Synergistic catalytic liquefaction of hyperaccumulators using acid and steel slag: enhanced phenolic bio-oil production and stable arsenic sequestration.

This study investigated the hydrothermal liquefaction of the arsenic hyperaccumulator Pteris vittata L. using sulfuric acid (H2SO4) and pristine steel slag (P-SS) synergistic catalysis (SA2-SS), with the aim of simultaneously upgrading bio-oil and immobilizing arsenic. By promoting biomass decomposition and acid activation of the P-SS surface, the SA2-SS system significantly increased the bio-oil yield to 29.85% and promoted hydrogenation and deoxygenation reactions, raising the higher heating value (HHV) to 31.01 MJ/kg. The resulting bio-oil contained 64.78% phenolic compounds and consisted mainly of phenol, guaiacol, alkylphenols, and methoxyphenols. Under acid-catalyzed conditions, H+, CaO, and MgO promoted the activation and cleavage of lignin ether linkages, while Lewis acid sites associated with Fe2O3 and Al2O3 facilitated C-O bond cleavage and phenolic formation. Synergistic acid activation with metal oxides promoted the formation of Ca-, Fe-, and Mg-associated crystalline arsenate phases in hydrochar, resulting in an arsenic immobilization efficiency of 94.4%. A 21-day leaching test demonstrated low arsenic release (< 0.5 mg/L in acidic media). The synergistic H2SO4 and P-SS mechanism improved phenolic selectivity and hydrocarbon content, thereby enhancing bio-oil stability and fuel compatibility. This study presents a low-cost waste resource utilization strategy for the simultaneous production of phenol-rich bio-oil and stable arsenic immobilization.