Mechanism for Photopromoted Release of Vanadium from Vanadium Titano-Magnetite

Abstract

The release of V from vanadium titano-magnetite, a predominant natural source of V, was studied under light irradiation. The release rate of V from vanadium titano-magnetite was accelerated by light irradiation, and the oxidation of V was detected. The essence of the photopromoted release of V is that the immobile low valence V is transformed to the mobile V(V) by photoinduced active species generated from the photocatalysis process of magnetite. Among the photoinduced active species, •OH and HO were recognized as the most important oxidizing agents. Not only can they directly convert the immobile low-valence V to the mobile V(V) but also initiate the Fenton reaction, which produces more •OH and then further promotes the oxidation of low-valence V. In addition, a conceptual model of the photo promoted release of V was proposed. This study, as part of a broader study of the release behavior of V, can improve the understanding of the pollution problem about V, as well as the fate and environmental geochemistry cycling of V in the natural environment.

Visible-light photocatalysis accelerates As(III) release and oxidation from arsenic-containing sludge

“…As2S3 + •O2¯ + H + → 3S•¯(s) + HO2¯ + 2As(III) fast (14) As2S3 + 3•OH + 3H + → 3S•¯(s) + 3H2O + 2As(III) k = 9×10 9 M -1 s -1 (15) During the photo-reaction process, As(III) can be released. The specific species of the released As(III) is highly dependent on the pH values and S 2concentration.…”

“…Recently, the effect of light on the dissolution of minerals containing heavy metals has been studied to elucidate the mechanism of photocorrosion reactions on the release of metal ions, such as antimony and vanadium, from their parental minerals or the synthesized substitutes (e.g. senarmontite (Sb2O3) [13], stibnite (Sb2S3) [14], and vanadium titano-magnetite [15]. It has been demonstrated that simulated sunlight or UV irradiation can promote the dissolution of minerals and thus release heavy metal ions.…”

Sunlight-Driven Production of Reactive Oxygen Species from Natural Iron Minerals: Quantum Yield and Wavelength Dependence

“…Natural iron minerals are a group of inorganic compounds widespread in water, atmosphere, and soil. − Recent studies have revealed the semiconducting properties of iron minerals, where sunlight irradiation triggers the generation and separation of charge carriers (i.e., electrons and holes). − Those photogenerated charge carriers could migrate to the iron mineral surface, producing photocurrents and mediating numerous biogeochemical reactions. For instance, photooxidation of organic compounds and arsenite was observed on the surface of hematite and goethite. − In addition, microbes can utilize the photogenerated electrons from hematite for Cr­(VI) reduction .…”

Vanadium in the Environment: Biogeochemistry and Bioremediation

“…28 The transformation of less mobile V(III) and V(IV) to mobile V(V) by photoinduced active species (•OH and H 2 O 2 ) produced by the photocatalysis of vanadium titano-magnetite under light irradiation, which supplements the geochemical V processes, has been revealed in laboratory studies. 115 Protonpromoted dissolution of V(III), V(IV), and V(V) oxides at pH 3.1−10.0 has also been studied, and these processes follow a surface-controlled reaction mechanism accompanied by redox reactions under environmental conditions. 116 Natural oxidizing minerals, such as birnessite, can oxidize V(IV) into highly mobile and toxic V(V) under neutral pH conditions.…”

“…V­(III) and V­(IV) precipitates in minerals tend to be oxidized to soluble V­(V) in the presence of oxygen, causing V mobilization . The transformation of less mobile V­(III) and V­(IV) to mobile V­(V) by photoinduced active species (•OH and H 2 O 2 ) produced by the photocatalysis of vanadium titano-magnetite under light irradiation, which supplements the geochemical V processes, has been revealed in laboratory studies . Proton-promoted dissolution of V­(III), V­(IV), and V­(V) oxides at pH 3.1–10.0 has also been studied, and these processes follow a surface-controlled reaction mechanism accompanied by redox reactions under environmental conditions .…”