Utilization of leached spent vanadium catalyst residue as active silica filler in sulfur concrete: A chemical pathway for industrial waste valorization

This study presents a resource-efficient chemical pathway for valorizing leached silica residue from spent vanadium catalysts as an active mineral filler in dicyclopentadiene (DCPD)-modified sulfur concrete.X-ray diffraction confirmed the silica residue as alpha-cristobalite (ICDD 00-039-1425) with a specific surface area of 15.0 ± 1.2 m²/g and mesoporous structure (6-8 nm pore size).The optimal 15 wt.% loading increased compressive strength by 42% to 68.4 ± 1.2 MPa and flexural strength by 56% to 8.4 ± 0.2 MPa, with water absorption below 0.5%.FTIR spectroscopy revealed enhanced Si-O-Si stretching at 1098 cm⁻¹ and surface Si-OH groups at 3400-3740 cm⁻¹, indicating active interfacial sites.SEM analysis showed transition from adhesive failure (SC-0) to cohesive failure (SC-15) with sulfur infiltration depth of 2-5 μm, as confirmed by EDX elemental line scan (98.2% S bulk → 85% S interface → 45% Si core).Thermal cycling (100 cycles, -20 to +60 °C) demonstrated 92 ± 3% strength retention.Chemical resistance testing over 28-day immersion in 5% H₂SO₄, 5% NaOH, and 5% Na₂SO₄ confirmed 97.2-98.5% strength retention with absolute residual strength of 66.5-67.4MPa.Thermogravimetric analysis showed 0.12% mass loss at 200 °C, confirming absence of catalytic oxidation by residual vanadium (0.075% V₂O₅).Long-term monitoring over 90 days revealed gradual beta-toalpha transformation at ~0.08%/day with 94% strength retention.CO₂ emissions of approximately 13 kg/m³ represent 97% reduction versus Portland cement.A unified three-scale stabilization mechanism is proposed, encompassing molecular-level DCPD/Si-OH interactions, microstructural capillary infiltration, and macroscopic void filling.This work establishes a dual waste valorization route for cement-free construction materials with exceptional chemical durability.