging and corrosion during co-combustion with coal, thereby limiting industrial utilization. To address these challenges, this study proposes a green pretreatment combining Fenton and photocatalytic processes. Walnut shells (WS) were treated with g-C 3 N 4 -loaded calcium alginate microbeads under simultaneous simulated daylight irradiation and Fenton oxidation. Thermogravimetric analysis was employed to investigate the combustion characteristics of coal blended with pretreated and untreated WS. Results demonstrated a 170 % enhancement in the combustion performance index ( S ) at a heating rate of 20 °C/min. X-ray fluorescence (XRF) analysis revealed that the pretreatment reduced AAEMs content by 53.5 %, specifically decreasing K₂O and Na₂O concentrations in ash from 5.21 % to 0.87 %. Slagging indices analysis further confirmed mitigated fouling risks, showing a low slagging index of 0.158 and a fouling index of 0.129. Kinetic analysis using model-free methods indicated a 12.8 % increase in activation energy ( E = 149.94 kJ/mol for pretreated walnut shells-coal blends compared to 132.91 kJ/mol for untreated blends), indicating a suppression of the catalytic effects of AAEMs on coal degradation. This work establishes a sustainable strategy for optimizing biomass-coal co-combustion systems with improved environmental compatibility and industrial applicability. • Fenton-photocatalytic coupling pretreatment achieves 53.5 % AAEMs removal in biomass. • A synergistic pretreatment strategy markedly enhances combustion performance index. • Slagging/fouling indices reduced to 0.158/0.129, enabling sustainable co-firing. • Kinetic analysis confirms F2 reaction dominance in pretreated biomass-coal blends.