ABSTRACT
Vanadium (V), an element dependent on redox conditions, may be found in the oxidation states of −1, 0, +2, +3, +4, and +5, but its prevalent species are V(III), V(VI), and V(V). Among them, the latter species is of environmental concern: it is mobile, toxic and thermodynamically stable in aerated conditions. In this chapter, we aimed to review V behavior as related to its dynamics and its soil solution speciation in the aqueous-colloids interphase, as well as its extraction and analysis (geochemical and spectroscopic techniques). When present in anoxic conditions, V(V) is reduced to V(IV), a less soluble species, and thus the metal’s mobility is decreased. This may prevail when V reacts with H2S, organic C or some certain soil micro-organisms. However, the decreased V solubility may subsequently increase when Fe (hydr)oxides are present in the system: in that case, partial dissolution of the oxides crystals may occur due to the reduction of Fe(III) (the species constituting the oxides) to the more soluble divalent Fe(II), and thus all embedded elements are also released, including previously retained V. The metal is not only affected directly by EH but also indirectly via redox-affected soil pH. Moreover, important soil constituents other than the oxides also affected by redox can indirectly influence V behavior, that is, organic C. In this chapter we clarify the redox-related geochemical behavior of V, including its mobilization dynamics, and this would help in elucidating its fate in the complex soil environments, including oxic upland soils, wetlands and agro-ecosystems (Larsson et al., 2015). We recognize that the debate is not complete, and thus further research directions that are necessary are also suggested.
