Upcycling Treated Micrometric Silica Fume Industry Waste into a High-Performance Adsorbent: Surface Characterization and Application in Water Purification

This study investigates the adsorption performance of thermally treated silica fume waste (SFW1000) for removing Basic Blue 41 (BB41), a cationic dye, from aqueous solutions. Silica fume was heat-treated at 1000 °C to modify its physicochemical and textural properties. BET analysis showed an increase in specific surface area from 14.82 to 84.99 m2 g−1 after treatment. X-ray diffraction, Raman spectroscopy, Fourier-transform infrared spectroscopy, and scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy were used to characterize the material before and after adsorption, revealing a crystalline quartz phase and changes associated with dye uptake. Batch experiments achieved a maximum BB41 removal efficiency of 99.22% within 60 min at the natural solution pH (approximately 6). Nonlinear regression identified the Freundlich model as the best fit (adjusted R2 = 0.9949), indicating adsorption onto a heterogeneous surface. The Langmuir model yielded an estimated maximum adsorption capacity of 357.6 ± 20.81 mg g−1. Thermodynamic analysis indicated spontaneous and endothermic adsorption, with ΔH° = +16.27 kJ mol−1 and ΔS° = +65.60 J mol−1 K−1. Overall, SFW1000 demonstrates potential for BB41 removal, combining industrial waste valorization with aqueous pollution control. Further studies involving real wastewater, competing ions, regeneration, and environmental assessment are needed to establish its practical applicability and sustainability.