Extraction and Separation of Tungsten and Vanadium from Spent V2O5-WO3/TiO2 SCR Catalysts and Recovery of TiO2 and Sodium Titanate Nanorods as Adsorbent for Heavy Metal Ions

Abstract The storage and landfill of spent V2O5-WO3/TiO2 Selective Catalytic Reduction (SCR) catalysts can pose environmental hazards, and the valuable tungsten, vanadium and titanium resources are wasted due to the lack of appropriate recycling technology. In this study, we explore an effective and low-cost method to simultaneously recycle tungsten, vanadium and titanium from spent SCR catalysts. We extract tungsten and vanadium are from spent SCR catalysts by a Na2CO3-NaCl molten salt roasting-leaching method, then obtain enriched tungsten, vanadium solution through an ion-exchange and NaOH elution process, and separate tungsten and vanadium via an ammonium salt precipitation method. By optimizing the experimental conditions, 95.5% of tungsten and 94.9% vanadium are leached from the spent SCR catalysts, among which 93.4% of vanadium and 96.2% of tungsten can be precipitated. The leached residue mainly consists of nano-sized TiO2 and sodium titanate nanorods, which is used as adsorbent for heavy metal ions (Pb(Ⅱ), Cd(Ⅱ) and Cr(Ⅲ)). The maximum adsorption capacities are 338.503 mg g-1 for Pb(Ⅱ), 227.675 mg g-1 for Cd(Ⅱ) and 97.262 mg g-1 for Cr(Ⅲ) at pH = 6.0. Competitive adsorption among the three metal ions follows the sequence of Pb(Ⅱ) > Cd(Ⅱ) > Cr(Ⅲ). The adsorption data can be well fitted by the Langmuir model, and the adsorption kinetic follows the pseudo-second-order model. Furthermore, the X-ray Photoelectron Spectroscopy (XPS) analysis shows that the adsorption of Pb(Ⅱ), Cd(Ⅱ) and Cr(Ⅲ) by our adsorbent can be ascribed to the ion exchange of heavy metal ions with Na ions.