Deciphering Vanadium Speciation in Smelting Ash and Adaptive Responses of Soil Microorganisms

Abundant smelting ash is discharged during pyrometallurgical vanadium (V) production. However, its associated V speciation and resultant ecological impact have remained elusive. In this study, V speciation in smelting ash and its influence on the metabolism of soil microorganisms were investigated. Smelting ashes from V smelters contained abundant V (19.6-115.9 mg/g). V(V) was the dominant species for soluble V, while solid V primarily existed in bioavailable forms. Previously unrevealed V nanoparticles (V-NPs) were prevalently detected, with a peak concentration of 1.3 × 10¹³ particles/g, a minimal size of 136.0 ± 0.6 nm, and primary constituents comprising FeVO₄, VO₂, and V₂O₅. Incubation experiments implied that smelting ash reshaped the soil microbial community. Metagenomic binning, gene transcription, and component quantification revealed that Microbacterium sp. and Tabrizicola sp. secreted extracellular polymeric substances through epsB and yhxB gene regulation for V-NPs aggregation to alleviate toxicity under aerobic operations. The V K-edge X-ray absorption near-edge structure (XANES) spectra suggested that VO₂ NPs were oxidized to V₂O₅ NPs. In the anaerobic case, Comamonas sp. and Achromobacter sp. reduced V(V) to V(IV) for detoxification regulated by the napA gene. This study provides a deep understanding of the V speciation in smelting ash and microbial responses, inspiring promising bioremediation strategies to reduce its negative environmental impacts.