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Vanadium Speciation in Soil Aqueous and Solid Phases
Published in Jörg Rinklebe, Vanadium in Soils and Plants, 2023
Worachart Wisawapipat, Yohey Hashimoto, Shan-Li Wang
In solutions with low V concentrations in the absence of organic ligands, V(V) occurs mainly as the pervanadyl ion (VO2+) in strongly acidic conditions and vanadate oxyanions (H2VO4− and HVO42−) in neutral and alkaline conditions, respectively (Figure 6.3a). Vanadic acid (H3VO40) is a minor species in the pH around 3–4, and VO43− is predominant under extremely alkaline conditions (pH > 12). Vanadium(V) forms complexes with organic ligands at acidic pH conditions in which VO2+ is predominant. Figure 6.3b shows that V5+ complexes with oxalate [VO2(oxalate)−] occur in acidic conditions at an oxalate concentration of 100 μM. Formations of V5+-organic complexes may be enhanced in the rhizosphere at higher organic acid concentrations, depending on the abundance of major cations (e.g., Al3+) that preferentially form complexes with organic ligands. The aqueous chemistry of V(V) is extremely complex at higher V concentrations due to formations of poly-nuclear V(V) species. Various poly-nuclear V(V) species have been reported, which contain up to 10 vanadium atoms (e.g., V10O286−). The poly-nuclear V(V) complexes are minor species at low V concentrations (10−6 M, Figure 6.1), whereas these species become predominant at high V concentrations (>10−4 M) in acidic solutions (Pettersson et al., 2003).
Extraction of Vanadium(V) from Mixed Chloride/Thiocyanate Solutions with Two Commercial Solvating Extractants
Published in Solvent Extraction and Ion Exchange, 2018
Soad. E. Rizk, Naglaa. E. El-Hefny, Jacqueline. A. Daoud
In acidic media (pH <2), the major species of vanadium(V) is the cationic species pervanadyl ion VO2+.[19] The software MEDUSA program[27] also supported the main vanadium species in the mixed chloride/thiocyanate aqueous media at pH = 0.76. Moreover, as NH4SCN is a strong electrolyte, only NH4+ can be found in solution at the considered pH.[10] Accordingly, based on the obtained results, and considering that the main predominant species of vanadium(V) is VO2+ in HCl/NH4SCN mixed solutions, the extraction equilibrium of V(V) by CYANEX 925 (0.1–0.5 M) can be represented through a solvation process by one of the following equations: