Analysis of Heavy Metals Pollution Sources Caused by Sulfide Minerals in Tunnel Waste under Photocatalytic Oxidation Conditions

The rapid expansion of global transportation infrastructure has significantly increased tunnel construction in mountainous regions, generating substantial amounts of sulfide-rich excavation waste. Current disposal practices relying on open-air storage pose critical environmental risks through land occupation and potential heavy metals pollution, while the intrinsic pollutant release mechanisms from sulfide mineral weathering remain insufficiently investigated. This study elucidates a novel pollution pathway through photocatalytic oxidation-triggered heavy metals liberation in tunnel waste. Conducted comprehensive mineralogical characterization of sulfide-bearing tunnel residues and systematically examined heavy metals migration patterns under controlled photooxidative conditions (variable illumination duration, temperature (25–45°C), moisture content (20–60%), and aeration status). Parallel experiments monitored pH evolution and heavy metals release kinetics, particularly focusing on Cd, As, Cr, Pb, and Mn. Results revealed the presence of photochemically active Fe- and Ti-bearing phases in sulfide matrices that drive acid generation through solar-induced sulfite oxidation. This catalytic process established strongly acidic conditions (pH 2.0 ± 0.3) under optimal parameters: 35°C, 40% moisture content, and 48-hour photoexposure with aeration. The resultant acidification promoted mineral dissolution, yielding maximum leachate concentrations of 0.09 mg/L Cd, 1.8 µg/L As, 0.05 mg/L Cr, 0.36 mg/L Pb, and 8.54 mg/L Mn, representing 3–8 fold increases compared to dark controls. This work provides the first mechanistic evidence of photocatalysis-mediated acid mine drainage formation in tunnel waste systems, challenging conventional geochemical weathering paradigms. The findings establish a theoretical framework for predicting heavy metals pollution risks and inform remediation strategies through photochemical parameter control, ultimately supporting sustainable management of tunnel excavation byproducts.