Revised Pourbaix diagrams for the vanadium – water system

Abstract

<p><span lang="EN-US">The forms of occurrence of vanadium metal are determined by the major chemical reactions in the aquatic environment such as hydrolysis, oxidation, reduction, and precipitation. Depending on pH, potential and total concentration of inorganic ions and organic ligands, vanadium compounds may undergo various transformations to produce a whole range of chemical forms in aqueous systems. In this paper, a novel approach has been applied for calculating potential</span><span lang="EN-US">-</span><span lang="EN-US">pH (Pourbaix) diagrams, based on the developed thermodynamic analysis of chemical equilibria in the V–H<sub>2</sub>O system. On the basis of currently revised thermodynamic data for V(III), V(IV) and V(V) hydrolysis and original thermodynamic and graphical approach used, the repartition of their soluble and insoluble chemical species has been investigated. By means of ΔG–pH diagrams, the areas of thermodynamic stability of V(IV) and V(V) hydroxides have been established for a number of analytical concentrations of vanadium in heterogeneous mixtures. The obtained results, based on the thermodynamic analysis and graphic design of calculated data, are in good agreement with available experimental data.</span></p>

Vanadium removal from spent sulfuric acid plant catalyst using citric acid and Acidithiobacillus thiooxidans

“…It was also confirmed by pH/Eh diagram (Fig. 6) where the Eh values measured fell into VO 2+ region from Pourbaix diagram [45]. The pH profiles recorded during the procedure (Fig.…”

“…The graph shows that the Eh values were mostly between 400 and 700 mV. These values combined with pH values between 1 and 2 were compared with Pourbaix diagram for vanadium [45]; the results suggest that vanadium is present in the CA solution in the form of VO 2+ ion, which means that V exhibits + 4 oxidation state. This is congruent with the blue color of the solution, typical for V 4+ ions.…”

“…This is congruent with the blue color of the solution, typical for V 4+ ions. The vanadium ions presumably did not form any complexes with citric acid, but are just dispersed in the solution, in which they are stable due to low pH [45,46] and bonded with one another by oxygen bridging [47]. Therefore, it may be easy to precipitate vanadium ions using, e.g., ammonium salts or simply by increasing the pH of the solution, as proved by other authors [24,25].…”

Dissolution of BiVO4 Photoanodes Revealed by Time-Resolved Measurements under Photoelectrochemical Conditions

“…However, further oxidation of V(V), which would require removal of the inner shell 3s/3p electrons from V, has not been reported in the V− H 2 O Pourbaix diagrams. 24,25 The oxidation of Bi(III) has also been proposed as a possible mechanism for the PEC dissolution. 1 17 resulting in Bi(III) species such as BiO + at neutral pH.…”

Polygenic chamosite from a hydrothermalized oolitic ironstone (Saint-Aubin-des-Châteaux, Armorican Massif, France): crystal chemistry, visible–near-infrared spectroscopy (red variety) and geochemical significance

“…Oxidation states 2+ and 5+ can be excluded for V because V 2+ prevails only in strongly reducing conditions (below the iron/wüstite buffer), while V 5+ implies a high f O 2 (Papike et al , 2016). In aqueous systems (normal conditions; pH neutral to acid) and at low Eh, V 3+ (solid or aqueous species) is the stable oxidation state (Takeno, 2005; Povar et al , 2019), which coexists with Fe 2+ . V 4+ species appear at higher Eh, always in the stability field of Fe 2+ (Takeno, 2005).…”